Article

A Layer-by-Layer Architecture for PrintableOrganic Solar Cells Overcoming the ScalingLag of Module Efficiency

Rui Sun, Qiang Wu, Jie Guo, ...,

Fei Huang, Yongfang Li, Jie Min

min.jie@whu.edu.cn

HIGHLIGHTS

A layer-by-layer (LbL)-bladedOSC

shows a PCE of 16.35%

LbL approach can also be

employed for optimizing other

photovoltaic systems

An LbL-bladed solar module

exhibits a PCE of 11.86%

LbL strategy can effectively

reduce the scaling gap of module

efficiency

The layer-by-layer (LbL) strategy exhibits unique advantages of combining the

merits of high photo-absorption rate, suitable vertical phase separation, and good

practicability, endowing the LbL-bladed devices with a higher power conversion

efficiency (PCE) of 16.35% compared to the bulk heterojunction (BHJ)-bladed

device (15.37%). Importantly, this LbL approach can effectively reduce the scaling

lag of module efficiency. An LbL-bladed solar module with a geometrical fill factor

of over 90% exhibited an outstanding PCE of 11.86%.

Sun et al., Joule 4, 407–419

February 19, 2020 ª 2019 Elsevier Inc.

https://doi.org/10.1016/j.joule.2019.12.004

Article

A Layer-by-Layer Architecture forPrintable Organic Solar Cells Overcomingthe Scaling Lag of Module EfficiencyRui Sun,1 Qiang Wu,1 Jie Guo,1 Tao Wang,1 Yao Wu,1 Beibei Qiu,2 Zhenghui Luo,3 Wenyan Yang,1

Zhicheng Hu,4 Jing Guo,1 Mumin Shi,1 Chuluo Yang,3 Fei Huang,4 Yongfang Li,2 and Jie Min1,2,5,6,*

Context & Scale

With the improvement of

photovoltaic efficiencies,

solution-processed organic solar

cells (OSCs) have shown a bright

prospect for inexpensive and

sustainable light-to-energy

conversion. However, when we

adopt the donor-acceptor bulk

heterojunction (BHJ) strategy to

fabricated large-scale OSC

modules, there is a huge gap in

efficiency. In this work, we

introduced an alternative method

layer-by-layer (LbL) approach into

SUMMARY

To date, organic solar cells (OSCs) with the development of photovoltaic ma-

terials have realized high power conversion efficiencies (PCEs) through the

solution processing strategy with bulk heterojunction (BHJ) structure, but

the BHJ morphology is difficult to control in large-scale fabrication of OSCs.

Herein, we report an alternative film-forming technology known as layer-by-

layer (LbL). As compared to its BHJ counterpart, LbL presents many unique

advantages including controllable ‘‘p-i-n’’ morphology, good charge transport

and extraction properties, and great universality. By using the LbL-bladed

coating strategy, a high PCE of 16.35% was achieved in the PM6:Y6 OSCs.

Notably, a large-area solar module of 11.52 cm2 with a geometrical fill factor

of over 90% exhibited an outstanding PCE of 11.86%, which represents the

highest efficiency of large-area solar modules. The results may pave the way

for the fabrication of the photoactive layer in the future industrial production

of OSCs.

the fabrication of OSCs through

blading-coating to obtain higher

photovoltaic performance as

compared to its BHJ counterpart.

In addition, we found the LbL

coating is a successful and general

processing technology that can

quickly bridge the huge gap

between the ‘‘hero’’ lab-scale

produced solar cells and large-

area solar modules.

INTRODUCTION

Solution-processed organic solar cells (OSCs) have been regarded as one of next-

generation photovoltaics owing to their key advantages such as light-weight,

low cost solution processing, and easy fabrication of flexible and semitransparent

devices.1–6 During the past decade, continuous efforts have been devoted to the

development of OSCs, including synthesis of numerous donor and acceptor

photovoltaic materials,4,7–10 morphology control strategies,11,12 and development

of device engineering techniques.13–16 With these tremendous exertions, power

conversion efficiency (PCE) has consequently increased up to 16% for polymer-

non-fullerene single OSCs.4,9 Although the efficiency of OSCs is now high

enough for commercial applications,5,17 there are still certain obstacles that

should be overcome to enter the industrial application in the near future. On

one hand, almost all high efficient OSCs and small-area OSC modules have

been fabricated by spin-coating method so far, which cannot be transferred to

high-throughput roll-to-roll (R2R) manufacturing for competing with other photo-

voltaic technologies.5 On the other hand, it is well known and understood, that

many up-scaling coating technologies cannot easily bridge the huge efficiency

gap between the ‘‘hero’’ lab-scale cells and large-area modules, while reduce

the geometric fill factor (GFF) losses.17 Thus, it is urgent to demonstrate that

high-performance large-area OSCs and OSC modules can be fabricated by scal-

able printing strategies under optimized conditions for standing out their great

potential applications.

Joule 4, 407–419, February 19, 2020 ª 2019 Elsevier Inc. 407

1The Institute for Advanced Studies, WuhanUniversity, Wuhan 430072, China

2Beijing National Laboratory for MolecularSciences, Beijing 100190, China

3Hubei Key Lab on Organic and PolymericOptoelectronic Materials, Department ofChemistry, Wuhan University, Wuhan 430072,P. R. China

4Institute of Polymer Optoelectronic Materialsand Devices, State Key Laboratory ofLuminescent Materials and Devices, South ChinaUniversity of Technology, Guangzhou 510640,People’s Republic of China

5Key Laboratory of Materials Processing andMold (Zhengzhou University), Ministry ofEducation, Zhengzhou 450002, China

6Lead Contact

*Correspondence: min.jie@whu.edu.cn

https://doi.org/10.1016/j.joule.2019.12.004

Many attempts to address the technological challenges upon up-scaling efficient

cells toward efficient modules have been made already.18–25 However, the cell-to-

module efficiency loss still remains,17,26,27 mainly due to the change in the process-

ing techniques from spin-coating to scalable printing method as well as the

inhomogeneities and varying film quality upon scaling to large areas.17 Of note is

that the bulk heterojunction (BHJ) processing approach via a mixture solution of

donor and acceptor has taken an irreplaceable lead in the photoactive layer forma-

tion of large-scale cells and modules.27–36 However, there is a creation of the

‘‘islands’’ of donor and acceptor in BHJ-based devices.37 These ‘‘islands’’ have no

connection with any electrodes, resulting in the inevitable losses in the cell’s effec-

tiveness. In addition, analogical losses are caused by the attendance of the ‘‘bad

peninsulas,’’ i.e., the donor’s seeds against the cathode and the acceptor’s seeds

against the anode. These losses in large-scale solar modules will stand out as the

cell or module area is increasing, along with the intensifications of non-geminate

recombination in the bulk and surface recombination at the active layer-electrode

interfaces. These negative factors of BHJ morphology were recognized very long

ago, but surprisingly, the estimate of the scale of these effects, especially for the

large-area solar cells and modules, is yet to be fully understood.

One widely held view is that an optimal morphology in OSCs should be a pseudo-

bilayer configuration (such as a p-i-n structure).37–42 In previous studies, it was

demonstrated that solution processing layer-by-layer (LbL, as depicted in Figure 1A)

approach applied to the fabrication of small-area OSCs is a promising alternative

option to construct the pseudo-bilayer.37,38,43 Furthermore, we have shown that

LbL approach not only possessed many special advantages as compared to the

BHJ method but also could effectively reduce the efficiency-stability gap of

OSCs.43 Nevertheless, the fabrication of well-controlled pseudo-bilayer in solu-

tion-processed large-scale technology is another matter. It is not clear that some

inevitable PCE losses caused by the attendance of the ‘‘islands’’ and ‘‘bad penin-

sulas’’ of donor and/or acceptor aggregations can be weakened or eliminated in

large-scale solar cells and modules via the LbL solution processing technology. In

addition, until now, no studies have reported the application of sequential blade

LbL approach into the fabrication of large-area solar modules. Whether this strategy

can construct the optimal morphology of large-area devices needs to be verified by

large-scale coating technologies, i.e., doctor-blade-coating method and slot-die

coating method, which are inexpensive and easily transferable to an R2R coating

environment. Overall, from these reasons, to move on the crucial step for industrial

application, efforts to investigate the influence of the blend microstructure and pro-

cessing strategies as well as the evaluation of their application potential have to be

directly involved in the printed large-area OSCs.

