Management of Intramolecular Noncovalent Interactions in Dopant-Free Hole Transport Materials for High-Performance Perovskite Solar Cells

Organic semiconductors with intramolecular noncovalent interactions are promising hole transport materials (HTMs) for efficient and stable perovskite solar cells (PSCs), but the effects of different types of noncovalent bonds on the properties of HTMs are rarely reported. Here, three thiazolo[5,4-d]thiazole (TzTz)-based HTMs with different side chains were developed. Compared with alkyl side chains, functional side chains can improve the crystallinity and charge transport ability of HTMs by forming intramolecular noncovalent interactions. However, the steric hindrance of S···O in TzTzTPA-SO distorted the molecular skeleton, leading to edge-on stacking and local aggregation of film. Fortunately, TzTzTPA-NH with intramolecular hydrogen bond showed high planarity, proper crystallinity, and preferred stacking orientation. Consequently, a remarkable power conversion efficiency (PCE) of 24.2% with a nice long-term stability was achieved by dopant-free TzTzTPA-NH-based PSCs, which is superior to the doped Spiro-OMeTAD-based PSCs. In addition, TzTzTPA-NH is well used as HTM in wide-bandgap PSCs and perovskite/organic tandem solar cells (TSCs). Encouragingly, the TSCs based on TzTzTPA-NH achieved an excellent PCE of 25.4%, which is the highest PCE of n-i-p perovskite/organic TSCs. This work clearly illustrates the effect of intramolecular noncovalent interactions on the properties of HTMs, and provides guidance for designing high-performance dopant-free HTMs in PSCs.