AgBiS₂ presents a promising environmentally benign photovoltaic material that addresses ecological and performance limitations of conventional solar technologies. Comprising earth-abundant, non-toxic elements (Ag, Bi, S), it circumvents the toxicity of lead-based perovskites and critical material constraints of cadmium telluride. Its superior optoelectronic properties, such as a high absorption coefficient (> 10⁵ cm^-1) and tunable bandgap (1.1-1.7 eV), allow over 90%solar radiation capture with~30 nm films, significantly reducing material consumption while enabling single-junction or tandem device integration. Solution-processability at low temperatures (< 100 ℃) facilitates scalable manufacturing. Combined with a theoretical efficiency of~26%, this material provides pathways to cost-effective lightweight flexible photovoltaics. Ongoing advances in interfacial engineering and defect passivation (demonstrated by 10% certified efficiency) are able to optimize carrier dynamics, positioning AgBiS₂ as a competitive alternative for next-generation solar technology that integrates environmental sustainability, high performance and industrial viability.

Recent advances in the ultrathin AgBiS₂ quantum dot solar cells (QDSCs) have been driven by synergistic progress in three domains: synthesis optimization, ligand engineering and device architecture. Initial breakthroughs began with the classical hot-injection routine. Subsequent refinements, including stoichiometric precursor control, octadecene (ODE)pre-addition for ligand stabilization, oleylamine-assisted uniform nucleation and two-step injection for large-sized quantum dots, which progressively elevated power conversion efficiency from 5.61% to 6.37%. This methodological foundation enabled novel techniques, such as room-temperature synthesis, cation exchange and eco-compatible sulfur sources. Concurrently, limitations of solid-state ligand exchange were addressed through solution-phase ligand exchange (SPLE)strategies. Molecular ink optimization, [AgI₂]^- complex design, AgI/AgBr dual-ligand synergistic passivation and the eco-friendly MPA-methanol system enhanced quantum dot dispersibility and interfacial passivation. These advances culminated in a record PCE of 10.8% achieved by using 3-chloro-1-propanethiol as co-ligands. Complementary innovations emerged in device architecture. Conventional ZnO/SnO₂ electron transport layers (ETLs) evolved into band-aligned TiON systems, while hole transport layers expanded beyond costly organic materials (PTB7 or PTAA) to cost-effective NiO_x-based inorganic structures with enhanced operational stability, highlighting the potential for the ultrathin photovoltaic commercialization.

Recent advances have propelled environmentally benign AgBiS₂ solar cells with power conversion efficiency of beyond 10%, underscoring their commercial viability. Nevertheless, research on this material remains underrepresented in photovoltaics compared to perovskite or organic counterparts, with both scientific output and device performance lagging. This review consolidates progress in AgBiS₂ quantum dot through three critical dimensions, including material synthesis, surface engineering and photovoltaic applications, while identifying unresolved challenges.

(1) Synthesis Optimization: Low-temperature processing of AgBiS₂ quantum dots frequently induces cationic site disorder, leading to phase segregation and defect proliferation. Future synthesis strategies must prioritize thermodynamic control of nucleation kinetics to suppress defect-driven growth in solution-based routes.

(2) Liquid-Phase Passivation Mechanisms: Although solution-phase ligand exchange (SPLE)-processed quantum dot inks enable scalable coating, inefficient passivation persists due to scarce atomic-scale ligands and undefined competitive exchange dynamics between long-/short-chain ligands. Elucidating these interfacial processes is essential for fabricating large-area, defect-minimized active layers.

(3) Holistic Cost Engineering: Beyond synthesis expenses, parity attention must address device architecture costs and operational expenditures (e.g., stability limitations). Conventional structures depend on expensive hole-transport materials (e.g., PTB7) with suboptimal thermal resilience. Inverted p-i-n architectures, drawing on perovskite photovoltaics, could enhance efficiency while reducing costs, necessitating development of charge-transport layers that concurrently optimize electrical properties and broadband transparency for this configuration.

