Guanidinium induced phase separated perovskite layer for efficient and highly stable solar cells

Guanidinium (GA) has been proposed as an effective organic cation in improving the stability of lead halide perovskite solar cells (PSCs). However, the reported efficiency of GA based PSCs is far behind traditional GA-free devices. Herein, a novel GA doped quadruple cation perovskite, Cs 0.05 (FA 0.83 (MA 1− x GA x ) 0.17 ) 0.95 Pb(I 0.83 Br 0.17 ) 3 (CsFAMA 1− x GA x ), is presented. It is found that the introduction of GA induces a phase separation of 3D CsFAMA 1− x GA x , 2D FAGAPbI 4 , and 1D δ-FAPbI 3 . By tuning the content of GA, a δ-FAPbI 3 /CsFAMA 1− x GA x (1D/3D) perovskite with superior optoelectronic properties is demonstrated. The novel 1D/3D perovskite shows an overall improvement in stability. The corresponding solar cell exhibits a PCE of 20.29% with negligible hysteresis, being the highest reported efficiency for GA based PSCs thus far. This study introduces a new perovskite model toward efficient and highly stable PSCs. A large grain sized and pinhole free guanidinium doped quadruple cation based perovskite is demonstrated with superior optoelectronic properties. The resulting devices reach a PCE of 20.29% with negligible hysteresis and enhanced stability.