Efficient　electron　transport　layers　(ETLs)　not　only　play　a　crucial　role　in　promoting　carrier　separation　and　electron　extraction　in　perovskite　solar　cells　(PSCs)　but　also　significantly　affect　the　process　of　nucleation　and　growth　of　the　perovskite　layer.　Herein,　crystalline　polymeric　carbon　nitrides　(cPCN)　are　introduced　to　regulate　the　electronic　properties　of　SnO2　nanocrystals,　resulting　in　cPCN-composited　SnO2　(SnO2-cPCN)　ETLs　with　enhanced　charge　transport　and　perovskite　layers　with　decreased　grain　boundaries.　Firstly,　SnO2-cPCN　ETLs　show　three　times　higher　electron　mobility　than　pristine　SnO2　while　offering　better　energy　level　alignment　with　the　perovskite　layer.　The　SnO2-cPCN　ETLs　with　decreased　wettability　endow　the　perovskite　films　with　higher　crystallinity　by　retarding　the　crystallization　rate.　In　the　end,　the　power　conversion　efficiency　(PCE)　of　planar　PSCs　can　be　boosted　to　23.17%　with　negligible　hysteresis　and　a　steady-state　efficiency　output　of　21.98%,　which　is　one　of　the　highest　PCEs　for　PSCs　with　modified　SnO2　ETLs.　SnO2-cPCN　based　devices　also　showed　higher　stability　than　pristine　SnO2,　maintaining　88%　of　the　initial　PCE　after　2000 h　of　storage　in　the　ambient　environment　(with　controlled　RH　of　30%　±　5%)　without　encapsulation.[Figure　not　available:　see　fulltext.]　©　2021,　The　Author(s).