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Doping of all-inorganic lead halide perovskites to enhance their photovoltaic performance and stability has been reported to be effective. Up to now most studies have focused on the doping of elements in to the perovskite lattice. However, most of them cannot be doped into the perovskite lattice and the roles of these dopants are still controversial. Herein,the authors introduce CdI 2 as an additive into CsPbI 3−x Br x and use it as active layer to fabricate high-performance inorganic perovskite solar cells (PSCs). Cd with a smaller radius than Pb can partially substitute Pb in the perovskite lattice by up to 2 mol%. Meanwhile, the remaining Cd stays on the surface and grain boundaries (GB) of the perovskite film in the form of Cs 2 CdI 4−x Br −x , which is found to reduce non-radiative recombination. These effects result in prolonged charge carrier lifetime, suppressed defect formation, decreased GBs, and an upward shift of energybands in the Cd-containing film. A champion efficiency of 20.8% is achieved for Cd-incorporated PSCs, together with improved device ambient stability. This work highlights the importance of simultaneous lattice engineering, defectcontrol and atomic-level characterization in achieving high-performance inorganic PSCs with well-defined structure-property relationships.

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Due to their excellent thermal stability and ideal bandgap, metal halide inorganic perovskite based solar cells (PSCs) with inverted structure are considered as an excellent choice for perovskite/silicon tandem solar cells. However, the power conversion efficiency (PCE) of inverted inorganic perovskite solar cells (PSCs) still lags far behind that of conventional n–i–p PSCs due to interfacial energy level mismatch and high nonradiative charge recombination. Herein, the performance of inverted PSCs is significantly improved by interfacial engineering of CsPbI3−xBrx films with 2‐mercapto‐1‐methylimidazole (MMI). It is found that the mercapto group can preferably react with the undercoordinated Pb2+ from perovskite by forming Pb–S bonds, which appreciably reduces the surface trap density. Moreover, MMI modification results in a better energy level alignment with the electron‐transporting material, promoting carrier transfer and reducing voltage deficit. The above combination results in an open‐circuit voltage enhancement by 120 mV, yielding a champion PCE of 20.6% for 0.09 cm2 area and 17.3% for 1 cm2 area. Furthermore, the ambient, operational and heat stabilities of inorganic PSCs with MMI modification are also greatly improved. The work demonstrates a simple but effective approach for fabricating highly efficient and stable inverted inorganic PSCs.

Previous reports have demonstrated significant effects of hole transport layer (HTL) on the morphology of quasi-2 dimensional (2D) perovskites, hole injection, and interfacial defect density. However, the effects of HTL on energy landscape and energy funneling of quasi-2D perovskites have not been revealed so far. Herein, the PEA 2 Cs n−1 Pb n Br 3n+1 perovskite films are fabricated on four types of HTLs including poly(9-vinylcarbazole):poly(ethylene oxide) (PVK:PEO), PVK, poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and nickel oxide (NiO x ). The steady-state and transient absorption spectroscopies reveal that the energy landscape and energy funneling of quasi-2D perovskites vary significantly on different HTLs. All domains with n = 1, 2, 3, and higher order (n ≥ 4) are formed with desired population ratios on the PVK:PEO HTL, leading to the most efficient energy funneling. Furthermore, the interfacial passivation effect of PEO on the energy funneling process is studied. The light-emitting diodes (LEDs) based on PEA 2 Cs n−1 Pb n Br 3n+1 and PVK:PEO (with an optimized ratio of 5.3:0.7 w/w) HTL result in a maximum luminescence of ≈23 110 cd m -2 and maximum external quantum efficiency of ≈11.5%, respectively. This is the best performance reported so far using pure PEA 2 Cs n−1 Pb n Br 3n+1 without perovskite composition modifications. This study provides new insights into the HTL for the development of highly efficient quasi-2D perovskite LEDs.