The Solar Energy Technologies Office (SETO) supports research and development projects that increase the efficiency and lifetime of hybrid organic-inorganic perovskite solar cells that speed the commercialization of perovskite solar technologies and decrease manufacturing costs. Learn more about perovskite R&D challenges and the benchmarks associated with them.
What are Perovskite Solar Cells?
Perovskites are a family of materials with a specific crystal structure, named after the mineral with that structure. When used to create solar cells, they have shown potential for high performance and low production costs.
Perovskite solar cells have shown remarkable progress in recent years with rapid increases in conversion efficiency, from reports of about 3% in 2006 to over 25% today. While perovskite solar cells have become highly efficient in a very short time, a number of challenges remain before they can become a competitive commercial technology.
Much of the recent work on perovskite solar cells has been dominated by absorber materials based on methylammonium lead halide. Although perovskite materials have been studied for more than a century, initial studies on methylammonium lead halides for semiconductor applications started in the past two decades. Initial applications of perovskite absorbers in solar cells occurred in 2006 and were published in 2009. However, these cells were not very efficient (less than 4%) and were not stable, since they relied on a corrosive liquid phase that slowly disrupted other layers within the device. By 2012 the liquid-phase components had been replaced with solid-state contacts and the efficiency was improved to 10%. Subsequent improvements in performance and stability have come through continued investigation of new materials, new device architectures, and improved fabrication processes, leading to a reported 20% cell efficiency in 2014.
SETO has identified four primary challenges that must be simultaneously addressed for perovskite technologies to be commercially successful. Each challenge represents a unique set of barriers and requires specific technical and commercial targets to be achieved. The office is supporting projects working to address these challenges through the SETO 2020 and SETO FY20 PVSK funding programs, as well as the Perovskite Startup Prize.
The basic challenge framework is shown below, including examples of prior and current project efforts that address each challenge.
PRIORITY ONE – Power Conversion Efficiency: Perovskite devices have exceeded all thin-film technologies, except III-V technologies, in power conversion efficiency, showing rapid improvements over the past five years. However, high-efficiency devices have not necessarily been paired with viable stability and fabrication characteristics. For large-scale terrestrial deployment of perovskites, maintaining these high efficiencies while achieving stability and scaling will be necessary. In the meantime, continued improvement in efficiency by itself could be valuable for mobile, disaster response, or operational energy markets where lightweight, high-power devices are critical.
Perovskites can be tuned to respond to different colors in the solar spectrum by changing the material composition, and a variety of formulations have demonstrated high performance. This bandgap flexibility opens up another useful application for perovskite solar cells in high-performance tandem device architectures, with potential power conversion efficiencies over 30%. In these structures, perovskites are combined with another, differently tuned absorber material to deliver more power. Perovskite solar cells of certain compositions can convert ultraviolet and visible light into electricity very efficiently, meaning they might be excellent hybrid-tandem partners for absorber materials such as crystalline silicon that efficiently convert infrared light. It is also possible to combine two perovskite solar cells of different composition together to produce a perovskite-only tandem. Doing so could lead to even higher efficiency and more cost-effective tandem photovoltaic (PV) applications. Perovskite-only tandems could be particularly competitive in the mobile, disaster response, and defense operational energy areas, as they can be produced on flexible substrates with high power-to-weight ratios.
PRIORITY TWO – Stability and Degradation: Perovskite solar cells have demonstrated competitive efficiencies with potential for higher performance, but their stability is quite limited compared with that of leading PV technologies: They don’t stand up well to moisture, oxygen, extended periods of light, or high heat. To increase stability, researchers are studying degradation in both the perovskite materials and the contact layers. Improved cell durability is paramount for the development of commercial perovskite solar products.
Despite significant progress in understanding the stability and degradation of perovskite solar cells, current operational lifetimes are not commercially viable. Mobile markets may tolerate a shorter operational life, but stability during storage (prior to use) is still a key performance criterion for this sector. For mainstream solar power generation, technologies that cannot operate for more than two decades are unlikely to be viable regardless of other benefits.
Early perovskite devices degraded rapidly. A few years ago, typical perovskite devices would degrade within minutes or hours to non-functional states. Now multiple groups have demonstrated lifetimes of several months of operation. For commercial, grid-level electricity production, SETO is targeting an operational lifetime of at least 20 years, and preferably more than 30 years.
The perovskite PV R&D community is heavily focused on operational lifetime and is considering multiple approaches to understand and improve intrinsic and extrinsic stability and degradation. Efforts include improved surface passivation of absorber layers; alternative materials and formulations for absorber layers, charge transport layers, and electrodes; and advanced encapsulation materials and approaches that mitigate degradation sources during fabrication and operation.
One issue with assessing degradation in perovskites relates to developing consistent testing and validation methodologies. Research groups frequently report performance results based on varied test conditions, including variability in encapsulation approaches, atmospheric composition, illumination, electrical bias, and other parameters. While such varied test conditions can provide insights and valuable data, the lack of standardization makes it challenging to directly compare results and difficult to predict field performance from test results. This affects the entire perovskite research and development (R&D) community, independent of any specific research area, material set, or stability improvement approach.
