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BaTiO 3 is used to fabricate the electron transport layer of perovskite solar cells due to its spontaneous polarization. Li+ ions were doped into BaTiO 3 by the hydrothermal synthesis to increase the spontaneous polarization. The particle size of the as-prepared BaTiO 3 nanoparticles becomes smaller and more uniform for doping of Li+ ions with a molar ratio of 1.0 during the synthesis processes. The absorption edge shifts towards the short wavelength with the increase in the doping amount. Further, TiO 2 nanocrystalline thin film was deposited on the Li-doped BaTiO 3 thin film, the double layer was used as an electron transport layer of perovskite solar cell to indirectly demonstrate the effect of doping on the spontaneous polarization of BaTiO 3. The perovskite solar cell based on BaTiO 3 with 1.0 doping molar ratio of Li+ ions shows the highest light-to-electric conversion efficiency of 14.3% accompanying with the highest short-circuit photocurrent density. The measurements of impedance spectra and intensity modulating photocurrent spectra indicate that the photocurrent enhancement of perovskite solar cells is attributed to the spontaneous polarization enhancement of Li-doped BaTiO 3 thin films. The enhanced internal electric field in the BaTiO 3 thin layer accelerates the photogenerated electron transport in the electron transport layer of perovskite solar cell. Image 1 • The Li+ doping affects spontaneous polarization on BaTiO 3. • The spontaneous polarization in Li-doped BaTiO 3 promotes the electron transport. • Li-doped BaTiO 3 in electron transport layer improves performance of perovskite solar cell. [ABSTRACT FROM AUTHOR]