A heterostructure of a 2D semiconductor (WS2) and a layered perovskite lets an applied voltage switch between mobile interlayer excitons and localised intralayer excitons, while also changing valley polarisation — offering an electrical handle on exciton transport and information-carrying valley states without precise twist-angle stacking.
Applied voltage toggles the heterostructure between Type-II and Type-I band alignments, switching excitons between interlayer (mobile) and intralayer (localised) states.
Switching also changes valley polarisation, enabling electrical control over a form of information encoded in valley states.
The WS2/perovskite combination avoids the precise rotational alignment required by stacked TMD bilayers, simplifying device fabrication.
Researchers built a heterostructure combining monolayer WS2 and a layered organic–inorganic perovskite. Their objective was to obtain electrical control over exciton behaviour and over valley polarisation — the preference of carriers for one of two equivalent energy minima (valleys) in momentum space — and thereby to control both energy transport and an information degree of freedom in a single device.
Voltage also changes valley polarisation. The team measured polarization-resolved photoluminescence under circularly polarised excitation and found that opposite voltages produced different valley-polarisation states. That means the same electrical control that governs transport also alters a carrier-based information state.
Interlayer excitons are useful because spatial separation of electron and hole extends lifetime and allows excitonic energy transport over longer distances than typical excitons. Controlling whether excitons are mobile or localised with a voltage is a direct way to route energy on chip without moving charges.
Valley polarisation provides a non-charge information channel. Being able to switch valley polarisation electrically — while simultaneously switching transport — puts two controls (energy flow and information state) under the same, simple external input.
Previous demonstrations of interlayer exciton devices often used stacked transition-metal dichalcogenide (TMD) pairs, such as MoSe2/WSe2 or WS2/WSe2. Those systems typically require extremely precise rotational alignment between layers (twist-angle engineering) to produce strong interlayer exciton emission. The WS2/perovskite heterostructure reported here does not require that level of twist-angle precision, making device fabrication more practical.
The paper presents a schematic of the heterostructure and energy-band diagrams showing the electrically induced switch between band alignments. Polarization-resolved photoluminescence spectra taken at opposite voltages under circularly polarised laser excitation show the change in valley polarisation associated with the exciton-state switch.
Implications and near-term relevance
This work demonstrates a straightforward electrical method to control exciton transport and valley-based information in a 2D system. That capability is directly relevant to efforts aiming to build excitonic circuits and valleytronic devices — components that would use excitons to move energy and valley degree of freedom to carry information — while lowering fabrication constraints by using a hybrid perovskite/TMD stack.
The experimental demonstration and analysis are reported in the paper "Switchable band alignment in 2D-perovskite/WS2 heterostructures for tunable exciton transport and valley polarization" by Yingying Chen et al., Rep. Prog. Phys. 89 078004 (2026).
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Author(s): David Ehrenstein A newly predicted effect should provide a clean way to distinguish between a Bose-Einstein condensate of quasiparticles called excitons and a more mundane collection of these particles. [Physics 19, s124] Published Tue Sep 22, 2026
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