Organic‐inorganic hybrid perovskite solar cells are susceptible to multiple influencing factors such as moisture, oxygen, heat stress, ion migration. Given the complex practical working conditions for solar cells, a fundamental question is how different failure mechanisms collaborate and substantially accelerate the device degradation. In this study, it is found that ion migration can accelerate the reaction between oxygen and methylammonium lead iodide perovskite in light conditions. This is suggested since regions with local electric fields suffer from more severe decomposition. Here it is reported that cesium ions (Cs+) incorporated in perovskite lattice, with a moderate doping concentration (e.g. 5%), can function as stabilizers to efficiently interrupt such a synergistic effect between oxygen induced degradation and ion migration while retaining the high performance of perovskite solar cells. Both experimental and theoretical results suggest that 5% Cs+ ions incorporation simultaneously suppresses the formation of reactive superoxide ions (O2−) as well as ion migration in perovskites by forming additional energy barriers. This A‐site cations engineering is also a promising strategy to circumvent the detrimental effect of oxygen molecules in FA‐based perovskites, which is important for developing high‐efficiency perovskite solar cells with enhanced stability.

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Dion–Jacobson (DJ)‐type quasi‐two‐dimensional perovskites exhibit improved stabilities than their 3D counterparts but meanwhile limited charge transport properties. Knowledge to manipulate the crystal orientation and crystallinity is the primary issue for DJ perovskite with high power conversion efficiencies (PCEs). Herein, the nucleation of DJ perovskite films is divided into three stages and the formation of PbI2–N,N‐dimethylformamide (DMF)‐based solvated phase (PDS) is highlighted as the initial stage. For the first time, it is demonstrated that regulating the amount of PDS precipitation in stage I by MACl additive is the key to ensure the downward growth of DJ perovskites with out‐of‐plane orientation and high crystallinity in stage III, which is valid for DJ perovskites with different bukly organic cations including p‐phenylenediamine (PPD), p‐xylylenediamine (PXD), and propane‐1,3‐diammonium (PDA). For (PXD)(MA)2Pb3I10‐based perovskite solar cells, the PDS engineering lead to a dramtically improved PCE from 1.2% to 15.6%. Moreover, based on temperature‐dependent ionic conductivity measurement, it is confirmed that the ion migration in DJ perovskite films is efficiently suppressed, despite the possible coexisting 3D perovskite phase. The unencapsulated PXD‐based DJ perovskite devices retain over 90% efficiencies after 700 h of continuous illumination or 1500 h of storage in glove box.

Lead halide perovskite solar cells (PSCs) with solution processability, low defect concentration, low cost and high output manufacturing have emerged as promising third-generation photovoltaic technologies. After an unprecedented speed of development, the power conversion efficiencies of small-area PSCs have exceeded 25%, and meanwhile large-scale perovskite modules are also on a rapid rise. At this stage, considering the significant progress in the fabrication of perovskite films with controllable morphology and crystallinity, it is necessary to conduct reviews on the updated understandings of the nucleation and crystal growth behaviors of perovskites. This review aims to clarify the related mechanisms of the complex perovskite formation process, and is devoted to giving a timely summary of the recent advances. Strategies for controlling perovskite nucleation and crystal growth are also discussed.

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