A blockchain-based solution for the traceability of rare earth metals used in thin-film photovoltaics

The supply chain of rare earth metals plays a crucial role in producing thin-film solar photovoltaics (PVs), which are vital for renewable energy generation. However, this supply chain is often characterized by opacity, inefficiencies, and security concerns especially since those rare earth metals come from mainly one supplier, China. Also, the solar PVs' certificates are purely technical and fail to consider the ethical sourcing and sustainable supply chain management conditions of mining. The working conditions of the miners are often neglected and are least prioritized. In this paper, a blockchain-based solution was proposed to leverage the intrinsic decentralized blockchain features including traceability, transparency, non-repudiation, and accountability in the supply chain of thin-film solar PVs, to safeguard not only the technical conditions of the mined products but also the ethical conditions of the workers during mining. Ethical mines must uphold good safety standards, pay their workers a fair wage, adhere to working hours, and legal working age. The solution paves the way to ethical mining where the certification of the PVs is not granted unless both technical and ethical conditions are met. The supply chain of thin-film PVs that goes from mining the rare earth metals in China, where more than 70% of the rare earth metals used are extracted from, to the disposal at the end-of-life (EOL) of the PVs was presented. Smart contracts to enable the on-chain traceability of the registration, manufacturing, assessment, delivery, and disposal of PVs were developed. The solution exploits the tamper-proof logs of the distributed ledger to ensure accountability and record transactions as part of the data provenance. The proposed solution includes a system design with sequence diagrams, smart contracts with algorithms, and a testing and analysis section.