Rational\nDefect Passivation of Cu₂ZnSn(S,Se)₄ Photovoltaics\nwith Solution-Processed Cu₂ZnSnS₄:Na Nanocrystals

Abstract

An effective defect passivation route\nhas been demonstrated in\nthe rapidly growing Cu₂ZnSn­(S,Se)₄ (CZTSSe)\nsolar cell device system by using Cu₂ZnSnS₄:Na\n(CZTS:Na) nanocrystals precursors. CZTS:Na nanocrystals are obtained\nby sequentially preparing CZTS nanocrystals and surface decorating\nof Na species, while retaining the kesterite CZTS phase. The exclusive\nsurface presence of amorphous Na species is proved by X-ray photoluminescence\nspectrum and transmission electron microscopy. With Na-free glasses\nas the substrate, CZTS:Na nanocrystal-based solar cell device shows\n50% enhancement of device performance (∼6%) than that of unpassivated\nCZTS nanocrystal-based device (∼4%). The enhanced electrical\nperformance is closely related to the increased carrier concentration\nand elongated minority carrier lifetime, induced by defect passivation.\nSolution incorporation of extrinsic additives into the nanocrystals\nand the corresponding film enables a facile, quantitative, and versatile\napproach to tune the defect property of materials for future optoelectronic\napplications.