In this study, inspired by the previous works and requirements of large-area device

fabrication, we firstly explored the effect of BHJ and LbL blading-coating

approaches on optical simulation, three-dimensional morphological characteristics,

physical dynamics, and device performance in the investigation of PM6:Y6

system (Figure 1B). Benefiting from the better optical properties, pseudo-bilayer

morphology, and charge transport and extraction properties, a higher PCE of

16.35% was achieved in an LbL-based OSC device based on PM6:Y6, which is higher

than that of BHJ-bladed devices (15.37%) with a same active area of 0.04 cm2.

Furthermore, under optimized conditions, the LbL-based OSCs with different pho-

toactive layers all exhibit the best device performance in comparison with their high-

est values in the BHJ-based devices. More importantly, we demonstrated that LbL

processing strategy could also be useful for making large-area solar modules; i.e.,

408 Joule 4, 407–419, February 19, 2020

A B

C D E

Figure 1. Schematic Illustration, Chemical Structures, and Optical Properties of BHJ and LbL Systems

(A) Schematic illustration of the LbL blade-coating approach, and schematic device architecture of OSCs.

(B) Chemical structures of the donor and acceptor materials investigated in this work.

(C) Optical properties of the optimal BHJ and LbL active layers.

(D and E) Simulated photo-absorption rate in BHJ (D) and LbL (E) based OSCs with an active layer thickness of 120 nm.

a PM6:Y6 based solar module of 11.52 cm2 was fabricated by using LbL-bladed

approach and an outstanding PCE of 11.86% was achieved, which is higher than

that (10.15%) of BHJ-based module with the same scale. To the best of our knowl-

edge, the PCE of 11.86% is the highest value reported in literature to date for

large-area organic solar modules.

RESULTS AND DISCUSSION

The schematic illustration of LbL film-forming technique investigated in this study,

and the chemical structures of PM644 (polymer donor) and Y68 (non-fullerene

acceptor, NFA) are presented in Figures 1A and 1B, respectively. The LbL blends

were formed by sequentially doctor-bladed coating from donor PM6 solution and

acceptor Y6 solution using chloroform as a solvent. In addition, the BHJ strategy is

understood as such a process that PM6 and Y6 were blended in chloroform

solutions with a 1:1 mixed molar ratio; they assembled to form quite a representa-

tive BHJ microstructure upon solvent evaporation.38 Details of the BHJ and

LbL processing approaches are described in the Experimental Procedures. All

the solar cells and modules were fabricated, with a conventional device architec-

ture of indium tin oxide (ITO)/PEDOT:PSS (poly(3,4-ethylene dioxythiophene)

polystyrene sulfonate)/active layer/PNDIT-F3N-Br (Poly[[2,7-bis(2-ethylhexyl)-

1,2,3,6,7,8-hexahydro-1,3,6,8-tetraoxobenzo[lmn][3,8] phenanthroline-4,9-diyl]-

2,5-thiophenediyl[9,9-bis[30((N,N-dimethyl)-N-ethyl-ammonium)]propyl]-9H-fluorene-

2,7-diyl]-2,5-thiophenediyl]))/Ag. Of note is that the active layer and the interface

layers, including PEDOT:PSS and PNDIT-F3N-Br, are all fabricated by blade-

coating techniques in air (Figure 1A).

Joule 4, 407–419, February 19, 2020 409

Figure 1C exhibits the optical properties of the bladed BHJ and LbL active layers. As

compared to the BHJ active layer, the LbL blend shows a slightly red-shifted absorp-

tion spectra and a remarkably higher absorption coefficient of approximately 8.33

104 cm�1, indicating the enhanced molecular ordering of Y6 acceptors. The high ab-

sorption coefficient of the LbL blend also suggests that a higher number of photons

can be absorbed and converted into energy.41 Furthermore, the difference of optical

absorption drove us to employ spectroscopic ellipsometry to determine accurate

optical constants (n and k) of the BHJ and LbL blends (Figure S1). The results were

calculated from the used films with different thicknesses (Figure S2). Figures 1D

and 1E show the field distribution for the wavelength range of 300–900 nm for visu-

alizing the modulation of the electric field inside BHJ and LbL devices with the

bladed active layer thickness of 120 nm, respectively. As compared to the BHJ

blend, the photon absorption rate profile of LbL is slightly stronger. Notably, those

images can be viewed as the charge generation profiles within the BHJ and LbL de-

vices because most of excitions can be effectively separated into free charges,

demonstrated by the photoluminescence (PL) measurements (Figure S3). It should

be noted that the simulated photo-absorption rates of BHJ and LbL devices are

different with the absorption spectra of BHJ and LbL blends, probably resulting

from the complexities in the absorption, transmission, refraction, and reflection of

solar photons in devices. In addition, the morphology complexity of the LbL active

layer as well as the same layer thickness set in the simulation also lead to the

above-mentioned difference. Undoubtedly, the above-mentioned optical absorp-

tion profiles indicate the distinctly different three-dimensional microstructures of

BHJ and LbL blends as described in the following section.

To clarify the morphological characteristics of the BHJ- and LbL-bladed PM6:Y6

active layers, we applied grazing-incidence wide-angle X-ray scattering (GIWAXS),

photo-induced force microscopy (PiFM) and time-of-flight secondary ion mass spec-

trometry (ToF-SIMS) measurements. From the two-dimensional (2D) GIWAXS in Fig-

ure S4, the neat PM6 film shows a disordered arrangement implying a less ordered

nature of the film, in contrast the neat Y6 film is revealed to adopt a face-on prefer-

ential orientation with respect to the substrate. Notably, the 2D GIWAXS measure-

ments (Figures S4C and S4D) did not reveal distinctly different scattering patterns of

the BHJ and LbL blends acquired at the critical incident angle of 0.13�. Despite this,

the shallow incidence angle of 0.02� was further chosen to investigate the crystalli-

zation close to the top surface of the BHJ and LbL films, as exhibited in Figures 2A

and 2B, respectively. It was found that Y6 acceptor is much more ordered at the

top of LbL film than that of the BHJ blend, as evidenced by such diffraction (Fig-

ure 2C). The mean size of the crystallites was acquired by calculating the crystal

coherence length (CCL) using the Scherrer equation.45 The CCL values of BHJ and

LbL films are 24.5 and 25.1 nm, respectively, indicating the existence of ordered

Y6 top layers in the LbL blend. TheGIWAXS results are consistent with the PiFMmea-

surements. The PiFM images at the characteristic Fourier transform infrared (FTIR)

wavelengths corresponding to absorption peaks of Y6 acceptor (1,536 cm�1) with

BHJ and LbL blading approaches are shown in Figures 2D and 2E, respectively.

The LbL-bladed blend shows the enhanced molecular aggregation and increased

domain size in comparison with the BHJ film. The observed crystallization phenom-

ena explained in terms of the dynamical patterns for the corresponding BHJ and LbL

morphologies were derived from the competing processes between molecular

interdiffusion and molecular aggregation during the film formation process.43

We further conducted TOF-SIMS measurement, which quantitatively monitors the

vertical profiles of each component across the whole thickness of the active layers.46

410 Joule 4, 407–419, February 19, 2020

A B C

D E F

G H

Figure 2. Film-Forming Properties of BHJ and LbL Blends as well as Their Schematic Representation of 3DMorphological Characteristics and Possible

Physical Dynamics

(A and B) 2D GIWAXS profiles for BHJ (A) and (B) LbL films bladed on the PEDOT:PSS layer. All images are corrected for monitor and film thickness and

displayed on the same logarithmic color scale.

(C) The 1D GIWAXS line curves with respect to the in-plane (IP) direction and out-of-plane (OOP) direction. The IP and OOP profiles of BHJ and LbL films

acquired at the critical incident angle of 0.02�.(D and E) PiFM topography images of relevant (D) BHJ and (E) LbL films based on FTIR absorption at 1,536 cm�1 (Y6).

(F) TOF-SIMS ion yield as a function of sputtering time for BHJ and LbL samples. The depth profile of Y6 by trancing N element is shown here.

(G and H) Visual illustrations of the morphological characteristics and possible physical dynamics of BHJ (G) and LbL (H) blend-based devices.

