Perovskite solar cells (PSCs), as an emerging renewable energy technology, are expected to play an important role in the transition to a sustainable future. However, lead toxicity of PSCs remains a major flaw hindering their large-scale implementation and compromising their sustainability, as lead is currently inevitable in making high-performance PSCs.

Several approaches have been developed to mitigate the lead leakage issue via physical encapsulation or chemical absorption once the PSCs are damaged in extreme weather conditions. In addition, one should also concern the lead-absorbing layer can gradually saturate or defunctionalize upon long-term exposure to rainwater containing various metal ions, ultraviolet (UV) radiation in sunlight or being damaged in cleaning processes. The currently reported strategies of preventing lead leakage only target to physically or chemically capturing lead from leakage, but the post-adsorption products still need to face the secondary lead contamination, and lead recycling and management require further consideration. To this end, an ideal strategy that can simultaneously minimize lead leakage and reduce the lead toxicity via in-situ encapsulation and chelation by built-in interconnected lead-absorbing network, while not compromising the device efficiency, is highly desirable, but this has not been explored and reported yet.

Fig. 1. Embedding crosslinking supramolecular complex into perovskite simultaneously enhances the device performance and reproducibility, prevent lead leakage, reduce lead toxicity and realizes a close-loop Pb recycling and management for making perovskite photovoltaics sustainable and bio-safe.

In order to achieve the above aim, we comprehensively considered the following aspects and rationally designed the lead-absorbing materials in PSCs. First, how to maximal the material's lead absorption capacity while does not compromise the device performance? Second, how to mitigate lead leakage of PSCs especially under extreme weather conditions? Third, can the lead-absorbing materials reduce lead toxicity when they are saturated or defunctionalized? Finally, the post-adsorption products still need to face the secondary lead contamination, and the lead recycling and management require further consideration.

Fig. 2. a, Schematic illustration of lead capturing by crosslinking HPβCD-BTCA supramolecular complex. b, Demonstration of Pb-absorbing capabilities of HPβCD-BTCA complex. c, Comparison of Pb sequestration for the damaged PSCs with or without HPβCD-BTCA. d, Schematic illustration of preparing E. coli culture solution with perovskites incorporation and the impact of different perovskites on the growth performance of E. coli as a function of time. e, The impact of control or target perovskites on the growth performance (the change of OD₆₀₀ over time) of E. coli. f, Effects of different perovskite compositions and components on growth performance of E. coli.

Fig. 3. Schematic illustration of Pb recycling and management in PSCs.

In this work, we report a built-in self-cross-linking supramolecular complex composed of 2-hydroxypropyl-β-cyclodextrin (HPβCD) and 1,2,3,4-butane tetracarboxylic acid (BTCA) renders to fabricate more efficient, durable and reproducible PSCs. More importantly, the lead leakage is minimized and the lead toxicity is reduced in resultant PSCs via robust chemical coordination and multidentate chelation, between HPβCD-BTCA complex and Pb²⁺ ions. The heavily broken devices maintain 97% of the initial efficiency after 522 h dynamic water scouring, with only < 14 ppb of Pb²⁺ contamination in water, a level compliant with the standards of the US Environmental Protection Agency (15 ppb). Furthermore, recycling Pb from end-of-life PSCs can be reused to fabricate high-efficiency devices, which is cost-effective and environmentally friendly. This work provides a new, low-cost and sustainable strategy to perfectly address the instability, poor reproducibility, lead leakage and toxicity issues commonly encountered in the perovskite photovoltaics community. These results will dispel the concerns of end-users and accelerate the commercialization and practical application of perovskite solar technology and other related optoelectronic devices.

To know more about this reduced lead toxicity technology by Sun Yat-sen University, please refer to paper by Yang et al. “Yang M., Tian T., Fang Y. et al. Reducing lead toxicity of perovskite solar cells with a built-in supramolecular complex. Nat. Sustain. (2023) https://doi.org/10.1038/s41893-023-01181-x”