# Progress in Improving Photovoltaics Longevity
## 5 Discussion
The establishment of revised and updated regulatory frameworks will also motivate the PV manufacturing sector to invest in sustainable and environmentally friendly recycling initiatives. The goal of achieving sustainability in PV systems has led to the investigation of environmentally friendly materials capable of both eliminating the environmental footprint and improving efficiency. Traditional PV modules often rely on scarce or even toxic materials, such as lead and cadmium, and their utilization raises legitimate concerns about their long-term environmental impact. Therefore, a gradual transition to non-toxic, easily recyclable, and plentiful materials is deemed necessary. Improving the recyclability of silicon-based PV systems can promote a more robust lifecycle for the solar technology industry. Organic PV cells also offer a viable alternative, as their construction requires carbon-based components that are both easily recyclable and abundant as resources. Perovskites and tandem cells are also emerging powerfully as attractive alternatives in PV systems, providing environmental benefits and excellent mechanical flexibility. Perovskite-based solar cells are known for their low production expenses and high efficiency, and they can be manufactured at lower temperatures. This capability is lucrative in terms of energy consumption and emissions generation. Additionally, their enhanced flexibility provides the opportunity for bendable and lightweight solar panels, making perovskites the ideal candidates for integration into various surfaces, such as building facades, windows, and roofs. Tandem cells, on the other hand, are hybrid stratified structures consisting of different material layers, such as silicon and perovskites, and promise increased efficiency, as they are capable of capturing a broader spectrum of sunlight. This property indirectly reduces the overall material use, as the energy generated per panel is maximized. As current research is oriented toward lead-free perovskites and easily recyclable materials for PV systems, future efforts should prioritize efficiency and diminishing the environmental footprint. On the one hand, this approach will ensure the sustainable character of PV manufacturing and disposal processes and, on the other hand, will pave the way for a greener, circular, and environmentally friendly solar energy industry. Another intriguing challenge that attracts the interest of the scientific community is the stability of the PV system. Improving the long-term stability of emerging solar cells, such as perovskite solar cells, is critical to the deployment of this technology [225]. Besides qualification standards based on the International Electrotechnical Commission (IEC), mainly developed to address the field performance of silicon panels, protocols such as those developed by the International Summit on Organic PV Stability (ISOS) are useful in unifying the procedures to assess the stability of emerging solar cells and understand the mechanisms that affect their operational stability and failure modes [225]. In Figure 9, a schematic representation of the stress factors that impact solar cells in different ISOS protocols is presented, emphasizing and comparing the results of various aging procedures with each other. The ISOS protocols involve controlled combinations of key stress factors, including light exposure (visible and UV, dark or 1-sun equivalent), ambient temperature (65 \({}^{\circ}\)C or 85 \({}^{\circ}\)C), atmosphere (inert, ambient, controlled humidity),and electrical bias (open circuit, MPP tracking, or fixed voltage), to rigorously assess the stability of emerging solar cells. These protocols are categorized into five aging testing groups, ISOS-D (dark-storage/shelf-life), ISOS-L (light-soaking), ISOS-O (outdoor testing), ISOS-T (thermal cycling), and ISOS-LT (light-humidity-thermal cycling). Each of these groups evaluates specific stress conditions to simulate a real-world environment where emerging PV technologies are deployed.