Of note is that nitrogen (N) was used to track the Y6 acceptor. Combining with the N

signal as depicted in Figure 2F, we can easily conclude that Y6 acceptors were

assembled at the LbL/air surface, and PM6 polymer donors were enriched in the bot-

tom of LbL blend. In contrast, Y6 acceptors were evenly distributed throughout the

BHJ active layer. Therefore, by combining all findings from these morphological

characterizations, we can depict the detailed description of the surface aggregation

patterns and vertical phase separation in optimal BHJ and LbL blends as presented

in Figures 2G and 2H, respectively. The obviously different microstructures of BHJ

and LbL blends are directly reflected in their physical mechanisms (Figures 2G and

2H). Of note is that for a full dynamical analysis and explanation of corresponding

microstructures the reader is referred to Sun et al. (2019).

Joule 4, 407–419, February 19, 2020 411

A B C

D E F

Figure 3. Photovoltaic Parameters of BHJ and LbL Devices and Their Physical Dynamics

(A and B) J-V (A) and EQE (B) curves of the best-performing BHJ and LbL-based devices.

(C) Histograms of the PCE counts for 30 individual BHJ- and 30 individual LbL-based devices.

(D) Hole-only mobilities measured in single carrier diodes obtained from BHJ and LbL films; carrier mobilities of BHJ and LbL-based devices calculated

from photo-CELIV.

(E) Numbers of the extracted carrier in the BHJ and LbL devices as a function of delay time, obtained from photo-CELIV, and the fit.

(F) Charge carrier lifetime t, obtained from TPV, as a function of charge density n, calculated from CE under Voc conditions (from 0.15 to 2.50 suns). The

dashed lines represent linear fits of the data.

The key fabrication conditions of the devices, including the speed of doctor-blade

and the temperature of the bottom, plate to adjust the thicknesses and microstruc-

tures of the BHJ and LbL blends. Here, the device performance based on BHJ and

LbL layers were optimized by the adjustment of blade speeds as provided in Fig-

ure S5, and the related photovoltaic parameters are summarized in Table S1. The

optimal blade speeds were found to be 35 mm/s for BHJ blend and 12 mm/s

(donor)/12 mm/s (acceptor) for LbL blend, respectively. The current-density-voltage

(J-V) characteristics of the optimized devices and relevant parameters are shown in

Figure 3A and Table 1. The LbL device delivered the best PCE of 16.35%, along with

a short-circuit current density (Jsc) of 25.90 mAcm�2, an open-circuit voltage (Voc) of

0.834 V, and a fill factor (FF) of 75.68%, which is higher than that of the BHJ-based

device with an optimized PCE of 15.37% and a Jsc of 25.22 mAcm�2. The slightly

higher Jsc is probably attributed to the increased absorption spectra and higher

photo-absorption rate as well as the better charge dissociation probability in the

LbL devices (Figure S6), which is directly demonstrated by the external quantum ef-

ficiency (EQE) curves provided in Figure 3B. Figure 3C further presents the statistical

photovoltaic metrics and PCE histogram obtained from BHJ and LbL devices, which

indicate the good reproducibility of photovoltaic performance of the PM6:Y6 based

OSCs. Besides, our results provide the impetus for measurements on other high-

performance systems to probe the generality of these LbL morphology guidelines

to maximize performance. Thus, LbL blade-coating approach was employed

for optimizing other efficient active layers, including PM6:Y6-2Cl,9 PM6:Y6-C2,47

412 Joule 4, 407–419, February 19, 2020

Table 1. Photovoltaic Parameters of the BHJ and LbL Devices Based on Various Photovoltaic

Systems under the Illumination of AM 1.5 G at 100 mW cm�2

Active Layer Area (cm2) BHJ/LbL Voc (V) Jsc (mA cm�2) FF (%) PCE (%)

PM6:Y6 0.04 BHJ 0.840 25.22 72.49 15.37 (15.17 G 0.2)

1 BHJ 0.835 25.52 65.74 14.01 (13.71 G 0.3)

PM6/Y6 0.04 LbL 0.834 25.90 75.68 16.35 (16.15 G 0.2)

1 LbL 0.831 25.64 71.42 15.23 (15.03 G 0.2)

PM6:Y6-2Cl 0.04 BHJ 0.847 25.67 70.74 15.38 (15.18 G 0.2)

PM6/Y6-2Cl 0.04 LbL 0.849 25.88 72.30 15.89 (15.69 G 0.2)

PTQ10:Y6 0.04 BHJ 0.855 22.62 70.32 13.62 (13.42 G 0.2)

PTQ10/Y6 0.04 LbL 0.849 24.49 72.63 15.10 (14.90 G 0.2)

PM6:Y6-C2 0.04 BHJ 0.844 25.76 71.69 15.59 (15.39 G 0.2)

PM6/Y6-C2 0.04 LbL 0.834 25.82 73.99 15.93 (15.73 G 0.2)

and PTQ10:Y6.48 The chemical structures of relevant photovoltaic systems as well

as the J-V curves of their devices are provided in Figures S7–S9, and the correspond-

ing photovoltaic parameters are summarized in Table 1. All the LbL devices

exhibited higher PCE values than those of relevant BHJ devices, indicating that

LbL is a universal and effective strategy for a wide range of highly efficient photovol-

taic systems.

The better device properties of the photovoltaic systems fabricated by the blading

LbL approach are mainly attributed to their vertical phase morphology as depicted

in Figure 2H. As is well known, the relevant physical dynamics determined by the

blendmicrostructures caused the difference of photovoltaic performance in relevant

devices. Taking the PM6:Y6 system as an example, we calculated the hole mobilities

from space charge limited current (SCLC) measurements (Figure S10), as presented

in Figure 3D and summarized in Table S2. It was found that the hole mobility values

of LbL blends were slightly lower than that of the BHJ blends, even though their de-

vices exhibited better photovoltaic performance. It is because a more aggregation

of Y6 acceptors at the top layer probably suppressed the hole transport in the hole-

only devise. Here the photo-induced charge carrier extraction by linearly increasing

the voltage (photo-CELIV) over the nanosecond-microsecond (ns-ms, Figure S11)

was employed to determine the ambipolar charge extraction from an actual photo-

voltaic device. As shown in Figure 3D, the average mobility of LbL device (1.07 3

10�4 cm2V�1s�1) is higher than BHJ device (5.94 3 10�5 cm2V�1s�1), indicating

that charge carriers can be transmitted more effectively in a real LbL device.

The time dependence of charge carrier density resulting from the photo-CELIV mea-

surements was further employed to investigate the charge carrier recombination

mechanisms in the BHJ and LbL blends. As shown in Figure 3E, the number of ex-

tracted carriers reduce with increasing delay time between photogeneration and

extraction due to various recombination processes in the devices. Using the

following equation nðtÞ= nð0Þ=1+�

ttB

�g

, where nð0Þ is the initial density of photo-

generated carriers at t = 0 and g is the time-independent parameter), the effective

2nd order recombination coefficient (tB) were calculated.43 Relevant parameters

fitted and calculated by the above-mentioned equation are summarized in Table

S2. The LbL device showed the shorter 2nd order recombination coefficient than

that of BHJ device, which partially fit the description in Figures 2G and 2H. In addi-

tion, the transient time ttr values calculated from Figure 3E are 3.373 10�7 s for BHJ

Joule 4, 407–419, February 19, 2020 413

device and 1.87 3 10�7 s for LbL device. This result is identical to the transient pho-

tovoltage (TPV) measurements (Figure S12 and Table S2). The BHJ device showed a

carrier lifetime of 7.22 ms when the light intensity is around 1 sun, whereas the life-

time of PM6/Y6 system using an LbL structure decreased to 5.84 ms at the same in-

tensity. Additionally, combining the TPV and charge extraction (CE) techniques, a

non-geminate recombination order R (R = l + 1) can be calculated via the equation

t = t0ðn0=nÞl, where t0 (calculated from TPV curves) and n0 (adopted from CE curves,

Figure S13) are constants and l is the so-called recombination exponent.43 As shown

in Figure 3F, a slightly higher recombination order value (R = 2.11) for the BHJ device

as compared to the LbL device (R = 2.02) can be found. Overall, the results of the

carrier recombination dynamic analysis coupled with the charge carrier mobility

finally underpin the complex morphology outline above and give detailed insight

into subtle mechanisms being responsible for device parameters.

