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Tin‐lead (Sn‐Pb) mixed perovskite with a narrow bandgap is an ideal candidate for single‐junction solar cells approaching the Shockley‐Queisser limit. However, due to the easy oxidation of Sn2+, the efficiency and stability of Sn‐Pb mixed perovskite solar cells (PSCs) still lag far behind that of Pb‐based solar cells. Herein, highly efficient and stable FA0.5MA0.5Pb0.5Sn0.5I0.47Br0.03 compositional PSCs are achieved by introducing an appropriate amount of multifunctional Tin (II) oxalate (SnC2O4). SnC2O4 with compensative Sn2+ and reductive oxalate group C2O42− effectively passivates the cation and anion defects simultaneously, thereby leading to more n‐type perovskite films. Benefitting from the energy level alignment and the suppression of bulk nonradiative recombination, the Sn‐Pb mixed perovskite solar cell treated with SnC2O4 achieves a power conversion efficiency of 21.43%. More importantly, chemically reductive C2O42− effectively suppresses the notorious oxidation of Sn2+, leading to significant enhancement in stability. Particularly, it dramatically improves light stability. [ABSTRACT FROM AUTHOR]

The poor film stability of Sn-Pb mixed perovskite film and the mismatched interface energy levels pose significant challenges in enhancing the efficiency of tin–lead (Sn-Pb) mixed perovskite solar cells. In this study, polyvinylpyrrolidone (PVP) is introduced into the PVK perovskite precursor solution, effectively enhancing the overall stability of the film. This improvement is achieved through the formation of robust coordination bonds between the carbonyl (C=O) in the pyrrole ring and the undercoordinated SnII and PbII, thereby facilitating the passivation of defects. Furthermore, the introduction of PVP inhibits the oxidation of tin (Sn), thereby enhancing the n-type characteristics of the perovskite film. This adjustment in the energy level of the PVK perovskite film proves instrumental in reducing interface energy loss, subsequently improving interface charge transfer and mitigating device recombination. Consequently, perovskite solar cells incorporating PVP achieve an outstanding champion power conversion efficiency (PCE) of 21.31%. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile surface modification method using alkylamines to treat the CsPbI 3 surface is proposed. • HDA treatment can ameliorate defect passivation and energy level alignment to reduce voltage loss. • A champion PCE of 18.21% is achieved for the HDA-treated inverted CsPbI 3 PSCs. • HDA treatment promotes the humidity stability both of CsPbI 3 films and solar cells. Inorganic CsPbI 3 perovskite has been regarded as a kind of promising light-harvesting material due to its outstanding photoelectrical characteristics especially in perovskite solar cells (PSCs). However, there are still some problems hindering its further development, among which non-radiative recombination induced by traps and voltage loss are very pivotal. Here, the passivation of surface defects and energy level alignment of perovskite films are greatly ameliorated by facile surface modification with alkylamines. It is found that the undercoordinated Pb2+ are effectively passivated by the terminal amino group, leading to significantly reduced surface trap density, while the charge lifetime of treated perovskite films is prolonged. Besides, the bilateral amino groups from hexanediamine (HDA) can provide additional hydrogen bond to coherently connect the PbI 6 4− octahedra. Moreover, gradient energy levels are created after surface treatment, which promote the carriers transfer and reduce the voltage deficit. Consequently, a champion power conversion efficiency (PCE) of inverted CsPbI 3 PSCs over 18 % with higher fill factor (FF) of 81.21 % and open circuit voltage (V OC) of 1.10 V is obtained compared to the pristine device with a lower PCE of 12.69 % (V OC of 1.01 V, and FF of 62.49 %). Besides, the unencapsulated device with HDA treatment exhibits good stability with keeping 80 % of its initial efficiency after being aged for 1000 h at 35 % relative humidity. Our work can offer a facile but effective approach for the development of highly efficient and stable inverted CsPbI 3 PSCs. [ABSTRACT FROM AUTHOR]