Halogen Bond Involved Post‐Treatment for Improved Performance of Printable Hole‐Conductor‐Free Mesoscopic Perovskite Solar Cells

Perovskite solar cells (PSCs) are considered to be the most promising next‐generation photovoltaic technology. Among all the configurations of PSCs, the printable hole‐conductor‐free mesoscopic PSC (p‐MPSC) has unique advantages on low cost, large‐area fabrication and fabulous stability, which endows it with the greatest potential for industrialization. The interfacial recombination losses, especially at the perovskite/carbon interface, are the bottleneck for further improving the power conversion efficiency (PCE) of p‐MPSCs. 2‐Bromo‐6‐fluoronaphthalene is introduced as an interfacial modulator for p‐MPSCs through post‐treatment. The bromo‐terminal acts as an electrophilic site to interact with the iodine ion in perovskite via the noncovalent halogen bond. Meanwhile, the fused ring of naphthalene is capable to accommodate electron density that is attracted from the perovskite. This interaction induces a more favorable band structure at the interface. The hole extraction is promoted and the interfacial nonradiative recombination is inhibited. Accordingly, a champion p‐MPSC with an improved PCE of 16.77% from 15.50% of the pristine device is obtained.