Enhanced light trapping in thin-film solar cells by a directionally selective filter

21 June 2010 / Vol. 18, No. 102 / OPTICS EXPRESS

Carolin Ulbrich,1,* Marius Peters,2 Benedikt Bläsi,2

Thomas Kirchartz,1 Andreas Gerber,1and Uwe Rau1

1IEF5 - Photovoltaik, Forschungszentrum Jülich, 52425Jülich, Germany 2Fraunhofer-Institut für Solare Energiesysteme,Heidenhofstraße 2, 79110 Freiburg, Germany

Advisor : H.C. Kuo / C.C. Lin

Student : H.W. Han

NCTU IPS STUDENT2010/09/29 2/8

Outline

Introduction

Experiment

Result

Conclusions

NCTU IPS STUDENT2010/09/29 3/8

Introduction

enhancement of the optical path length improving the performance of devices reducing material consumption

optical path length

with threshold value θth

this paper compare the reflection and the external quantum efficiency before and after filter deposition

wnkwwopt24

)(sin/4 22thopt wnkww

NCTU IPS STUDENT2010/09/29 4/8

Experiment

Bragg-like filter 73 alternating layers of

SiO2 and Ta2O5

total thickness of 5.5 µm

threshold wavelength λth

Superstrate textured SnO2:F on

AsahiU glass etched ZnO:Al on Corning

glass

Absorber layer thickness 175 nm ~ 410 nm

])(sin)()(sin2)([ 221

20

20

22 ndth

NCTU IPS STUDENT2010/09/29 5/8

Result (1/3)

Thickness : 322 nm ; Corning glass with etched ZnO:Al 650nm < λ < 770nm due to the directional selectivity of the filter

suppressing re-emission of non-absorbed light 350nm < λ < 650nm due to the antireflective properties of the filter short-circuit current densities Jsc : 13.40 mAcm −2 13.66 mAcm −2

- 40%

NCTU IPS STUDENT2010/09/29 6/8

Result (2/3)

κr represents a factor quantifying the additional light path

prolongation in the device. The large difference between the improvement factor κEQE

and κr is due to parasitic absorption in the TCO and at the back contact.

AsahiU

NCTU IPS STUDENT2010/09/29 7/8

Result (3/3)

the external quantum efficiency EQEfi of a 414nm thick

a-Si:H solar cell (prepared on Corning glass) The dashed line is calculated from Eq. using λ0 = 767nm

and λ1 = 600nm.)(sin)()(sin2)( 22

120

20

22 ndth

NCTU IPS STUDENT2010/09/29 8/8

Conclusions

a directional selective filter can improve light trapping in solar cell and enhance the overall short-circuit current density

For a-Si:H thin film solar cells the improvement depends on the texture of the front TCO and the thickness of the active absorber layer.

A maximum improvement of ΔJsc = 0.26mAcm −2

textured ZnO and an absorber thickness of 322 nm 0.06 mAcm−2 due to the antireflective effect of the filter 0.20 mAcm−2 due to its directional selectivity

limited by parasitic absorption

NCTU IPS STUDENT2010/09/29 9/8

Thanks for your attention!!