Interface Effects in Triazine‐Based g‐C3N4/MAPbI3 Van der Waals Heterojunctions: A First‐Principles Study

2D materials (TDMs) have demonstrated their great potential as functional materials in perovskite solar cells (PSCs) to boost conversion efficiency. As a versatile TDM, g‐C 3 N 4 has far less applications in PSCs than in medical science, energy storage, supercapacitors, and catalysis. Is 2D g‐C 3 N 4 naturally incompatible with perovskites limiting their cooperation? Herein, the capacity of two kinds of triazine‐based g‐C 3 N 4 as interfacial modifiers for CH 3 NH 3 PbI 3 (MAPbI 3 ) perovskite based on density functional theory is discussed. Due to the existence of two feasible atomically exposed surfaces in MAPbI 3 perovskite, denoted as PbI and MAI interfaces, four heterojunction structures are constructed. The interfacial carrier transport kinetics and charge recombination region distribution of the heterojunctions are systematically investigated. The results show that the NPCN/MAI heterojunction facilitates the separation and transport of charges due to its type‐II energy band alignment and smaller charge recombination region. Herein, a promising interface‐modified 2D material for perovskite photoactive layer is introduced and an avenue to reduce the charge recombination loss in PSCs is provided.