The most recent application of OLEDs:

Structurally-integrated OLED-based

luminescent chemical & biological sensors

Ruth Shinar

Microelectronics Research Center & ECpE Dept, ISU

Integrated Sensor Technologies, Inc. (ISTI)

Joseph Shinar

All of the aforementioned & ISTI

Support by DOE, NASA, NSF, & NIH also gratefully acknowledged

Outline

Photoluminescence (PL)-based sensors: issues, goalPhotoluminescence (PL)-based sensors: issues, goal Approach:Approach:

Structural integration: OLED excitation sourceStructural integration: OLED excitation source and sensing componentand sensing component

* Applications:* Applications:

Single analyte detectionSingle analyte detection

Multianalyte detectionMultianalyte detection Advanced structural integration: OLED/sensing component/thin film-basedAdvanced structural integration: OLED/sensing component/thin film-based

photodetectorphotodetector

* Application example:* Application example: OO22 sensing sensing

Joseph Shinar and Ruth Shinar,

“Organic Light-Emitting Devices (OLEDs) and OLED-Based Chemical and

Biological Sensors: An Overview,” J. Phys. D: Appl. Phys. 41, 133001 (2008).

Components of PL-Based Sensors:

Excitation sourceExcitation source: : lasers, inorganic LEDs, lampslasers, inorganic LEDs, lamps

Sensing elementSensing element: : a porous film with an embedded luminescent dye, surface immobilizeda porous film with an embedded luminescent dye, surface immobilized

species, or microfluidic channels with recognition elements in solution species, or microfluidic channels with recognition elements in solution

PhotodetectorPhotodetector: : photomultiplier tube, Si photodiode photomultiplier tube, Si photodiode

Electronics and readoutElectronics and readout

Not IntegratedNot Integrated

Issues:Issues: Light-source is either bulky, or the integration with the sensing Light-source is either bulky, or the integration with the sensing

element/microfluidics involves intricate design (fibers, lens)element/microfluidics involves intricate design (fibers, lens) Sensors are often immobile, costlySensors are often immobile, costly Sensors are limited in use for real-world applications; often used for single Sensors are limited in use for real-world applications; often used for single

analyte detectionanalyte detection

Long-Term Goal:Long-Term Goal:

PD

long-pass filter

OLED

band- pass filter sensing component

glass

glass

a-(Si,Ge):H photodetector

OLED PD PD

Back-detection modeBack-detection mode

long-pass filter

glass

low gap a-(Si,Ge):H PD

transparent cover

OLED OLED OLED

band-pass filter over OLED pixels

OLED

microfluidic wells

Front-detection modeFront-detection mode

OLEDs Advantages for Sensor ApplicationsOLEDs Advantages for Sensor Applications

Are simple to fabricate and uniquely simple to integrate Are simple to fabricate and uniquely simple to integrate

with a sensing componentwith a sensing component Can be easily fabricated in any 2-D shapeCan be easily fabricated in any 2-D shape Are compatible with microfluidic structuresAre compatible with microfluidic structures Can be fabricated on plastic substratesCan be fabricated on plastic substrates Can be operated at an extremely high brightnessCan be operated at an extremely high brightness Consume little power and dissipate little heatConsume little power and dissipate little heat Cost is expected to drop to a near-disposable levelCost is expected to drop to a near-disposable level

OLED/Sensing Component IntegrationOLED/Sensing Component Integration

Basic Structure

GLASS OR PLASTIC SUBSTRATE

SENSOR FILM

ORGANIC LAYERS

TRANSPARENT ANODE

CATHODE

+ --

SensingSensing

ElementElement

OLEDOLED

ApproachApproach:structural integration of two structural integration of two componentscomponents:

OLEDs are easily fabricatedOLEDs are easily fabricatedas an array of pixelsas an array of pixels

Sensor operation modes:Sensor operation modes:

(1)(1) monitoring changes in monitoring changes in II

(2)(2) monitoring changes inmonitoring changes in

Back-detectionBack-detection

mode usingmode using

an array of an array of

OLED pixelsOLED pixels photodetectorphotodetector

glasssubstrate

ITOITO

OLEDOLED layerslayers

cathode

Luminescent sensor

OLEDOLEDpixelspixels

EL P LL PP LL

EL

liquid or gas analyteliquid or gas analyte

cathode

1. Oxygen Sensor 1. Oxygen Sensor

R. Shinar et al., Anal. Chim. Acta R. Shinar et al., Anal. Chim. Acta 568568, 190 (2006), 190 (2006)

Principle of operation:Principle of operation:

An oxygen sensitive dye is embedded in a thin film matrix or dissolved in solutionAn oxygen sensitive dye is embedded in a thin film matrix or dissolved in solution

Collisions of OCollisions of O22 with the dye result in quenching of the PL intensity with the dye result in quenching of the PL intensity II and shortening of and shortening of the PL decay time the PL decay time

Stern-Volmer (SV) equationStern-Volmer (SV) equation

II00//II = = 00// = 1 + = 1 + KKSVSV[O[O22]]

II00 and and 00 – unquenched PL intensity and decay time; – unquenched PL intensity and decay time; KKSVSV - Stern-Volmer constant - Stern-Volmer constant

Sensor operation modes: (1) monitoring changes in Sensor operation modes: (1) monitoring changes in II (2) monitoring changes in (2) monitoring changes in

The need for optical filters and frequent calibrationThe need for optical filters and frequent calibrationis eliminated when using the PL decay time mode.is eliminated when using the PL decay time mode.

Results for Gas-Phase Oxygen:Results for Gas-Phase Oxygen:

Integrated OLED/sensing element; back-detectionIntegrated OLED/sensing element; back-detection

Green OLED (AlqGreen OLED (Alq33))//Pt octaethylporphyrinPt octaethylporphyrin ((PtOEPPtOEP)) in a polystyrene filmin a polystyrene film

Wavelength (nm)

350 400 450 500 550 600

Ab

sorb

ance

0.0

0.5

1.0

1.5

2.0

2.5

PtN

N

N

N

C2H5

C2H5

C2H5

C2H5

C2H5

C2H5

C2H5C2H5

II00//II = = 00// = 1 + = 1 + KKSVSV[O[O22]]

S S [[00//((100%100% OO22)]~30-50)]~30-50

PtOEPPtOEP

emission ~635emission ~635 nmnm

Results for Gas-Phase Oxygen:Results for Gas-Phase Oxygen:

Integrated OLED/sensing element; back-detectionIntegrated OLED/sensing element; back-detection

Rubrene (0.5%)-dopedRubrene (0.5%)-doped AlqAlq33//Pd octaethylporphyrin Pd octaethylporphyrin ((PdOEPPdOEP) in a polystyrene film) in a polystyrene film

% O2

0 20 40 60 80 100

0/

0

50

100

150

200

250

Wavelength (nm)

350 400 450 500 550 600

Ab

sorb

ance

0.0

0.5

1.0

1.5

S S [[00//((100%100% OO22)]~240)]~240

PdOEPPdOEP

emission ~645 nmemission ~645 nm

Results for Dissolved Oxygen:Results for Dissolved Oxygen:

Integrated OLED/sensing element; back-detectionIntegrated OLED/sensing element; back-detection

AlqAlq33//PtOEPPtOEP in a polystyrene film or in solutionin a polystyrene film or in solution

II00//II = = 00// = 1 + = 1 + KKSVSV[O[O22]]

% O2

0 20 40 60 80 100

0/

0

5

10

15

20

25

30

toluenetoluene0.01 mg/mL PtOEP0.01 mg/mL PtOEP

ethanolethanol

waterwater

waterwater

Long-term stabilityLong-term stabilitygas-phase oxygengas-phase oxygen

Long-term stabilityLong-term stabilitydissolved oxygendissolved oxygen

Time (days)0 10 20 30 40 50 60

PL

Lif

etim

e (

s)

20

21

22

23

24

25Time (days)

0 5 10 15 20 25 30

(s

)

