Perovskite-Based PV Technologies
Emboldened by the promise of high module performance at low production costs, companies developing perovskite-based solar cells hope to deploy something new under the sun.
Credit: Dennis Schroeder / NREL
The adage that what has been done will be done again largely holds true for a terrestrial solar market dominated by crystalline silicon (c-Si) PV technologies. To date, only cadmium telluride (CdTe) thin-film modules, popularized by First Solar, have challenged the c-Si hegemony at scale, claiming roughly 5% market share worldwide and 40% in the U.S. utility sector. Companies developing perovskite-based solar cells are looking to flip this script and deploy novel PV technologies under the sun at an unprecedented scale.
As an independent testing laboratory, RETC tests next-generation solar products and technologies to qualify product designs and provide value to market entry activities. Based on its unique and privileged perspective on the industry, RETC believes the event horizon for commercial solar products using perovskite-based materials may be nearer than some industry stakeholders realize. With that in mind, this article provides a technical primer and an overview of the disruptive market potential and potential pitfalls of perovskite-based PV modules.
MATERIALS AND APPLICATIONS
Named after Russian mineralogist Lev Perovski, the term “perovskites” describes a class of chemical compounds with a crystalline lattice structure similar to that of naturally occurring calcium titanium oxide. As a semiconductor material, the mineral perovskite can absorb light and generate the photovoltaic effect. Perovskite compounds generally have a chemical formulation of ABX3, where A and B represent divalent and tetravalent cations and X is an anion that bonds to both.
As a compound, perovskites offer excellent compositional flexibility, allowing for perovskite structures combined from many different atoms and molecules. This flexibility has made perovskites an exciting new field for material scientists, chemists, and physicists. Depending on the combination of elements, perovskite compounds offer different optical and electrical properties. There are many potential applications for synthetic perovskites, including X-ray detectors, lasers, nanoscale antennas, super-high-resolution displays—and solar cells.
Harnessing the tunability of perovskites, scientists have succeeded in creating semiconductor materials with properties akin to those of silicon. Halide perovskites have shown great promise for PV applications, offering excellent light absorption, photoexcitation properties, and charge-carrier mobility. Best of all, one can tune these materials for an ideal match with the spectrum of solar radiation.
MARKET OPPORTUNITY
Perovskite-based PV technologies fit the profile of an insurgent technology capable of disrupting the solar market as we know it today. Meeting the world’s climate risk mitigation goals will require a rapid expansion in solar manufacturing capacity. To address energy security concerns and bolster regional economic benefits, policymakers in the United States and European Union are supporting clean energy investments at unprecedented levels. These market forces could help perovskites level up from research and development to commercialization.
The fundamental value proposition of perovskites in solar applications is multifaceted and undeniably compelling. In terms of performance, perovskite-only PV cells have rapidly evolved from conversion efficiencies of 3% in 2009 to almost 26% today. This unprecedented learning curve allows small-area perovskite hero cells to achieve efficiency levels that outperform those of other single-junction thin-film solar technologies. Moreover, manufacturers can combine thin-film perovskites with conventional c-Si PV cells. Record efficiencies for perovskite-on-silicon tandem PV cells surpass 33%.
Regarding manufacturability, perovskites are thin-film materials suitable for either vacuum deposition on a rigid base or roll-to-roll processing on a flexible base. Though continuous roll-to-roll processing is relatively novel in solar applications, manufacturers have long used this approach to produce photographic and chemical film. Perovskite fabrication at scale could one day look like newspaper printing, with affordable ink-like coatings ushering in a transformative era of terawatt-scale solar development.
“Part of what makes perovskites compelling is the streamlined supply chain,” notes Brian Grenko, vice president of VDE Americas, a firm specializing in technical due diligence. “Consider all the steps required to make conventional crystalline silicon PV modules. We process silica at high temperatures to refine it into polysilicon, which is very energy intensive. We typically ship polysilicon over long distances to another manufacturing location where we remelt it in another high-temperature operation to form ingots, which are later sliced into wafers. Those wafers may be shipped to yet another facility for conversion into solar cells prior to PV module assembly.
“Now imagine a perovskite-based PV module manufacturing process where raw materials enter one end of the factory and finished products exit the other. Roll-to-roll manufacturing would be revolutionary from a cost-per-watt standpoint—and it is not the only path to market for perovskites. Manufacturers are also working on innovative ways to deposit perovskites on silicon. With manufacturers nearing efficiency limits for conventional single-junction crystalline-silicon PV cells, tandem silicon-plus-perovskite cells are one way the industry can extend its existing technology roadmap.”
Larger-than-lab–scale vapor-deposited halide perovskites. (Credit: Dennis Schroeder / NREL)
BANKABILITY CONSIDERATIONS
The path to commercial adoption for perovskite-based solar products poses meaningful technical challenges and performance risks. Compared to conventional PV cell technologies, perovskites are more susceptible to light-, temperature-, and voltage-induced degradation, presenting potential problems associated with long-term product durability. Some promising perovskite compounds include trace amounts of lead, adding environmental concerns associated with lead toxicity.
Beyond materials science considerations, perovskites present manufacturing challenges. Scaling from laboratory equipment and processes to high-volume commercial operations is inherently difficult. Doing so with a novel cell technology while maintaining high conversion efficiencies in large-area product designs is even more challenging.
“There is also a commercial aspect to new technology that makes it hard to integrate,” says Benjamin Lemkau, senior director of solar PV systems technology for RWE. “It’s one thing to have a better, more efficient cell technology. Convincing customers to buy it is another thing. Stakeholders sitting on the other side of the table from us are often very conservative. It’s hard to sell a utility on a 25- or 30-year power purchase agreement using technology with limited history in the field.”
RETC’s expertise with beyond-qualification and bankability testing programs will be invaluable to scaling perovskite-based PV module technologies. On the one hand, the IEC 61215 product qualification standard is an excellent way to identify design, materials, and process flaws already known to lead to premature field failures. On the other hand, minimum requirements will not characterize long-term field durability or performance. Moreover, minimum test standards are generally blind to as-yet-undiscovered field failure modes.
In a best-case scenario, today’s minimum product qualification tests could characterize the durability of emerging PV cell technologies over a 5- to 7-year period. In a worst-case scenario, novel cell technologies could degrade or fail in novel ways within a shorter timeframe. Beyond-qualification testing, by contrast, uses highly accelerated extended test sequences to probe for known and unknown wearout mechanisms and failure modes. As such, RETC’s Thresher Test—so named for its ability to separate the wheat from the chaff—can help manufacturers and project stakeholders characterize the long-term durability and performance of next-generation perovskite-based PV cells and modules.
—This article originally appeared in RETC’s 2023 PV Module Index Report.
