Van der Waals epitaxy of (BA)2PbI4/WSe2 heterostructures with strong interlayer exciton emission

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Van der Waals (vdW) epitaxy enables tailored excitonic interactions and charge separation in two-dimensional (2D) perovskite heterostructures, addressing optoelectronic integration challenges. Utilizing a two-step chemical vapor deposition process, pre-deposited PbI2 layers on monolayer WSe2 are transformed to (BA)2PbI4 by controlled introducing of BAI vapor during the second growth, overcoming challenges of (BA)2PbI4 formation caused by low organic ligand mobility and limited PbI2 vapor pressure. This method facilitates the growth of nanosheets and thickness-tunable (BA)2PbI4 nanofilm, achieving strong interlayer coupling as evidenced by dominant interlayer exciton (IX) emissions at 83 K. Notably, epitaxial heterostructures exhibit interlayer coupling coefficients of 0.75 for nanosheets and 0.65 for nanofilm, outperforming transferred heterostructures and highlighting the advantage of the vdW epitaxy in improving interfacial exciton interactions and structural precision. Additionally, laser-induced IX emission blue shifts up to 111 meV in epitaxial grown (BA)2PbI4/WSe2 samples, confirming superior excitonic interactions and coupling strength. These findings demonstrate the feasibility of vdW epitaxy for integrating organic 2D perovskites with TMDCs, establishing the structural and optical significance of such heterostructures for exploring IX physics.