19.6

19.8

20.0

20.2

20.4

2. Recent Improvements in OLED-Based Oxygen Sensors: 2. Recent Improvements in OLED-Based Oxygen Sensors: Dispersion of TiO Dispersion of TiO22 Particles in the PS:PtOEP Film Particles in the PS:PtOEP Film

Enables use of reduced brightness for enhanced OLED lifetime and reduced Enables use of reduced brightness for enhanced OLED lifetime and reduced

photo-degradation photo-degradation [Zhou et al., Adv. Func. Mater. [Zhou et al., Adv. Func. Mater. 1717, 3530 (2007)], 3530 (2007)]

A uniquely simple approach, using 360 nm-diameter TiOA uniquely simple approach, using 360 nm-diameter TiO22 particles. particles.

Enhancement is due to light scattering by the high refractive index particles, & possibly by Enhancement is due to light scattering by the high refractive index particles, & possibly by voids induced by the particles.voids induced by the particles.

Typically, the sensor films were prepared by drop casting 40-60Typically, the sensor films were prepared by drop casting 40-60 LL of the solution of the solution onto the glass substrate; the resulting films were all ~ 8onto the glass substrate; the resulting films were all ~ 8 mm thickthick

SEM images of PS films doped with PtOEP and titania particles: SEM images of PS films doped with PtOEP and titania particles: (a)(a) 2 mg/mL TiO2 mg/mL TiO22 in the solution used for film fabrication, (b) 8 mg/mL particles in the solution used for film fabrication, (b) 8 mg/mL particles..

(a) (b)

The PL spectra in air, excited at ~The PL spectra in air, excited at ~535535 nm by the nm by the AlqAlq33 OLEDOLED, of , of PtOEPPtOEP:PS doped with :PS doped with

different concentrations of TiOdifferent concentrations of TiO22, measured in reflection geometry., measured in reflection geometry.

In Air

The effect of titania particles on the PtOEP:PS The effect of titania particles on the PtOEP:PS PLPL decay curves and on the decay curves and on the ELEL of the of the AlqAlq33 OLEDOLED in a 100% gas-phase Ar environment at 295 K. Shown is the intensity measured by in a 100% gas-phase Ar environment at 295 K. Shown is the intensity measured by the PD during and following the 50the PD during and following the 50 ss AlqAlq33 OLED OLED pulse at titania particle concentrations pulse at titania particle concentrations of 0, 1.5, 2, 4, and 8 mg/mL. A 610 nm long-pass filter was placed in front of the PD, so of 0, 1.5, 2, 4, and 8 mg/mL. A 610 nm long-pass filter was placed in front of the PD, so that only a small fraction of the OLED emission reached the PD. Inset: the PL signal that only a small fraction of the OLED emission reached the PD. Inset: the PL signal enhancement vs. the titania particle concentration. enhancement vs. the titania particle concentration.

Gas-Phase

The PL decay curves in Ar- and OThe PL decay curves in Ar- and O22-saturated solutions for: (a) PtOEP and (b) PdOEP with -saturated solutions for: (a) PtOEP and (b) PdOEP with

and and

without titania doping; the exponential (Ar) and bi-exponential (Owithout titania doping; the exponential (Ar) and bi-exponential (O22) fitting are also shown.) fitting are also shown.

(a)

DO in Water

Green Alq3 OLED/PtOEP

The green The green AlqAlq33 OLED array is behind the OLED array is behind the PtOEPPtOEP-film, which is largely confined to a -film, which is largely confined to a

region in front of the middle two OLED pixels.region in front of the middle two OLED pixels.

The The greengreen emission from these pixels combines with the emission from these pixels combines with the redred PL of the PL of the PtOEPPtOEP dye to dye to

produce the observed produce the observed yellowishyellowish spots. spots.

The photodetector is located behind the OLED array.The photodetector is located behind the OLED array.

