Multi-functionalized molecule enabled high-performance inverted all-inorganic perovskite solar cells and perovskite/silicon tandem devices

All-inorganic perovskite materials are promising candidates for tandem devices, while poor phase stability and high photovoltage losses limit their practical application in ambient air with high relative humidity (RH). Here, a strategy is reported to minimize voltage losses by reconstructing the surface with a multi-functionalized theophylline molecule for fabricating highly efficient and stable inverted all-inorganic perovskite solar cells (PSCs). Instead of penetrating into the lattice and forming a two-dimensional (2D) structure, theophylline was mainly employed to react the uncoordinated Pb 2+ with its functional group of C O, resulting in the few lead-based defects and low nonradiative recombination loss. Moreover, a homogeneous surface potential and high work function were observed on the surface of the samples with theophylline, contributing to the optimal band energy alignment and enhanced carrier extraction at the interface between CsPbI 3 films and the electron transport layer (ETL). Finally, the optimized inverted CsPbI 3 PSCs and perovskite/silicon mechanically tandem devices delivered remarkable efficiencies of 20.07 % and 29.04 %, respectively, dramatically enhanced environmental stability. This work provides a new insight on inhibiting the interfacial defects and preparing the all-inorganic perovskite/silicon tandem solar cells. • The multifunctional molecule theophylline interacted with the uncoordinated Pb 2+ to low nonradiative recombination loss. • The theophylline resulted in optimal band energy alignment and enhanced carrier extraction at the interface. • The hydrophobic properties prevented erosion from humidity and improved the phase stability. • The inverted CsPbI 3 PSCs delivered a remarkable efficiency of 20.07 % and enhanced stability. • The 2T mechanically perovskite/silicon tandem devices achieved an efficiency of 29.04 %.