Rapid Cooling After Device Annealing Suppresses Interface Losses in Cu₂ZnSnS₄ Solar Cells Enabling High Efficiency...

Wide-bandgap kesterite (Cu₂ZnSnS₄, CZTS) is an earth-abundant and environmentally friendly absorber, making it a promising candidate for both outdoor and indoor photovoltaic applications. However, device performance remains limited by multiple loss mechanisms, including recombination at the CdS/CZTS heterojunction and resistive back-contact losses at the Mo/CZTS interface. Here, we report solution-processed CZTS devices in which controlling the cooling dynamics after device annealing in ambient air provides an effective and scalable strategy to overcome these limitations and enable stable, high-performance devices. By implementing a rapid cooling process (RCP), we suppress non-radiative recombination at the CdS/CZTS heterojunction, resulting in a decrease in saturation current density (J₀) by three orders of magnitude. Moreover, RCP improves the Mo/CZTS back contact by modifying the MoS₂-related region, which may facilitate hole extraction and reduce back-contact losses. As a result of these combined interface improvements, RCP-treated devices retain a PCE of 11.1% after ∼1500 h of damp heat aging at 85°C, with a Voc corresponding to 62.4% of the thermodynamic limit. The RCP device also delivers an indoor PCE of 15.9% under 2700 K LED illumination, representing the highest reported performance for kesterite solar cells under indoor conditions at 1000 lux.