Solar Energy Materials and Solar Cells, Vol.126, 88-95, 2014
Composition dependent characterization of copper indium diselenide thin film solar cells synthesized from electrodeposited binary selenide precursor stacks
CuInSe2 solar cells were prepared from electrodeposited and annealed stacks of indium selenide and copper selenide on molybdenum (Mo/In2Se3/Cu-Se). In comparison to a simultaneous electrodeposition of all elements at once the electrodeposited binary selenide stack leads to larger grains and lattice coherence length if annealed under the same conditions (30 min at 550 degrees C). Absorbers with atomic Cu/In ratios < 1, 1 and > 1 and their corresponding solar cells were characterized. An incomplete reaction in case of the Cu-poor precursor caused a Cu-deficient layer at the back contact of the absorber leading to the formation of a reverse electronic barrier reducing fill factor and short circuit current and thus the solar power conversion efficiency. Photoluminescence measurements showed a strongly compensated semiconductor for the Cu-poor absorber and an incomplete charge carrier collection was identified by quantum efficiency measurements under reverse bias. The reverse electronic barrier, the high compensation and the incomplete carrier collection could be avoided by Cu-rich growth conditions. The appearance of an excitonic transition in photoluminescence indicated a high semiconductor quality in this case. It was linked with a high quantum efficiency resulting in a local short-current density of 38.3 mA/cm(2). Temperature-dependent JV measurements identified interface recombination as the limiting recombination loss mechanism for the Cu-rich grown solar cell reducing the open-circuit potential and decreasing the conversion efficiency. The solar cell prepared from the precursor with Cu/In approximate to 1 had similar properties as the Cu-poor device without the reverse electronic barrier at the back contact but instead dominating interface recombination. It reached a best solar power conversion efficiency of 5.5%. (C) 2014 Elsevier B.V. All rights reserved.
Keywords:Electrodeposition;CIGS solar cells;Indium selenide;Copper selenide;Photoluminescence;Interface recombination