No solar cell material ever has enjoyed such a rapid trajectory of improvements — nor the subsequent attention from researchers, industry, and media — as perovskite. This material, known for decades but whose ability to convert sunlight wasn’t appreciated until the past few years, has suddenly gained popularity with a velocity proportional to the flood of performance improvements coming out months and even weeks apart: from barely 3 percent conversion efficiency in 2009 to 10 percent in 2012, 16 percent in 2013, and as high as 19 percent according to recent conference reports. (A combination of c-Si cells and perovskite is thought to be able to achieve 32 percent efficiency.) That’s tantalizingly alongside the performance of mainstream conventional silicon-based PV, but with the potential for far simpler and cheaper processes and manufacturing.
Here’s why perovskite is attracting so much attention:
• It can better absorb sunlight, meaning thinner films can be used, which means less materials (bringing costs down)
• Perovskite requires only familiar wet chemistry techniques and simple benchtop processes — manufacturing is vastly simpler than other solar technologies, from c-Si to liquid DSC
• It’s not liquid, which also makes for much simpler manufacturing especially at larger scale, and also means better lifetime stability
• It offers significantly higher voltages because less energy is lost from activation and regeneration
NanoMarkets sees very important ramifications from perovskite’s unprecedented trajectory for one specific market segment: dye-sensitized solar cells (DSC). Several key DSC firms already have been at the forefront of the perovskite solar revolution:
• The École Polytechnique Fédéral de Lausanne (EPFL) in Switzerland, a pioneer of modern-day DSC technology, touched 15 percent efficiency a year ago, and more recently behind closed doors has shown north of 17 percent efficiency, sources tell NanoMarkets. EPFL’s DSC uses an inorganic-organic composite material with a perovskite, such as a dye and a hole-transporting material consisting of organic materials in place of electrolyte. (Specifically, the structure is a solid-state DSC of glass-FTO-TiO2-CH3NH3PbI3-HTM-Au.) Performance fluctuations have been resolved by tightening the perovskite material’s particle diameters, through a two-step deposition (Pbl2 accumulated on TiO2, then immersed in a CH3NH3I solution),resulting in a DSC with relatively high power conversion efficiency and high reproducibility.
• Another DSC-perovskite pioneer is Oxford Photovoltaics in the U.K., which is developing DSC modules with ambitious cost targets of $0.32/W for its technology which emphasizes transparency and color ideal for BIPV applications on building glass facades and rooftops. The company, a spinoff from the U. of Oxford (with 13 exclusive patents), believes it can achieve 20 percent conversion efficiencies with perovskite DSC panels. In fact, the company tells NanoMarkets that it’s entirely shifting its strategy and future business away from DSC to focus on perovskite thin-film solar cells, targeting the same BIPV markets with broader reach while also exploring the aforementioned hybrid silicon-perovskite cells.
• Dyesol, a longtime leader in DSC and organic PV, is transitioning from expensive liquid-based materials to relatively cheaper solid-state materials, including perovskite sensitizers and the Spiro solid-state electrolyte — a significant move considering the higher efficiency, lower cost, and better scalability prospects for solid-state DSCs. Dyesol also has a long association with EPFL.
The flip side of perovskite’s promise is its disruption to suppliers. A major reason why it’s received so much research attention is because as mentioned above its simplicity is utterly the opposite of a barrier to entry. According to some back-of-the-napkin math from one DSC materials provider, a 1 MW system with 100,000 sq. m of surface area would require up to 25 lbs of film layers but just 1.5 kg of perovskite material at a market value of $100.
All this excitement about perovskite material is, of course, happening at small-scale R&D. NanoMarkets understands much more work is needed before commercial viability can happen, most importantly in understanding the mechanics behind their degradation, making them stable and reliable over years of lifetime, improving their sensitivity to humidity, improving and simplifying how to properly package them, and all the while wringing costs out. A newer area of focus is replacing the tiny amounts of lead in current perovskite with other substances such as tin; the Pb amounts are tiny but could be subject to penalties of toxicity, not to mention negative marketplace perceptions. We reiterate that all of this hoopla about perovskite is still several years away from translating into commercial-ready large-size (e.g. 1 square meter) modules with 10 percent conversion efficiencies.
NanoMarkets believes, though, that perovskite’s rapid trajectory of efficiency improvement, with potential pairing of DSC’s features, could very well attract heightened interest from investors, strategically from within the industry and/or from capital markets, which could accelerate innovation and product development efforts and shorten the combined technologies’ runway toward commercialization.