Plasmon Enhanced Solar Cells

Björn Törngren,1 Simon Sandén,2 Kenta Akitsu,3 Takaya Kubo,3

Hiroshi Segawa,3 Ronald Österbacka,2 Jan-Henrik Smått1

1 Center for Functional Materials, Physical Chemistry, Åbo Akademi University, Turku, Finland.

2 Center for Functional Materials, Physics, Åbo Akademi University, Turku, Finland.

3 Research Center for Advanced Science and Technology (RCAST),

The University of Tokyo, Tokyo, Japan

FunMat annual symposium – Helsinki 14.08.2013

Joint project with RCAST

Plasmon Enhanced Organic Hybrid Solar Cells (POHSC) – 3 yr

Physical Chemistry (Lindén/Smått) and Physics (Österbacka)

Research Center for Advanced Science and Technology (RCAST), The

University of Tokyo, Japan (Prof. Segawa)

Several research visits between Finland and Japan

POHSC – general outline

PhysChem (ÅAU):

Synthesis and

modification of core-

shell nanoparticles

RCAST (UT):

Development of novel

dyes (NIR) –

porphyrin-based

Solar cell applications:

Assembly into DSSC and organic SC

Physics (ÅAU):

Modeling of

plasmonic core-shell

particles

Plasmon enhanced NPs

NPs with

tunable

absorption

properties 300 400 500 600 700 800 900

Ab

sorb

an

ce

(a.u

.)

Wavelength (nm)

Surface plasmons (SPs) are coherent oscillations of conduction

electrons on a metal surface excited by electromagnetic radiation

at a metal-dielectric interface

Resonance at a specific wavelength (Au NPs: ~530 nm)

Willets, K. A.; Van Duyne, R. P. Ann. Rev. Phys. Chem. 2006, 58, 267.

The surface plasmon effect

10 nm

Glass

ITO

P3HT

PCBM

Gold

P3HT PCBM

Dye-sensitized solar cells Organic or hybrid solar cells

Surface plasmons in solar cells

Current topics of the project

Stability issues of core/shell nanoparticles in DSSCs

Plasmon-enhanced polymer-sensitized solar cells

(PSSC)

Charge generation and charge transport studies

Gold nanorods to modify the light absorption range

Plasmonic particles in organic bulk hetero-junction

solar cells

Core-shell Au@SiO2 nanoparticles

Why is a thin silica shell needed?

Prevents quenching of the generated

plasmons

Should be thin enough to allow the

dye molecules to be close enough

(near-field enhancement)

Gold is very soluble in the electrolyte

solution used in DSSCs (I3–)

A silica coating protects the gold core

Sheehan et al. J. Phys. Chem. C, 2013, 117, 927−934

Synthesis approaches

Turkevich approach:

~15 nm gold cores

Na2SiO3

Coating thickness and completeness APS APS +

Stöber

MPTMS Direct Stöber

Gold core diameter: 16 nm

Modeling of silica thickness (Mie theory)

APS: 0.5 nm APS + Stöber: 5 nm MPTMS: 1.3 nm Direct Stöber: ~20 nm

Chemical stability in iodide electrolyte

Coating methods:

A: APS B: APS + Stöber

C: Direct Stöber D: MPTMS

Temperature stability of Au@SiO2 NPs

Au@SiO2 NPs (MPTMS method)

RT 500 ºC

Heating required for sintering of TiO2 NPs in a DSSC could

potentially damage the silica shell No detectable difference!

Assembly of (plasmon-enhanced) DSSC

TiO2 nanoparticle paste (w/ or w/o Au@SiO2 NPs) screen-printed on the substrate, and sintered at 500 °C

Electrolyte injection Placing two electrodes

FTO/Glass substrate

TiO2 nanoporous layer

Pt coated-FTO

The TiO2 substrate was immersed in the solution overnight

Solar cell structure

Dye solution

Photoanode

Spacer

Injection hole

Electrolyte

(30 µm)

Pt-coated FTO

Photoanode

Solar cell fabrication (I3

–/I– redox couple

in acetonitrile)

