Magic guanidinium cations in perovskite solar cells: from bulk to interface

Guanidinium (GA(+)) has been proven as the multifunctional cation in halide perovskite solar cells (PSCs), attracting considerable attention due to its improved power conversion efficiencies (PCE) and operational stability. This review introduces the elementary properties of the GA cation and GA-based perovskite. Then, we summarize the development history of utilizing guanidinium materials in PSCs, including composition engineering, additive engineering, and interface engineering, accompanied by their optimization mechanisms. Moreover, we propose a perspective on the potential opportunities in this popular field and challenges to the future design of guanidinium-based PSCs with enhanced performance.