Eco-design Strategies from R&D Level Towards a Sustainable Perovskite Tandem Technology

The solar photovoltaic (PV) energy has become a fast-growing competitive sector. Innovation is a prerequisite for the survival of many PV companies. In the last years, the perovskite solar cells has gained much attention in the solar community because of the high efficiencies obtained in single and multi-junction devices and low fabrication projected cost. Due to the massive scale of the energy sector, it is essential that this new emerging PV technology progresses in a way that is consistent with the requirements of sustainable development before large scale deployment.<br/>Sustainability is defined as an interaction between economic, social, technical and environmental criteria. Nevertheless, R&D activities are often focused on technical and economic improvements as a priority to enter the market. In addition, the limitations of current eco-design tools, as identified in the literature, hinder their adoption by R&D organizations. In fact, environmental impact assessment is relatively complex for a non-mature technology under development because its characteristics and manufacturing processes are not yet fully defined. Life Cycle Assessment (LCA) is a reliable environmental assessment tool, but it is limited to the evaluation of the investigated technology without proposing eco-design alternatives.<br/>This study proposes a methodology to provide eco-design strategies from the earliest stages of design to develop sustainable all-perovskite tandem technology. In the research stage, the device architecture is often not defined yet. Therefore, we start with a review of the existing LCA studies on perovskite solar cells to identify the hotspots from an environmental point of view. Then, the list of the reported materials that could be used for the solar cell, including packaging materials, is defined. We analyze this list from an environmental point of view based on results obtained from the literature and legislative constraints. Finally, we propose eco-design guidelines that could reduce the cost, increase the performance, and decrease the environmental impact for the development of a sustainable perovskite tandem solar cell technology.<br/>Based on this approach, key recommendations toward a sustainable perovskite tandem technology are :<br/>- For the Transparent Conductive Oxide (TCO), indium-containing oxides are good candidates from a technical and economical point of view. However, indium is a critical material. Aluminum-doped zinc oxide (AZO) would be a more suitable candidate but vigilance is required on the electricity required for its production process.<br/>- For the metal electrodes, copper should replace silver for economic and environmental criteria. However, there are few studies in the literature on its technical reliability.<br/>- Fullerene (C₆₀) remains technically one of the best electron transport layer materials, but attention must be paid to its environmental impact and its high production cost.<br/>- The contribution of the material of the perovskite layer to the environmental impact in the module is small. Nevertheless, some components in the layer and auxiliary materials need to be eco-designed<br/>- Compared to glass, polymer-packaging materials do not pose a problem from economic and environmental points of view. Their choice must be based on technical criteria, primarily good barrier properties.<br/>- In view of the circularity potential, a closed loop wet chemical recycling process is preferable over other approaches such as thermal decomposition, electrochemical refinement, or physical separation routes (e.g. adsorption/desorption).<br/>- The challenges addressed by this recycling process are i) green solvent recycling development, ii) complex perovskite composition separation and recovery (with a focus on lead recovery and reuse), and iii) functional layer recovery.<br/><br/>These recommendations will help to guide technological choices from the early design process to ensure the development of sustainable perovskite tandem technology.