Electron-selective layers (ESLs) processed at low temperature play a vital role for planar perovskite solar cells (PSCs), especially for flexible devices. In this scheme, a novel strategy namely seeding-method is developed to prepare highly-compact anatase TiO2 ESLs at dramatically low temperature of 150 degrees C. This method allows the preparation of anatase TiO2 via hydrolyzation of Titanium diisopropoxide bis (acetylacetonate) (TiAcAc) induced by TiO2 crystal seed. Seeding-method permits the hydrolyzation of TiAcAc occurs at just 70 degrees C to obtain anatase TiO2, which is greatly reduced compared with normal procedure where 500 degrees C is desired. Accordingly, the acquired anatase TiO2 reacted with hydrochloric acid to prepare Cl-doped TiO2 (Cl@TiO2). Highly-compact anatase TiO2 ESLs were formed by spin-coating Cl@TiO2 onto FTO and then annealed at 150 degrees C. Power conversion efficiency of planar PSCs based on anatase Cl@TiO2 ESLs was 15.73%. Seeding-method processed at low temperature can be an effective way to advance the development of flexible perovskite photovoltaic.