Conjugation Engineering of Spiro-Based Hole Transport Materials for Efficient and Stable Perovskite Solar Cells

The spiro-type hole transport materials (HTMs) highly depend on the dopants, which increase the hygroscopicity and damage the stability of perovskite solar cells (PSCs). Herein we propose an effective linearization strategy and conjugate engineering modulation to improve the hole mobility and hydrophobicity of spiro-type HTMs. It is found that the spiro-type HTMs with a larger conjugation unit outperforms the short ones with respect to the power conversion efficiency (PCE) and long-term stability, regardless of whether or not the dopants are used. Due to good hole transport and film formation properties, the doped M6-F exhibits high efficiency in both large-area (1.01 cm2, 20.31%) and small-area (0.1 cm2, 22.17%) devices. Moreover, a PSC based on dopant-free M6-F yields an efficiency of 21.21% (stabilized PCE is 20.59%). This work provides a rational and effective way to break the bottleneck of developing spiro-type HTMs.