A multifunctional additive of scandium trifluoromethanesulfonate to achieve efficient inverted perovskite solar cells with a high fill factor of 83.80%

High-quality perovskite films are critical to realize efficient photovoltaic performances of perovskite solar cells (PSCs). An unprocessed perovskite film contains a high density of defects, which results in low film quality. In order to reduce the trap density and passivate non-radiative recombination centers of perovskite films, scandium trifluoromethanesulfonate (Sc(OTF)(3)) is introduced into the perovskite precursor solution as a multifunctional additive. The sulfonic group could coordinate with lead ions, thus reducing the perovskite crystallization process, and a high quality perovskite film with large grain size, high crystallinity and few defects is obtained. Meanwhile, the doping of the rare earth ion Sc(3+)in the perovskite precursor solution could lead to the interaction of Sc(3+)with the perovskite, thereby improving film morphology and prolonging the charge carrier lifetime. In addition, the strong hydrogen bonding interaction between Sc(OTF)(3)and MA(+)could immobilize methylamine ions (MA(+)), contributing to the improved stability of the perovskite film. As a result, inverted PSCs with Sc(OTF)(3)at a low doping amount of 0.1 mg ml(-1)show a remarkable efficiency of 20.63% along with an open circuit voltage (V-oc) of 1134 mV, a short circuit current density (J(sc)) of 21.71 mA cm(-2), and a high fill factor (FF) of 83.80%. So far, the FF of this system represents one of the highest results for inverted PSCs.