A molecularly engineered hole-​transporting material for efficient perovskite solar cells

Soln.-​processable perovskite solar cells have recently achieved certified power conversion efficiencies of over 20​%, challenging the long-​standing perception that high efficiencies must come at high costs. One major bottleneck for increasing the efficiency even further is the lack of suitable hole-​transporting materials, which ext. pos. charges from the active light absorber and transmit them to the electrode. In this work, we present a molecularly engineered hole-​transport material with a simple dissym. fluorene-​dithiophene (FDT) core substituted by N,​N-​di-​p-​methoxyphenylamine donor groups, which can be easily modified, providing the blueprint for a family of potentially low-​cost hole-​transport materials. We use FDT on state-​of-​the-​art devices and achieve power conversion efficiencies of 20.2​% which compare favorably with control devices with 2,​2',​7,​7'-​tetrakis(N,​N-​di-​p-​methoxyphenylamine)​-​9,​9'-​spirobifluorene (spiro-​OMeTAD)​. Thus, this new hole transporter has the potential to replace spiro-​OMeTAD.