Triphenylimidazole substituted D-π-D porphyrin based dopant-free hole transport materials for perovskite solar cells

Abstract

Hole-transport materials (HTMs) contribute an important function in perovskite solar cells (PSCs) for achieving favourable photovoltaic performance with durability. In this work, we designed and synthesized a series of porphyrin based hydrophobic HTMs based on donor-π-donor (D-π-D) tactic in which triphenylimidazole as donor and either free-base porphyrin (H2LD) or metalloporphyrin (Cu, CuLD or Zn, ZnLD) as π-spacer for PSCs. All three HTMs were characterized by a variety of spectroscopic and electrochemical methods. Optical and electrochemical properties propose that the highest occupied molecular orbital (HOMO) energy levels were healthily aligned with the valence band of MAPbI3 perovskite. Among these HTMs, CuLD exhibited higher hole mobility of 7.39 × 10-5 cm2V-1s-1, when compared to ZnLD 5.77 × 10-5 cm2V-1s-1, and H2LD 2.7 × 10-5 cm2V-1s-1. We fabricated PSCs with these HTMs and among them the CuLD based PSCs showed highest power conversion efficiency of 12.44%. The better PCE for the PSCs fabricated with CuLD could be attributed to the higher conductivity and better hole mobility which could be correlated to the better film formation.