Solid oxide fuel cell (SOFC) is a highly efficient electrochemical device that can be used to directly convert chemical energy of hydrogen and hydrocarbon fuels into electricity in an environmentally friendly manner. While the typical operating temperatures of SOFCs have been reduced to 600–850 ℃, ferritic stainless steels (FSS), such as ZMG 232, AISI 441, SUS430, etc., can be utilized as interconnect materials, due to their high electrical conductivity, low material/manufacturing cost, excellent mechanic strength and similar coefficient of thermal expansion (CTE) to other cell components. However, it still exists several issues during their operation at 600–850 ℃, including continuous growth of Cr₂O₃ scale, Cr migration to cathode and dimensional tolerance at interconnect-cathode interface. These issues will cause serious performance degradation for stacks. To solve these problems, a dense protective coating and a porous contact layer are typically prepared between the metallic interconnect and the cathode. The dense protective coating is utilized to inhibit the growth of Cr₂O₃ scale and prevent Cr migration to the cathode, while the porous contact layer can provide better electrical pathway to decrease the power losses and compensate for the dimensional tolerance between the interconnect and the cathode.

In this study, MnCoNiFeCu alloy powder was selected as the precursor materials for dense protective coating and porous contact layer. A coating/contact dual-layer structure was fabricated through reactive co-sintering in the simulated SUS 430 interconnect/coating/contact/cathode/cathode support test cells. The precursors were calcined in air at 900 ℃ for 2 h to study phase evolution and microstructure of the protective coating and the contact layer. The phases in the sintered layers were characterized by using X-ray diffraction (XRD), whereas scanning electron microscopy (SEM) featured with energy-dispersive spectroscopy (EDS) was utilized to analyze the microstructure and obtain the compositional information. The test cells were fabricated to examine the electrical performance of the dual-layer structure via Area-Specific Resistance (ASR). After the initial sintering, the furnace temperature was then dropped to 800 ℃ for isothermal oxidation for 1000 h and ten thermal cyclic test. The tested samples were then epoxy-mounted, sectioned, and polished for examining cross-sectional microstructure after oxidation. EDS line scans near at the interconnect-coating and contact-LSM cathode interfaces were obtained to identify the possible interdiffusion between the cell components. Furthermore, the effectiveness of the dual layer in inhibiting the growth of the Cr₂O₃ layer and blocking Cr migration from the interconnect to cathode was also assessed.

XRD results of the protective coating and contact layer after thermal conversion revealed that the sintered samples predominantly consisted of spinel phase, with minor oxides, while no metallic phases were detected. Specifically, the protective coating exhibited a majority of the spinel phase along with CuO and CoO, as confirmed by EDS mappings, indicating the aggregation of Cu and Co on the surface. In contrast, the contact layer primarily contained the spinel phase and CuO, with EDS mappings indicating uniform distribution of Fe, Co, Ni, Mn and Cu, while no delamination was observed. In ASR measurements, the tested sample exhibited stable behavior with an ASR of only 22.04–22.71 mΩ·cm² during the 1000 h isothermal oxidation, while the thermal cycling led a dramatic increase in ASR. Once the ASR measurement was completed, the sample cross-sectional surface was characterized. For isothermal oxidation, a dense protective coating and a relatively porous contact layer were observed between the interconnect and cathode. The dual-layer structure was well-boned with the interconnect and cathode after the isothermal oxidation, indicating that the double-layer structure exhibited exceptional thermal compatibility with the adjacent cell components. Importantly, no Cr was detected within both the contact layer and cathode, further confirming the effectiveness of the double-layer structure in inhibiting the migration of Cr from the interconnect to cathode. Conversely, the thermal cycling test sample exhibited serious cracking at the interface between the porous contact layer and the LSM cathode, which was responsible for the rapid increase in ASR during thermal cycling testing.

In this study, MnCoNiFeCu alloy powder was utilized as the precursor material to develop a dense protective coating and a porous contact layer simultaneously through reactive co-sintering, forming a (Mn,Co,Ni,Fe,Co)₃O₄-based dual-layer structure. The sample exhibited stable behavior with an ASR of only 22.04–22.71 mΩ·cm² after 1000 h of isothermal oxidation, while the thermal cycling led a dramatic increase ASR in. Notably, the growth of the Cr₂O₃ scale was dramatically suppressed, while no Cr was detected in the LSM cathode, confirming the effectiveness of the thermally converted dual-layer structure in blocking the migration of Cr. The HEA used as the dense protective coating and porous contact layer offers several advantages, including uniform microstructure, improved electrical performance, exceptional Cr-blocking capability and simple fabrication process. In the future study, more efforts should focus on optimizing the elements in the precursor alloy to further enhance the uniformity and CTE matching of the dual-layer structure after sintering.