Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
DOI: https://doi.org/10.29363/nanoge.hopv.2022.016
Publication date: 20th April 2022
Current state-of-the-art perovskite solar cells (PSCs) provide power conversion efficiency (PCE) higher than 25%, which makes PSCs rivalling established technologies (CIGS, CdTe) and approaching crystalline silicon (c-Si) records. The abundance of the starting materials and the solution processing of the perovskite promises an energy payback time of about 0.5 instead of 1-2 years for c-Si. For such a shorter energy payback time to result in a long run lower electricity cost, PSCs should also retain 80% of their initial PCE for 20-25 years, like in current c-Si installations. Accelerated ageing testing indicates that PSC can reach a lifespan of over 20 years using the most robust perovskite formulations. Unfortunately, the most robust perovskite formulations contain lead (Pb).
Pb is one of the most toxic elements ever used. With only a few exceptions remaining so far, each widespread application of Pb has been banned systematically because of dramatic environmental and health consequences. Unlike other toxic heavy metals like cadmium used in CdTe solar cells, the threat is the non-negligible water solubility of Pb halide salts comprising the perovskite (PbI2 and PbBr2). PbI2 is up to a billion times more water-soluble than CdTe. During the outdoor operational life of the solar cell, the possibility of water accessing the perovskite creates the risk of dispersing Pb into the soil. We demonstrated that vegetables growing in soil contaminated with legal levels (a few ppm) of Pb from perovskite could accumulate Pb beyond any safe threshold (hundreds of ppm) reported for Pb-contaminated food. Without any doubt, the regulations currently in force for Pb pollution are inappropriate for Pb perovskite.
Among the lead-free alternatives, tin (Sn) perovskite is the most promising, with a certified power conversion efficiency of around 15%. We will show the further steps towards 25% tin perovskite to make lead unnecessary.