Antimony selenide (Sb₂Se₃) is an ideal photovoltaic candidate profiting from its advantageous material characteristics and superior optoelectronic properties, and has gained considerable development in recent years. However, the further device efficiency breakthrough is largely plagued by severe open‐circuit voltage (V_OC) deficit under the existence of multiple defect states and detrimental recombination loss. In this work, an effective absorber layer growth engineering involved with vapor transport deposition and post‐selenization is developed to grow Sb₂Se₃ thin films. High‐quality Sb₂Se₃ with large compact crystal grains, benign [hk1] growth orientation, stoichiometric chemical composition, and suitable direct bandgap are successfully fulfilled under an optimized post‐selenization scenario. Planar Sb₂Se₃ thin‐film solar cells with substrate configuration of Mo/Sb₂Se₃/CdS/ITO/Ag are constructed. By contrast, such engineering effort can remarkably mitigate the device V_OC deficit, owing to the healed detrimental defects, the suppressed interface and space‐charge region recombination, the prolonged carrier lifetime, and the enhanced charge transport. Accordingly, a minimum V_OC deficit of 0.647 V contributes to a record V_OC of 0.513 V, a champion device with highly interesting efficiency of 7.40% is also comparable to those state‐of‐the‐art Sb₂Se₃ solar cells, paving a bright avenue to broaden its scope of photovoltaic applications.

A dual-cation-substituted Cu₂ZnSn(S,Se)₄ involving Ag and Ti to separately occupy partial Cu and Sn is developed. Such a new strategy can simultaneously promote crystal growth and suppress detrimental defects, leading to a high efficiency of 12.73%.

A flexible n-type Ag₂Se thin film with a high power factor (PF) of 21.6 μW cm⁻¹ K⁻² and a ZT value over 0.6 was successfully prepared by a facile self-assembled growth method.

Despite being an excellent candidate for a photocathode, Cu₂ZnSnS₄ (CZTS) performance is limited by suboptimal bulk and interfacial charge carrier dynamics. In this work, we introduce a facile and versatile CZTS precursor seed layer engineering technique, which significantly enhances crystal growth and mitigates detrimental defects in the post-sulfurized CZTS light-absorbing films. This effective optimization of defects and charge carrier dynamics results in a highly efficient CZTS/CdS/TiO₂/Pt thin-film photocathode, achieving a record half-cell solar-to-hydrogen (HC-STH) conversion efficiency of 9.91%. Additionally, the photocathode exhibits a highest photocurrent density (J _ph) of 29.44 mA cm⁻² (at 0 V _RHE) and favorable onset potential (V _on) of 0.73 V _RHE. Furthermore, our CTZS photocathode demonstrates a remarkable J _ph of 16.54 mA cm⁻² and HC-STH efficiency of 2.56% in natural seawater, followed by an impressive unbiased STH efficiency of 2.20% in a CZTS-BiVO₄ tandem cell. The scalability of this approach is underscored by the successful fabrication of a 4 × 4 cm² module, highlighting its significant potential for practical, unbiased in situ solar seawater splitting applications.