The development of eco-friendly optoelectronic devices has gained significant attention due to increasing environmental concerns and the demand for sustainable technologies. Among the promising candidates for green electronics are biodegradable and earth-abundant two-dimensional (2D) materials, such as germanane, phosphorene, and transition metal dichalcogenides (TMDCs) derived from non-toxic elements. These materials offer unique optoelectronic properties while minimizing ecological harm. This article examines their potential in optoelectronic applications, lifecycle considerations, and toxicity profiles.

Germanane, a hydrogen-terminated germanene derivative, is an emerging 2D material with a direct bandgap of approximately 1.6 eV, making it suitable for visible-light optoelectronics. Unlike conventional semiconductors requiring rare or toxic elements, germanane consists of germanium and hydrogen, both abundant and relatively benign. Studies have demonstrated its high carrier mobility, exceeding 10,000 cm²/Vs, and strong light absorption, enabling efficient photodetectors and solar cells. Its layered structure allows for easy integration into flexible devices, further enhancing its appeal for sustainable electronics.

Phosphorene, derived from black phosphorus, is another biodegradable alternative with a tunable bandgap ranging from 0.3 eV in bulk to 2.0 eV in monolayers. This property enables broadband photodetection from infrared to visible wavelengths. However, its susceptibility to oxidation in ambient conditions poses a challenge for long-term stability. Encapsulation techniques using inert 2D materials like hexagonal boron nitride (hBN) have been explored to mitigate degradation while maintaining eco-friendly credentials.

TMDCs based on molybdenum (MoS₂) and tungsten (WS₂) are also considered due to their moderate abundance and low toxicity compared to cadmium- or lead-based semiconductors. These materials exhibit strong excitonic effects and layer-dependent bandgaps, useful for light-emitting diodes (LEDs) and phototransistors. Recent advances in solution processing of TMDCs using water-based solvents have reduced reliance on hazardous organic chemicals during fabrication.

Lifecycle analysis of these materials reveals advantages over traditional semiconductors. For instance, the energy required to synthesize germanane is significantly lower than that for gallium arsenide (GaAs), owing to simpler processing and lower growth temperatures. Additionally, germanane decomposes into non-toxic germanium oxides and water under environmental conditions, eliminating persistent waste. Similarly, black phosphorus degrades into phosphates, which are naturally occurring and non-hazardous. In contrast, conventional III-V or II-VI semiconductors often involve toxic byproducts during production and disposal.

Toxicity assessments indicate that germanane and phosphorene exhibit minimal cytotoxicity in vitro, unlike cadmium selenide (CdSe) quantum dots or lead halide perovskites. Studies on MoS₂ and WS₂ show low acute toxicity in aquatic environments, though long-term ecological impacts require further investigation. The absence of heavy metals in these materials reduces bioaccumulation risks, making them safer for consumer electronics and biomedical applications.

Device performance metrics of eco-friendly 2D materials are approaching those of conventional counterparts. Germanane-based photodetectors have achieved responsivities of 100 mA/W under visible light, comparable to silicon devices. Phosphorene phototransistors demonstrate detectivities exceeding 10¹² Jones in the near-infrared spectrum. TMDC LEDs have reached external quantum efficiencies of 10%, sufficient for display technologies. While these values are currently lower than those of toxic high-performance semiconductors, ongoing research in defect passivation and contact engineering is closing the gap.

Scalability remains a challenge for widespread adoption. Current synthesis methods for germanane, such as topotactic deintercalation of CaGe₂, yield limited quantities. Phosphorene production suffers from batch-to-batch variability due to anisotropic exfoliation. Advances in electrochemical exfoliation and chemical vapor deposition (CVD) are addressing these issues, with recent reports of wafer-scale MoS₂ growth suggesting viable industrial pathways.

End-of-life considerations favor biodegradable 2D materials. Unlike silicon or GaAs devices requiring energy-intensive recycling, germanane and phosphorene devices can decompose naturally or through mild chemical treatments. This characteristic aligns with circular economy principles, reducing electronic waste accumulation. Regulatory frameworks are beginning to recognize these benefits, with some jurisdictions incentivizing research into non-toxic alternatives for consumer electronics.

The economic viability of these materials depends on reducing production costs. Germanium, while more abundant than indium or gallium, is still costlier than silicon. However, thinner active layers in 2D devices minimize material usage, potentially offsetting raw material expenses. Black phosphorus costs have decreased significantly since 2020 due to improved synthesis methods, now approaching $10 per gram for research-grade samples.

Future directions include hybrid systems combining biodegradable 2D materials with organic semiconductors to enhance performance while maintaining sustainability. For instance, germanane-polymer heterostructures have shown improved charge separation for photovoltaic applications. Another promising avenue is the development of transient electronics that fully degrade after a service period, particularly for medical implants or environmental sensors.

In conclusion, biodegradable and abundant 2D materials present a viable pathway toward sustainable optoelectronics. While challenges in stability and scalability persist, their environmental advantages and competitive device performance justify continued investment. As synthesis techniques mature and lifecycle benefits become quantifiable in industrial settings, these materials may redefine the ecological footprint of the electronics industry. Regulatory support and consumer demand for green technology will likely accelerate this transition in the coming decade.