Deposition of CuIn(Se, S)2 thin films by sulfurization of selenized Cu/In alloys

The relatively small band gap values (close to 1eV) of CuInSe2 thin films limits the conversion efficiencies of completed CuInSe2/CdS/ZnO solar cell devices. In the case of traditional two-stage growth techniques, limited success has been achieved to increase the band gap by substituting indium with gallium. In this study, sputtered copper-indium alloys were exposed to a H2Se/Ar atmosphere under defined conditions in order to produce partially reacted CuInSe2 structures. These films were subsequently exposed to a H2S/Ar atmosphere to produce monophasic CuIn(Se, S)2 quaternary alloys. The homogeneous incorporation of S into CuInSe2 led to a systematic shift in the lattice parameters and band gap of the ab- sorber films. From these studies optimum selenization/sulfurization conditions were determined for the deposition of homogeneous CuIn(Se, S)2 thin films with an optimum band gap values between 1.15 and 1.2 eV. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)