Complete Intrinsic Coincident Polarimetry using Stacked Organic

Photovoltaics

MS - Thesis Defense…………………………..

Subharup Gupta Roy

Committee………………………………………

Michael W Kudenov

Brendan T O’Connor

John F Muth

Overview

Motivation State of the Art Organic Photovoltaics Device Characterization Polarimeter Model Calibration & Experiment Results Model Validation Polarimeter Design Validation Conclusion Future Scope

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Abundance of polarized light

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Polarized Light

&

Imaging Polarimetry

Needs Assessment

Polarimetry or quantifying polarization state of light has numerous applications in –i. Ellipsometryii. Biomedical imagingiii. Remote sensingiv. Deep space imagingv. Atmospheric sciencesvi. Telecommunications

etc.

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State of the Art

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a) Division of Focal Plane Polarimeter

b) Division of Amplitude polarimeter (BS = beam-

splitter, PO = polarization optics)

c) Division of time polarimeter

(a) (c)

(b)

Shortcomings of Imaging Polarimeters

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Technique Size Weight Power Cost Calibration Registration Temp. Res.

Spatial Res.

DoT DoAM DoA CB CH DoF

State of the art polarimeters have consistently suffered from lack of spatial and temporal resolution, and thereby triggered the

need to design a polarimeter with inherent spatial and temporal registration.

Acronyms: Division of Time (DoT); Division of Amplitude (DoAM); Division of Aperture (DoA); coboresighted (CB);

channeled (CH); Division of Focal Plane (DoF).

Research Approach

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Key features:

• Cascaded photo-

detectors

• Semitransparent, organic

photovoltaics

Organic Photovoltaics (OPVs)

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P3HT:PCBM

Fabrication process to strain align the active layers of the OPVs

Structure of semi-transparent, strain-aligned, polarization sensitive OPVs

Gold Layer

ITO Layer

Device1Device 2

Glass Substrate

P3HT:PCBM

Properties of OPVs

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• OPVs respond to incident light, spanning a wavelength range of approx. 450 nm to 650 nm.

• A marked difference in current density, generated by parallel and perpendicular polarization states of incident

light, is observable.

Device Characterization

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Aim: Establish a feasible range of values for:

• Tx

• Ty

• D.

• φ.

No. of Samples: 14

• LP1 and LP2 are aligned parallel

• OPV is rotated from 0o to 360

o, steps of 10

o

• Intensity recorded for each orientation of OPV

Characterization Results

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Sample # Strain (%) Diattenuation Retardance (o)

1 30 0.317 6.3562 30 0.3456 3.21853 30 0.2866 5.8244 30 0.2826 3.1475

Average values of:

• Tx ~ 0.6

• Ty ~ 0.2

• D ~ 0.3

• Φ ~ 7o

Range:

• 0.52 < Tx < 0.65

• 0.19 < Ty < 0.42

• 0.27 < D < 0.41

• 2o

<φ<12o

. OPV R DM M M

Polarimeter Model

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• T+A+R=1, while R=0

• For transmission:

while,

• For absorption:

where,

A = 1 - T

1 0 01 0 0

,0 0 2 00 0 0 2

DD

EE

DM

, ,x y x y

x y x y

T T T TD E

T T T T

,x y

x y

A AD

A A

,x y

x y

A AE

A A

• MOPV1 = MAOPV1

• MOPV2 = MAOPV2 . MTOPV1

• MOPV3 = MAOPV3 . MTOPV2 . MTOPV1

R. M. A. Azzam, Arrangement of four photodetectors for measuring the state of polarization of light, Opt. Lett, vol. 10, pp. 309- 311,

1985.

Experimental Setup

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• 532 nm laser source

• 3 laser powers (5.24 mW,

5.84 mW, 6.81 mW)

• Rotating HWP generates

different input Stokes

vectors

• OPV1 - OPV3 detect S0,

S1, and S3

• Continuous monitoring of

incident laser power to

correct for fluctuations

Data Acquisition Techniques

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• OPVs are reverse biased (0.4

V)

• Load resistance of 10 kΩ

• Chopper modulates input

signal at 200 Hz

• Oscilloscope detects voltage

across OPV

Oscilloscope Output

Primary data acquisition for this thesis was performed by a Semiconductor Parameter Analyzer (SPA). Alternate

acquisition methods were also experimented.

Radiometric Calibration The acquired data provides P (3x1). S (3x1) is different polarization

states of incident light. W is the measurement matrix. η is the responsivity of the devices.

