Towards Self-scrubbing Stable and Scalable Perovskite Solar Cells

Perovskite solar cells (PSCs) show unprecedented levels of efficiency for such easy to process solar cells, and are higher than those of most common, but more expensive, silicon cells. They have an excellent potential to provide low-cost solar electricity. Spectacular impact is expected but is hindered by poor stability of the perovskite phase and concerns about the use of lead and especially its potential release into the environment. Lead is also a relatively highly regulated element. In this proposal, our team of leading chemists, materials scientists, device physicists and theorists, will address these issues through an integrated collaborative study. Building on our previous work we will improve the understanding of the key mechanisms responsible for PSC degradation, by exploring new perovskites, morphologies and stabilisation by the use of additives. The link between defects (structural imperfections) and PSC performance/stability will be investigated experimentally and using state-of-the-art modelling techniques. The approach will provide a sound basis for predictive guidelines for perovskite formulation to enable stable environmentally benign, inexpensive PV units for mass use. Among the most intriguing aspects of perovskite materials are the high efficiency of charge pair photo-generation and the long lifetime of these charges. We will use new ultrafast timescale spectroscopic techniques to obtain new insights concerning the dynamics of the perovskite photo-excited states. We will address issues of potential heavy metal contamination, in the event of PSC failure (and water ingress) by studying new lead-free perovskites as well as by developing new heavy metal self-scrubbing scaffolds within lead- and tin-containing PSCs. A new aerosol-assisted film deposition approach for fabrication of large area, high performance, stable and environmental safe PSCs will result. Our ambition is to provide prototype environmentally safe, demonstration, large area PSCs with enhanced operational stability that could be mass produced and have power conversion efficiencies exceeding 20%. A successful outcome to this project would provide improved fundamental understanding of the interplay between perovskite composition and device performance and new PSCs that would bring about the large-scale deployment of perovskite photovoltaics for CO2-free electricity generation closer.

It is now increasingly recognised by policy and opinion formers and by the public generally that the development of new low CO2-emission energy technologies is essential for the future economic and environmental health of both the developed and the developing world. Solar is the fastest growing renewable energy technology and has excellent potential to provide a substantial proportion of UK and global electricity. Indeed, perovskite solar cells (PSCs), in particular, have shown remarkable increases in their power conversion efficiencies (PCEs) and would seem very well placed to make a major contribution to future (urgently needed) terawatt-scale photovoltaics. Unfortunately, the potentially enormous impact of simple and cheap to produce PSCs has not been realised because of poor stability and concerns about Pb use. A successful outcome to our project would provide solutions to both of these concerns and lead to development of new PSCs for large-scale deployment.

A successful outcome would provide solutions to the PSC stability and environmental concerns and should result in much lower cost solar energy compared to that which can be achieved with established solar technologies because of the combination of low cost materials, solution processability and high PCEs that apply to PSCs. The longer term beneficiaries from a successful outcome of our ambitious research programme would be the energy consumer and, more generally, the developed and developing world through a new and affordable, mass-deployed low CO2 emission renewable energy technology. Because of the potential to lower the cost of electricity beneficiaries of this research are also the UK government (due to increased energy security and CO2 mitigation obligations) and solar cell industries. Solar energy will make an important contribution to the UK government meetings its international obligation to reduce CO2 emissions as part of the Paris agreement. Low cost building integrated solar cells (e.g., rooftop solar cells) would enable microgeneration as well as increase the proportion of zero-carbon homes, both of which will provide local employment. Success would provide longer term commercial opportunities for UK manufacturers of PSC solar materials, devices and modules. The commercial interest in our proposed research is demonstrated by the letter of support from Johnson Matthey.

A successful outcome to our project would also provide a new self-scrubbing technology that could be applied to other third-generation solar cells that contain Pb and Sn. This could accelerate commercialisation of solar cells containing Pb- or Sn-based quantum dots such as colloidal quantum dot solar cells and hybrid polymer solar cells in the longer term. Moreover, the self-scrubbing technology envisaged in this program has potential to be applied to other Pb-based electronic devices. Indeed, a fully successful outcome with 100% Pb capture (for a damaged cell with water ingress) could open up new areas of research such as using implantable PSCs for bioelectronics applications.

In this study an advanced ultrafast timescale spectroscopic technique will be used to probe the photoexcited states in new perovskites. The approach draws upon previous work involving natural photosynthetic species and applies this to the problem of understanding light harvesting in PSCs. This new ultrafast spectroscopic approach will provide new fundamental mechanistic information concerning photo-induced charge pair generation which is urgently needed to fully understand the structure-light harvesting behaviours of PSCs and will benefit all perovskite solar cell researchers.

The proposal resides within the Materials for Energy them which has been identified as grow. The research programme fits with underpinning applications in the grand challenge areas of Energy, Environment and Manufacturing. The programme is also fully aligned with the strategic energy research priorities of RCUK.