Conjugated small molecules based on alkylsilyl-modified triphenylamine: promising hole transport materials in perovskite photovoltaics

There is a renascence in the use of triphenylamine (TPA)-based donor materials in the field of perovskite photovoltaics. This work presents the synthesis of two novel conjugated small molecules (CSMs), TPA-t and TPA-t EH, which are functionalized with triisopropylsilyl groups and 2-ethylhexyl side chains. These molecules show promise as hole transport materials, which possess high hole mobilities of 1.5 x 10-4 and 2.9 x 10-3 cm2 V-1 s-1. TPA-t and TPA-t EH possess HOMO energy levels at -5.38 and -5.31 eV, which are well-aligned with the valence band of standard perovskite MAPbI3. This resulted in outstanding open-circuit voltages of 1100 and 1080 mV. TPA-based molecules were investigated as HTLs in n-i-p PSCs without additional doping and enabled high efficiency (17.3%) same as for devices with the state-of-the-art polytriarylamine (PTAA) HTL. The obtained results suggest that the developed materials could potentially compete with PTAA with further material structure modification. Our research presents novel TPA-based hole-transport materials with triisopropylsilyl side chains, which possess good alignment of HOMO energy level with MAPbI3 increasing VOC of perovskite solar cells up to 1.1 V.