Perovskite solar cells: Hero, villain or just plain fantasy?
By SPW | February 4, 2020
By Dave P. Buemi, Managing Director, Prescient Energy Consulting
With my experience throughout the PV industry supply chain and thin-film commercialization, perovskite solar appeared at first glance to be yet another unsubstantiated claim of printing and spraying simple solar cells on everything to provide the world with endless, cheap energy. But what was missing from those previous efforts was a material that could be high efficiency, exponentially lower cost and highly manufacturable.
Perovskite is that material.
There is a lot of misunderstanding in the industry around the perovskite solar cell (PSC), and often reporting from outside the industry adds to the confusion. As with all new technologies, irrational exuberance and naysaying abound.
So let's start by getting a few baseline items out of the way.
First the pronunciation: pe·​rov·​skite | \ pə-ˈräv-ˌskīt — it took me forever to get this right!
Record efficiencies of perovskite solar cells shown in the yellow circles. Credit: NREL
Perovskite is comprised of a class of minerals in crystalline cube- and diamond-like structures that were first discovered over 170 years ago in the Ural Mountains of Russia. Named after Russian mineralogist Lev Perovski, it's abundantly found mainly in the earth's mantle and occasionally in near-surface deposits. Fortunately, perovskite can be synthesized from common chemicals for use in solar cells and other applications including light emitting diodes, catalyst electrodes, fuel cells, IC chips, lasers and sensors, to name a few.
Perovskite as a solar cell material was initially discovered when it was used in lab-tested organic dye sensitized solar cells in the mid-2000s. While that solar cell effort was not successful, the perovskite compound was shown to be quite photo-reactive by itself. Fast forward 10 years and academia, national labs and corporations have taken the PSC efficiency from 2% to 25% in lab settings on approximately 30-cm x 30-cm forms. It's a staggering advancement when looking at the history of other solar cell technologies that took 40+ years to reach similar lab-scale efficiencies.
Perovskite offers a large number of advantages in the solar cell/module realm:
It has wide bandgap, which results in greater tunability and more sunlight being converted to electricity.
Current lab efficiencies mirror those in silicon crystalline and other thin-film products, and tandem PSCs have a viable roadmap to reach greater than 33%.
Perovskite production is highly simplified via solutions processing and does not require high-cost machinery and facilities, which are required for semiconductor processing.
It is manufactured as a thin-film product resulting in 20-times less materials.
It requires no rare earth or supply-limited materials.
Perovskite is highly defect-tolerant which creates high manufacturing yields and ease when working in modules larger than 300 W (current thin-films require exceptional engineering, cost and risk to increase the manufacturing deposition area).
PSC-based modules can be shaped as traditional rectangular solar panels or be flexible, opening up new applications and markets.
Perovskite solar module manufacturing has a small environmental footprint depending on the manufacturing method employed.
Return on energy invested is measured in months vs. years with current solar module products.
So what's not to like here? When looking at perovskite solar cells, the number of misunderstandings are large.
Light-induced cell degradation and environmental stability are the continually cited villains. Early on, PSC stability was a large problem. But just as there were rapid advancements in cell efficiency, there has also been similar quick advancements in stability.
Perovskite Mineral Crystal
Light-induced degradation is now well understood. A major hinderance was the choice of materials for the electron transfer layers on either side of the perovskite cell. Multiple labs and other entities have successfully substituted new materials and solved LID issues.
On the weatherization front, just like with other thin-films and crystalline silicon solar cells, exposure to moisture, oxygen and other common environmental substances can cause rapid module degradation in PSCs. Using standard "packaging" assembly schemes, the concerns about environmental degradation have largely been solved. This reminds me of the early days of copper indium gallium selenide (CIGS) cell development where the commonly cited bogeyman was intolerance to moisture. But now CIGS-based modules are widely deployed with no major environmental stability issues.
Both light-induced and environmental PSC degradation parameters have exceeded 1,000-hour accelerated life cycle testing (the PV industry standard for new technologies) with some going as far as 10,000 hours.
Other stability challenges related to mechanical durability, applied voltage heating and thermal influences and current-voltage behaviors are similarly understood with a number of fixes in the testing phase.
Two whitepapers on light-induced and environmental stability cures can be found here and here. A more recent paper from Solliance partners TNO, imec and the Eindhoven University of Technology shows encapsulated perovskite solar modules using standard manufacturing methods successfully completed standard PV industry stability tests including light soak, damp-heat and thermal cycling.
Lead is used in the most common PSC cell structure, methylammonium lead halide. The amount of lead used is miniscule (average: 2 mg/Watt). For comparison, a common automobile battery contains 20 pounds (9,000,000 mg) on average.
