Crystal Growth Modulation of Tin-Lead Halide Perovskites via Chaotropic Agent

Mixed tin-lead (Sn-Pb) halide perovskites, with their tunable bandgaps (1.2-1.4 eV), show great promise for the development of highly efficient all-perovskite tandem solar cells. However, achieving commercial viability and stabilized high efficiency for Sn-Pb perovskite solar cells (PSCs) presents numerous challenges. Among various optimization strategies, the incorporation of additives has proven critical in modulating the crystallization of Sn-Pb perovskites. Despite the widespread use of additives to improve performance, detailed photophysical mechanisms remain unclear. In this work, we elucidate the mechanistic role of guanidinium thiocyanate, a chaotropic agent, in the crystallization of Sn-Pb perovskites. We combine hyperspectral imaging with real-time in situ photoluminescence spectroscopy to study the crystallization process of Sn-Pb perovskites. Our findings reveal that the chaotropic agent modulates the crystal growth rate during perovskite crystallization, resulting in more homogeneous films with reduced nonradiative recombination. We challenge the common assumption that crystallization stops once the solvent evaporates by identifying photoluminescence variations during the cooldown process. The resulting films exhibit a photoluminescence quantum yield of 7.28% and a charge carrier lifetime exceeding 11 μs, leading to a device efficiency of 22.34% and a fill factor of over 80%. This work provides a fundamental understanding of additive-mediated crystal growth and transient cooldown dynamics, advancing the design of high-quality Sn-Pb perovskites for efficient and stable optoelectronics.