An in situ bifacial passivation strategy for flexible perovskite solar module with mechanical robustness by roll-to-roll fabrication

Abstract

The inevitable interfacial defects in the under layer of perovskite films still hinder the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs), especially of large-area flexible devices up-scaled by roll-to-roll (R2R) technology. Herein, we demonstrate an in situ bifacial passivation strategy via a simple hydroiodic acid (HI) soaking of NiO_x-based hole transport layer during R2R printing. Concretely, the trivalent nickel compound on the film surface is reduced to nickel iodide (NiI₂) by a HI redox reaction, thereby optimizing the interface contact and ameliorating the work function. Meanwhile, NiI₂ coordinates with lead atoms in the perovskite to form a Pb–I bond, which induces the orderly growth of the perovskite lattice and enhances the quality of the crystalline film. Consequently, the PCE of the optimized flexible devices reaches up to 19.04% (1 cm²) and 16.15% (15 cm²). Moreover, the stability and mechanical property of these devices are also improved. This work provides a deep understanding of the NiO_x/perovskite interface and an approach for printable interface optimization.