P= η x W x S Measure η (3x3) and each row of W (3x3) with lots of S’s. [η x W] is expressed as:

W is obtained from first row of the following matrices:

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• MOPV1 = MAOPV1

• MOPV2 = MAOPV2 . MTOPV1

• MOPV3 = MAOPV3 . MTOPV2 . MTOPV1

1 11 12 13

2 21 22 23

3 31 32 33

0 0

0 0 ,

0 0

w w w

w w w

w w w

η W[η x W]

η1

η2

η3

w11 w12 w13

w21 w22 w23

w31 w32 w33

Radiometric Calibration contd…

In the calibration process, the responsivity η and the measurement matrix (W) of the polarimeter was determined. W is a 3x3 matrix.

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Different Stokes vectors generated by a HWP

(57x3)

Power detected

by OPVs (57x3)ith

row of W matrix

where Q is the number of measurements, subscript i denotes the ith

OPV, S0, S1, S2 are Stokes parameters of light, incident on ith OPV, ηi

is responsivity of ith

OPV, and subscript i also corresponds to the row number of W matrix.

0,0 1 0 2,0

0,1 1,1 2,1

1

1

2

,1

2

3

,0 ,

0,Q ,Q ,

i

i

i,Q

i

i

i

Q

i

S S S

S S

P

P

P S

wS

w

Sw

S

Results

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Electrical power versus HWP orientation

• (a) OPV1

• (b) OPV2

• (c) OPV3

𝐖=[1 0.126 −0.0021 −0.321 −0.1591 −0.312 0.283 ]

Measured by the SPA at

• P1 (5.24 mW)

• P2 (5.84 mW)

• P3 (6.81 mW)

• The elements of the W matrix are modified to achieve the best fit.

• The best coefficients of the fitting function provided the W matrix.

Electrical power calculated by RADIOMETRIC

fit

• P1F

• P2F

• P3F

𝛈=[0 .0194 0 00 0.0168 00 0 0.0124]

Model Validation

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Electrical power versus HWP orientation

• (a) OPV1

• (b) OPV2

• (c) OPV3

𝐖=[1 0.1259 0 01 −0.3195 −0.167 −0.02211 −0.3195 0.295 0.0391 ]

Measured by the SPA at

• P1 (5.24 mW)

• P2 (5.84 mW)

• P3 (6.81 mW)

• The OPVs’ parameters (Ty, D, φ) are modified to achieve the best fit.

• The best coefficients of the fitting function provided the W matrix.

Electrical power calculated by PARAMETRIC

fit

• P1F

• P2F

• P3F

Model Validation contd…

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Transmittance Retardance Responsivity (mA/W)

Ty1 Ty2 ϕ1 ϕ2 η1 η2 η3

0.373 0.348 10.008 7.557 14.41 13.7 12.12

• W matrix obtained by parametric and radiometric calibration

procedures resemble closely (RMS error 4.7%).

• Ty, φ values obtained by the fitting procedure fall within acceptable

range, determined during characterization.

Hence, the model was concluded to be an accurate representation of the OPV devices.

Acceptable Range:

• 0.52 < Tx < 0.65

• 0.19 < Ty < 0.42

• 0.27 < D < 0.41

• 2o

<φ<12o

Polarimeter Design Validation

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PL (mW) LP1 (Deg) Type S0(mW) Error

(%) S1/S0 S2/S0 Error (%)

5.24 70Theo 2.409

-2.24-0.766 0.643

0.56Meas 2.355 -0.771 0.649

5.84 90Theo 2.685

-1.75-1.000 0.000

1.58Meas 2.638 -1.000 -0.022

6.81 40Theo 3.134

-1.530.174 0.98

1.64Meas 3.086 0.169 1.007

6.81 120Theo 3.134

3.19-0.500 -0.866

0.95Meas 3.234 -0.494 -0.851

The average S0 error was 2.2%. Normalized Stokes parameters

RMS error was 1.2%.

Conclusion

The theoretical model, calibration procedure, and experimental validation of an intrinsic coincident polarimeter were presented.

It was demonstrated that the use of semi-transparent, polarization sensitive OPVs allowed us to leverage the advantages of the cascaded photo-detector approach and thereby ensured inherent spatial registration.

Since, the responses of each OPV were measured simultaneously, high temporal resolution was also achieved.

This new polarimeter design could predict unknown incident S0 with an absolute average error of 2.2%, while RMS error of normalized Stokes parameters was 1.2%.

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Future Scope

1. Extend the linear polarimeter design to include circular polarization detection.

2. Modify the structure of the OPVs, such that, a monolithic layered device can be used, instead of the stacked devices approach.

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Acknowledgement

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Funded by National Science Foundation

Award # ECCS-1407885

My committee members

Michael W Kudenov

Brendan T O’Connor

John F Muth

From O’Connor Research Group

Omar M Awartani

Pratik Sen

Complete Intrinsic Coincident Polarimetry using Stacked Organic

Photovoltaics

Questions

MS - Thesis Defense…………………………..

Subharup Gupta Roy

Committee………………………………………

Michael W Kudenov

Brendan T O’Connor

John F Muth