Methylthiophene terminated D–π–D molecular semiconductors as multifunctional interfacial materials for high performance perovskite solar cells

Abstract

Rationally modulating the physicochemical properties at a perovskite-charge transporting layer interface is crucial for further improvement of metal halide perovskite solar cell (PSC) performance. Here, we present two methylthiophene terminated molecular semiconductors with a donor–π spacer–donor configuration (MT1 and MT2) as multifunctional interfacial materials for PSCs. The terminal methylthiophene groups endow the molecular semiconductors with defect passivation capability by coordinating with Pb²⁺ on the perovskite surface. Besides, both MT1 and MT2 exhibit a stabilized HOMO level and a high lying LUMO level which are favorable for selectively extracting holes while preventing electron transfer. When the two molecular semiconductors were inserted between the perovskite film and hole transporting layer (HTL), the defect density of the perovskite films was significantly reduced, and the charge carrier dynamics was simultaneously improved due to the semiconducting nature of the interfacial materials, as well as the cascade interfacial energy level alignment, which effectively reduces non-radiative recombination losses in PSC devices. Consequently, planar n–i–p structured PSCs based on molecular semiconductors exhibit remarkably increased V_OC and FF values, and less hysteresis, along with an increased efficiency from 18.64% to 20.11% with MT2 as the interlayer. Moreover, hydrophobic molecular semiconductors could improve the long term stability of PSC devices by shielding the perovskite layer from external moisture.