Recent trends in direct solution coating of kesterite absorber layers in solar cells

This review describes a specific group of non-vacuum methods for depositing kesterite solar cell absorbers, which we refer to as direct solution coating (DSC). These methods work by coating a layer of precursor-containing solution on the surface of a substrate followed by appropriate thermal processing to yield the desired kesterite Cu2ZnSn(S,Se)4 phase. General aspects, challenges and future prospects of the DSC are discussed in detail. Two research highlights are presented in which kesterite layers are processed from solutions of metal salts in simple non-toxic organic solvents to yield up to 7.5% efficient solar cells.