The above-mentioned photovoltaic systems demonstrated that the photovoltaic

performance of LbL-based devices is superior to corresponding BHJ devices with

an active area of 0.04 cm2. Due to the special advantages as mentioned above,

we further manufactured large-area LbL-bladed devices with an active area of

1 cm2 (1 3 1 cm). The best performances of the LbL-bladed devices reach a higher

performance of 15.23% compared to BHJ-based devices (14.01% PCE, Figure S14

and Table 1), mainly attributed to different FF values (65.74% for the BHJ device

and 71.42% for the LbL device, respectively). Importantly, direct, trap-free charge

percolation routes through mixed phases and excellent charge extraction and

collection properties of LbL devices with the low non-geminate recombination los-

ses are the likely reasons for the high FF values in the LbL devices. More importantly,

in the LbL-based conventional devices, the acceptors located on the surface and do-

nors deposited on the bottom can effectively suppress the surface recombination

demonstrated in Figure S15,49 and depicted in Figures 2G and 2H, respectively.

Thus, the excellent device area insensitivity of LbL strategy for fabricating single-

junction OSCs investigated in this work is crucial for processing the large-scale solar

modules by printing methods.

As we known, modules have become an important step from the laboratory to the

market toward large-scale production. However, the number of reports of large solar

module with the active area more than 10 cm2 is rather low until now. To demon-

strate the compatibility of the LbL approach with large-area printing techniques

and find an effective processing strategy to overcome the scaling lag of large-area

devices, we fabricated the large-area PM6:Y6-based solar modules with a

3.74 cm2 total area consisting of three series-connected cells with a dimension of

34 3 11 mm and a 12.60 cm2 total area consisting of four series-connected cells

with a dimension of 3.5 3 36 mm, respectively. The deal area of each cell in the

3.74 cm2 based module was determined to be 2 3 11 mm, resulting in an active

area of 3.3 cm2 and a GFF17,50,51 (defined as the ratio between active area and total

area of a monolithically interconnected module) of 88.2%. While the real area of the

12.6 cm2 based module was determined to be 13 36 mm, resulting in an active area

of 11.52 cm2 and aGFF of 91.4%. The LbL-based process of relevant solar modules is

depicted in Figure 4A, and the detailed fabrication processes investigated in this

study are explained in the Experimental Procedures. Figure 4B exhibits a digital

photo of the solar modules based on LbL PM6/Y6 film with an active area of

11.52 cm2 and a GFF of 91.4%. A schematic image of the large-area module fabri-

cation design is provided in Figure S16. In addition, Figure 4C shows the corre-

sponding J-V curves of the resulting BHJ and LbL modules with active areas of 3.3

414 Joule 4, 407–419, February 19, 2020

A B

C D E

F G

Figure 4. Fabrication and Device Performance of Large-Area Solar Modules

(A) Process flow diagram of the LbL-based process for large-area solar modules.

(B) Image of solar modules based on LbL PM6/Y6 film with an active area of 11.52 cm2 and an optimal GFF of 91.4%.

(C) Illuminated J-V curves of BHJ and LbL devices using a doctor-blade coating.

(D) Histograms of the PCE counts for 15 individual BHJ- and 15 individual LbL-based solar modules.

(E) Series resistance values of BHJ and LbL devices and solar modules.

(F) Chronological evolution of PCEs determined by J-V measurements of optimized devices with different device areas and processing technologies

and distribution of the PCEs of solar modules in terms of the device area fabricated with different printing or coating techniques. Here, SC is a spin-

coating method, DB is a doctor-blade-coating approach, and SD is a slot-die processing method.

(G) Distribution of the PCEs of organic solar modules in terms of the GFF values.

and 11.52 cm2, respectively, and the relevant photovoltaic parameters are summa-

rized in Table 2. As presented in Figure 4C and Table 2, the 11.52 cm2 solar module

fabricated by the LbL-based process exhibits a PCE of 11.86% with a Voc of 3.20 V, a

Jsc of 6.41 mAcm�2, and a FF of 57.85%, which is much better than that of the BHJ

module with a PCE of 10.15% and a FF of 50.12%. Moreover, the statistical photo-

voltaic metrics and PCE histogram obtained from BHJ and LbL modules with an

active area of 11.52 cm2, presented in Figure 4D, further indicating the good repro-

ducibility of the solar modules. Besides, the LbL module with an active area of

3.3 cm2 showed better photovoltaic performance (13.88%) than those of BHJ mod-

ule (11.86%), as exhibited in Figure 4C. In short, the LbL processing strategy strongly

Joule 4, 407–419, February 19, 2020 415

Table 2. Photovoltaic Parameters of the BHJ and LbL-Based Devices and Module Devices with

Various Areas under the Illumination of AM 1.5 G at 100 mW cm�2

Active Layer Area (cm2) Voc (V) Jsc (mA cm�2) Fill Factor (%) PCE (%)

PM6:Y6 3.3 2.51 8.61 55.78 12.06 (11.76 G 0.3)

11.52 3.21 6.25 50.12 10.15 (9.75 G 0.4)

PM6/Y6 3.3 2.49 8.72 63.92 13.88 (13.68 G 0.2)

11.52 3.20 6.41 57.85 11.86 (11.56 G 0.3)

exhibits an outstanding tolerance to device area variation in fabricating large-scale

OSCs and solar modules.

Obviously, the photovoltaic performance difference of BHJ and LbL-based modules

are mainly attributed to the difference of FF values (3.3 cm2: 55.78% for BHJ and

63.92% for LbL, respectively; 11.52 cm2: 50.12% for BHJ and 57.85% for LbL, respec-

tively). These can be partially explained by the above-mentioned advantages of LbL

architecture, including suitable blend morphology, high photo-absorption rate, and

good charge transport and extraction properties on the one hand. On the other

hand, the increase of FF values of the LbL modules as compared to that of the

BHJ modules can also be caused by the decrease of the series resistance (Rs), as

shown in Figure 4E. The lower series resistance of the larger area LbL OSCs could

result from the weakening or elimination of the above-mentioned ‘‘islands’’ and

‘‘bad peninsulas’’ of donor and/or acceptor aggregations in devices as depicted in

Figure 2G. Besides, we also measured the atomic force microscopy (AFM) images

of the large-scale BHJ and LbL films collected at different spots, as presented in Fig-

ure S17. All the collected AFM images (bottom, Figure S17) exhibited the smoother

surfaces in the whole LbL film with a size of 5 3 5 cm, suggesting a perfectly homo-

geneous LbL-coated active layers.

It should be noted that the dependence of photovoltaic performance (especially for

the FF values) on the device area by enlarging effective area from 0.04 to 11.52 cm2

are obvious and unavoidable.17 This is understandable since electrical loss from the

bottom ITO electrode, geometric loss induced by increasing cell width, and addi-

tional losses caused by film inhomogeneity, defects, or particles can significantly

limit the photovoltaic parameters of BHJ- and LbL-based OSCs with the enlarged

active area,17,52 as presented in Tables 1 and 2. Anyway, the LbL-bladed large-

area OSC modules of 3.3 and 11.52 cm2 exhibits outstanding PCEs of 13.88% and

11.86%, respectively. To the best of our knowledge, this is the highest efficiencies

reported thus far for large-area OSC modules, as depicted in Figure 4F. In addition,

as compared to the BHJ-bladed devices, our results demonstrated that the LbL

coating process is a successful technology which can quickly bridge the huge gap

between the ‘‘hero’’ lab-scale produced cells and large-area solar modules. Of

note is that the GFF values of all manufactured BHJ and LbL modules with an active

area of 11.52 cm2 are over 90% (Figure 4G), further underscoring the good repro-

ducibility for this highly attractive module layout.

Conclusions

In summary, we reported an LbL processing approach as a printable strategy for

high-performance large-area solar cells and modules. The LbL method exhibits

unique advantages of combining the merits of high photo-absorption rate, suitable

vertical phase separation, and good practicability, endowing the LbL devices with

excellent charge transport and extraction properties. As a result, the LbL-based

PM6:Y6 OSCs showed a higher PCE of 16.35% compared to the BHJ-bladed device

416 Joule 4, 407–419, February 19, 2020

(15.37%). Furthermore, the other three high-performance non-fullerene systems

investigated in this study, including PM6:Y6-2Cl, PTQ10:Y6, and PM6:Y6-C2, further

demonstrated the excellent universality of the LbL coating approach. Benefiting

from the excellent physical dynamics and good surface homogeneity of the LbL

blends, we applied this LbL processing strategy to fabricate solar modules with

larger active areas. As compared to its BHJ counterpart (10.15%), the LbL-based

modules with an active area of 11.52 cm2 and a GFF of over 90% deliver 11.86% po-

wer conversion efficiency, indicating that the LbL processing strategy can signifi-

cantly reduce the scaling gap, which taken as a sign of technological maturity.

