Polymeric, Cost-Effective, Dopant-Free Hole Transport Materials for Efficient and Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) has skyrocketed in the past decade to an unprecedented level due to their outstanding photoelectric properties and facile processability. However, the utilization of expensive hole transport materials (HTMs) and the inevitable instability instigated by the deliquescent dopants represent major concerns hindering further commercialization. Here, a series of low-cost, conjugated polymers are designed and applied as dopant-free HTMs in PSCs, featuring tuned energy levels, good temperature and humidity resistivity, and excellent photoelectric properties. Further studies highlight the critical and multifaceted roles of the polymers with respect to facilitating charge separation, passivating the surface trap sites of perovskite materials, and guaranteeing long-term stability of the devices. A stabilized power conversion efficiency (PCE) of 20.3% and remarkably enhanced device longevity are achieved using the dopant-free polymer P3 with a low concentration of 5 mg/mL, qualifying the device as one of the best PSC systems constructed on the basis of dopant-free HTMs so far. In addition, the flexible PSCs based on P3 also exhibit a PCE of 16.2%. This work demonstrates a promising route toward commercially viable, stable, and efficient PSCs.