Ethylenediamine chlorides additive assisting formation of high-quality formamidinium-caesium perovskite film with low trap density for efficient solar cells

Dual-cation formamidinium-caesium (FACs) perovskite shows good thermal stability, but a great number of trap states existing in the FACs perovskite film impair its photoelectric conversion efficiency and long-term stability. In this work, ethylenediamine chlorides (EDACl2), a new type Lewis base trap deactivator, is synthesized and then applied to the perovskite precursor solution to assist the formation of FACs perovskite film with less trap states. A series of photoelectric measurements reveal that the charge transport of FACs perovskite film, mediated by EDACl2 additive, is promoted and the non-radiative recombination process is reduced as well. By optimizing the EDACl2 additive amount and Br composition, the EDACl2-engineered perovskite solar cells (PSCs) with structures of ITO/SnO2/Cs0.15FA0.85PbI2.7Br0.3/Spiro-MeOTAD/Ag and ITO/SnO2/Cs0.15FA0.85PbI2.7 Br0.3/carbon, achieve their respective champion efficiencies of 19.68% and 15.56%, along with negligible hysteresis. Particularly, the carbon-based FACs device with EDACl2 exhibits good air-, thermal- and photostability. This work provides a facile and efficient ion additive engineering for fabrication of high-quality perovskite films and high-performance PSCs.