A low cost azomethine-based hole transporting material for perovskite photovoltaics

Most hole transporting materials (HTMs) prepared for perovskite solar cell applications are synthesized via cross-coupling reactions that require expensive transition metal catalysts, inert reaction conditions and extensive product purification; making large-scale production cost-prohibitive. Here, we describe the synthesis of a simple azome-thine-based conjugated small-molecule (EDOT-OMeTPA) which is easily prepared in a cost effective Schiff base condensation reaction, with water being the only by-product. As the hole transporter in planar CH3NH3PbI3 perovskite solar cells, efficiencies exceeding 11% were reached. This result is comparable to state-of-the-art materials such as Spiro-OMeTAD on a like-to-like comparison, while cost estimations show that the material cost is about one order of magnitude lower for EDOT-OMeTPA, resulting in a negligible cost-per-peak-Watt contribution of 0.004 $ W-1. In addition, the high synthetic accessibility of EDOT-OMeTPA also reduces the toxic chemical waste and therefore greatly reduces its environmental impact. Our results pave the way towards low-cost, environmentally friendly and efficient HTMs.