Novel trifluoropropoxy-substituted asymmetric carbazole derivatives as efficient and hydrophobic hole transporting materials for high-performance and stable perovskite solar cells

For highly efficient and stable perovskite solar cells (PSCs), small molecular hole transporting materials (HTMs) with high glass transition temperature, hydrophobicity, excellent film-formation and excellent hole mobility is highly desireable. However, developing a single molecule, which could meet all the above mention properties, is challenging. Herein, novel small molecules were design and synthesized, which show a suitable HOMO energy level and fulfill the above metioned properties simultaneously. For this purpose, we incorporate a hydrophobic trifluoropropoxy-terminal group to diphenylamine in SGT-405(3,6), a carbazole-based promising non-spiro-type small molecular HTM with excellent performance and low-cost, leading to two new HTMs (SGT-405s(C₂,CF₃) and SGT-405d(C₂,CF₃)). Among them SGT-405s(C₂,CF₃) showed an excellent hole mobility of 3.32 × 10^–4 cm² V⁻¹ s⁻¹, a remarkable high T_g of 183 ℃ and increased water contact angle of 87° compared to that of spiro OMeTAD (77.7°). Due to these superior properties, compared to those of spiro-OMeTAD, PSCs based on SGT-405s(C₂,CF₃) showed a remarkable power conversion efficiency (PCE) of 20.14%, which is higher than that of spiro-OMeTAD (18.97%), together with enhanced long-term and thermal stability. Our work revealed for the first time that trifluoropropoxy is a potential terminal group and an effective strategy for the design of new HTMs possessing superior properties in terms of glass transition temperature, hydrophobicity and film formation, for realizing efficient PSCs with enhanced moisture and thermal stability, simultaneously.