Small molecule interfacial cross-linker for highly efficient two-dimensional perovskite solar cells

The nonradiative recombination of charge carriers at the hole transport layer (HTL)/perovskite interface generally induces remarkable performance loss of the inverted two-dimensional perovskite solar cells (2D PSCs). Herein, a cross-linkable small molecule of 2-mercaptoimidazole (2-MI) was introduced into the nickel oxide (NiO x )/2D perovskite interface. Experiments have confirmed the formation of Ni-N covalent bond by N atom in the 2-MI and Ni in the NiO x and the coordinating between S atom of 2-MI and under-coordinated Pb 2+ near to the NiO x /perovskite interface, which contributes to creating a cross-linking between NiO x /perovskite interface to restrain charge carrier recombination and enhance   the extraction of hole carriers at the interface. Besides, the 2-MI modification layer is also beneficial for promoting the crystallinity of 2D perovskite. Consequently, the inverted 2D PSCs with 2-MI modification achieved the best power conversion efficiency of 15%. This paves a route to acquire highly efficient 2D PSCs by constructing a cross-linking at the NiO x HTL/2D perovskite interface.