Besides, to the best of our knowledge, this is the highest efficiency thus far for

large-area organic solar modules. Overall, this work not only further sheds light on

the unique advantages of LbL coating strategy but also demonstrates a successful

printing technique of processing the photoactive layer via the LbL strategy for up-

scaling organic solar cells toward high-performance large-scale production and in-

dustrial applications.

EXPERIMENTAL PROCEDURES

Full details of experimental procedures can be found in the Supplemental

Information.

SUPPLEMENTAL INFORMATION

Supplemental Information can be found online at https://doi.org/10.1016/j.joule.

2019.12.004.

ACKNOWLEDGMENTS

This work was financially supported by the National Natural Science Foundation of

China (NSFC) (grant nos. 21702154 and 51773157). We also thank the support of

the opening project of Key Laboratory of Materials Processing and Mold and Beijing

National Laboratory for Molecular Sciences (BNLMS201905).

AUTHOR CONTRIBUTIONS

R.S. and J.M. conceived and developed the ideas. R.S. designed the experiments

and performed device fabrications. R.S. and Q.W. fabricated the module devices.

J.G. performed optical simulation and analysis. T.W. synthesized the PM6 material.

Y.W. synthesized the Y6-2Cl material. Z.H.L. and C.L.Y. provided the Y6-C2, and

Z.C.H. and F.H. provided the PNDIT-F3N-Br material. B.B.Q. conducted the P-iFM

measurement. R.S. and J.M. wrote the manuscript.

DECLARATION OF INTERESTS

The authors declare no competing interests.

Received: September 29, 2019

Revised: November 14, 2019

Accepted: December 4, 2019

Published: December 31, 2019

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JOUL, Volume 4

Supplemental Information

A Layer-by-Layer Architecture for

Printable Organic Solar Cells Overcoming

the Scaling Lag of Module Efficiency

Rui Sun, Qiang Wu, Jie Guo, Tao Wang, Yao Wu, Beibei Qiu, Zhenghui Luo, WenyanYang, Zhicheng Hu, Jing Guo, Mumin Shi, Chuluo Yang, Fei Huang, YongfangLi, and Jie Min

SUPPLEMENTAL INFORMATION

Supplemental Data Items

Figure S1. Optical constants (n and k) of the involved active layers.

Figure S2. Transmission and reflection spectra of (A) BHJ and (B) LbL blends with

different thicknesses.

Figure S3. Photoluminescence (PL) spectra of neat donor PM6 and acceptor Y6 films,

and the BHJ and LbL blends. Comparative studies of PL quenching (PLQ) efficiency

shows that LbL blend (93.4%) is slightly more efficient PL quencher than the BHJ blend

with a PLQ of 92.1%.

Figure S4. Two-dimensional (2D) GIWAXS patterns for (A) neat PM6 film, (B) neat

Y6 film, (C) BHJ film and (D) LbL film; (E) The in-plane (IP) and out-of-plane (OOP)

profiles of neat PM6, neat Y6, BHJ and LbL films acquired at the critical incident angle

of 0.13o.

Figure S5. J-V curve characteristics of BHJ (PM6:Y6). and LbL (PM6/Y6) devices

based on different coating speeds under the illumination of an AM 1.5G solar simulator,

100 mW cm-2.

Table S1. Photovoltaic parameters of the OSCs of BHJ (D:A) and LbL (D/A) devices

based on different coating speeds under the illumination of an AM 1.5G solar simulator,

100 mW cm-2.

Active

layer

Speed

[mm/s]

Thickness

[nm]

Voc

[V]

Jsc

[mA cm-²]

FF

[%]

PCE

[%]

BHJ

20 60 0.847 20.66 77.78 13.61(13.41±0.2)

25 74 0.848 22.76 75.73 14.62(14.32±0.3)

30 84 0.846 24.70 73.18 15.30(15.10±0.2)

35 98 0.841 25.22 73.49 15.37(15.17±0.2)

40 108 0.833 25.43 70.76 14.99(14.79±0.2)

45 150 0.828 24.28 68.18 13.71(13.51±0.2)

LbL

10/10 36/40 0.835 24.24 75.16 15.21(15.11±0.1)

12/12 44/52 0.834 25.90 75.68 16.35 (16.15±0.2)

15/15 52/55 0.832 25.69 73.83 15.77(15.57±0.2)

18/18 68/66 0.832 25.01 72.14 15.01(14.91±0.1)

20/20 74/80 0.830 23.25 61.69 11.90(11.70±0.2)

0.0 0.2 0.4 0.6 0.8 1.0

-25

-20

-15

-10

-5

0

Cu

rren

t D

en

sit

y (

mA

cm

-2)

Voltage (V)

10 mm/s

12 mm/s

15 mm/s

18 mm/s

20 mm/s

0.0 0.2 0.4 0.6 0.8 1.0

-25

-20

-15

-10

-5

0

Cu

rren

t D

en

sit

y (

mA

cm

-2)

Voltage (V)

20mm/s

25mm/s

30mm/s

35mm/s

40mm/s

45mm/s

BA

Figure S6. Photocurrent density (Jph) versus effective bias (Veff) characteristics based

on optimized BHJ and LbL devices.

The difference on exciton dissociation and charge collection were gained by photocurrent density (Jph)

and the effective (Veff) of the BHJ and LbL-based devices. As depicted in Figure S6, photocurrent density

(Jph) versus effective voltage (Veff) characteristics for the optimal BHJ and LbL-based devices. Jph is

defined as 𝐽𝑝ℎ = 𝐽𝐿 − 𝐽𝐷 where JL and JD are the current densities under one sun illumination and in

the dark, respectively. The Veff is given by 𝑉𝑒𝑓𝑓 = 𝑉𝑜 − 𝑉 where Vo is the voltage at which Jph is 0 and

V is the applied voltage. P(E,T) = 𝐽𝑝ℎ/𝐽𝑠𝑎𝑡 reflect the exciton dissociation and charge collection

efficiency, where Jsat represents the saturation photocurrent density. When the Veff ≫2.0V, Jsat of the

LbL-based solar cell is 26.00 mA cm-2, which is higher than that of the solar cell of BHJ processing

(Jsat= 25 mA cm-2). This result mainly caused by the larger absorptivity to harvest more light in LbL

blend films. For the short-circuit conditions, P(E,T) is 94.00% for the PM6:Y6, however the value for

the PM6/Y6-based device is 98.00%. The larger value of Jph/Jsat for the PM6/Y6-based device implies

the better charge extraction and collection, which contributes to the higher Jsc value.

0.01 0.1 11

10

Jp

h (

mA

cm

-2)

Veff

(V)

BHJ,Pdiss=94%

LbL,Pdiss=98%

Figure S7. J-V curves of BHJ (PM6:Y6-2Cl) and LbL (PM6/Y6-2Cl) devices measured

under the illumination of an AM 1.5G solar simulator, 100 mW cm-2.

Figure S8. J-V curves of BHJ (PM6:Y6-C2). and LbL (PM6/Y6-C2) devices measured

under the illumination of an AM 1.5G solar simulator, 100 mW cm-2.

0.0 0.2 0.4 0.6 0.8 1.0

-25

-20

-15

-10

-5

0

Cu

rre

nt

De

ns

ity

(m

A c

m-2

)

Voltage (V)

BHJ-PM6:Y6-2Cl

LbL-PM6/Y6-2Cl

Y6-2Cl

0.0 0.2 0.4 0.6 0.8 1.0

-25

-20

-15

-10

-5

0

BHJ-PM6:Y6-C2

LbL-PM6/Y6-C2

Cu

rre

nt

De

nsit

y (

mA

cm

-2)

Voltage (V)

Y6-C2

Figure S9. J-V curves of BHJ (PTQ10:Y6). and LbL (PTQ10/Y6) devices measured

under the illumination of an AM 1.5G solar simulator, 100 mW cm-2.

Figure S10. The dark J-V characteristics of BHJ and LbL hole-only devices. The solid

lines represent the best fitting using the SCLC modified Mott-Gurney model.

