Water based spray pyrolysis of metal-oxide solutions for Cu2ZnSn(S,Se)4 solar cells using low toxicity amine/thiol complexants

Cu ZnSnS(e) 2 4 deposited using solution processes has potential for terrawatt-scale deployment. The champion highest efficiency Cu ZnSn(S,Se) 2 4 cell published in literature is spin-coated using the highly dangerous hydrazine which is an impractically scalable solvent and deposition combination. As an alternative solvent amine-thiol mixtures have shown to complex with a wide range of binary chalcogenides with much lower health risks than hydrazine. Herein we present two further toxicity reductions, first by employing a less harmful amine-thiol pairing and second by using water as a diluting solvent. We exclude extraneous elements from the precursor solution such as halogens and with a sub-micron thickness crystalline absorber achieve an efficiency of 6.8 %. With the modified solution deposited by ultrasonic spray pyrolysis, this solution process is scalable, abundant, and relatively non-toxic.