As a rising star in the photovoltaic field, perovskite solar cells (PSCs) have attracted extensive attention. However, the industrialization development of PSCs still faces the dual challenges of improving efficiency and stability. Herein, a cage polyamine molecule hexamethylenetetramine (HMTA) as additive is incorporated into the tin oxide electron transport layer (ETL). The introduction of HMTA improves the electron extraction ability of SnO2 and optimizes the energy‐level alignment of function layers. The modification of HMTA also passivates the uncoordinated Pb2+ in the perovskite and reduces the oxygen vacancy defects of SnO2, which alleviate trap‐state density and carrier nonradiative recombination. As a result, the PSC based on the SnO2 ETL modified with HMTA achieves a high power conversion efficiency of 22.37% along with good stability. The research results demonstrate a typical case of using cage polyamines to improve the performance and stability of PSCs.

The rapid development of the perovskite solar cell (PSC) makes its best research efficiency comparable with that of silicon solar cells. However, the large‐scale application of PSCs still faces the dual challenges of improving efficiency and stability. Herein, an interfacial modifier of polyethylene glycol dodecyl ether (Brij) with ether group (C–O–C) and long alkyl chain is introduced into the interface of the perovskite layer and hole transport layer. It is demonstrated that the interaction of the ether group on Brij with uncoordinated lead ions on the perovskite passivates the point defects and reduces carrier recombination. The introduction of Brij tunes the energy gradient among electron transport layer/perovskite layer/hole transport layer and promotes the carrier extraction and transportation. The long alkyl chain of Brij covers the surface of perovskite and effectively improves the moisture resistance of perovskite films and the environmental stability of devices. Under an optimal Brij concentration, the modified perovskite solar cell achieves the best power conversion efficiency of 22.57%, along with improved environmental stability, while the pristine device obtains an efficiency of 20.66%.