Highly Efficient Large-Area Flexible Perovskite Solar Cells Containing Tin Oxide Vertical Nanopillars without Oxygen Vacancies

Fabrication of high-quality electron transporting layers (ETLs) on large-area flexible electrodes is necessarily required, but challenging, to improve photovoltaic performance of flexible perovskite solar cells (PSCs) that are demanded for wearable electronic devices. This work shows one-step, oxygen-assisted glancing angle deposition to facilely deposit polycrystalline SnO2 nanopillars (NPs) that are free of oxygen deficiencies and vertically protrude on large-area transparent electrodes. Functioning as ETLs, SnO2 NPs comprehensively lead to an enhancement of light harvesting in perovskites, exciton separation, electron extraction and collection, and hole blocking, as well as the prevention of perovskite decomposition and the formation of perovskite defects. Large-area (1 cm2) flexible PSCs containing the SnO2 NPs show the champion power conversion efficiency (PCE) of 14.9%, which undergoes only 10% degradation for approximately 800 h storage and 20% degradation by manual bending for around 400 times. These photovoltaic performances are remarkably superior to large-area flexible PSCs having the conventionally used spin-coated SnO2 thin films that contain oxygen vacancies. These results pave the way toward scale-up fabrication of flexible PSCs that simultaneously satisfy the commercial requirements of high photovoltaic efficiency, shelf stability, and mechanical stability.