Example of sensor design & operation – Example of sensor design & operation – GreenGreen OLEDOLED//PtOEPPtOEP embedded in polystyrene embedded in polystyrene

3. Oxidases-Based Multianalyte Sensor Array3. Oxidases-Based Multianalyte Sensor Array

(based on the preceding O(based on the preceding O22 sensor) sensor)

glucose + O2 glucose oxidase

PtOEPnormal level:~100 mg/dL (5.5 mM)

ethanol + O2

lactate + O2

alcohol oxidasePtOEP

Legal limit: ~0.1% = 0.1 mg/dL (~2.2 mM)

H2O2 + gluconic acid

H2O2 + pyruvic acid

O

H2O2 + H3C C H

lactate oxidase PtOEPNormal level:Venous blood: 4.5-19.8 mg/dL (0.56-2.46 mM); Arterial blood: 4.5-14.4 mg/dL

Choudhury et al., J. Appl. Phys. Choudhury et al., J. Appl. Phys. 9696, 2949 (2004)., 2949 (2004).

OxygenOxygen GlucoseGlucose EthanolEthanol LactateLactate

0 100 200 300 400 500

0.000

0.001

0.002

0.003

Alcohol = 80 s

Time (s)

0 100 200 300 400 500

0.000

0.001

0.002

0.003

Lactate = 87 s

Time (s)

0 100 200 300 400 5000.000

0.002

0.004

0.006Oxygen = 100 s

PL

In

ten

sit

y (a

. u)

Time (s)

0 100 200 300 400 5000.000

0.002

0.004

0.006

Glucose = 83 s

Time (s)

OLED pixel pair #1 2 3 4 5 6

R. Shinar et al., SPIE Conf. Proc. 6007, 600710-1 (2005).

Multianalyte Sensor in Operation: consecutive sensing using a Multianalyte Sensor in Operation: consecutive sensing using a single photodetectorsingle photodetector

Multianalyte Sensor Array: simultaneous monitoringMultianalyte Sensor Array: simultaneous monitoring

small-size sensor array (e.g., total size small-size sensor array (e.g., total size ~1.5x1.5 cm~1.5x1.5 cm22))

sensing element: Osensing element: O22-sensitive dye (-sensitive dye (PtOEPPtOEP) ) and an analyte-specific oxidase enzymeand an analyte-specific oxidase enzyme

each sensing element is associated with 2 each sensing element is associated with 2 OLED pixelsOLED pixels

sensing of the different analytes in a single sensing of the different analytes in a single sample is obtained by addressing the sample is obtained by addressing the appropriate OLED pixelsappropriate OLED pixels

simultaneous sensing of the different analytes simultaneous sensing of the different analytes in a single sample is obtained when all OLED in a single sample is obtained when all OLED pixels are lit simultaneously, and the PL of pixels are lit simultaneously, and the PL of each analyte is monitored by its associated Si each analyte is monitored by its associated Si photodiode. A Labview program enables such photodiode. A Labview program enables such simultaneous monitoring via separate simultaneous monitoring via separate channels.channels.

ITO anode

OLED pixel

Al cathode

silicon photodiode array

6 mm

Y. Cai et al., Sensors & Actuators B 134, 727 (2008).

In reactions performed in In reactions performed in sealedsealed wells, where there is no replenishing of O wells, where there is no replenishing of O22, and , and

the initial concentration of the analyte does not exceed that of the initial DO the initial concentration of the analyte does not exceed that of the initial DO

(~0.25 mM in water at 23(~0.25 mM in water at 23ooC)C)::

Sensing in Sealed Wells: Assessing the limit of detectionSensing in Sealed Wells: Assessing the limit of detection

[DO][DO]finalfinal = [DO] = [DO]

initialinitial – [analyte] – [analyte]initialinitial

Modified SV equationModified SV equation::

II00//II = = 00// = 1 + = 1 + KKSVSV××{{[DO][DO]initialinitial – [analyte] – [analyte]

initialinitial}}

GOxGOxGlucose +OGlucose +O22 HH22OO22 + gluconic acid + gluconic acid

Reaction Time (sec)

0 20 40 60 80 100 120

PL

Lif

etim

e (

s)

20

40

60

80

1000.05 mM 0.1 mM 0.15 mM 0.2 mM 0.25 mM 0.3 mM 0.35 mM

37oC; cell open to air; lactate monitoring

Multianalyte mixture sensingMultianalyte mixture sensing

sequential monitoringsequential monitoring simultaneous monitoring simultaneous monitoring

23oC; sealed containers

Modified SV equation:Modified SV equation:

II00//II = = 00// = 1 + = 1 + kkSVSV××{{[DO][DO]initialinitial – [analyte] – [analyte]initialinitial}}

circles: ethanolsquares: lactatetriangles: glucose

Simultaneous detection using a 5×5 mmSimultaneous detection using a 5×5 mm22 Si photodiode array. Si photodiode array.

