Se as hetero-nucleation seeds reinforcing intermetallic diffusion for improved electrodeposition-processed CZTS solar cells

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Pure sulfide-based Cu2ZnSnS4(CZTS) stands as a competitive photovoltaic material, composted of earth-abundant, low-cost, and stable constituent elements. The stacked electrodeposition process has garnered attention owing to its facile regulation of elemental composition, and its non-vacuum, room-temperature, water-based solvent operating conditions. However, the limitation based on the stacked electrodeposition-processed CZTS primarily stems from the numerous defects and detrimental interfaces induced by the deficient intermetallic diffusion. Herein, a Se nanoparticle layer at the back interface is introduced to enhance the intermetallic diffusion, optimize the precursor morphology, and subsequently accelerate the grain growth. Comprehensive characterizations reveal Se, acting as the hetero-nucleation seeds, catalyzes Cu deposition and promotes a highly porous structure with a homogeneous elemental distribution. Consequently, high-quality CZTS with enhanced crystallinity and passivated defects is achieved, thereby promoting carrier transport and suppressing non-radiative recombination. These sequential positive effects result in a substantial improvement in short current density (Jsc) and fill factor (FF), attaining an improved efficiency. Our findings offer a promising strategy to overcome the issues of the stacked electrodeposition-processed films and highly contribute to the development of high-quality CZTS-based solar cells.