Microscopic origins of performance losses in highly efficient Cu In, Ga Se2 thin film solar cells

Thin film solar cells based on polycrystalline absorbers have reached very high conversion efficiencies of up to 23 25 . In order to elucidate the limiting factors that need to be overcome for even higher efficiency levels, it is essential to investigate microscopic origins of loss mechanisms in these devices. In the present work, a high efficiency 21 without anti reflection coating copper indium gallium diselenide CIGSe solar cell is characterized by means of a correlative microscopy approach and corroborated by means of photoluminescence spectroscopy. The values obtained by the experimental characterization are used as input parameters for two dimensional device simulations, for which a real microstructure was used. It can be shown that electrostatic potential and lifetime fluctuations exhibit no substantial impact on the device performance. In contrast, nonradiative recombination at random grain boundaries can be identified as a significant loss mechanism for CIGSe solar cells, even for devices at a very high performance leve

Evaluation of electron beam induced current profiles of Cu(In,Ga)Se2 solar cells with different Ga-contents

The measurement of electron beam induced current profiles in junction configuration (JEBIC) is a settled method for several semiconductor devices. We discuss the JEBIC method in the light of the special conditions present in the case of thin film Cu(In,Ga)Se-2 solar cells.Our previously published results indicate that the charge state of defects close to or at the Cu(In,Ga)Se-2/CdS interface depends on the minority carrier distribution, which changes strongly during a scan of the cross section with an electron beam. The charge distribution influences the electrostatic potential and therewith the collection of minority carriers.Here, we present an evaluation method of JEBIC profiles that accounts for this effect. Monte Carlo simulations of the carrier generation help us to consider in detail the influence of surface recombination. We determine the diffusion length, space charge width, surface- and back contact recombination velocity of Cu(In(1-r),Ga-r)Se-2 devices with different Ga-contents r from JEBIC line scans. (C) 2009 Published by Elsevier B.V

Band offset at the CuGaSe₂∕In₂S₃ heterointerface

We have investigated the electronic properties of the CuGaSe₂/In2S₃ heterointerface by photoelectron spectroscopy. In₂S₃ was evaporated by physical vapor deposition onto contamination free polycrystalline CuGaSe₂ surface prepared by the selenium decapping process. A valence band offset DEVB=0.78±0.1 has been determined