CuIn/sub 0.75/Ga/sub 0.25/Se/sub 2/ thin films for photovoltaic applications

Copper Indium/Gallium di selenide (CuIn/sub 0.75/Ga/sub 0.25/Se/sub 2-CIGS) has been established as one of the most promising new materials for solar cell applications. In this paper we will present data on the growth, annealing and analysis of thin films deposited using a specially designed evaporation unit. Structural analysis of the as-grown CIGS films revealed a strong preferred growth direction, the <112> plane being parallel to the substrate. Compositional analysis indicated that the as-grown films were slightly deficient in selenium, otherwise the composition was comparable with that of the starting polycrystalline material. Electrical measurements revealed both n- and p- type conductivities with surface resistivity values in the range 10/sup -1/ to 10/sup 3/ omega-cm. The formation of donor and acceptor states is attributed to defects such as V/sub Se/, In/sub i/ and/or anti-sites. Optical transmission data was used to determine the band gap, which was calculated to be 1.15 eV. The as-grown films were annealed under various ambients and the effect on the stoichiometry, grain size, homogeneity and hence the electrical properties is reported. Some common deposition problems which can produce deviations in composition and hence creat variations in properties of the films are also discussed. (author)