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[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]