Periphery group engineering in hole transport materials for efficient perovskite solar cells

At present, organic small molecule-based hole transporting materials (HTMs) are extensively investigated in perovskite solar cells (PSCs), and a variety of structures have been developed. Most of the studies in HTMs focus on the central scaffolds, while little attention is paid to the periphery groups. In this work, two small organic molecules (TPE-2Cz and TPE-3Cz) are designed and synthesized, with tetraphenylethylene as the core structure, N-ethylcarbazole and methoxyphenyl as the peripheral groups. The C2 or C3 position on N-ethylcarbazole is connected to the arylamine N atom in TPE-2Cz and TPE-3Cz, respectively. We systematically investigate how the N-ethylcarbazole modified at different positions (C2 or C3) affect the property of HTMs and finally the performance of PSC devices. Compared with TPE-2Cz, TPE-3Cz shows a higher hole mobility, better hole extraction and hole transport ability. The device based on TPE-3Cz as the hole transport material achieves a decent power conversion efficiency of 20.94%. Therefore, our work reveals that the periphery group engineering should be taken into consideration when designing organic HTMs.