Room-temperature-processed fullerene single-crystalline nanoparticles for high-performance flexible perovskite photovoltaics

Abstract

Organic–inorganic hybrid perovskite solar cells (PSCs) employing a mesoporous metal-oxide scaffold are now at the forefront of solution-processed photovoltaic cells, yielding a power conversion efficiency exceeding 23%. However, processing temperatures of up to 450 °C are typically required to sinter 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 paper, we develop for the first time an organic-scaffold architecture, which consists of room-temperature-processed 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 them 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 TiO₂ enhances the charge transfer from the perovskite to electron transport layers and reduces charge carrier accumulation at the interface, demonstrating the advantage of an organic scaffold over inorganic metal-oxides for mesoporous scaffold PSCs. A power conversion efficiency (PCE) of 19.45% was obtained in organic-scaffold MAPbI₃-based perovskite solar cells (OPSCs), outperforming standard reference devices based on a TiO₂ mesoporous scaffold (maximum PCE = 17.07%). Furthermore, the high UV stability of C₆₀-NPs enables the realisation of ultra-stable OPSCs stressed under ambient conditions and working under both UV and full-sun illumination. Moreover, the devices can be easily processed at 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 MAPbI₃-based flexible PSCs to date. This work reveals that organic nanostructures as n-type charge collection layers are ideal replacements for inorganic mesoporous scaffolds as they achieve remarkably high efficiency and long-term operational stability in both rigid and flexible perovskite solar cells.