New Metal−Free Porphyrins as Hole−Transporting Materials in Mesoporous Perovskite Solar Cells.

Abstract

AbstractTwo A2B2 type free base porphyrins have been synthesized and examined as hole−transporting materials (HTMs) in perovskite solar cells (PSCs). These molecules contain a porphyrin ring as a π−spacer, two N,N’‐dimethylphenyl groups and either two phenylcarboxylic acid or two phenyl‐methyl‐ester units respectively. These molecules have been chosen as alternative HTMs to the well−known Spiro‐MeOTAD (N2,N2,N2′,N2′,N7,N7,N7′,N7′‐octakis(4‐methoxyphenyl)‐9,9′‐spirobi[9H‐fluorene]‐2,2′,7,7′‐tetramine) since porphyrins exhibit high versatility in molecular engineering towards the best performance in solar cells. Thus, they were characterized in terms of their electrochemical properties as the HOMO and LUMO levels are very important regarding their behaviour as HTMs. Mesoporous PSCs were constructed using both molecules and compared with standard ones based on Spiro‐MeOTAD. To the best of our knowledge this is the first study in which metal−free porphyrins are employed as HTMs in PSCs. The cells that incorporated the phenylcarboxylic acid based porphyrin showed similar current density (23 mA cm−2) with those based on Spiro‐MeOTAD but lower open circuit voltage which overall constitutes a promising result consolidating metal−free porphyrins as a new class of HTMs.