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To simultaneously stabilize cesium lead triiodide (CsPbI3) precursor solution and passivate the defects in CsPbI3 film is greatly significant for achieving highly stable and efficient CsPbI3 perovskite solar cells (PSCs). Herein, an effective redox 4‐fluorobenzothiohydrazide (FBTH) is developed to stabilize the precursor solution and passivate iodine/lead‐related defects for high‐quality CsPbI3 film. The comprehensive research confirms that 1) a new compound FBTH‐I is obtained from an effective redox interaction between FBTH and molecular iodine (I2) in perovskite precursor solution, which can effectively impede the formation of I2 molecule and restrain I− migration in perovskite film by forming N–H···I bond; 2) FBTH‐I can also passivate Pb‐related defects via forming S···Pb interaction. Consequently, the CsPbI3 PSC based on FBTH‐treated precursor solution exhibits a fascinating power conversion efficiency (PCE) of 21.41%, which is one of the highest PCE values among the reported pure CsPbI3 PSCs so far, and an outstanding stability against the harsh conditions, such as thermal annealing and continuous light‐illumination. [ABSTRACT FROM AUTHOR]

The poor interface quality between cesium lead triiodide (CsPbI3) perovskite and the electron transport layer limits the stability and efficiency of CsPbI3 perovskite solar cells (PSCs). Herein, a 4‐amino‐2,3,5,6‐tetrafluorobenzoate cesium (ATFC) is designed as a bifacial defect passivator to tailor the perovskite/TiO2 interface. The comprehensive experiments demonstrate that ATFC can not only optimize the conductivity, electron mobility, and energy band structure of the TiO2 layer by passivation of the undercoordinated Ti4+, oxygen vacancy (VO), and free OH defects but also promote the yield of high‐quality CsPbI3 film by synergistic passivation of undercoordinated Pb2+ defects with the CO group and F atom, and limiting I− migration via F···I interaction. Benefiting from the above interactions, the ATFC‐modified CsPbI3 device yields a champion power conversion efficiency (PCE) of 21.11% and an excellent open‐circuit voltage (VOC) of 1.24 V. Meanwhile, the optimized CsPbI3 PSC maintains 92.74% of its initial efficiency after aging 800 h in air atmosphere, and has almost no efficiency attenuation after tracking at maximum power point for 350 h. [ABSTRACT FROM AUTHOR]

Surmounting complicated defects at the electron transport layer (ETL) and perovskite interface plays a non‐trivial role in improving efficiency and stability of perovskite solar cells (PSCs). Herein, an asymmetric interface modification strategy (AIMS) is developed to passivate the defects from both a SnO2 ETL and the perovskite buried surface via incorporating 1,3‐thiazole‐2,4‐diammonium (TDA) into the SnO2/perovskite interface. Detailed experimental and calculated results demonstrate that N3 (the nitrogen atom bonding to the imine) in the TDA preferentially cures the free hydroxyl (OH), oxygen vacancy (VO), and the Sn‐related defects on the SnO2 surface, while N1 (the nitrogen atom bonding to the vinyl) is more inclined to passivate the Pb2+ and I− related defects at the perovskite buried surface. As a result, the TDA‐modified FACsPbI3 PSC yields a champion power conversion efficiency (PCE) of 24.96% with a gratifying open‐circuit voltage (Voc) of 1.20 V. In addition, the optimized PSCs exhibit charming air‐operational stability with the unencapsulated device sustaining 97.04% of its initial PCE after storage in air conditions for 1400 h. The encapsulated device maintains 90.21% of its initial PCE after maximum power point tracking for 500 h. [ABSTRACT FROM AUTHOR]

Formamidinium methylammonium lead iodide (FAMAPbI3) perovskite has been intensively investigated as a potential photovoltaic material because it has higher phase stability than its pure FAPbI3 perovskite counterpart. However, its power conversion efficiency (PCE) is significantly inferior due to its high density of surface detects and mismatched energy level with electrodes. Herein, a bifunctional passivator, methyl haloacetate (methyl chloroacetate, (MClA), methyl bromoacetate (MBrA)), is designed to reduce defect density, to tune the energy levels and to improve interfacial charge extraction in the FAMAPbI3 perovskite cell by synergistic passivation of both CO groups and halogen anions. As predicted by modeling undercoordinated Pb2+, the MBrA shows a very strong interaction with Pb2+ by forming a dimer complex ([C6H10Br2O4Pb]2+), which effectively reduces the defect density of the perovskite and suppresses non‐radiative recombination. Meanwhile, the Br− in MBrA passivates iodine‐deficient defects. Consequently, the MBrA‐modified device presents an excellent PCE of 24.29%, an open‐circuit voltage (Voc) of 1.18 V (Voc loss ≈ 0.38 V), which is one of the highest PCEs among all FAMAPbI3‐based perovskite solar cells reported to date. Furthermore, the MBrA‐modified devices without any encapsulation exhibit remarkable long‐term stability with only 9% of PCE loss after exposure to ambient air for 1440 h. [ABSTRACT FROM AUTHOR]

Inorganic CsPbI2Br perovskite is promising for solar cell applications due to its excellent thermal stability and optoelectronic characteristics. Unfortunately, the current high‐efficiency CsPbI2Br perovskite solar cells (PSCs) are mostly fabricated in an inert atmosphere due to their instability to moisture. Herein, a low‐dimensional intermediate‐assisted growth (LDIAG) method is reported for the deposition of CsPbI2Br film in ambient atmosphere by introducing imidazole halide (IMX: IMI and IMBr) into the precursor solution to control both nucleation and growth kinetics. The IMX first combines with PbI2 in the precursor film to form a 2D intermediate which then gradually releases PbI2 to slowly form high‐quality CsPbI2Br film during annealing. It is found that the LDIAG method produces a uniform, highly crystalline, pinhole‐free, and stable CsPbI2Br film with low defect density. Consequently, the solar cell efficiency is increased to as high as 17.26%, one of the highest for this type of device. Furthermore, the bare device without any encapsulation shows excellent long‐term stability with ≈86% of its initial efficiency retained after being exposed to the ambient environment for 1000 h. This work provides a perspective to tune the intermediate phases and crystallization pathway for high‐performance inorganic PSCs formed under ambient conditions. [ABSTRACT FROM AUTHOR]