Heterojunction interface cation substitution to enhance the performance of antimony selenide thin-film solar cells

Abstract

Antimony selenide (Sb₂Se₃) has attracted growing interest as a promising thin-film photovoltaic absorber owing to its favorable optoelectronic properties and intrinsic chemical stability. However, device efficiency remains limited by several intrinsic challenges, including quasi-one-dimensional (Q1D) structural constraints that cause ineffective lattice doping, suboptimal crystallinity, high defect density, and unfavorable band alignment at the cadmium sulfide (CdS)/Sb₂Se₃ heterojunction. Here, we propose a lanthanide doping strategy based on ionic antisite diffusion- using neodymium (Nd³⁺) to simultaneously engineer bulk crystal growth and interface energetics. By introducing neodymium chloride (NdCl₃) onto the CdS surface and exploiting reverse gradient diffusion, Nd³⁺ ions are effectively incorporated into Sb₂Se₃ without inducing significant lattice distortion. Meanwhile, the CdS surface is passivated and its roughness reduced, facilitating the deposition of high-quality films. This strategy promotes preferential [hk1] orientation, enhances crystallinity, enlarges grain size, and suppresses deep-level defects. Density functional theory calculations further corroborate the role of Nd in lowering defect formation energies and modulating the electronic structure. Moreover, Nd incorporation optimizes conduction band alignment, suppresses Shockley-Read-Hall recombination, and improves carrier extraction. As a result, the champion device achieves a power conversion efficiency of 9.17%, with a fill factor (FF) of 64.58%, an open-circuit voltage (V_OC) of 0.46 V, and a short-circuit current density (J_SC) of 30.54 mA/cm². This work provides fundamental insights into doping in Q1D semiconductors and offers a practical route toward high-efficiency Sb₂Se₃ photovoltaics.

Keywords

Antimony selenide / lanthanide element neodymium / ionic antisite diffusion / heterojunction interface / density functional theory

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