Regulating Hydrothermal Deposition Kinetics via an Acid–Base Buffering Strategy for Efficient HTL-Free Sb2Se3 Solar Cells

Abstract The hydrothermal method, known for its operational simplicity, environmental benignity, and low cost, has been established as a viable route for fabricating high-efficiency antimony selenide (Sb2Se3) photovoltaic devices. However, the closed nature of this system poses a significant challenge to gaining an intuitive and comprehensive understanding of the underlying reaction mechanisms during hydrothermal deposition. In this work, we reveal a “self-accelerating” phenomenon that occurs during the selenium releasing process from the sodium selenosulfate (Na2SeSO3) selenium precursor. To address this issue, this work introduced an HAc/Na2SO3 buffering pair to regulate the hydrothermal chemistry, thereby achieving controlled release of HSe- species. The introduction of the buffer additive promotes the heterogeneous nucleation of Sb2Se3 on the substrate and prolongs the sustained release of the Se source, enabling a thicker film with distinctly strengthened enhanced (221) and (301) crystallographic orientations. The resulting Sb2Se3 solar cell without a hole transport layer delivers a champion power conversion efficiency of 6.77%. Overall, this work expands the possibilities for manipulating reaction pathways in solution-based deposition from a chemical perspective.