Valence Alternation in Quasi-One-Dimensional Antimony Selenide

Antimony selenide (Sb₂Se₃) has emerged as an earth-abundant and environmental-friendly alternative among thin-film photovoltaic light absorbers due to its promising optoelectronic properties. A distinguishing feature of Sb₂Se₃ is its anisotropic crystal structure, which is composed of quasi-one-dimensional (1D) [Sb₄Se₆]<i>_n</i> ribbons. However, the current record conversion efficiency of Sb₂Se₃ (~ 10%)^[1] is far from optimal. It has been reported that orientation control of Sb₂Se₃ films is important to achieve high device performance^[2], but the underlying physics remains unclear.<br/><br/>In this talk, I will present our most recent work^[3-5] investigating reasons that affect the conversion efficiency in Sb₂Se₃ based on first-principles calculations. I will first introduce the anisotropy in bulk Sb₂Se₃ structure and the resulting impacts on structural, electronic and optical properties. Then I will present results on the unusual defect physics. Multi-electron negative-<i>U</i> transitions between defect charge states can be understood from valence alternation enabled by large local structural rearrangements. Finally, I will discuss potential strategies to optimize the performance of Sb₂Se₃-based photovoltaics.<br/><br/><b>References</b><br/>[1] Zhao Y, Wang S, Li C, et al. <i>Energy & Environmental Science</i>, 2022, 15(12): 5118-5128.<br/>[2] Zhou Y, Wang L, Chen S, et al. <i>Nature Photonics</i>, 2015, 9(6): 409-415.<br/>[3] Wang X, Li Z, Kavanagh S R, et al. <i>Physical Chemistry Chemical Physics</i>, 2022, 24(12): 7195-7202.<br/>[4] Wang X, Ganose A M, Kavanagh S R & Walsh A. <i>ACS Energy Letters</i>, 2022, 7(9): 2954-2960.<br/>[5] Wang X, Kavanagh S R, Scanlon D O & Walsh A<i>. arXiv preprint:</i>2302.04901, 2023.