LOD LOD ~0.02 mM~0.02 mM; dynamic range: ; dynamic range: 0.25 mM0.25 mMat 23at 23ooC in the final, diluted sample.C in the final, diluted sample.

4. Bacillus Anthracis (Anthrax) Lethal Factor (LF)

Principle of Operation: R. T. Cummings et al. Proc. Nat. Acad. Sci. 99, 6603 (2002)

The LF enzyme, one of three proteins of the Anthrax toxin, a Zn-dependent

metalloprotease, cleaves certain peptides at specific sites.Fluorescence detection of LF is therefore possible by using a peptide- based

FluorescenceResonance Energy Transfer (FRET) assay.

FRET-labeled peptide sequence:

(donor)-Nle-K-K-K-K-V-L-P--I-Q-L-N-A-A-T-D-K- (acceptor) G-G-NH2

Peptides with donor and acceptor on either side of the cleaving site are synthesized

In this D-A configuration, the fluorescence of the donor is quenched by the acceptor

Following exposure to LF, the peptide is cleaved; the donor and acceptor are

separated, resulting in an increase in the detected intensity of the donor fluorescence.

cleaving site

Selected examples showing the effect of the concentration of the peptide on the photoluminescence using 25 nM LF

Time (min)

0 10 20 30 40 50 60

PL

Ch

ange

(%

)

0

10

20

30

40

50

60

70

3.2 M

4.5 M

7.5 M

22.5 M

37.5 M76.5 M The maximal increase in the PL

following exposure of the labeled peptide to LF was by a factor of 2 at 37 oC

To improve sensitivity, need to eliminate OLED tail that overlaps the donor emission.Turn to Ru dye (exc=385 nm, red emission):bis(2,2’-bipyridine)-4’-methyl-4-carboxybipyridine-Ru N succinimidyl ester-bis(hexafluorophosphate)& QSY21 quencher.

5. Hydrazine (N2H4)

Highly toxic but popular NASA monopropellant & common precursor in the

synthesis of some polymers, plasticizers and pesticides M. P. 2°C, B. P. 113.5°C, room temp vapor pressure 14.4 torr Gov’t recommended exposure limit is 10 ppb for 8 hrs Immediately dangerous to life or health at ~50 ppm Detection based on reaction of hydrazine with

anthracene 2,3-dicarboxaldehyde (ADA).

Reaction product emits at 549 nm (exc= 476 nm) Signal proportional to N2H4 concentration Good for air, solution Fast and very selective response

S. Rose-Pehrsson and G. E. Collins, US Patent 5,719,061)

ADA

H

H

PL change upon ADA exposure to 60 ppb hydrazine in Ar

The limit of detection (LOD) is

60 ppb in ~1 min, or ~1 ppb in

1 h, exceeding the OSHA-

allowed limit of 10 ppb over 8

hrs by a factor of 80

Hydrazine

6. Enhanced Integration: OLED/Sensing Element/Photodetector6. Enhanced Integration: OLED/Sensing Element/Photodetector

PDPD

long-pass filterlong-pass filter(large gap; cuts blue)(large gap; cuts blue)

OLEDOLED

band-pass filter over OLED pixelsband-pass filter over OLED pixelssensing componentsensing component

(thin) glass(thin) glass

glassglass

nanocrystalline ornanocrystalline ora-(Si,Ge):H low-gap PDa-(Si,Ge):H low-gap PD

OLEDOLEDPDPD PDPD

Back DetectionBack Detection

Envisioned fully integrated OLED/sensing film/thin film PD array in a back Envisioned fully integrated OLED/sensing film/thin film PD array in a back

detection configuration. Grounded Al stripes between the OLEDs and PDs will detection configuration. Grounded Al stripes between the OLEDs and PDs will

block the edge EL and the synchronous electromagnetic noise generated by block the edge EL and the synchronous electromagnetic noise generated by

modulated OLEDs.modulated OLEDs.

