WIDEGAP SULFIDE-BASED SEMICONDUCTOR THIN FILMS ON TRANSPARENT AND CONDUCTIVE SUBSTRATES FOR MULTIJUNCTION PHOTOVOLTAIC DEVICES

摘要

Semi-transparent photovoltaic structures have been developed using indium tin oxide (ITO) transparent and conductive layers for the frontal and dorsal electrical contacts, and several widegap sulfide-based semiconductor thin films for the heterojunction: CuInS_2 or CuGaS_2 for the absorber and In_2S_3 for the buffer. Thus, multilayered structures have been prepared on conventional soda lime glass substrates in the sequence SLG/ITO/CuInS_2(or CuGaS_2)/In_2S_3/ITO, growing the ITO layers by sputtering from ceramic target and the sulfide semiconductors by evaporation from elemental sources. In order to apply such structures as top cells in multijunction photovoltaic devices, the study has been focused on three main aspects: 1) high dorsal layer conductivity (sheet resistance about 10 Ω/sq) with the highest possible transmittance, 2) wide gap absorber (energy gap E_g > 1.5 eV) with maximum sub-bandgap transmission and 3) high transparent top layers and acceptable frontal conductivity (sheet resistance around 20 Ω/sq). These requirements have been achieved by adjusting the preparation conditions for each layer, mainly the film thickness and the deposition temperature, after determining their influence on the electrical and optical characteristics.