As lead is a heavy toxic metal substance, it needs to be tightly controlled in all parts of an application from manufacturing to end-of-life recycling, especially when it is deployed in a water soluble form such as a perovskite solar cell. The lead recycling stream is the largest and most complete of any material in the world and the PSC industry would use only 0.0007 grams of the total stream. Looking at it another way, PSC recycling would annually represent one-tenth of 1% of all lead recycled at a 1-terawatt recycling rate.
Looking at current fossil fuel energy generation — where lead and other heavy metal particulates and toxic waste streams permeate our daily lives — the benefits of solar modules with only trace amounts of heavy metals far outweighs the overall risk.
Scalability to meet zero emissions by 2050 mandate
The topic of whether PSCs can scale fast enough to meet the United Nations' 2050 zero emissions targets is a continual conversation. The established crystalline silicon solar module based industry is pointed to as mature and ready to scale. But silicon-based solar faces challenges to meet these energy needs.
A perovskite cell using methylammonium lead triiodide thin films. Photo credit: Dennis Schroeder / NREL
To meet 20% of all global energy for the U.N.'s emissions reduction scenario, the solar industry would need to install 300 to 500 GW annually (linear example) over the next 30 years. Current global PV module manufacturing at 100 GW per year presents an enormous supply chain challenge. The silicon module industry's large capital intensity issues limits solar supply to 5% of all global energy. It's a common misunderstanding that silicon modules' low margins are principally because they are highly commoditized products. The capital intensity is preventing large and durable margins, contributing to supply chain scale-up financing challenges.
The cost of solar energy is also still too expensive especially when looking at value deflation at the kilowatt-hour level. Looking at many studies, solar energy needs to have an installed cost lower than $0.30/W to solve this problem even when coupled with low cost energy storage.
Perovskite solar with its unique simplified manufacturing attributes, raw material, performance and small environmental footprint makes it highly scalable — quickly. Depending on the business model, perovskite modules can be manufactured in facilities that cost 50% less than other solar factories and use less materials. The supply chain to support PSC manufacturing is also small, allowing for factories to be sited close to end markets.
The PSC industry is in a state where its lab developments exceed prior solar panel commercialization launch points. The challenge is how quickly the simplified manufacturing can scale-up for a given production method to enter high-volume production.
If you believe, as I do, that the acceleration of climate-related events will also accelerate global energy decarbonization timelines, the solar industry will need all existing and new arrows in the module sector quiver to meet 20% of all global energy, let alone 45% as some scenarios demand. Perovskite-based modules can be a timely addition to the solar energy industry's push to zero energy emissions.
Check back for the second article in this series, focusing on product design, raw materials and manufacturing.
Leveraging a 23-year career in renewable energy with broad experience across the solar PV industry supply chain, Dave Buemi is Managing Director of Prescient Energy Consulting which provides strategic and tactical business consulting to renewable energy related entities throughout the low carbon energy transition ecosystem. He has held senior-level positions throughout the PV supply chain including technology commercialization, manufacturing, EPC and project development with companies that include Brightphase Energy, Daystar Technologies, Empower Energies, Gehrlicher Solar/M&W, Suniva and Willdan Energy Solutions. He also played a key role developing the community energy model and commercialization of both advanced thin-film solar cell and solar tri-generation technologies. His work early in renewable energy overlapped with the U.S. Department of Defense renewable energy and microgrid strategy deployment where he provided strategy and knowledge in the warrior, forward deployed, home base and airborne sectors. A climate change and climate resiliency activist and consultant, Dave believes that urgent innovation throughout the PV industry ecosystem is key to meeting the Paris Climate Accords 2050 timeline while enabling a more profitable and stable industry for all stakeholders.
Opinions expressed here are of the author only.
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S .Srinivasarao says
An opt answer for to day's Global mission of achieving 20 % power requirement through non polluting resources. Since the technology for manufacturing is understood the commercialization needs to be fastened solving the issues as we come across.I have been working in the areas of energy efficiency and alternate energy sources as ahead of an organization helping establishing small and medium sized manufacturing companies. Beeing a chemical engineer my self I can play a role .
I believe some of the 'new' technologies of the mono crystalline solar PV cell manufacturing processes could be adaptable to perovskites. In adapting topologies like TOPcon cell manufacturing, could allow two differently tuned perovskite chemistries to be sprayed onto a mono crystalline cell structure with the proper 'moisture sealing' as part of the process. Tandem cells, what about tertiary cells in one manufacturing line process?