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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, 1 and Uwe Rau 1

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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,2Benedikt Bläsi,2

Thomas Kirchartz,1 Andreas Gerber,1and Uwe Rau1

1IEF5 - Photovoltaik, ForschungszentrumJülich, 52425Jülich, Germany

2Fraunhofer-Institut fürSolareEnergiesysteme,Heidenhofstraße 2, 79110 Freiburg, Germany

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

Student : H.W. Han


Outline
Outline directionally selective filter

Introduction

Experiment

Result

Conclusions


Introduction
Introduction directionally selective filter

  • 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


Experiment
Experiment directionally selective filter

  • 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


Result 1 3
Result (1/3) directionally selective filter

- 40%

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


Result 2 3
Result (2/3) directionally selective filter

AsahiU

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.


Result 3 3
Result (3/3) directionally selective filter

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.


Conclusions
Conclusions directionally selective filter

  • 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


Thanks for your attention!! directionally selective filter


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