A new study from the University of Sheffield shows that Perovskite solar cells have the potential to dramatically reduce the energy payback periods for solar cells and can be a game changer in future energy systems. We interviewed Professor Lenny Koh about the results.

Can you explain what Perovskite is and how it can be used in solar cells?

Perovskites refers to a class of materials that share a similar structure, which exhibit a wide array of exciting properties including superconductivity, magneto resistance and many more. Perovskite are easily synthesized materials with distinctive structures which makes them perfect for enabling low-cost and efficient photovoltaic’s, rendering them materials for future solar cells. They are also predicted to play a role in next-gen electric vehicle batteries, sensors, lasers and much more. Perovskite is the mineral CaTiO3, named after L.A. Perovski, a Russian mineralogist and entails all compounds which crystallizes in the same ABX3 structure, where A and B are cations and X is the anion species.

How do Perovskite cells compare with silicon cells in terms of yield and life expectancy?

Currently, with recent improvements in materials design and device architecture performance conversion efficiency (PCE) of > 20% are routinely reported for laboratory-based Perovskite solar cell. Lifespan (i.e. life expectancy) of other existing PV technologies are already well-established, but no exact value in terms of lifespan has been reported for PSC technologies given that they are still at an early research and development phase. On a lab scale, PCE of > 20% was sustained for up 2.5 days for a compact-layer-free planar cell. Similarly, it has been demonstrated that in an instance where a hole conductor- free mesoscopic,  PSC exhibit stability across one month at ambient temperature under light source.

What is the energy payback period for Perovskite cells?

Depending on the Perovskite architecture, they offer an ultra-low energy payback period of less than one year.

Availability of resource materials can be a bottleneck for some solar technologies. How is this for Perovskite cells?

Part of the success of Perovskites is due to their ability to form crystals of very high quality rapidly using solution processing methods and moderate temperatures. The material requirements for PSC may depend on critical and precious materials, so consideration of resource materials availability is essential to achieve optimum trade-off which may be needed to meet overall supply chain sustainability.

Can you explain what a hybrid life cycle assessment is?

Hybrid life cycle assessment (HLCA) is a well-established systematic approach used for the identification, quantification and assessment of the associated environmental impacts throughout the entire value chain of an activity, product or process. It has the competitive edge of addressing the limitation of the general approach to LCA, which is termed process-based LCA, which suffers from system boundary truncation, through the augmentation of upstream and downstream inputs within the LCA system in instances where specific process LCA data are lacking. It enhances supply chain visibility, yielding results that are more complete.

What was the outcome of the assessment for Perovskite solar cells?

The main outcomes, presented along with sensitivity analysis, show that PSCs offer more environmentally friendly and sustainable option, with the least energy payback period, as compared to other PV technologies.  The analysis presented provide valuable insight and guidance in identifying pathways and windows of opportunity for future PV designs towards cleaner and sustainable energy production.

What do you consider to be the biggest shortcomings of Perovskite cells?

Although PSC benefits from most essential parameters of PV technologies including material and performance parameters, production processes and manufacturing complexity, economics, and key technological challenges for further developments, there exist challenges pertaining to their high proneness to moisture, cell stability and scalability. There are also concerns about how end-of-life scenario such as recycling and decommissioning will influence the environmental impact of PSC due to the toxicity of lead, however improved encapsulation materials can help in addressing this potential shortcoming.

Can you give an estimate of the cost per kWh with a Perovskite cells in the UK?

Given that PSC is still operating on the lab scale, there is currently no information on the cost per kWh of electricity produced by PSC. However, if the PCE values reported so far can be maintained and the issue of scalability is addressed, the cost per kWh will be considerably lower compared to other PV technologies. The cost of fabricating one cell is below 20 cents, based on simple laboratory experiment leading to fabrication of methyl ammonium lead triiodide (MAPbI3) PSC using a simple step-by-step deposition procedure, followed by measurements with routine equipment and it takes 2−5 h.

With the advantages that you mentioned, what is the industry waiting for?

Clearly, the use of expensive materials such as gold and operations such as vapour deposition and spin coating which are energy-intensive will require material substitution and optimisation respectively, to achieve better environmental profile for PSCs. Furthermore, to migrate from lab scale production to large scale industrial production, a number of issues including the use of flexible substrates, ease of deposition, patterning, chemical stability and encapsulation must be addressed. Once all these issues are addressed, then PSC have the potential to revolutionise the PV industry.

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Graphics: courtesy of Professor Lenny Koh