Fullerene Single-Crystalline Nanoparticles For Flexible Perovskite Photovoltaics

Organic-inorganic hybrid perovskite solar cells(PSCs)employing a mesoporous metal-oxide scaffold are now at the forefront of solution-processing photovoltaic cells,yielding a power conversion efficiency exceeding 25%.However,processing temperatures of up to 450?are typically required to sinter the mesoporous metal-oxide scaffolds,which hinders the fabrication of low-cost and flexible devices.Moreover,these metal-oxide scaffolds usually suffer from high charge carrier recombination rates and inherent UV instability.in this work,we develop for the first time an organic-scaffold architecture,which consists of room-temperature-processing C₆₀ single-crystalline nanoparticles(C₆₀-NPs)serving as an electron selective contact covering on C₆₀ compact films(c-C₆₀).C₆₀-NPs act as a three-dimensional framework to support perovskite crystals,enabling it to cover the substrate more uniformly and thus demonstrating an advantage over planar heterojunction PSCs.Furthermore,the higher electron mobility of C₆₀-NPs compared with commonly-used Ti O₂ enhances the charge transfer from perovskite to electron transport layers and reduces charge carrier accumulation at the interface,demonstrating the advantage of an organic scaffold over inorganic metal-oxide for mesoporous scaffold PSCs.A power conversion efficiency(PCE)of 19.45%was obtained in organic-scaffold MAPb I₃-based perovskite solar cells(OPSCs),outperforming standard reference devices based on a Ti O₂ mesoporous scaffold(maximum PCE=17.07%).Furthermore,the high UV stability of C₆₀-NPs enables the realisation of ultra-stable OPSCs stressed in ambient conditions and working under both UV and full-sun illumination.Most importantly,the devices can be easily processed under low temperatures,providing an efficient method for the large-scale production of flexible PSCs.These flexible PSCs show remarkable performance with an excellent PCE of 17.28%,which is among the highest values reported for MAPb I₃-based flexible PSCs to date.This work reveals that organic nanostructures as n-type charge collection layers are ideal replacements for the inorganic mesoporous scaffold as they achieve remarkably high efficiency and long-term operational stability in both rigid and flexible perovskite solar cells.