long-pass filterlong-pass filter

glassglass

glass/PDMSglass/PDMS

low gap a-(Si,Ge):H PDlow gap a-(Si,Ge):H PD

wells or wells or microfluidic microfluidic channels channels

transparent covertransparent cover

Towards complete integration: front detectionTowards complete integration: front detection

OLEDOLED OLEDOLED OLEDOLED

Band-pass filter over OLED pixelsBand-pass filter over OLED pixels

OLEDOLED

OLED/Sensing Component/Photodetector IntegrationOLED/Sensing Component/Photodetector Integration

First Step:First Step:

Structural integration of two components:Structural integration of two components:

the the sensing elementsensing element and an and an

a-Si thin film-based a-Si thin film-based photodetectorphotodetector

Second Step: single element; front detectionSecond Step: single element; front detection

structural integration of three components:structural integration of three components:

OLEDOLED//sensingsensing elementelement//PD; PD; II mode of operation mode of operation

The three-component integration is attractive due to the potential for The three-component integration is attractive due to the potential for

miniaturization of sensor arrays, their fabrication on flexible substrates, and miniaturization of sensor arrays, their fabrication on flexible substrates, and

integration with microfluidicsintegration with microfluidics

R. Shinar et al., J. Non Cryst. Solids R. Shinar et al., J. Non Cryst. Solids 352352, 1995 (2006)., 1995 (2006).

OLED lightOLED light

gas flow

530 nm band-pass filter

long-pass filter

sensor

PD

PDsPDs

PECVD-grown p-i-n and n-i-p structures, based on a-Si and a-(Si,Ge), or PECVD-grown p-i-n and n-i-p structures, based on a-Si and a-(Si,Ge), or

nc-Si.nc-Si.

The p-i-n structures were fabricated on an ITO-coated glass substrate; the The p-i-n structures were fabricated on an ITO-coated glass substrate; the

ITO was protected from reduction by the hydrogen plasma with a 0.1 ITO was protected from reduction by the hydrogen plasma with a 0.1 m m

thick ZnO layer grown by RF sputtering.thick ZnO layer grown by RF sputtering.

The composition and thickness of the p & i layers were tuned to increase The composition and thickness of the p & i layers were tuned to increase

the sensitivity at wavelengths matching the emission band of the oxygen-the sensitivity at wavelengths matching the emission band of the oxygen-

sensitive dye and to reduce the sensitivity to the OLED background.sensitive dye and to reduce the sensitivity to the OLED background.

The emphasis was on The emphasis was on

(a)(a)improving the Oimproving the O22 detection sensitivity by improving the PDs & reducing detection sensitivity by improving the PDs & reducing

the synchronous OLED-generated electromagnetic noise the synchronous OLED-generated electromagnetic noise

(b)(b)understanding factors that affect the speed of the PDsunderstanding factors that affect the speed of the PDs

The PDs were first tuned for high sensitivity at the PtOEP/PdOEP emission wavelength The PDs were first tuned for high sensitivity at the PtOEP/PdOEP emission wavelength

(~635/650 nm) and minimal response at the OLED excitation (~535 nm). The a-(Si,Ge)-(~635/650 nm) and minimal response at the OLED excitation (~535 nm). The a-(Si,Ge)-

based PDs are preferred due to their match with the dye PL, and lower response at the EL based PDs are preferred due to their match with the dye PL, and lower response at the EL

band. However, their dark current was higher and their speed lower.band. However, their dark current was higher and their speed lower.

