Inexpensive methodology to prepare TiO₂/CuInS₂hetero-junctions for photovoltaic applications

TiO 2 and CuInS 2 (CIS) hetero-junctions were prepared using low-cost, solution-based techniques. Using conducting glass (FTO) as substrate, a thin film of TiO 2 and an ultrathin film of In 2 S 3 that acts as buffer layer were deposited by spray pyrolysis. CIS was electrodeposited on top of this duplex layer, at pH 8, room temperature and at constant potential. A solar cell consisting of FTO/TiO 2 /In 2 S 3 /CIS/graphite was built in superstrate configuration. Morphology, thickness, crystalline structure and chemical composition were analyzed by electronic microscopy, x-ray diffraction and Raman spectroscopy. CuInS 2 films were found to be crystalline with a thickness of 0.4 µ m and showed good adhesion. Current–voltage curves in the dark and under illumination proved that the solution-based and vacuum-free deposition of these materials has promising photovoltaic applications. Different thicknesses of the buffer layer were evaluated and the best results were found for In 2 S 3 layers deposited with 6 spray cycles. The best solar cell performance showed an efficiency equal to 3.3% with a V oc = 0.583 V, J sc = 17.7 mA cm −2 , FF = 0.32.