Figure S11. Photo-CELIV measurements on the optimized (A) BHJ and (B) LbL

0.0 0.2 0.4 0.6 0.8 1.0

-25

-20

-15

-10

-5

0

Cu

rre

nt

De

nsit

y (

mA

cm

-2)

Voltage (V)

BHJ-PTQ10:Y6

LbL-PTQ10/Y6

PTQ10

0 1 2 3 4 5 6

100

101

102

103

104

J (

A m

-2)

V-IR (V)

Hole-only device

BHJ,h=3.2410

-4cm

2v

-1s

-1

LbL,h=2.5510

-4cm

2v

-1s

-1

Fitting

-3

-2

-1

0

1

2

3

Time (s)

BHJ

1 2 5 7

10 20 50 70

100 250 500 750

1000 2500 5000 Dark

0 10 20 30 40

Cu

rre

nt

Den

sit

y (m

A c

m-2

)

-3

-2

-1

0

1

2

3

40302010

Cu

rre

nt

De

ns

ity

(m

A c

m-2

)

Time (s)

0

LbL

1 2 5 7

10 20 50 70

100 250 500 750

1000 2500 5000 Dark

BA

devices for different delay times between the light pulse and the extraction voltage ramp.

To determine the mobility, fifteen photo-CELIV curves have been recorded using

different experimental conditions for each sample. As shown in Figure S11, photo-

CELIV measurements carried out on BHJ blend and LbL blend devices, photocurrent

transients recorded by applying a 2V/40 μs linearly increasing reverse bias pulse after

a 1 μs delay time. A very sharp peak is observed in the LbL devices indicated that charge

extraction faster for LbL devices as compared to BHJ devices. By change the delay time

and applied voltage to measuring the maximum charge extraction current (characterized

by tmax), which occurs at maximum photocurrent.

Table S2. Parameters extracted from photo-CELIV signals and SCLC based on these

two systems.

aFor the SCLC measurements, the values were obtained based on six devices of each

type, and the error bars represent plus or minus 1 standard deviation from the mean

values (SCLC mobility). bThe lifetime of BHJ and LbL-based devices calculated from

the TPV measurements under one sun.

Figure S12. TPV measurements on the optimized (A) BHJ and (B) LbL devices for

light intensities of 0.15 to 2.50 sun. Transient photovoltage (TPV) measurements were

used to analyze the recombination of free charges within the working devices by

recording the transient voltage decay of the device under open-circuit conditions under

continuous illumination before a small perturbative light pulse was injected.

0.00

0.02

0.04

0.06

8642

Ph

oto

vo

ltag

e (

V)

Time (s)

LbL

2.5 5 7.5 10

12.5 15 17.5 20

22.5 25 27.5 30

32.5 35 37.5

00.00

0.02

0.04

0.06

8642

Ph

oto

vo

lta

ge

(V

)

Time (s)

BHJ

2.5 5 7.5 10

12.5 15 17.5 20

22.5 25 27.5 30

32.5 35 37.5

0

BA

Active

layer

µha

[cm2V-1s-1]

µ

[cm2V-1s-1]

n0

[cm-3]

τB

[s]

γ

𝑡𝑡𝑟

[s] 𝑡b [s]

PM6:Y6 3.24×10-4 5.94×10-5 8.73×10-15 5.37×10-5 3.98×10-11 3.37×10-7 7.22×10-6

PM6/Y6 2.55×10-4 1.07×10-4 9.51×10-15 4.82×10-5 7.17×10-11 1.87×10-7 5.84×10-6

Figure S13. CE measurements on the optimized BHJ (A) and LbL (B) devices for light

intensities of 0.15 to 2.50 sun.

Figure S14. J-V curve characteristics of BHJ (PM6:Y6). and LbL (PM6/Y6) devices

with an active area of 1 cm2, measured under the illumination of an AM 1.5G solar

simulator, 100 mW cm-2.

Figure S15. (A) Voltage and (B) current density against light intensity of the relevant

0.000

0.004

0.008

0.012

0.016

10.80.60.40.2

Ch

arg

e c

arr

ier

de

ns

ity

(m

A c

m-2

)

Time (s)

BHJ

2.5 5 7.5 10

12.5 15 17.5 20

22.5 25 27.5 30

32.5 35 37.5 40

00.000

0.004

0.008

0.012

0.016

Ch

arg

e c

arr

ier

de

ns

ity

(m

A c

m-2

)

Time (s)

LbL

2.5 5 7.5 10

12.5 15 17.5 20

22.5 25 27.5 30

32.5 35 37.5 40

0 0.2 0.4 0.6 0.8 1

BA

10 100

10

Light Intensity (mW cm-2)

BHJ,S=0.99

LbL ,S=0.99

Cu

rren

t D

en

sit

y (

mA

cm

-2)

10 100

0.78

0.8

0.82

0.84 BHJ,a=1.4kT/q

LbL ,a=1.2kT/q

Vo

lta

ge

(V

)

Light Intensity (mW cm-2)

A B

devices. Intensities are corrected for AM1.5G spectral mismatch.

To gain deeper insight into the influence of the BHJ and LbL layers on the device

performance (especially for the FF values), we studied the bimolecular recombination

mechanism by measuring the photocurrent (Jsc) at various light intensities (I) from 100

to 10 mAcm-2, as shown in Figure S15A. A power-law dependence of Jsc upon

illumination intensity, which could effectively quantify the bimolecular recombination

mechanisms, can be expressed as 𝐽𝑠𝑐 = 𝛽(𝐼)𝛼 , where β is a constant and α is the

exponential factor. The best fit for the data is obtained when the value α is close to unity,

which indicates negligible bimolecular recombination during sweep-out. The slop (α)

of the BHJ device is 0.99, whereas that of LbL device is also 0.99, suggesting that the

bimolecular recombination are not prominent in these two types of devices as described,

probably due to favorable morphology without obvious space charge effects. In addition,

the high charge transport properties in BHJ and LbL devices may further contribute to

the high α value, which is close to unity.

Multiple studies have demonstrated that the light intensity dependence of the Voc can

directly provide insight into the role of trap-assisted recombination versus 2nd order

recombination at the open circuit condition. The Voc and light intensity (I) can be

correlated by the expression of 𝑉𝑂𝐶 =𝐸gap

𝑞−

𝑘𝑇

𝑞ln[

(1−𝑃)𝛾𝑁𝑐2

𝑃𝐺], where Egap is the energy

difference between the highest occupied molecular orbital (HOMO) of the electron

donor and the lowest unoccupied molecular orbital (LUMO) of the electron acceptor, q

is the elementary charge, k is the Boltzman constant, T is temperature in Kelvin, P is

the dissociation probability of the electron-hole pairs into free carriers, 𝛾 the

recombination constant, Nc the density of states in the conduction band, and G the

generation rate of electron-hole pairs. Following the rules, the formula predicts a slope

S = (kT/q) of the Voc versus the natural logarithm of the incident light intensity. This

implies that the slope of Voc versus ln(I) is equal to kT/q for bimolecular recombination.

When the additional mechanism of Schockley-Real-Hall (SRH) or trap-assisted

recombination is involved, a stronger dependency of Voc on the light intensity is

observed and in this case, the slope of Voc versus ln(I) is equal to 2 kT/q. Figure S15B

shows the Voc versus light intensity relationship for devices based on BHJ and LbL

active layers. The LbL device exhibits a logarithmic dependence on light intensity with

a slope of 1.19 kT/q. While the slope yields 1.25 kT/q for the BHJ device. As compared

to the LbL devices, the slightly stronger dependence of Voc on light intensity implies

that carrier dynamics at open circuit in BHJ device is slightly governed by a

combination of trap-assisted (SRH) type and bimolecular recombination. The use of

LbL layer reduces the trap-assisted recombination as seen from a slope of 1.19 kT/q.

We speculate that LbL morphology might not only reduce the number of trapping

defects in bulk, but also reduce the density of interfacial traps between the active layer

and electrode contacts. Thus, defect or trap-assisted bulk recombination and interface

recombination is suppressed.

Figure S16. (A) schematics of the large area module fabrication design: (A) the section

diagram of solar modules, (B) the real configuration of the investigated solar modules

based on four series-connected single cells of 8 mm × 36 mm. The total device area

is 12.60 cm2, and the active area is 11.52 cm2.

Glass

ITOP1

PEDOT:PSS

PM6

PNDIT-F3N-Br

P2

P3

Active area

Interconnection

area (dead area)

Ag

Y6

1mm

P3

36mm

P1

8mm

50mm

ITO

Ag

BA

Figure S17. Top (a)-(i) and bottom (A)-(I) 5 µm× 5 µm AFM topography images of

nine different spots of the 25 cm2 photoactive layer films processed with BHJ and LbL

approaches, respectively.

