When US energy policy took a sharp U-turn last year, it was a real head-scratcher. The new policy supports expensive, polluting energy resources while throttling back on the most accessible and economical solutions, particularly solar. Still, the domestic solar industry continues to out-perform its competitors by a wide margin in terms of adding new generating capacity to the nation’s power profile, and it is about to get a fresh turbo-boost from new perovskite solar cell technology. The Perovskite Solar Cell Difference Silicon has long held the preferred position for balancing solar cell efficiency and durability with cost, and the cost of silicon solar cells has dropped significantly since the early 2000’s. Still, further declines may be incremental in the absence of a new technology breakthrough. Solar advocates have been scouting for a next-level change in the cost of solar cells, and that’s where perovskite comes in. Based on the naturally occurring mineral perovskite, synthetic perovskites offer cost, efficiency, and supply chain advantages over silicon. In the form of an ink or paint, perovskite solar cells can simply be sprayed or printed on a surface, deploying commonly used roll-to-roll fabrication methods. Perovskite was first demonstrated as a promising solar material in 2009, but a lack of durability initially held it back. More recently, commercial-level workarounds have been emerging, such as pairing a layer of perovskites with silicon in a tandem solar cell. In the search for efficiency gains, perovskite researchers have also ventured into the area of triple-junction solar cells. As the name suggests, triple junction refers to the use of three different materials. Last year, for example, a team based in Australia achieved a solar conversion efficiency of 23.3% for a triple junction cell measuring about 2.5 square inches, composed of two types of perovskite and silicon. They also reported a 27.06% conversion efficiency for a smaller version measuring 1 square centimeter. The latest news from the triple junction world comes from Germany, where researchers at HZB (Helmholtz-Zentrum Berlin für Materialien und Energie) have combined another 21st century material, graphene, with perovskite. The new cell takes advantage of the SAMs (self-assembled monolayers) nature of the materials (see lots more graphene background here). To improve durability, the team focused on replaced the commonly used conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), or PEDOT:PSS for short, deploying a graphene-based formula instead. “Overall, our findings demonstrate the immense potential of SAM-based all-perovskite multi-junctions and bring this promising technology a step closer to higher industrial readiness levels,” they reported in the peer-reviewed journal Joule. Lighter Solar Panels, More Rooftop Solar When time former President Obama took office in 2009, the US Department of Energy threw its weight behind perovskite R&D. Although the solar conversion efficiency of the first perovskite solar cells barely tapped into the single digits back then, policy makers recognized the potential for a sea change in solar cell costs and efficiency. HZB is just one among many examples around the world. In the UK, last year the country’s Innovate UK funding organization supported a partnership between Queen Mary University of London and the startup Power Roll, aiming to fill a gap in the global rooftop solar market. “Traditional silicon solar panels are heavy and rigid – which limits where you can put them. Almost 30% of commercial rooftops worldwide can’t support their weight. This helps explain why only 2% of buildings globally have solar panels – despite the sun giving earth enough energy in an hour to power the whole world for a year,” summarizes the school. The figure includes an estimated 12 billion square meters of rooftop in the UK alone that are incapable of supporting conventional solar panels, but could carry the lighter weight provided by perovskite technology. Queen Mary also points out that silicon manufacturing is an energy intensive process. In that regard, it falls short of realizing the full decarbonization potential of solar technology. The challenge for perovskite is scale-up. For Power Roll, that means adding a defect detection element that can spot imperfections in a thin, sub-millimeter film. Queen Mary is lending a hand by applying new optical inspection technology to the manufacturing equipment. The new process was developed by Queen Mary scientist Dr Stoichko Dimitrov, and the partnership with Power Roll represents the first time it is being applied in an industrial-scale system. Power Roll’s contribution to the field is a perovskite formula that eliminates the commonly used but expensive material iridium tin oxide. Earlier this year the company launched its first trial outside of Europe, in partnership with the Japanese firm Tokyo Gas. The joint effort will leverage Tokyo Gas’s proprietary adhesive-based construction process, among other capabilities. Meanwhile, Over In The USA Despite the political headwinds at work, US innovators have not exactly been sitting on their hands, with the perovskite solar cell startup Tandem PV being one example. Another US startup on the move is Swift Solar. The company surfaced on the CleanTechnica radar in March, when it acquired manufacturing equipment from the bankrupt Germany-based solar firm Meyer Burger. Earlier this year the startup Puerto Rican firm Solx also announced plans to manufacture tandem solar cells in the US, in a partnership with the California perovksite specialist Caelux Corporation. Keep an eye on Kentucky, the home state of the startup Sofab Inks. Sofab has been working on a cost-shaving formula based on tin, in partnership with the firm Alpha Precision Systems. Last year, Sofab teamed up with the Australian firm Halocell to integrate its perovskite technology with Halocell’s roll-to-roll manufacturing systems. Halocell is currently shipping samples to its partners for evaluation. For the record, the Kentucky location did not materialize out of thin air. Although not particularly well known as a hotspot for next generation solar technology, Kentucky is home to the University of Louisiana, where Sofab spun out of a joint effort by researchers and co-founders Sashil Chapagain, Blake Martin and Peter Armstrong. “Originating within UofL’s Conn Center for Renewable Energy Research, the startup gained early support through LaunchIt, UofL’s innovation bootcamp that is part of the NSF I-Corps Site program,” the school reported March, referring to a risk-reducing startup support program under the umbrella of the National Science Foundation. “Sofab Inks develops advanced liquid ‘nanoparticle inks’ that replace expensive and difficult-to-manufacture materials traditionally used in perovskite solar cells,” Uof L notes. “These inks enable manufacturers to deposit critical layers using scalable, low-cost coating and printing techniques rather than complex vacuum-based or clean-room processes, significantly reducing production costs while improving device performance and stability,” the school emphasizes. Hold on to your hats… Photo: The US startup Sofab is among the stakeholders pushing perovskite solar cell technology out of the laboratory and into the marketplace, offering improved supply chain stability alongside further cuts in the cost of solar power (cropped, courtesy of Sofab).
