Low-temperature solution-processed SnO₂ nanoparticles as a cathode buffer layer for inverted organic solar cells

SnO₂ recently has attracted particular attention as a powerful buffer layer for organic optoelectronic devices due to its outstanding properties such as high electron mobility, suitable band alignment, and high optical transparency. Here, we report on facile low-temperature solution-processed SnO₂ nanoparticles (NPs) in applications for a cathode buffer layer (CBL) of inverted organic solar cells (iOSCs). The conduction band energy of SnO₂ NPs estimated by ultraviolet photoelectron spectroscopy was 4.01 eV, a salient feature that is necessary for an appropriate CBL. Using SnO₂ NPs as CBL derived from a 0.1 M precursor concentration, P3HT:PC₆₀BM-based iOSCs showed the best power conversion efficiency (PCE) of 2.9%. The iOSC devices using SnO₂ NPs as CBL revealed excellent long-term device stabilities, and the PCE was retained at ∼95% of its initial value after 10 weeks in ambient air. These solution-processed SnO₂ NPs are considered to be suitable for the low-cost, high throughput roll-to-roll process on a flexible substrate for optoelectronic devices.