Facile star shape tetraphenylethylene-based molecules with fused ring-terminated diarylamine as interfacial hole transporting materials for inverted perovskite solar cells

In this work, three p-type small molecules (CL-1–3) based on tetraphenylethylene as the core and fused ring-terminated diarylamine as electron donating groups were synthesized. The design strategy for fused ring-terminated diarylamines involved the use of benzene for CL-1, naphthalene for CL-2, and pyrene for CL-3. We then investigated the effects of various electron-donating groups on their electronic properties. Among them, the CL-3 sample showed the highest Tg value (192 °C) and 5 wt% decomposition temperature (473 °C). In the presence of urea as an additive, inverted perovskite solar cells (PSCs) employing inorganic/organic (NiOx/CL series) bilayer HTLs and reference inorganic (NiOx)-only HTL were fabricated. Notably, the NiOx/CL-3-based cell exhibited the champion power conversion efficiency of 20.15%, which outperformed the NiOx-only cell (PCE = 18.66%) due to its smoother surface morphology, better interface charge transfer and matched energy-level alignment. Furthermore, this device also exhibited greater hydrophobicity and acceptable long-term stability. This work presents a new molecular design and in-depth understanding of the bilayer HTL strategy and its potential for the development of highly efficient cell performances.