The shift toward environmentally benign chalcogenide semiconductors is driven by increasing regulatory pressures and the need for sustainable materials in optoelectronics, photovoltaics, and other applications. Traditional chalcogenides like cadmium telluride (CdTe) and lead sulfide (PbS) offer excellent optoelectronic properties but pose significant environmental and health risks due to their toxicity. Alternatives such as antimony sulfide (Sb2S3) and copper zinc tin sulfide (Cu2ZnSnS4, CZTS) have emerged as promising candidates due to their lower toxicity, earth-abundant constituents, and competitive performance. This article evaluates these materials, focusing on their life-cycle impacts, recycling potential, and regulatory implications.

Sb2S3 and CZTS belong to the family of chalcogenide semiconductors, which are compounds containing sulfur, selenium, or tellurium. Unlike CdTe or PbS, these materials avoid the use of highly toxic heavy metals while maintaining reasonable bandgaps and absorption coefficients for optoelectronic applications. Sb2S3 has a bandgap of approximately 1.7 eV, making it suitable for solar cells and photodetectors, while CZTS has a tunable bandgap between 1.0 and 1.5 eV, ideal for thin-film photovoltaics. Both materials exhibit strong light absorption, with absorption coefficients exceeding 10^4 cm^-1 in the visible spectrum, comparable to conventional chalcogenides.

From a life-cycle perspective, Sb2S3 and CZTS present clear advantages over Cd/Pb-based alternatives. The extraction and processing of antimony, copper, zinc, and tin are less environmentally damaging than cadmium or lead mining, which generates hazardous waste and requires stringent containment measures. A comparative life-cycle assessment of CZTS and CdTe solar cells indicates that CZTS modules have a lower environmental footprint in terms of human toxicity potential and ecotoxicity. The energy payback time for CZTS-based photovoltaics is estimated at 1.5 to 2 years, similar to CdTe but with reduced long-term environmental risks.

Recycling methods for benign chalcogenides are also less complex than those for toxic variants. CdTe solar panels require specialized recycling processes to prevent cadmium leaching, involving high-temperature treatment and chemical stabilization. In contrast, Sb2S3 and CZTS can be processed using conventional metal recovery techniques. Hydrometallurgical methods, such as acid leaching followed by solvent extraction, efficiently recover copper, zinc, and tin from CZTS with minimal environmental impact. Antimony recovery from Sb2S3 involves oxidative roasting or reductive smelting, which are well-established in the metallurgical industry. These processes are more economically viable and safer to implement at scale.

Regulatory frameworks increasingly favor non-toxic alternatives. The European Union’s Restriction of Hazardous Substances (RoHS) directive restricts the use of cadmium and lead in electronics, pushing manufacturers toward compliant materials. Similarly, the U.S. Environmental Protection Agency (EPA) imposes strict limits on cadmium emissions, increasing compliance costs for CdTe-based products. Sb2S3 and CZTS are exempt from these restrictions, reducing regulatory burdens and facilitating market adoption. Policies such as the EU’s Circular Economy Action Plan further incentivize the use of recyclable and low-toxicity materials, aligning with the advantages of benign chalcogenides.

Despite their benefits, challenges remain in optimizing the performance and scalability of Sb2S3 and CZTS. CZTS suffers from efficiency limitations due to secondary phase formation and defect complexes, with record efficiencies around 12% for lab-scale devices, lagging behind CdTe’s 22%. Sb2S3 solar cells face interfacial recombination losses, limiting their efficiency to approximately 8%. Research efforts focus on defect passivation, interface engineering, and compositional tuning to close this performance gap. Advances in solution processing and vapor deposition techniques have improved film quality, but further development is needed for industrial-scale production.

The economic viability of these materials depends on raw material availability and processing costs. Antimony and tin are subject to price volatility due to geopolitical factors and supply chain constraints, though their global reserves are sufficient to support large-scale deployment. Copper and zinc are widely available, ensuring stable supply chains for CZTS. Manufacturing costs for Sb2S3 and CZTS are projected to decrease with process optimization and economies of scale, potentially undercutting CdTe production costs in the long term.

In conclusion, environmentally benign chalcogenides like Sb2S3 and CZTS offer a sustainable pathway for replacing toxic Cd/Pb-based semiconductors. Their lower environmental impact, simpler recycling processes, and regulatory compliance make them attractive for next-generation optoelectronics and photovoltaics. While performance and scalability challenges persist, ongoing research and policy support are expected to accelerate their adoption, contributing to a greener semiconductor industry. The transition to these materials aligns with global sustainability goals, reducing reliance on hazardous substances without compromising technological progress.