Carbazolyl phenylacetone-based asymmetric hole transport material enables high-performance perovskite solar cells

Abstract

Hole transport materials (HTMs) have a critical impact on the performance of perovskite solar cells (PSCs). Most of the current organic HTMs are in symmetric structures. In comparison, asymmetric structures tend to have excellent solubility, thermal stability, and hold potential for application as HTMs. Yet, asymmetric HTMs have been relatively less studied to date compared to their symmetric counterparts. In this work, two asymmetric small molecules 3,6-BOC and 2,7-BOC are designed and synthesized as HTMs for PSCs, with the asymmetric N-methyl-3-benzoylcarbazole (BOC) core structure connected to the peripheral carbazole-diphenylamine groups. The asymmetric BOC unit endows good thermal stability and film formation ability to the new HTMs. Notably, 3,6-BOC exhibits more suitable energy levels with perovskite materials, a higher hole mobility and stronger defect passivation effect when compared with those of 2,7-BOC. Ultimately, devices using 3,6-BOC as the HTM show a high efficiency of 21.52%, with excellent long-term and thermal stabilities. The results show that an asymmetric structure design strategy for HTMs has the potential to improve the efficiency and stability of PSCs.