Grain Enlargement and Defect Passivation with Melamine Additives for High Efficiency and Stable CsPbBr₃ Perovskite Solar Cells

Abstract

The preparation of high-quality perovskite films with low grain boundaries and defect states is a prerequisite for achieving high-efficiency perovskite solar cells (PSCs) with good environmental stability. An effective additive engineering strategy has been developed for simultaneous defect passivation and crystal growth of CsPbBr₃ perovskite films by introducing 1,3,5-triazine-2,4,6-triamine (melamine) into the PbBr₂ precursor solution. The resultant melamine-PbBr₂ film has a loose, large-grained structure and decreased crystallinity, which has a positive effect on the crystallization process of the perovskite as it retards the crystallization rate as a result of the interaction between melamine and lead ions. Additionally, the passivation by melamine gives a high-quality CsPbBr₃ perovskite film with fewer grain boundaries, lower defect densities, and better energy level matching is achieved by multistep liquid-phase spin-coating, which greatly suppresses the nonradiative recombination resulting from the defects and promotes charge extraction at the interface. A champion power conversion efficiency as high as 9.65 % with a promising open-circuit voltage of 1.584 V is achieved for PSCs with an architecture of fluorine-doped tin oxide/c-TiO₂ /m-TiO₂ /melamine-added CsPbBr₃ /carbon-based hole-transporting layer. Furthermore, the unencapsulated melamine-added CsPbBr₃ PSC shows superior thermal and humidity stability in ambient air at 85 °C or 85 % relative humidity over 720 h.