In Situ Alloying Cs _1−x FA _x Pbl ₃ Perovskite Quantum Dots with Suppressed Composition Confinement for Solar Cells with 18.34% Efficiency

Cesium-formamidinium lead triiodide perovskite quantum dots (Cs_1-xFA_xPbI₃ PQDs) exhibit high potential for efficient photovoltaics due to their ideal bandgap and good phase stability. However, synthesizing the Cs_1-xFA_xPbI₃ PQDs with tunable composition and high optoelectronic properties remains a significant challenge due to the large difference in the crystallization temperature and chemical environment between the mono-cation Cs- and FA-based PQDs. Herein, a low-temperature sequential injection (LTSI) strategy is introduced to in situ alloying Cs_1-xFA_xPbI₃ PQDs for efficient solar cells. Compared with the PQDs synthesized using the conventional cation exchange method, the LTSI-based PQDs demonstrate improved optoelectronic properties and phase stability. Meanwhile, the LTSI-based PQD also shows a lower surface ligand intensity, greatly facilitating charge carrier transport in the PQD solids. Consequently, the PQD solar cell demonstrates an efficiency of up to 18.34%. The high photovoltaic performance realized in LTSI-based PQD solar cells is attributed to the broadened light absorption spectra, reduced surface defects, and the favorable energy level arrangement in the solar cells, enhancing the charge carrier extraction. This work provides a new cation alloying methodology to manipulate the composition of PQDs for high-performance solar cells or other optoelectronic devices.