Flexible Backbone-Assisted Green-Solvent Processable Polymer Hole Transport Material in Perovskite Solar Cells

Developing green-solvent processable polymer hole transport materials (p-HTMs) is considered imperative for industrial-scale production. However, the introduction of a large conjugated structure into molecules that ensures strong intermolecular interactions as well as high hole mobility compromises their solubility in green solvents. Lacking solubility could result in excessive phase separation and heterogeneous thin films for p-HTMs, while it would sacrifice device performance. In order to address this trade-off, we propose an effective design strategy that combines backbone flexibility and rigid conjugate engineering modulation. The delicate collocation of flexible amide chains, polar solubilizing ethylenedioxythiophene (EDOT) units, and conjugated binaphthalene groups contributes to high hole mobility and multiple defect passivation effects. Moreover, the resulting p-HTM (A-EDOT) can be processed by the green solvent 2-methylanisole (2MA). Once used as an HTM in inverted perovskite solar cells, a significant fill factor (FF) of 81.9% and a champion efficiency of 20.23% are achieved for the A-EDOT, outperforming the state-of-the-art polymer PTAA (FF = 80.5%, efficiency = 19.68%) that is processed with chlorobenzene. Moreover, due to the passivation effects of A-EDOT, the quality of perovskite films is improved; correspondingly, a significantly promoted long-term device stability and thermal stability are realized. This work provides a competitive design strategy of green-solvent processable p-HTMs for photovoltaic devices.