NiO@carbon spheres: A promising composite electrode for scalable fabrication of planar perovskite solar cells at low cost

Efficiencies of perovskite solar cells (PSCs) are now hitting such high levels that scalable fabrication at low-cost is becoming pivotal. However, this remains challenging due to expensive metal electrodes and organic holetransporting materials (OHTMs) typically used in PSCs. By simplifying the device structure, OHTMs-free and noble metal-electrodes-free planar PSCs with the aperture area of 1 cm(2) are fabricated with novel NiO@CSs-composite electrodes. The distribution of hole-accepting nickel oxide (NiO) as closely-packed shells on the core carbon spheres (CSs) in the rambutan-like NiO@CSs-composite enhances the photogenerated hole collection efficiency and reduces recombination loss. The small porosity of this composite inhibits the intrusion of the oxygen/moisture through the counter electrode, thus enabling a stable device's efficiency of 11.70% up to 1500 h under 40-60% humidity without encapsulation. The ability to fabricate large-sized planar devices with NiO@CSs-composite electrodes represents a significant step towards the cost-effective and scalable manufacturing with numerous possibilities to choose and optimize the materials, and device's architecture.