p‐Type Transparent Conducting Material Realized by Composite Thin Film of Chalcogenide Perovskite LaScS 3 and Graphene

ABSTRACT Chalcogenide perovskites (CPs) have recently emerged as promising alternatives to oxide and halide perovskites, owing to their tunable band gaps, high chemical stability, and environmental benignity. Here, we demonstrate the first synthesis of transparent LaScS 3 (LSS) thin films via an air‐compatible, cost‐effective, and environmentally friendly polymer‐assisted deposition (PAD) method. The resulting thin films show high phase purity, uniform morphology, and an optical band gap of ∼2.9 eV, consistent with density functional theory predictions. The optical transmittance exceeds 80% at 550 nm wavelength. Nevertheless, defects hinder the introduction of effective conductivity in the LSS thin films. To overcome this limitation, we employ a composite thin‐film strategy, in which heavy doping with group IIA elements (Mg, Ca, Sr, Ba) promotes the in‐situ growth of graphene layers during sulfurization by CS 2 , thereby giving rise to p‐type conductivity while maintaining optical transparency. The Mg‐doped film exhibits the lowest sheet resistance (16.6 kΩ/sq) while maintaining 84%–95% of the optical transmittance of the undoped thin films. Our work not only establishes a scalable route for solution‐based fabrication of chalcogenide perovskite thin films, but also presents a new strategy for developing p‐type transparent conducting materials for transparent electronic devices.