Planar perovskite solar cells (PSCs) based on low-temperature solution-processed SnO<inf>2</inf> electron transport layers (ETLs) usually suffer from energy losses within SnO<inf>2</inf> ETLs or at SnO<inf>2</inf>/perovskite interfaces. Doping is an effective strategy to modify the properties of SnO<inf>2</inf> and reduce such energy losses. Herein, Ce ions are incorporated into solution-processed SnO<inf>x</inf> and Ce-doped SnO<inf>x</inf> ETLs are fabricated for planar PSCs via inkjet printing. The Ce-doped SnO<inf>x</inf> ETL shows enhanced conductivity and improved energy level alignment with the perovskite layer, which can facilitate charge extraction and transport capabilities. Ce doping also effectively passivates the surface defects of SnO<inf>x</inf>. The photoluminescence characterization reveals that the carrier recombination is suppressed within the perovskite film. As a result, an improved power conversion efficiency (PCE) of 15.77% is obtained for the planar PSC with a Ce-doped SnO<inf>x</inf> ETL, compared to that of 14.66% for the undoped device. Furthermore, this work demonstrates a sustainable fabrication method which has great potential for the upscaling of PSCs.