Electrodeposition of CuInSe2 in citrate-containing electrolytes

Abstract

CuInSe2 is a frequent constituent of solar cells. Low-cost solar cells can be prepared by electrodeposition from a single bath, provided that the multiple variables affecting the process can be properly tuned. Our design includes an n-layer of TiO2 (dense and/or nanoporous), on top of which a p-layer of CuInSe2 is electrodeposited. The TiO2 layer is supported on conductive glass. When CuInSe2 is applied onto TiO2, a p–n junction is formed by which sunlight could be transformed into electricity. CuInSe2 films have been prepared by electrodeposition from a single bath aqueous solution. Citrate has been used as complexing agent, so as to shift the copper deposition potential in the negative direction, bringing it closer to the In deposition potential. Films are obtained potentiostatically at −0.8 V (vs. standard calomel electrode) for 1 h. The electrolyte consisted of 0.4 mol/L sodium citrate containing 3 mmol/L CuCl2, 6 mmol/L InCl3, and 5 mmol/L SeO2. Different pH values between 4 and 6 are investigated. The samples are annealed in a furnace under flowing Ar at 350 °C for 15 min, which proves to be essential to improve the crystallinity of the CuInSe2 films. TiO2 and CuInSe2 have been characterized using scanning electron microscopy, X-ray diffraction, and optical absorption spectroscopy. The morphology and the physical and optical properties are in good agreement with those reported in the literature. In order to investigate the photoresponse of the cells, current–voltage curves of prototype devices are performed in the dark and under light.