Dopant‐Free Hole Transporting Molecules for Highly Efficient Perovskite Photovoltaic with Strong Interfacial Interaction

Abstract

One of the attractive ways to develop efficient and cost‐effective inverted perovskite solar cells (PVSCs) is through the use of dopant‐free hole transporting materials (HTMs) with facile synthesis and a lower price tag. Herein, two organic small molecules with a fluorene core are presented as dopant‐free HTMs in inverted PVSCs, namely, FB‐OMeTPA and FT‐OMeTPA. The two molecules are designed in such a way they differ by replacing one of the benzene rings (FB‐OMeTPA) with thiophene (FT‐OMeTPA), which leads to a significantly improved coplanarity as manifested in the redshift of the absorbance and a smaller bandgap energy. Density functional theory calculations show that FT‐OMeTPA has a strong Pb 2+ –S interaction at the FT‐OMeTPA/perovskite interface, allowing surface passivation and facilitating charge transfer across interfaces. As a result, the PVSCs based on FT‐OMeTPA exhibit a much higher hole mobility, power conversion efficiency, operational stability, and less hysteresis as compared with devices based on FB‐OMeTPA.