Molecular Cooperation of Ion-Free Ternary Complexes Enhances Efficiency and Stability of Perovskite Solar Cells

Chemical dopants such as ionic additives are essential in hole-transport layers (HTLs) to enhance their charge-transport abilities in perovskite solar cells (PSCs). However, these ionic components often cause issues of ion migration and phase segregation, which limit the reliability and stability of PSCs. Herein, an effective strategy of cooperative ternary components (CTC) is developed to enhance device efficiency and stability by combining molecular additives and conjugated polymers into the conventional 2,2',7,7'-tetrakis (N,N-di-p-methoxyphenyl-amine) 9,9'-spirobifluorene (Spiro)-based HTLs. All-molecule-based CTC enables negligible phase segregation in the HTL compared to ionic doping. The collaborative roles of small molecules and conducting polymer in the CTC blend facilitate to enhance the interfacial charge extraction and the charge transport in the bulk HTL. Consequently, the CTC strategy contributes to a substantial increase of the device efficiency from 14.97% (the control) to 20.14% (CTC), which is among the highest reported efficiency for the ion-free spiro-based PSCs. More encouragingly, the CTC-based devices demonstrate remarkable environmental stability, maintaining 90% of the initial efficiency after about 2500 h under ambient conditions without any encapsulation. In this work, a novel doping approach is provided for the fabrication of stable and efficient PSCs.