Perovskite solar cells (PSCs) have received attention from researchers all over the world due to their excellent power conversion efficiencies (PCEs) and easy manufacturing. Despite being a low-cost, processable solution, their widespread implementation has been hindered by their lack of operational stability and the presence of lead (Pb). While the stability issue is being effectively addressed in several ways, more focus is needed to reduce potential lead leakage in the case of catastrophic device failure. In this regard, the high PCEs for PSCs seem to be linked to the presence of highly toxic lead.
Lead makes up to 30% of the mass in the photoactive layer of lead-based PSCs. Furthermore, the lead present in Pb-PSCs is water-soluble. It is a toxic, regulated substance with a half-life of 20-30 years in the human skeleton. Lead is very carcinogenic and poisonous to almost every organ in the body. This raises concerns about the negative impacts of damaged perovskite solar modules, especially if it is flooded and lead is leaked into the environment. A fail-safe strategy for preventing lead emissions is necessary if the PSCs are used extensively by the general public and contribute significantly to the next generation of renewable energy.
a Perovskite solar cell. b is a composite colour map combining elemental STEM-EDS data for Ca, Ti, P and Pb. The image shows that Hydroxyapetite (HAP) can capture Pb and prevent the leaching.
To prove this concept, our previous study (https://doi.org/10.1039/D0CC02957B) applied the bioinspired approach using hydroxyapatite (HAP) to partially contain lead leakage when there is PSCs catastrophic failure in the event of flooding or water submersion. Several considerations for these materials' development have been put forward. First, how to increase lead absorption capacity? Second, does combining HAP nanoparticles with different morphology in the PSC scaffold increase the PCE? Lastly, can the lead sequestration efficiency be improved so that the lead leaked during the simulated hail and flooding scenarios is below the safe-drinking water level? We address these crucial questions in the current investigation.
a Schematic of the device with a HAP encapsulation layer. b Photographs of failure tests from broken PSCs immersed in water for various times. The black colour turns to yellow showing perovskite degradation to PbI2. c Pb concentration in the water surrounding the broken cells as a function of time. d Pb residual concentration in water after 24 h for each of the devices. At 100% s-HAP the Pb concentration is below the safe level for drinking water in the US (red dashed line).
This innovative method, which relies on inorganic materials, offers a reliable method for removing lead from PSCs. Furthermore, the capturing mechanism is placed within the PSCs' lead source. This study developed an improved, effective spherical HAP nanoparticles (s-HAP) and investigated their effects on PSC performance and containing lead released from damaged devices. Post-mortem investigations were also conducted to determine the rate of lead absorption by the s-HAP in both the scaffold and the encapsulation layers. This study will improve the understanding of factors leading to higher performance for devices containing s-HAP. It can also demonstrate how to contain lead contamination in water in the event of flooding after damages in a simulated hail scenario to ensure a lower lead composition based on the safe drinking water standard. This study also demonstrated a potential opportunity to develop device lead containment systems for PSCs.
To know more about this improved lead sequestration technology by consortium of researchers from University of Manchester, University of Oxford, University of Bath and Universiti Teknologi Malaysia, please refer to paper by Mokhtar et al ‘Mokhtar, M.Z., Altujjar, A., Wang, B. et al. Spherical hydroxyapatite nanoparticle scaffolds for reduced lead release from damaged perovskite solar cells. Commun Mater 3, 77 (2022). https://doi.org/10.1038/s43246-022-00299-3’