TUNING of the PDsTUNING of the PDs

Wavelength (nm)500 600 700 800

Qua

ntum

Eff

icie

ncy

0.0

0.1

0.2

0.3

0.4

0.5

a-Si:Ha-Si:H a-(Si,Ge):Ha-(Si,Ge):H (0.7 m)

Wavelength (nm)

350 400 450 500 550 600A

bso

rban

ce0.0

0.5

1.0

1.5

2.0

2.5

emission ~635emission ~635 nmnm

PtOEPPtOEP (0.5 m)0.15 m p-layer

0.3 m p-layer1.6% Ge in p-layer10% Ge in i-layer

Detection of the photoluminescence of PtOEP embedded in polystyrene by the a-(Si,Ge):H- based photodetector, using a 600 nm long-pass filter

Sensor Film/Photodetector Integration

Excitation Wavelength (nm)

500 510 520 530 540 550 560

Res

pon

se (V

)

50

100

150 100% N2

100% O2

air

OO22 sensor: lamp-monochromator/ sensor: lamp-monochromator/

PtOEP-based sensor film/thin-film PDPtOEP-based sensor film/thin-film PD

% O2

0 20 40 60 80 1000

5

10

15

20

25

Detection of the photoluminescence ofDetection of the photoluminescence of PtOEP PtOEP embedded in polystyreneembedded in polystyreneby the a-(Si,Ge):H- based photodetector using a 620 nm band-pass filterby the a-(Si,Ge):H- based photodetector using a 620 nm band-pass filter to to reduce the background, and therefore increase the sensitivity.reduce the background, and therefore increase the sensitivity.

II00//II = = 00// = 1 + = 1 + KKSVSV[O[O22]]

S [I0/I(100% O2)]~23

I 0/I

OLED/Sensing Component/Thin-Film Photodetector IntegrationOLED/Sensing Component/Thin-Film Photodetector Integration

Single elementSingle element: front detection: front detection

Initial integration resulted in low Initial integration resulted in low S S attributed to a large attributed to a large background stemmingbackground stemming from the broad OLED EL, and high PDs’ dark current.from the broad OLED EL, and high PDs’ dark current. A major reason to the low A major reason to the low SS is the synchronous electromagnetic is the synchronous electromagnetic (EM) noise from (EM) noise from the pulsed OLED when using lockin detection of the intensity.the pulsed OLED when using lockin detection of the intensity. SS improved significantly by improved significantly by shielding the OLED. shielding the OLED.

To shield the PD from this EM noise, a grounded 150 nm thick ITO-coated To shield the PD from this EM noise, a grounded 150 nm thick ITO-coated

glass was placed above the OLED.glass was placed above the OLED.

OO22 sensor, sensor, II mode operation: mode operation: OLEDOLED//PdOEPPdOEP:PS/thin-film PD:PS/thin-film PD

Examples of Examples of SVSV plots of different sensors, each with the three-component plots of different sensors, each with the three-component

integration, i.e., unshielded and shielded Alqintegration, i.e., unshielded and shielded Alq33 OLED/PdOEP:PS/a-(Si,Ge) PD, OLED/PdOEP:PS/a-(Si,Ge) PD,

and double-shielded coumarin-doped Alqand double-shielded coumarin-doped Alq33 OLED/PdOEP:PS/nc-Si PD OLED/PdOEP:PS/nc-Si PD

Shielding the PD improved the Shielding the PD improved the

responseresponse. . The best results were The best results were

obtained for the double shielded, obtained for the double shielded,

coumarin-doped Alqcoumarin-doped Alq33;;

SS ~ 47, improved strongly over the ~ 47, improved strongly over the

value of ~7 achieved with value of ~7 achieved with

unshielded Alqunshielded Alq33 OLEDs. OLEDs.

0 20 40 60 80 1000

10

20

30

40

50

unshielded, Alqunshielded, Alq33 OLED OLED

shielded, shielded, AlqAlq33 OLED OLED

double shielded, coumarin-doped Alqdouble shielded, coumarin-doped Alq33 OLED OLED

I 0/I

% Oxygen

Towards operation in the Towards operation in the modemode

Concluding Remarks

OLED science and technology is undergoing explosive growth Structurally integrated OLED-based sensors are very promising Organic photovoltaics & organic field-effect transistors are also

growing at an extremely rapid clip. They deserve a separate

treatment. See Sumit Chaudhary’s ECpE course on Organic

Electronics.