Improved thermal stability of perovskite solar cells via hole transporting materials design

Long-term thermal stability is currently a great hurdle for perovskite solar cells (PSCs) on the way to commercialization. While spiro-MeOTAD has been successfully employed as a hole transporting material (HTM) in elaborating high performing PSCs with n-i-p architecture, the devices still suffer from poor thermal stability. In this study, three type of new HTMs (T3A, T3B, and T3C) are employed by introducing 9,9-diphenylfluorene as a bulky central core for three-dimensional molecular structure, aiming at achieving the morphological stability of HTM for thermally stable PSCs. Devices employing T3C demonstrate a remarkable thermal stability mainly due to its high glass transition temperature though photovoltaic performance is reduced. The employment of T3C enables devices to retain 70% of its initial power conversion efficiency after 1000 h under continuous thermal stress at 85 o C in N 2 atmosphere. Nevertheless, the formation of pinholes across the HTM layer, coupled with the layer exfoliation, makes the device difficult to adopt complete resistance under the persistent thermal stress.