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

Solution-processable perovskite solar cells have recently achieved certified power conversion e ciencies of over 20%, challenging the long-standing perception that high e ciencies must come at high costs. One major bottleneck for increasing the e ciency even further is the lack of suitable hole-transporting materials, which extract positive 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 dissymmetric 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 e ciencies of 20.2% which compare favourably with control devices with 2,20,7,70-tetrakis(N,N-di-p-methoxyphenylamine)-9,90-spirobifluorene (spiro-OMeTAD). Thus, this new hole transporter has the potential to replace spiro-OMeTAD.