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Chemical characterisation of evaporated In 2 S x buffer layers in Cu(In,Ga)Se 2 thin‐film solar cells with SNMS and SIMS
Author(s) -
Eicke Axel,
Spiering Stefanie,
Dresel Ariane,
Powalla Michael
Publication year - 2008
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.2856
Subject(s) - copper indium gallium selenide solar cells , stoichiometry , indium , thin film , solar cell , analytical chemistry (journal) , layer (electronics) , buffer (optical fiber) , sputtering , evaporation , deposition (geology) , cadmium telluride photovoltaics , materials science , chemistry , mineralogy , metallurgy , optoelectronics , nanotechnology , telecommunications , paleontology , physics , organic chemistry , chromatography , sediment , biology , computer science , thermodynamics
For the series production of Cu(In,Ga)Se 2 (CIGS)‐based thin‐film solar cells it is desirable to replace the thin CdS buffer layer between absorber and transparent front contact by non‐toxic, low‐absorbing semiconductors. In 2 S 3 , deposited by atomic layer deposition, has already been qualified as an alternative buffer material. In this work, results of indium sulphide buffer layers deposited by thermal evaporation are presented. Pressed powders with different compositions and morphology were used for evaporation at about 720 °C, resulting in different layer compositions and cell performances. The composition of the initial powder material and of the pellets after the deposition steps was determined by XRF. The deposited In 2 S x O y buffer layers and the buffer/absorber interface region were analysed by SIMS and sputtered neutral mass spectrometry (SNMS) depth profiling. Fine‐grained pressed In 2 S 3 powder evaporates rather homogeneously during the entire deposition run, resulting in nearly stoichiometric In 2 S 3 layers. S and Cl are evaporated preferentially from pellets of coarse‐grained, S‐poor In 2 S 2.4 powder containing 2 at% Cl, leading to excess S and high Cl concentrations in the first deposited layer. The subsequent layers are S‐poor and the In/S ratios continue to increase. In all interface regions additional amounts of Se, In, and Ga are detected, which could be attributed to the Cu‐poor defect layer on top of the CIGS absorbers. The best solar cell performance with efficiences of about 13% was achieved with the S‐rich buffer layers. Stoichiometric In 2 S 3 or S‐poor layers yield lower efficiences between 8 and 11%. Copyright © 2008 John Wiley & Sons, Ltd.