Liquid-selenium-enhanced grain growth of nanoparticle precursor layers for CuInSe2 solar cell absorbers

Abstract

Large-grained CuInSe2 absorber layers are synthesized using a non-vacuum process based on nanoparticle ink precursors and selenization by rapid thermal processing (RTP). The use of hydroxide-based particles in organic solvents allows for the conversion with elemental selenium without the need to employ explosive and/or toxic H2 or H2Se gasses. Lateral grain sizes up to 4 μm are obtained through a novel RTP route, overcoming the inherently high layer porosity for previous nanoparticle processes. Morphological and elemental characterization at interrupted selenization steps suggests that liquid selenium can play a beneficial role in promoting layer densification and grain growth. Long carrier collection lengths in CuInSe2 enable notable conversion efficiencies, despite the low minority carrier lifetimes of below 1 ns. Record efficiencies up to 8.73% highlight the potential of low-cost, non-vacuum deposition of chalcopyrite absorber layers with safe and simple precursors and processing routes.