Sustainable Design Strategies for Perovskite Solar Cells: Maximizing Resource Efficiency and Minimizing Waste
Mahboubeh Hadadian a, Elena S. Akulenko a, Annukka Santasalo-Aarnio b, Kati Miettunen a
a Department of Materials Engineering, Faculty of Science and Engineering, 20014 University of Turku, Finland
b Department of Mechanical Engineering, School of Engineering, 11000 Aalto University, Finland
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV23)
London, United Kingdom, 2023 June 12th - 14th
Organizers: Tracey Clarke, James Durrant and Trystan Watson
Poster, Mahboubeh Hadadian, 290
Publication date: 30th March 2023

With a current power conversion efficiency of over 25%, perovskite solar cells (PSCs) have gained extensive attention. Efforts are presently being made to improve the stability and reduce the toxicity of the materials and devices. However, existing environmental directions in PSCs deviate from profitable recycling, and the transition from a "linear economy" to a "circular economy" has received insufficient attention thus far [1, 2]. Some studies have considered the recycling of compounds such PbI2 [3], and some other studies have shown the recycling of components such as fluorine-doped tin oxide (FTO) glass [4]. However, the profitability and effect of material and solar cell design are not fully understood. In this study, we evaluate the profitability of recycling the full device and individual solar cell components from end-of-life PSCs based on the recycling approaches. The recycling process is separated into four levels based on energy inputs and product value [5,6]:

- Reviving devices, e.g., restoring the performance of solar cell by reloading the photoactive material.

- Reuse components, e.g., reutilizing the FTO substrate for further use.

- Recycle compounds, i.e., separating the compounds for the further application.

- Recovery of valuable elements, i.e., extracting elements such as Au from perovskite solar cell wastes.

Device architecture has a unique impact on recycling at different levels. Our findings showed that recycling at the revival level, which is the most beneficial strategy from a circular economy perspective, can be viable in PSCs with mesoporous architectures such as hole transport layer-free carbon-based PSCs. These structures utilize a mesoscopic scaffold that hosts the perovskite absorber, enabling the reloading or regeneration of the photoactive material [7,8].

When revival is not possible, for instance because of component deterioration, the reuse of components should be considered. In this level of recycling, individual layers are repurposed for solar cells or other applications. Reusing all functional layers can be challenging as they are prone to degradation. Nevertheless, due to the significant energy and costs involved in their production, substrates such as FTO glass, which account for over 99% of the device's weight, are appealing options for recycling. It is important to note that the reuse of substrates requires careful handling and cleaning to ensure their quality for subsequent use [4]. Additionally, FTO glass has been scribed to electrically separate different regions, necessitating the standardization of devices to reprint new PSCs with the same geometry.

The recycling of PbI2 compound for use in perovskite preparation has been previously reported [3]. While it would be advantageous to recycle expensive compounds like Spiro-OMeTAD, it is not practical without causing structural damage. Conversely, inorganic compounds like TiO2 and SnO2 are abundant and inexpensive, but the solvents used to recycle these components are often volatile and hazardous, requiring costly industrial safety precautions.

Finally, precious metal recovery is often the motivation behind element recovery. However, large-scale processes may be difficult. To make recycling profitable, the approach should be based on precious metal concentration and processing methods. Noble metals may be recovered using pyrometallurgy processing, which is a low-cost method that requires no manual or mechanical labor, albeit at the expense of the other elements. Our results showed that substrates play a major role in the recovery of precious metals from end-of-life PSCs.

PSCs are still in the development stage. Device complexity might make recycling less profitable and perhaps prevent the recovery of vital materials. Different recycling strategies should already be considered when developing new materials and designs for photovoltaic devices to assure the eco-design of the solar cells and minimize the need for virgin materials.

The authors thank the Academy of Finland (project ECOSOL, 347275) and the Academy of Finland (project BioEST, 336577 and 336441).

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