Novel Sea Urchin-Like Niobium Pentoxide as an Electron Transport Layer for Efficient and Stable Perovskite Solar Cells

Niobium pentoxide (Nb 2 O 5 ) has emerged as an outstanding electron transport material (ETM) for perovskite solar cells (PSCs), owing to its favorable band alignment and remarkable ultraviolet stability. Here, sea urchin-like Nb 2 O 5 nanoparticles, with diameters ranging from 20 to 100 nm, were synthesized via a hydrothermal reaction using niobium oxalate as a precursor. These nanoparticles could serve as a highly effective ETM layer for efficient and stable mesoscopic PSCs. By meticulously adjusting the precursor solution to optimize the size of Nb 2 O 5 nanoparticles, a power conversion efficiency (PCE) of 19.71% was attained for Nb 2 O 5 -based PSCs. Furthermore, through precise control of the device fabrication process, the maximum PCE could be improved to 23.11%. Notably, the Nb 2 O 5 -based devices exhibited enhanced stability. After being stored in air (at 25 ± 5 °C, with a relative humidity of 25 ± 5%) for 720 h, the Nb 2 O 5 -based device retained 84% of its initial PCE, in stark contrast to the pristine TiO 2 -based PSC, which only maintained 52% of its initial efficiency. The superior performance of the PSCs incorporating sea urchin-like Nb 2 O 5 nanoparticles (approximately 50 nm) can be ascribed to the well-adapted interfacial energy level alignment, which facilitates electron transfer between the perovskite layer and the electron transport layer (ETL). Additionally, the sea urchin-like Nb 2 O 5 nanoparticles provide an unobstructed pathway for the transport of extracted electrons, thereby effectively suppressing charge recombination.