Hole transporting materials for perovskite solar cells: molecular versus polymeric carbazole-based derivatives

Designing organic hole transporting materials (HTMs) for stable perovskite photovoltaic devices remains a great challenge. Herein, we have prepared two small carbazole-based HTMs bearing a polymerizable double bond and one of the corresponding polymers. All compounds can be easily synthetized by a short procedure from largely available commercial products. These compounds have thermal, morphological, optical and electrochemical properties suitable for an application in perovskite solar cells. The side chains at the N-position on the carbazole have a negligible influence on the opto-electrochemical properties. However, the thermal properties differ largely between the monomer and its corresponding polymer. While these materials have the same photovoltaic performance, the polymeric HTM led to more stable devices. This illustrates the higher thermal stability of polymeric HTM versus its corresponding monomer.