All‐inorganic CsPbI3 quantum 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 CsPbI3 QDs and reduce the pivotal iodine vacancy (VI) defect states is proposed. The Zn‐doped CsPbI3 (Zn:CsPbI3) QDs have been successfully synthesized employing ZnI2 as the dopant to provide Zn2+ and extra I−. Theoretical calculations and experimental results demonstrate that the Zn:CsPbI3 QDs show better thermodynamic stability and higher photoluminescence quantum yield (PLQY) compared to the pristine CsPbI3 QDs. The doping of Zn in CsPbI3 QDs increases the formation energy and Goldschmidt tolerance factor, thereby improving the thermodynamic stability. The additional I− helps to reduce the VI defects during the synthesis of CsPbI3 QDs, resulting in the higher PLQY. More importantly, the synergistic effect of Zn2+ and I− in CsPbI3 QDs can prevent the iodine loss during the fabrication of CsPbI3 QD film, inhibiting the formation of new VI defect states in the construction of solar cells. Consequently, the anion/cation synergy strategy affords the CsPbI3 quantum dot solar cells (QDSC) a power conversion efficiency over 16%, which is among the best efficiencies for perovskite QDSCs.

The high‐quality perovskite film is a prerequisite for high‐performance optoelectronic devices. Herein, CdSe colloidal quantum dots (QDs) serve as crystallization seeds for the first time to modulate the nucleation and crystal growth processes simultaneously of the CsPbI2Br film in the ambient environment. As additives, CdSe QDs help promote the nucleation process in the initial stage of perovskite formation. In addition, it is revealed that the surface ligands of QDs also have an essential influence on the subsequent crystal growth of the perovskite film. The bifunctional ligands on the surface of QDs are beneficial in delaying the growth process of perovskite due to the free functional groups at the ends. The CsPbI2Br film prepared with bifunctional organic ligand‐capped CdSe QD additives shows better crystallinity than that of the inorganic ligand‐based one due to the dual function of these kinds of QDs in not only promoting nucleation but also retarding crystal growth of CsPbI2Br crystals. As a result, the high‐quality CsPbI2Br film with a low defect state density is prepared in the ambient environment. The optimized efficiency of the assembled hole‐conductor‐free carbon‐based perovskite solar cells (C‐PSCs) is increased from 12.73% to 14.49%, which is one of the best results for all‐inorganic C‐PSCs.

The introduction of a two-dimensional (2D) perovskite into a three-dimensional (3D) perovskite has been proven to be effective in minimizing defect state density and improving the performance and stability of the corresponding perovskite solar cells (PSCs). However, it is a challenge to construct a 2D perovskite in 3D inorganic perovskites (CsPbX3, X = halogen) due to the limitation of the annealing temperature or the resistance of Cs+ toward the commonly used organic cation spacer. Here, we propose a strategy for the construction of an all-inorganic 2D/3D CsPb2I4Br/CsPbI2Br bulk heterojunction (BHJ) by the in situ reaction of excess PbI2 in a precursor solution with CsPbI2Br during the annealing process. The formed 2D/3D BHJ effectively passivates the defects at the surface and grain boundaries of 3D CsPbI2Br and reduces the nonradiative recombination loss in the resulting carbon-electrode-based perovskite solar cells (C-PSCs). The open-circuit voltage and efficiency of the champion C-PSCs are boosted to 1.32 V and 15.25%, respectively, which are the best results for CsPbI2Br-based C-PSCs.