Low temperature solution deposited niobium oxide films as efficient electron transport layer for planar perovskite solar cell

In high efficient planar perovskite solar cells (PSC), electron transportation layer (ETL) plays an important role in its photovoltaic performance. Except for TiO₂, Nb₂O₅ has also been considered as ideal electron selective layer material for planar perovskite solar cell due to its excellent optical transmittance and similar Femi level with TiO₂. Herein, we report niobium oxide film deposited by a simple and low temperature solution method, as an effective alternative to high temperature sintered TiO₂ film in the regular architecture of PSC. Nb₂O₅ modification of FTO has successfully tuned the surface work function from 4.59 eV to 4.28 eV without obviously affecting the surface roughness and optical transmittance, which could significantly decrease energy level offset and improve the open voltage. Appropriate UV ozone treatment could adjust the surface hydrophilicity of Nb₂O₅ film benefiting the growth of perovskite films on low temperature solution deposited Nb₂O₅ coated FTO substrate. Relatively high efficiency over 17% with less J–V hysteresis has been achieved by optimizing the precursor solution, spin rate, annealing temperature and UV ozone treatment time. The results indicate low temperature solution deposited Nb₂O₅ film can be a low cost and easy-prepared ETL material for high performance PSC.