Simple dopant-free hole-transporting materials with p-π conjugated structure for stable perovskite solar cells

Two simple hole-transporting materials, Me-QTPA and Me-BPZTPA, which consist of p-pi conjugated structure, have been synthesized and studied in solid-state perovskite solar cells. Me-QTPA and MeBPZTPA show outstanding thermal stabilities and appropriate HOMO levels; in addition, these two materials show wide band gaps, thus they can block the electron transport and hence suppress the carrier recombination. The solution-processed CH3NH3PbI3-based device using dopant-free Me-QTPA and Me-BPZTPA can achieve a power conversion efficiency of 9.07% and 8.16%, respectively. The perovskite solar cells with dopant-free Me-QTPA show better performance than the cells with dopant-free spiro-OMeTAD, especially in long-term stability. The power conversion efficiency for the perovskite solar cells with dopant-free Me-QTPA remains almost constant after 600 h. The dopant-free Me-QTPA layer shows strong hydrophobicity with a contact angle of 101.6 degrees to water, which indicates that Me-QTPA has a promising long-term stability at room temperature. (C) 2017 Elsevier B.V. All rights reserved.