TiO2-based　electron　transport　layers　(ETLs)　show　tremendous　advantages　in　constructing　efficient　perovskite　solar　cells　(PSCs),　but　the　power　conversion　efficiency　(PCE)　needs　further　improvements.　Thus,　in　this　study,　graphitic　carbon　nitride　(g-C3N4),　a　typical　two-dimensional　material,　was　synthesized　in-situ　and　introduced　into　TiO2-based　ETLs　as　an　additive　via　a　facile　glass-assisted　annealing　route.　The　results　demonstrated　that　the　addition　of　g-C3N4　positively　influenced　the　crystalline　quality　of　the　perovskite　layers,　as　well　as　the　conductivity　and　photovoltaic　properties　of　the　devices.　Furthermore,　favorable　energy　level　alignment　facilitated　rapid　migration　of　electrons　and　suppressed　charge　recombination　at　the　interfaces.　Consequently,　the　champion　device　fabricated　using　the　g-C3N4-modified　ETL　achieved　a　maximum　PCE　of　20.46%　owing　to　the　remarkable　improvement　in　the　V-OC,　J(SC),　and　fill　factor.　The　PCE　is　approximately　20%　higher　than　that　obtained　for　the　pristine　device,　i.e.,　17.18%.　(C)　2021　Elsevier　Inc.　All　rights　reserved.