Growth phases during electrochemical selenization of vacuum deposited CuIn metal layers for the formation of semiconducting CuInSe2 films

Abstract

A new two-stage process for electrochemical selenization of vacuum deposited Cu–In precursor films is demonstrated as an alternative to toxic and hazardous H2Se or Se vapour phase selenization techniques for the formation of semiconducting CuInSe2 thin films. The growth phases and microstructure of films are sensitive to Cu to In thickness ratios in the precursor, selenization current densities and time. Electrochemically selenized films show multiphase and polymorphic behaviour which strongly depends on the precursor structure and composition. The crystalline state of the film varies from a sphalerite to chalcopyrite CuInSe2 phase along with Cu and In binary compounds which are also observed. With In in excess in Cu+In mixed precursor films, use of low selenization currents (1mA/cm2) and longer periods (3h) yield the chalcopyrite CuInSe2 phase. Copper excess in bilayer precursor likewise favours chalcopyrite CuInSe2 growth after a post-selenization annealing. Single-phase chalcopyrite CIS film formation requires full selenization of the precursor and proper adjustment of the Cu/In thin film ratio in the precursor. Absence of free selenium at the post-selenization annealing stage led to secondary reactions and inclusion of binary phases.