Improving interfacial charge transfer by multi-functional additive for high-performance carbon-based perovskite solar cells

For perovskite solar cells with carbon electrodes (CPSCs) prepared using undoped hole transport materials and commercial carbon pastes, the poor interfacial carrier transport performance hinders the efficiency improvement. Herein, the use of additive 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) not only plays the role of passivating defects and assisting film formation but also regulates one to obtain more favorable interfacial energy band bending and energy level matching, while forming charge transfer complexes with perovskites due to its strong electron-withdrawing ability. Having all these functions at the same time makes CPSCs with F4TCNQ addition obtain high quality, low defect density films with suppressed non-radiative recombination, along with extremely fast carrier separation and extraction capabilities. Together with the optimization of the electron transport layer, the prepared CPSCs obtained an enhanced photovoltaic conversion efficiency of 15.1% and a V_OC of 1.07 V with long stability.