Hollow 3D TiO2 sub-microspheres as an electron transporting layer for highly efficient perovskite solar cells

In today's optoelectronic devices, particularly perovskite solar cells (PSCs), morphological engineering and microscopic architecture of metal oxide semiconducting materials are of great significance for enhanced charge collection, photonic structuring, and optical enhancement optimization. Herein, three-dimensional hollow TiO2 sub-microspheres (3D-HTS) composed of anatase nanocrystals are synthesized using the hydrothermal method and used as a novel and efficient type of electron transport layer (ETL) for high-performance mesoscopic PSC. The TiO2 sub–microsphere-based film features a 3D interconnected structure with tunable film thicknesses and pore sizes. The PSC based on such sub-microsphere films results in an outstanding power conversion efficiency (PCE) of 18.01% that is 28% greater than the TiO2 nanoparticles (TNPs) ETL-based counterpart (PCE = 14.08%). The better efficiency of the sub–microsphere-made PSC device can be ascribed to the considerably improved charge collection, charge-transport, and light-harvesting capabilities. These valuable properties are because of the titania macropores that allow effective infiltration of the perovskite precursor for efficient light absorption, with reduced charge recombination and enhanced charge-transport through the sub-microspheres architecture. This work shows a practical and straightforward method for preparing 3D metal oxide–based electrodes for superior photovoltaic devices.