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ARTICLE

Active Learning-Driven Optimization of Sulfurization–Selenization Processes in Sb₂(S,Se)₃ Thin Films for Enhanced Photovoltaic Efficiency

Yunpeng Wen^1,*, Bingyang Ke², Junrong Ding³

1 College of Engineering, Oregon State University, Corvallis, OR 97330, USA
2 College of Engineering, Northeastern University, Brighton, MA 02135, USA
3 College of Business, Oregon State University, Corvallis, OR 97330, USA

* Corresponding Author: Yunpeng Wen. Email:

Chalcogenide Letters 2026, 23(1), 4 https://doi.org/10.32604/cl.2026.076587

Received 19 September 2025; Accepted 23 November 2025; Issue published 26 January 2026

Abstract

This study reports an active learning (AL)-guided strategy to optimize the sulfurization–selenization processing conditions of Sb₂(S,Se)₃ thin-film photovoltaic absorbers for enhanced power conversion efficiency (PCE). By coupling Gaussian process modeling with iterative experimental feedback, we explored 20 targeted annealing conditions across the full compositional spectrum (x = 0–1) and identified an optimal S/(S + Se) ratio of 0.40 (x = 0.60), which yielded a band gap (Eg) of ~1.34 eV, close to the theoretical Shockley–Queisser optimum. The optimized process employed a controlled two-step 420°C anneal with sequential H₂Se→H₂S exposure, which produced large plate-like grains (300–500 nm) with columnar cross-sectional morphology and eliminated the ribbon-like anisotropy typical of pure Sb₂Se₃. XRD confirmed a single-phase orthorhombic structure with no secondary phases, while EDS mapping showed homogeneous S/Se distribution and a mild back-surface S gradient. Optical absorption coefficients exceeded 10⁵ cm⁻¹ (hν > 1.7 eV), and photoluminescence revealed a reduced Stokes shift (~40 meV) and low Urbach energy (~20 meV), indicating suppressed defect states. Devices fabricated with a Zn(O,S) buffer achieved average metrics of Voc = 0.58 V, Jsc = 25.0 mA cm⁻², FF = 78%, and PCE = 12.2%, representing a ~62% relative improvement over our baseline Sb₂Se₃ cells (7.5%). The EQE exceeded 90% across 400–900 nm, and the integrated Jsc matched measured values within 5%. Preliminary stability tests retained 95% of initial PCE after 100 h under 1-sun illumination at 45°C. These findings establish AL-driven exploration as a powerful method for rapidly converging on high-performance chalcogenide processing regimes.

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