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HL: Fachverband Halbleiterphysik

HL 38: Photovoltaics: CIGS and related Materials

HL 38.3: Talk

Tuesday, March 27, 2012, 11:45–12:00, ER 270

Sub-band-gap absorption of Cu(In,Ga)Se₂ thin film semiconductors — •Max Meessen, Rudolf Brüggemann, and Gottfried H. Bauer — Carl von Ossietzky University Oldenburg, Germany

The sub-band-gap absorption of Cu(In,Ga)Se₂ thin films has been studied by photothermal deflection spectroscopy (PDS) in conjunction with optical transmittance spectroscopy. The resulting absorption coefficients are compared to those calculated from photoluminescence spectra using Planck’s generalized law. Quantities related to the absorption like Urbach energy and defect densities are derived from the absorption curves.

This concept has been applied to a series of bromine-methanol etched Cu(In_x−1,Ga_x)Se₂ (x=0.3) absorbers with varying thicknesses. A shift in the band gap is observed with both methods and can be related to the gallium gradient in the samples. In contrast, the Urbach energy and defect absorption values are not substantially affected by the etching process.

The influence of CdS buffer layers or highly thermally conductive metallic back contacts on PDS results is studied by measuring nominally identical samples with and without those layers.