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.