Incoherent Propagation of Light in Coherent Models

Andrej Čampa, Janez Krč and Marko Topič

University of Ljubljana

Faculty of Electrical Engineering

Tržaška cesta 25, SI-1000 Ljubljana, Slovenia

Outline

Introduction

Incoherent propagation of light

Thinning down the incoherent layer

Model

Results

Conclusions

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 2

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 3

Example of a-Si thin-film solar cell structure

1. Incoherent propagation of light

2. Thining down of thick glass layer - mm range to nm range!

air

Incoherent propagation of light

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 4

In many optical cases light loses coherence: 1. Spatial incoherence 2. Spectral incoherence 3. Temporal incoherence

E

Incoherent light does not interfere, we have to eliminate constructive and destructive interference in coherent models

Constructive interference

+

=

+

=

Destructive interference

Incoherent propagation of light

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 5

In rigorous simulations interference term of Poynting vector has to be eliminated

Interference term Correcting the thickness by very small value

Incoherent propagation of light

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 6

Two approaches: a) Phase matching method

- the structure needs to be well defined to find the phase shift of the reflected wave interference term = 0

𝑑′ = 𝑅𝑒[

𝜋2 + 𝑚𝜋 − 𝜑

2𝑘], m = 0,±1,±2,…

a) Phase elimination approach

- the phase is eliminated by two simulation runs - more appropriate for structure that are not well defined interference term (d) − interference term (d‘) = 0

𝑑′ = 𝑑 − 𝑅𝑒[𝜆

4𝑁(𝜆)]

*A. Campa et al., "Two approaches for incoherent propagation of light in rigorous numerical simulations," Progress In Electromagnetics Research, Vol. 137, 187-202, 2013.

Thinning down the incoherent layer

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 7

glass

Solar cell

Solar cell glass d~500 nm + Dd(l)

*A. Campa et al., "Two approaches for incoherent propagation of light in rigorous numerical simulations," Progress In Electromagnetics Research, Vol. 137, 187-202, 2013.

Interference term

Model

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 8

*M. Sever et. al., Combined model of non-conformal layer growth for accurate optical simulation of thin-film silicon solar cells, Sol. energy mater. sol. cells., Vol. 119, 59-66 (2013)

gmc-Si:H =0.3

mc-Si:H

ZnO/Ag

ITO

gAg, ZnO =0.2

Dep

osi

tio

n d

irec

tio

n

excitation PML

Non-conformal growth model

Model

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 9

ITO Wavelength dependent mesh

Realistic optical constants (layers)

Results – thick glass layer

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 10

wavelength [nm]

300 400 500 600 700 800 900

R&

T

0.0

0.2

0.8

1.0

phase matching, d ~ 1 m

phase elimination, d ~ 1 m

coherent calculation, d = 1 mm

measured

R

T

wavelength [nm]650 651 652

T

R

Incoherent glass layer 1 mm thick

Incident plane wave

R

T

Results thin-film amorphous silicon solar cell

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 11

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 12

Air

Jülich TCO (0.8 mm)

a-Si:H cell (i- 350 nm)

mc-Si:H cell (i- 1.0 mm)

Thick glass

Results

Ag

Back TCO (80 nm)

Cell made and measured

at Inst. of Energy Research

(IEK-5) – Photovoltaics, FZJ

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 13

Results

measurements

simulations Air

B52 (2.5 mm)

a-Si:H cell (i- 250 nm)

mc-Si:H cell (i- 1.2 mm)

B52 (2.5 mm)

White paint

Thick glass

Cell made and measured

at École Polytechnique

Fédérale de Lausanne - EPFL

Conclusions

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Optical simulations including thick incoherent layer were shown

a) using phase matching method

b) using phase elimination method

c) thinning down thick layer

Results of simulations compared with realized cells of different

institutes

Acknowledgments

FP7 Fast Track project (GA No.: 283501)

Accelerated development and prototyping of nano-technology-

based high-efficiency thin-film silicon solar modules

Slovenian Research Agency - ARRS

15 COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al.

Thank you for your attention

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 16

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 17

COMSOL 2013, October 24th, Rotterdam, Netherlands A. Čampa et al. 18

wavelength [nm]

4.0e-7 6.0e-7 8.0e-7 1.0e-6 1.2e-6

A

0.0

0.2

0.4

0.6

0.8

1.0

incoherent glass

incidence from glass