A thermodynamic evaluation of metal halides for the recrystallization of Cu(In,Ga)Se2

Abstract

AbstractCdTe films are deposited at low temperatures and recrystallized to photovoltaic device quality using CdCl2 treatments, leading to competitive manufacturing costs. Cu(In,Ga)Se2 (CIGS) typically requires high‐temperature, low‐rate depositions to produce high‐efficiency devices, resulting in higher costs. A similar metal halide treatment of CIGS has been demonstrated by us previously for some metal halide sources. To understand and optimize the process, a thermodynamic evaluation of candidate metal halides for such treatments is presented as a guide for their selection. By comparing bond dissociation energies, mono‐ and di‐halide compounds are proposed to be ideal compounds to act as transport agents. Known recrystallization and temperature reduction benefits by Ag alloying suggest that Ag halides should be used to aid transport of all species. The high vapor pressure and mobility of Ga compounds still pose a problem for metal halide treatment, resulting in Ga etching and removal of intentional Ga gradients. Less severe but similar issues with In compounds may occur. Cu compounds have low vapor pressures that may limit transport; however, Cu is highly mobile in CIGS, and recrystallization still occurs.