A low-cost, high-performance, dopant-free phenyl-based hole transport material for efficient and stable perovskite solar cells

Perovskite solar cells (PSCs) with a dopant-free hole transport layer (HTL) have been widely studied for their excellent photoelectric conversion efficiency and outstanding stability. However, the high production cost and complicated preparation process of dopant-free hole transport materials (HTMs) have become a crucial hindrance for the commercial development of such PSCs. Herein, we chose phenyl as the central core of the molecule to synthesize two low-cost HTMs, namely, B1 and B2. Compared with B1, the extension of the conjugated structure endows B2 with effective intermolecular stacking and excellent solubility, thus improving the carrier mobility (2.56 x 10-4 cm2 V-1 s-1) and film-forming property. Additionally, the adaptive energy level of B2 provides a guarantee for hole extraction at the perovskite/HTL interface. Consequently, the dopant-free B2-based PSCs provide a prominent power conversion efficiency of 20.37%, which is higher than that of B1-based PSCs (17.57%). The B1- and B2-based PSCs retained over 85% of their initial efficiency after being placed in air for 60 days, benefiting from the hydrophobicity of dopant-free HTLs. Moreover, B2-based PSCs retained more than 80% of their initial efficiency after storage at 60 degrees C for 600 h, due to the excellent thermal stability of B2. In conclusion, this work not only provides a feasible strategy for expanding the conjugate structure of dopant-free HTMs but also enriches the high-performance and low-cost material system, which will pave the way for the commercialization of PSCs with dopant-free HTL.