LAUSR

Cesium‐formamidinium lead iodide perovskite quantum dots (FAxCs1−xPbI3 PQDs) show high potential for next‐generation photovoltaics due to their outstanding optoelectronic properties. However, achieving composition‐tunable hybrid PQDs with desirable charge transport remains a significant challenge. Herein, by leveraging an antisolvent‐assisted in situ cation exchange of PQDs, homogeneous FAxCs1−xPbI3 PQDs with controllable stoichiometries and surface ligand chemistry are realized. Meanwhile, the crystallographic stability of PQDs is substantially improved by substituting the cations of the PQDs mediated by surface vacancies. Consequently, PQD solar cell delivers an efficiency of 17.29%, the highest value among the homostructured PQD solar cells. The high photovoltaic performance is attributed to the broadened light harvesting spectra, flattened energy landscape, and rationalized energy levels of highly oriented PQD solids, leading to efficient charge carrier extraction. This work provides a feasible approach for the stoichiometry regulation of PQDs to finely tailor the optoelectronic properties and tolerance factors of PQDs toward high‐performing photovoltaics.