Slide courtesy of Kenta Akitsu

Plasmon-enhanced DSSC performance

Sample Au@SiO2 Thickness

[µm]

VOC

[V]

JSC

[mA/cm2]

FF PCE

[%]

A1 1 wt% 1.726 0.85 4.0 0.68 2.3

A2 1 wt% 1.899 0.85 3.9 0.68 2.3

T1 – 1.844 0.85 3.7 0.68 2.2

T2 – 1.868 0.85 3.4 0.69 2.0

B. Törngren et al. J. Colloid Interface Sci., in preparation.

Polymer-sensitized solar cell (PSSC)

Polythiophene derivative polymers where

COOH units are attached to the polymer

backbone to facilitate sensitization to TiO2

Uses a low molecular weight polymer as

dye (here: PT-C 85, i.e. HR 85%)

Electrolyte solution

Pt/FTO

TiO2/Polymer FTO

R=H, Me

PT derivative with carboxylic acid groups

MW: 1100, 2700

Hydrolysis ratio (H:Me ratio)

can be varied 0%-95%

Akitsu et al. Jpn. J. Appl. Phys. 51 (2012) 10NE04

Plasmon-enhanced PSSCs

TiO2 paste incorporating 1 wt% Au@SiO2 NPs was manufactured

Photoanode was made by screen-printing on FTO

PT-C 85 was adsorbed onto the TiO2 layer overnight

Akitsu et al., in preparation.

I-V and IPCE of Plasmon Enhanced PSSCs 7

6

5

4

3

2

1

0

Cu

rren

t d

ensi

y,

mA

/cm

2

0.60.50.40.30.20.10

Voltage, V

70

60

50

40

30

20

10

0

IPC

E,

%

700600500400300

Voltage, V

3 layers

2 layers

1 layer

Sample Voc Jsc FF

Au 1 0.52 2.2 0.55 0.6

Ref 1 0.52 1.1 0.52 0.3

Au 2 0.53 4.6 0.55 1.3

Ref 2 0.50 3.7 0.55 1.0

Au 3 0.53 5.9 0.51 1.6

Ref 3 0.50 5.0 0.54 1.4

Dashed: with

Au@SiO2 NPs

Solid: without

Au@SiO2 NPs

IPCE enhancement factor: IPCE(Au)/IPCE(Ref)

IPCE enhancement over 400-650 nm

Peak slightly red-shifted compared to absorption of Au@SiO2 NPs

in EtOH larger dielectric constant of TiO2

3.0

2.5

2.0

1.5

1.0

0.5

Au/R

ef., -

650600550500450400350300

Wavelength, nm

1.4

1.2

1.0

0.8

0.6

Au/R

ef., -

650600550500450400350300

Wavelength, nm

0.14

0.12

0.10

0.08

0.06

0.04

0.02

0.00

Abso

rban

ce, -

Au@SiO2 NPs in EtOH

Outlook of other possibilities

Au nanorods to enhance

absorption in NIR region

Plasmonic particles in organic

BHJ solar cells

0

0.2

0.4

0.6

0.8

1

1.2

1.4

300 400 500 600 700 800 900

Ab

sorb

an

ce (

a.u

.)

Wavelength (nm)

Gold nanoparticles

Gold nanorods

Longitudinal

mode

Aspect ratio ~3

Transverse

mode

10 nm

Glass

ITO

P3HT PCBM Gold

Au NPs

Summary

Plasmonic particles (e.g. gold nanoparticles) have proven

useful for improving the efficiency of photovoltaic devices

A thin but complete silica shell is needed to protect the Au

NPs in the harsh electrolyte solutions used in DSSCs

Plasmon-enhanced polymer-senisitized solar cells (PSSCs)

have been manufactured using novel polythiophene

derivative polymers

In both DSSCs and PSSCs the efficiency can be improved by

incorporating Au@SiO2 nanoparticles

Make your own DSSC

Within FunMat we would

like to give you the

opportunity to learn how

to make your own DSSCs

The plan is to start

sometime during the fall

Contact Björn Törngren

(btorngre@abo.fi) for

more information

Screen-printer device at ÅAU