Interface-Dipole-Driven Type-II Band Offset Engineering in Perovskite Heterostructures

Even though perovskite solar cells achieve high efficiency, interfacial energy mismatches with transport layers induce nonradiative recombination and limit performance. Here, we propose interface-dipole-driven band alignment engineering as a strategy to guarantee Type-II band alignment by integrating a Janus monolayer into a perovskite/Janus monolayer/perovskite heterostructure. The intrinsic out-of-plane dipole shifts the band edges of adjacent perovskite layers, thus enabling one layer to act as a light absorber and the other as a charge transport layer. Using CsPbBr₃/MSSe/CsPbBr₃ (M = Mo, W) as model systems, first-principles calculations confirm the formation of dipole-driven Type-II band alignment, while nonadiabatic molecular dynamics predict extended carrier lifetimes in CsPbBr₃/WSSe/CsPbBr₃, which can be attributed to its stronger dipole moment of monolayer WSSe and weaker nonadiabatic coupling. These results establish Janus monolayers as a versatile interfacial design platform to enhance carrier separation and suppress recombination, thus paving a way toward simplified, transport-layer-free, high-efficiency perovskite optoelectronics.