Unique Defect Characteristics of Antimony Chalcogenide Photovoltaic Materials

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Conspectus

Antimony chalcogenides, including Sb₂S₃, Sb₂Se₃ and alloyed Sb₂(S,Se)₃, have emerged as promising new generation solar cell materials owing to their excellent stability, tunable bandgap in 1.1–1.8 eV, and high extinction coefficient. Different from all the previous solar cell materials, the crystal structures of this class of semiconductors are composed of quasi-one-dimensional ribbons, which renders efficient directional carrier transport along the one-dimensional Sb₄(S/Se)₆ ribbon. This ribbon structure could generate inert grain boundaries since there is no dangling bond at the side of the ribbons. With these unique properties, it has attracted intense interests in solar cell applications. Over the past decades, device efficiencies have increased from ∼1% to above 11%. The advances in film fabrication, defect passivation and orientation control contribute to the efficiency breakthrough. However, there is still a large gap between current performance and the theoretical efficiency limit of ∼33%. It has been realized that the deep-level point defect plays critical role in increasing the efficiency. In this case, a comprehensive understanding of defect formation and passivation is essential for the fabrication of high quality Sb₂(S,Se)₃ films for further efficiency breakthrough.

Building on the foundational work from our research, this Account presents a unified conceptual framework that traces the defect chemistry of Sb₂(S,Se)₃ from their quasi-one-dimensional ribbon structures to multidimensional collaborative passivation strategies for device optimization. We first describe how the anion chemical potential and S/Se ratio regulate the formation of vacancies and antisite defects. These factors shape local bonding and lattice strain, which, in turn, influence defect energetics and carrier lifetime. We then examine how controlled chemical modification can adjust short-range coordination environments. Such adjustments refine the electronic structure and can transform harmful deep states into electronically benign ones. We also emphasize strategies that target grain boundaries and surfaces, where deep defects often concentrate due to ribbon termination and structural disorder. Well-designed passivation treatments can reconstruct these regions, reduce under-coordinated atoms, and improve interfacial band alignment. Finally, we discuss recrystallization approaches that promote favorable ribbon orientation and suppress chalcogen loss, a key source of deep donor states. Together, these directions have enabled the power conversion efficiency to exceed 11%. By establishing a unified chemical framework for understanding and controlling point defects, this Account provides guiding principles for advancing Sb₂(S,Se)₃ materials in terms of sophisticated defect-engineering.