Benzothiadiazole-based hole transport materials for high-efficiency dopant-free perovskite solar cells: Molecular planarity effect

Abstract

Abstract A new benzothiadiazole-based D -A-D hole transport material (DTBT) has been designed and synthesized with a more planar structure by introducing of thiophene bridges. The results indicate a lower band gap and quite higher hole mobility for the DTBT. Furthermore, the enhancement in molecular planarity with simple thiophene unit increases the hole mobility of DTBT (8.77 × 10−4 cm2 V−1 s−1) by about 40%. And when DTBT is used as hole transport material in perovskite solar cells, the photoelectric conversion efficiency of the corresponding dopant-free devices is also significantly improved compared with that of the conventional BT model molecule without thiophene. In terms of device stability, DTBT-based devices show a favorable long-term stability, which keep 83% initial efficiency after 15 days. Therefore, the introducing of thiophene bridges in D -A-D typed HTMs can improve the molecular planarity effectively, thereby increasing the hole mobility and improving device performance.