PRIORITY THREE – Manufacturability: Scaling up perovskite manufacturing is required to enable production of perovskite solar cells. Making the processes scalable and reproducible could increase manufacturing and allow perovskite PV modules to meet and potentially exceed the office’s levelized cost of electricity targets.
The cells are thin-film devices built with layers of materials, either printed or coated from liquid inks or vacuum-deposited. Producing uniform, high-performance perovskite material in a large-scale manufacturing environment is difficult and there is a substantial difference in performance between small-area cell efficiency and large-area module performance. The future of perovskite manufacturing will depend on solving this challenge, which remains an active area of work within the PV research community.
Various methods have been used to produce lab-scale perovskite devices. Many of these methods are not easily scalable, but there are significant efforts to apply highly scalable approaches to perovskite fabrication. For thin-film technologies, these can be split into two major types of production line:
- Sheet-to-Sheet: Device layers are deposited on a rigid substrate, which typically acts as the front surface of the completed solar module. This approach is commonly used in the cadmium telluride thin-film industry.
- Roll-to-Roll: Device layers are deposited on a flexible substrate, which can then be used as either an interior or exterior portion of the completed module. Researchers have tried this approach for other PV technologies, but it did not gain significant commercial traction owing to barriers to obtaining high solar conversion efficiency (independent of the fabrication approach). It is, however, widely used to produce photographic and chemical film and paper products, such as newspapers.
The scalability of these fabrication approaches give perovskites the potential to enable faster capacity expansion relative to silicon photovoltaics. The processes under consideration are well established in the film and display industry, making the knowledge and supply chains around the tooling and components easily leveraged to further reduce scaling costs and risk.
Additional barriers to commercialization are the potential environmental impacts related to the perovskite absorber, which is lead-based. As such, alternative materials are being studied to evaluate, reduce, mitigate, and potentially eliminate toxicity and environmental concerns.
PRIORITY FOUR – Technology Validation and Bankability: Validation, performance verification, and bankability—ensuring the willingness of financial institutions to finance a project or proposal at reasonable interest rates—are essential to the commercialization of perovskite technologies. Variability in testing protocols and minimal field data have limited the ability to compare performance across perovskite devices and to develop confidence in long-term operational behavior.
Current testing protocols for solar PV devices were developed for the existing mainstream PV technologies. These use indoor testing using protocols validated based on decades of correlation to outdoor performance. They may not be good predictors of the long-term outdoor performance of new PV technologies. Objective, trusted validation using test protocols that can adequately predict long-term outdoor performance is critical to obtaining sufficient confidence in perovskite technologies to enable investment in production scale-up and deployment. The rapidly changing material and device compositions of perovskite solar cells make this standardized validation particularly challenging and important.
SETO monitors progress in the R&D and manufacturing communities and engages with potential interested entities, investors, financiers, and end users to create benchmarks and targets for the commercial deployment of perovskite photovoltaics for the bulk-power generation market. These benchmarks and targets will likely evolve with increased understanding of what will enable the manufacture and deployment of perovskite photovoltaics at the gigawatt scale.
Various materials, device structures, and manufacturing techniques are being pursued, and it is unclear which of these approaches is the most promising. The targets for single-junction perovskite cells and modules will be different than those for hybrid perovskite tandems and all-perovskite tandems. What follows are some generalized early-stage targets relevant to spurring perovskite PV commercialization. Later-stage targets are under development and will be published in the future.
As perovskite PV is commercialized, there must be balance among demonstrating high power conversion efficiency and high stability, utilizing scalable manufacturing processes, and scaling from individual cells to multi-cell modules with larger active areas. The targets provided here are for modules rather than cells. Some loss in active-area efficiency is inherent in scaling up from cells to modules. For perovskite PV technology to move toward commercial viability, power conversion efficiency targets between 18% and 25% are necessary at the early stages, demonstrated with multi-cell modules that range from tens of square centimeters to square meters. More than half the layers (including the perovskite layer) in the device stack should be deposited with scalable deposition techniques at relevant throughputs or deposition speeds for high-volume manufacturing. Initially these modules should be able to demonstrate operational stability, retaining 80% to 95% of their original output after 1,000 hours of accelerated testing. These figures will need to further improve in the future to be representative of the desired decadal operational lifetime. In the meantime, these targets provide a useful metric to help the perovskite community to increase reliability.
SETO Perovskite R&D Funding
- SETO FY2020 Perovskite Funding Program
- SETO FY2019 Photovoltaics
- SETO FY2018 Photovoltaics
- Photovoltaics Research and Development: Small Innovative Projects in Solar (PVRD-SIPS)
- Next Generation Photovoltaics 3
You can also visit our solar projects map and search for "perovskite" to read more about these projects.
Learn more about solar office's photovoltaics program.
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