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Abstract All‐inorganic CsPbI₃quantum dots (QDs) have shown great potential in photovoltaic applications. However, their performance has been limited by defects and phase stability. Herein, an anion/cation synergy strategy to improve the structural stability of CsPbI₃QDs and reduce the pivotal iodine vacancy (V_I) defect states is proposed. The Zn‐doped CsPbI₃(Zn:CsPbI₃) QDs have been successfully synthesized employing ZnI₂as the dopant to provide Zn²⁺and extra I⁻. Theoretical calculations and experimental results demonstrate that the Zn:CsPbI₃QDs show better thermodynamic stability and higher photoluminescence quantum yield (PLQY) compared to the pristine CsPbI₃QDs. The doping of Zn in CsPbI₃QDs increases the formation energy and Goldschmidt tolerance factor, thereby improving the thermodynamic stability. The additional I⁻helps to reduce theV_Idefects during the synthesis of CsPbI₃QDs, resulting in the higher PLQY. More importantly, the synergistic effect of Zn²⁺and I⁻in CsPbI₃QDs can prevent the iodine loss during the fabrication of CsPbI₃QD film, inhibiting the formation of newV_Idefect states in the construction of solar cells. Consequently, the anion/cation synergy strategy affords the CsPbI₃quantum dot solar cells (QDSC) a power conversion efficiency over 16%, which is among the best efficiencies for perovskite QDSCs.