5 cm

5 c

m

a b c

d e f

g h i

A B C

D E F

G H I

BHJ AFM images

LbL AFM images

A B C

D E F

G H I

5 cm

5 c

m

a b c

d e f

g h i

Table S3. Efficiency evolution of organic solar cells via a range of coating technique.

Coating Technique Year

PCE(%)

Materials

[mA cm-²]

Ref.

[%]

BHJ

BHJ

2012 6 PBDT-FBTA: PC70BM [1]

2015 6.8 PTB7-TH: ITIC [2]

2016 11.77 J61: m-ITIC [3]

2016 11.4 J71: ITIC [4]

Spin coating 2017 13.1 PBDB-T-SF: IT-4F [5]

2018 13.24 J71: ZITI [6]

2018 14.4 PBDB-T-2Cl: IT-4F [7]

2019 15.7 PM6: Y6 [8]

2019 16.5 PBDB-TF: BTP-4Cl [9]

2019 16.4 S1: Y6 [10]

2009 3.8 P3HT: PCBM [11]

2012 6.69 POD2T-DTBT: PC71BM [12]

2016 6.09 PBDTTT-C-T: PC71BM [13]

Blade coating 2016 9.4 PBDT-TSR: PC71BM [14]

2016 9.9 PffBT4T-2OD: PC71BM [15]

2019 12.88 PBDB-TF:IT-4F [16]

2019 13.9 PBDB-T-2F: IT-4F [17]

BHJ

2012 3.07 P3HT: PCBM [18]

2014 5.18 PCDTBT: PC71BM [19]

2014 5.5 DPPBT: PCBM [20]

Slot-die coating 2015 7.5 PTB7-Th: PC70BM [21]

2017 2.4 P3HT: PC70BM [22]

2017 5.2 PBTZT-stat-BDTT-8: PCBM [23]

2018 7.61 PPDT2FBT: PC71BM [24]

2018 10 PBDB-T: ITIC [25]

2019 12.9 PBDB-T-SF: IT-4F [26]

LbL 2009 3.5 P3HT/ PCBM [27]

Table S4. Efficiency evolution of organic solar cells based different area via a range of

coating technique.

2011 3.8 P3HT/ PCBM [28]

2011 6.48 P3HT/ IC60BA [29]

Spin coating 2014 7.13 PBDTTT-C-T/ PC61BM [30]

2015 7.59 pDPP/ PC71BM [31]

2018 13 PBDB-TFS1/ IT-4F [32]

2019 12.08 J71/ ITC6-IC [33]

2019 12.23 PTQ10/ IDIC [33]

LbL Blade coating 2019 11.42 J71/ ITC6-IC [33]

2019 11.28 PTQ10/ IDIC [33]

BHJ Blade coating -- 15.37 PM6: Y6 This work

LbL Blade coating -- 16.35 PM6/ Y6 This work

Coating Technique Area(cm2)

PCE(%)

Materials

[mA cm-²]

Ref.

[%]

BHJ

0.05 15.7 PM6: Y6 [8]

0.09 16.5 PBDB-TF: BTP-4Cl [9]

0.12 7.29 PFBT-FTh: PC71BM [34]

0.12 9.02 PTAZDCB20: PC71BM [34]

0.12 6.94 PTAZDCB30: PC71BM [34]

0.64 4.9 PCDTBT: PC71BM [35]

Spin coating 0.81 10.5 PM6: IDIC [36]

1.44 6.7 BDTT-S-TR: PC70BM [37]

1 9.42 PDT2fBT-BT10: PC71BM [39]

1 11.43 PT3:ITCPTC0.7:meta-TrBRCN0.3 [38]

1 5.58 PFBT-FTh: PC71BM [34]

1 8.01 PTAZDCB20: PC71BM [34]

1 6.09 PTAZDCB30: PC71BM [34]

1 15.3 PBDB-TF: BTP-4Cl [9]

1 15.13 P2F-EHp:PCBM:Y6 [40]

BHJ

0.56 9.8 FTAZ: IT-M [41]

0.96 2.8 P3HT: PC61BM [42]

Blade coating 1 10.1 PB3T: IT-M [43]

1 13.9 PM6: IT-4F [17]

1 10.6 PBTA-TF:IT-M [44]

1 9.67 PBDB-T: IT-M [45]

BHJ

4.15 8.1 PTB7-Th: PC70BM [21]

8 6 PBDB-T: ITIC [46]

8.3 7.7 PTB7-Th: PC70BM [21]

11.3 1.5 P3HT: PCBM [47]

12.45 7.4 PTB7-Th: PC70BM [21]

12.6 10.2 PBDB-TF: IT-4F [48]

16 7.5 PTB7-Th: PC71BM [49]

16 7.11 PTB7-Th: PC71BM [50]

16 8.05 PTB7-Th: PC71BM [51]

16.6 7.4 PTB7-Th: PC70BM [21]

Module 17.1 1.5 P3HT: PCBM [47]

20 5.18 PTB7-Th: P-DTS(FBTTH2)2: PC71BM [51]

21 5.1 PBDB-T: ITIC [46]

52 2.2 PBDB-T: ITIC [46]

54.45 4.29 PNTz4T: PC71BM [52]

54.45 6.61 PNTz4T-5MTC: PC71BM [52]

60 4.5 P3HT: IDTBR [53]

60 5 P3HT: IDTBR [53]

66 6.1 PF2: PC71BM [54]

93 4.49 PTB7-Th: PC71BM [50]

108 3.64 POD2T-DTBT:PC71BM [55]

216 7.7 PBDB-T:PC71BM:ITIC [56]

LbL 0.04 11.4 PM6/ IT-4F [57]

Spin coating 0.04 13 PBDB-TFS1/ IT-4F [32]

0.04 12.08 J71/ ITC6-IC [33]

0.04 12.23 PTQ10/ IDIC [33]

LbL

1 10.6 PM6/ IT-4F [57]

Blade coating 1 10.35 J71/ ITC6-IC [33]

1 10.42 PTQ10/ IDIC [33]

BHJ Blade coating 0.04 15.37 PM6: Y6 This work

1 14.01 PM6: Y6 This work

BHJ Module 3.3 12.06 PM6: Y6 This work

11.4 10.15 PM6: Y6 This work

LbL Blade coating 0.04 16.35 PM6/ Y6 This work

1 15.23 PM6/ Y6 This work

BHJ Module 3.3 13.88 PM6/ Y6 This work

11.4 11.86 PM6/ Y6 This work

Supplemental Experimental Procedures

1. Materials

Materials: PM6 was synthesized by Tao Wang, Yao Wu synthesized the 2,2'-((2Z,2'Z)-

((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-

e]thieno[2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-

2,10-diyl)bis(methaneylylidene))bis(5,6-dichloro-3-oxo-2,3-dihydro-1H-indene-2,1-

diylidene))dimalononitrile (Y6-2Cl) material. Zhenghui Luo provided the 2,2'-

((2Z,2'Z)-((12,13-bis(3-ethylheptyl)-3,9-diundecyl-12,13-dihydro-

[1,2,5]thiadiazolo[3,4-e]thieno[2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-

g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis(methaneylylidene))bis(5,6-

difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (Y6-C2) and

Zhicheng Hu provided the PNDIT-F3N-Br. Y6 and PTQ10 were purchased from

Solarmer Materials Inc and used without further purification. Solvents (chloroform)

were dried and distilled from appropriate drying agents prior to use. The processes of

the purification of chloroform are as followed: The purifications involve washing with

water for several times to remove the ethanol, drying with potassium carbonate,

refluxing with calcium chloride, and then distilling. The distilled CF was stored in the

dark to avoid the photochemical formation of phosgene.

2. Blade-coating Device Fabrication and Testing

The small area solar cell devices were fabricated with a conventional structure of

Glass/ITO/PEDOT: PSS(40 nm)/(donor: acceptor (D:A) for bulk heterojunction (BHJ)

blend or D/A for layer-by-layer (LbL) blend, respectively) /PNDIT-F3N-Br (5nm) /Ag.

