Simple and low-cost thiophene and benzene-conjugated triaryamines as hole-transporting materials for perovskite solar cells

Two novel electron-rich linear small-molecules, containing benzene and thiophene as the cores with arylamine side groups, named HTM1 and HTM2, respectively, were synthesized via short, easy and efficient synthetic routes. The influence of the pi-linkers of the two materials on photophysical, electrochemical, and thermal properties, and hole mobility and photovoltaic performance was investigated. The compound with thiophene as p-linker (HTM2) shows better solubility and higher hole-transporting mobility than the compound with benzene as p-linker (HTM1). When these two materials were incorporated into perovskite solar cells as hole transporting materials (HTMs), short circuit photocurrent densities (J(sc)s) of 15.83 mA cm(-2) and 21.1 mA cm(-2), open circuit voltages (V(oc)s) of 0.79 V and 1.09 V, and fill factors (FFs) of 0.46 and 0.62, were obtained. These factors contributed to average overall power conversion efficiencies (PCEs) of 6.4% and 13.9% with the best PCEs of 7.5% and 14.7%, respectively. The performance of HTM2 is comparable to the PCE obtained using the current state-of-the- art HTM of 2,2 ',7,7 '-tetrakis(N, N '-di-p-methoxyphenylamine)-9,9 '-spirobifluorene (spiro-OMeTAD) with the best PCE of 17.4% using a similar device preparation method and measurement conditions. These results showed that selecting a suitable pi-linker is important for the performance of HTMs. And the simple HTM2 material is a promising HTM with the potential to replace the expensive spiro-OMeTAD due to its comparable performance with a much simpler synthesis route and much reduced cost (10 times less than that of spiro-OMeTAD). This study demonstrates that a compound with a suitable pi-linker could be a low-cost and high performance HTM to replace spiro-OMeTAD.