Revisiting the Photoelectric Conversion Mechanism in Hydrothermally Deposited Sb2(S,Se)3 Solar Cells

Why It Matters

The discovery shows that carrier separation can be engineered within the bulk absorber, opening pathways to higher efficiencies for low‑cost Sb2(S,Se)3 photovoltaics and influencing future device architectures.

Key Takeaways

• Selenium diffusion creates gradient-bandgap Cd(S,Se) layer
• V-shaped mixed absorber separates carriers within Sb2(S,Se)3/Cd(S,Se)
• Short-circuit current reaches 1.43 mA cm⁻² without external doping
• Na2S4O6 additive boosts heterojunction efficiency
• Findings prompt redesign of band alignment in Sb2(S,Se)3 cells

Pulse Analysis

Hydrothermal deposition of Sb2(S,Se)3 has attracted attention because the material combines earth‑abundant elements with a favorable bandgap for solar absorption. Historically, engineers assumed that a flat‑bandgap CdS buffer formed a classic heterojunction, with carrier separation occurring exclusively at the Sb2(S,Se)3/CdS interface. This conventional view guided buffer‑layer thicknesses, doping levels, and annealing recipes, but it left a performance ceiling that many research groups struggled to surpass.

The new study overturns that paradigm by demonstrating that annealing induces selenium diffusion into the CdS layer, producing a graded‑bandgap Cd(S,Se) region. The resulting V‑shaped band alignment spans both the Sb2(S,Se)3 and Cd(S,Se) layers, allowing electron‑hole pairs to separate throughout the mixed absorber rather than at a single junction. The device achieves a short‑circuit current density of 1.43 mA cm⁻²—a notable figure for a buffer‑free architecture—and the Na2S4O6 additive further improves charge transport and reduces recombination. These results highlight the importance of bulk‑level band engineering over simple interface optimization.

For the photovoltaic industry, the findings suggest a shift toward designing graded‑bandgap absorbers that exploit internal electric fields for carrier extraction. This could accelerate the commercialization of Sb2(S,Se)3 modules, offering a low‑cost alternative to silicon and perovskite technologies. Moreover, the methodology—combining controlled annealing with targeted additives—provides a template for other emerging thin‑film materials. Future research will likely explore scalable annealing processes, long‑term stability of the V‑shaped architecture, and integration with tandem cell concepts, positioning Sb2(S,Se)3 as a versatile platform in the renewable‑energy landscape.