Pre-patterned ITO coated glass substrates (purchased from South China Science ＆

Technology Company Limited ) washed with methylbenzene, deionized water, acetone,

and isopropyl alcohol in an ultrasonic bath for 15 min each. After blow-drying by high-

purity nitrogen, all ITO substrates are cleaned in the ultraviolet ozone cleaning system

for 15 minutes. Subsequently, a thin layer of PEDOT: PSS (Xi’an Polymer Light

Technology Corp 4083) was deposited through blade-coating at 10mm/s on pre-cleaned

ITO-coated glass from a PEDOT: PSS: IPA=1:3 aqueous solution and annealed at

140 °C for 5 mins in atmospheric air and then blade the PEDOT: PSS: IPA=1:3 aqueous

solution on the first layer at 10mm/s and annealed at 140 °C for 15 mins. Then the BHJ

layer was blade-coating in the ambient atmosphere from a solution of donor: acceptor

(1:1, wt%; 14 mg mL−1) in chloroform onto the PEDOT: PSS layer at a varied blade-

coating speed for controlling the morphology and thickness of the active layer. For the

solar cells with an LbL architecture, donor material in chloroform solution (8 mg mL-

1) was bladed on PEDOT: PSS layer to form a front layer with pre-annealing, then a

solution of the acceptor (8 mg mL−1) in chloroform was bladed onto the donor layer. Of

note is that the temperature of the bottom plate of doctor-blade equipment should be

controlled in the range of 40-45 oC, so that the upper acceptor solution can not seriously

permeate into the polymer film. Then methanol solution of PNDIT-F3N-Br at a

concentration of 1.0 mg ml-1 was blade-coated onto the active layer at 2mm/s. To

complete the fabrication of the devices, 100 nm of Ag was thermally evaporated

through a mask under a vacuum of ~5 × 10−6 mbar. The active area of the devices was

four mm2. The devices were encapsulated by glass slides using epoxy in nitrogen-filled

glovebox prior to measurement in ambient condition. For the fabrication of large-area

BHJ and LbL-based PSCs modules: the pre-patterned ITO coated glass substrates

(purchased from South China Science ＆Technology Company Limited ). The ITO,

PEDOT:PSS layer and active layer fabricated as small area devices. And then the

organic layers were partially removed by solvent- assisted mechanical scribing (thread

wiping) corresponding to the P2 scribe, for subsequent serial interconnection of the

individual solar cells. Then methanol solution of PNDIT-F3N-Br at a concentration of

1.0 mg ml-1 was blade-coated onto the active layer at 2mm/s. When coating, the ambient

temperature is about 25oC and the ambient humidity is about 20%. To complete the

fabrication of the devices, 100 nm of Ag was thermally evaporated through a mask

under a vacuum of ~ 5 × 10−6 mbar, during which the each single solar cells were

monolithically interconnected. The current-voltage characteristics of the solar cells

were measured under AM 1.5G irradiation on an Enli Solar simulator (100 mW cm-2).

Before each test, the solar simulator was calibrated with a standard single-crystal Si

solar cell (made by Enli Technology Co., Ltd., Taiwan, calibrated by The National

Institute of Metrology (NIM) of China).

3 Instruments and Characterization

Grazing incidence wide-angle X-ray scattering (GIWAXS) measurements: GIWAXS

measurement was performed at the small and wide-angle X-ray scattering beamline at

the Australian Synchrotron. The 2-dimensional raw data were reduced and analyzed

with a modified version of Nika. The GIWAXS patterns shown were corrected to

represent real Qz and Qxy axes considering the missing wedge. The critical incident

angle was determined using the maximized scattering intensity from sample scattering

with negligible contribution from bottom layer scattering. The shallow incident angle

scattering was collected at 0.02o, which rendered the incident X-ray an evanescent wave

along the top surface of the thin films.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements: TOF‐

SIMS experiments were conducted using a TOF‐SIMS V (ION TOF, Inc. Chestnut

Ridge, NY) instrument equipped with a Bi3+ liquid metal ion gun, Cesium sputtering

gun, and electron flood gun for charge compensation. Cs+ was used as the sputter

source with a 10 keV energy and 6 nA current. The typical sputter area was 50 µm by

50 µm.

Optical measurements and simulations: Absorption spectra of the different store time

blend solid thin films were measured on a Perkin Elmer Lambda 365 UV-Vis

spectrophotometer. The optical simulations were calculated by Fluxim Setfos software.

Space charge limited current (SCLC) measurements: Single carrier devices were

fabricated and the dark current-voltage characteristics measured and analyzed in the

space charge limited (SCL) regime. The structure of hole-only devices was

Glass/ITO/PEDOT: PSS/Semiconductor layer/MoOx (10 nm)/Ag (100 nm). The

reported mobility data are average values over the six devices of each sample.

Photo-induced charge carrier extraction by linearly increasing the voltage (photo-

CELIV) measurements: In photo-CELIV measurements, the devices were illuminated

with a 405 nm laser diode. Current transients were recorded across the internal 50

resistor of our oscilloscope. Here, a fast electrical switch was used to isolate the device

in order to prevent carrier extraction or sweep out. After the variable delay time, the

switch connected the device to a function generator. It applied a linear extraction ramp,

which was 40 μs long and 2.0 V high. Moreover, it started with an offset matching the

Voc of the device for each delay time. To determine the mobility in the devices, photo-

CELIV curves were measured using different experimental conditions, differing in

delay time and applied voltage.

Transient photovoltage (TPV) measurements: For TPV measurements, devices were

directly connected to an oscilloscope in open-circuit conditions (1MΩ). Then the device

was illuminated with a white light LED at different light intensities. A small optical

perturbation was applied using a 405 nm laser-diode which was adjusted in light

intensity to produce a voltage perturbation of ∆𝑉𝑜 < 10 𝑚𝑉 ≪ 𝑉𝑜𝑐. The amount of

charges generated by the pulse was obtained by integrating a photocurrent measurement

(50 Ω) without bias light.

Charge extraction (CE) measurements: For CE measurements, it can be used to

determine the charge density in the active layer of the device at any point in the J-V

curve. The devices were held at a specified voltage in the dark or under illumination.

At a certain time t0 the light is switched off, the cell is switched to short-circuit

conditions, and the resulting current transient is recorded with an oscilloscope. Most of

the charge is extracted in a few microseconds due to a high internal electrical field at

short circuit conditions. In addition, a fast analog switch from Texas Instruments

(TS5A23159) is used to perform the switching from the specified voltage to short

circuit conditions. It provides a very quick switching time (50 ns), a low on-state

resistance (1 Ω), high off-state resistance (> 1MΩ) and a very low charge injection (<<

1015 cm2V-1s-1). A Keithley 2440 source-measurement unit is used to set the initial

device voltage.

Photoluminescence (PL)measurements: The PL data and emission of relevant films

were collected using a Zolix Flex One Spectrometer. The PL excitation wavelength was

set to 532 nm.

Photo-Induced Force Microscopy (P-iFM) measurements: The microscope used is a

VistaScope from Molecular Vista, Inc., operated in dynamic mode using commercial

gold-coated silicon cantilevers (NCHAu) from Nanosensors. The excitation laser is a

LaserTune IR Source from Block Engineering.

Supplemental References

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Isolated D–A Copolymers Based on Benzo[1,2-b:4,5-b′]dithiophene-alt-

dithienylbenzotriazole: Synthesis and Photovoltaic Properties. Chem. Mater. 24,

3247-3254.

2. Lin, Y., Wang, J., Zhang, Z.G., Bai, H., Li, Y., Zhu, D., and Zhan, X. (2015). An

electron acceptor challenging fullerenes for efficient polymer solar cells. Adv.

Mater. 27, 1170-1174.

3. Yang, Y., Zhang, Z.G., Bin, H., Chen, S., Gao, L., Xue, L., Yang, C., and Li, Y.

(2016). Side-Chain Isomerization on an n-type Organic Semiconductor ITIC

Acceptor Makes 11.77% High Efficiency Polymer Solar Cells. J. Am. Chem. Soc.

138, 15011-15018.

4. Bin, H., Gao, L., Zhang, Z.G., Yang, Y., Zhang, Y., Zhang, C., Chen, S., Xue, L.,

Yang, C., Xiao, M., et al. (2016). 11.4% Efficiency non-fullerene polymer solar

cells with trialkylsilyl substituted 2D-conjugated polymer as donor. Nat. Commun.

7, 13651.

5. Zhao, W., Li, S., Yao, H., Zhang, S., Zhang, Y., Yang, B., and Hou, J. (2017).

Molecular Optimization Enables over 13% Efficiency in Organic Solar Cells. J.

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