Feasibility of Layered A3B2X9 Halide Perovskites for n -Type Transparent Semiconductors: A First-Principles Study

Abstract Transparent semiconductors with tunable conductivity are vital for optoelectronics. Halide perovskites have shown great promise in optoelectronic applications, but their potential as transparent semiconductors remains underexplored. To overcome the poor carrier transport in the zero-dimensional n-type transparent semiconductor Cs2PbCl6, we assess the feasibility of two-dimensional layered A3B2X9 halide perovskites as n-type transparent semiconductors via first-principles calculations. Guided by a systematic screening of constituent elements, selecting chlorine for its suitable electronegativity, cesium for its ability to stabilize the perovskite structure, and trivalent B-site cations based on their coordination capability and electronic configuration, we focus on the layered phases of Cs3Y2Cl9, Cs3Sc2Cl9, Cs3In2Cl9, and Cs3Tl2Cl9. Among these, only Cs3In2Cl9 exhibits the desired combination of a low CBM, a wide bandgap (>3 eV), and low in-plane electron effective masses, meeting the key electronic criteria for n-type transparent semiconductors. However, the electronically promising candidate (Cs3In2Cl9) and the other three layered perovskite phases considered are all thermodynamically less stable than their respective experimentally realized non-perovskite phases. Moreover, the corresponding stable non-perovskite phases possess less favorable electronic characteristics, such as higher estimated CBM positions, wider bandgaps, and larger carrier effective masses, rendering n-type doping difficult to achieve. Our work uncovers a core design dilemma: in the A3B2X9 family, the electronically favorable phases are synthetically inaccessible, while the stable phases are electronically unsuitable. This dichotomy highlights that achieving both electronic functionality and phase stability within a single A3B2X9 composition remains a fundamental challenge, directing future searches for viable halide perovskite-based transparent semiconductors beyond this structural paradigm.