Efficient Electron Transport Scaffold Made up of Submicron TiO₂ Spheres for High-Performance Hole-Transport Material Free Perovskite Solar Cells

Nanoporous submicron TiO2 spheres of diameters around 200 nm are synthesized by a hydrothermal process and used as a scaffold layer for improving light absorption, charge transportation, as well as photovoltaic performance in hole-transport-layer free perovskite solar cells employing carbon counter electrodes. The TiO2 submicron spheres show a porous feature with high specific surface area, which is essential for perovskite infiltration, charge extraction, and transportation in mesoscopic perovskite solar cells. Furthermore, big spheres exhibit better light scattering property compared to traditional TiO2 nanoparticles, thus enhancing light absorption in corresponding devices. The present perovskite solar cells employ a TiO2 scaffold layer of optimized thickness of about 600 nm and show an average power conversion efficiency of 13.46 ± 0.41%, which is 18.4% higher than that of counterparts based on TiO2 nanoparticle (11.37 ± 0.40%). The champion cell exhibits an impressive efficiency of 14.3%, which is very competitive in perovskite solar cells without a hole transport layer using a carbon electrode. Moreover, our carbon based perovskite solar cell shows excellent long-term stability against moisture and heat with negligible degradation for 210 days of storage under ambient conditions.