Preparation and Characterization of Vacuum Deposited CuInSe2 Thin Films

CuInSe₂ is a promising material for photovoltaic solar cells. Thin films of CuInSe₂ were prepared by vacuum evaporation of the constituent elements by the "three-temperature" method. Source temperatures rather than the elementary fluxes were controlled. The deposition set-up configuration permitted the simultaneous preparation of films with compositions varying around exact stoichiometry. CuInSe₂ thin films with indium concentrations of ±3 at.% around stoichiometry had predominantly chalcopyrite structure with {112} crystallographic texture. These films were p-type, with resistivities of 2 × 10^-2 - 27 Ω cm, carrier concentrations of 1 × 10¹⁸ - 4 × 10²⁰ cm^-3 and Hall mobilities of 0.2 - 2 cm² V^-1 s^-1. Films with about 5 at.% excess of indium showed mostly the sphalerite phase with {111} texture and a small proportion of the chalcopyrite phase. These films exhibited resistivities in the range 2 - 9 × 10³ Ω cm. The films with about 5 at.% excess of copper consisted of berzelianite and/or sphalerite phases. The band gaps of nearly stoichiometric CuInSe₂ thin films and those with 5 at.% excess of indium ranged from 0.99 to 1.01 eV.