Enel Green Power takes a risky gamble with the expansion of its HJT manufacturing facility

Photovoltaic (PV) technology is one of the most-relied upon solutions by every economy, both emerging and established, to reach its decarbonization goals, with globally installed PV capacity crossing the 1-TW mark in March 2022. This number is only expected to grow exponentially in the coming years, and the International Energy Agency predicts the installed capacity of solar PV to point upwards of 14 TW by 2050 if net-zero is to be achieved. Although most noticeable installations are utility-scale solar farms or rooftop solar systems, players in this space are coming up with innovative ideas to deploy solar technologies in every possible nook and cranny, ranging from indoor power sources for electronics to integrated PV. Innovations in PV can be broadly classified into two categories — cell architectures that unlock new use-cases via higher efficiencies or better yields (e.g., bifacial, tandem solar cells) and system innovations to cater to new customers, like "floatovoltaic" or agrivoltaic systems. Since the focus is on "advanced PV," this insight will highlight patent trends in novel cell chemistries and configurations. Efficiency and applicability are the two most important drivers (as is with any technology) prompting organizations in PV to invent advanced solar cell architectures that will make them stand out in an extremely crowded market. Given that the performance of the current version of crystalline silicon (c-Si) technologies is saturated, existing manufacturers are looking into other options that are versatile and have an excellent efficiency potential, like heterojunction solar cells, perovskites, or tandems. Moreover, the ever-improving policy landscape (which is already highly supportive of solar energy) will make markets that are niche today (e.g., building-integrated PV) attractive in the future, inviting new players targeting such applications with technologies like thin-film solar cells or organic PV (OPV). Advanced c-Si: Patent activity has been steadily growing over the years in c-Si, as innovations have tried improving effective solar cell areas used for capturing sunlight, minimizing recombination losses using passivation layers, or incorporating advanced interconnection methods to achieve greater efficiencies. There has been a shift from p-type architectures to n-type solar cells; major PV companies are also in hot pursuit of concepts such as heterojunctions (HJT) that utilize a thin amorphous silicon layer or tunnel oxide passivated contacts to reduce recombination losses. Manufacturers are also interested in developing bifacial modules that can generate more energy. For example, multiple large players including HuaSun, Longi, Hevel Solar, and Enel Green Power are investing in HJT as it can exceed the efficiency limits of incumbent c-Si solar cells and are extremely bifacial. Reduction in manufacturing costs for these solar cells remains the key issue that is being addressed by researchers. Thin films: Thin-film solar cells showed great promise during the early 2010s as both academia and industry were searching for new ways to differentiate them from c-Si solar cells. Moreover, thin films were (and still are) touted to be part of up-and-coming markets such as integrated PV, where aesthetics play a crucial role. Amorphous silicon, copper indium gallim selenide, cadmium telluride, and gallium arsenide were the primary technologies that were investigated. Activity is pretty much nonexistent in this space, especially since 2014 as perovskites started grabbing all the headlines. Thin-film solar cells have never passed c-Si efficiencies or costs, nor have they achieved greater life expectancies; they also raise eyebrows due to the toxicity and scarcity of the elements used in such devices. This has left behind just a handful of players, such as First Solar and MiaSolé. Perovskites: Patent activity in perovskites began skyrocketing during the mid-2010s, primarily because they have the potential to be a part of very-high-efficiency tandems (~37%) due to their inherent properties. Perovskites can be tuned to be sensitive to different parts of the incident solar spectrum, meaning they can be used in conjunction with other solar cells to create a device that interacts with all wavelengths of the spectrum. Research in this space is largely driven and dominated by startups like Tandem PV and Oxford Photovoltaics that aim to commercialize this technology. Perovskites are susceptible to humidity and are very expensive to manufacture; patent activity is naturally targeted to answer these questions. Tandems and Multijunctions: Multijunctions (solar cells with three or more junctions) and tandems (solar cells with two junctions) can capture energy from multiple parts of the solar spectrum as different solar cells sensitive to different parts of sunlight are stacked on top of one another and can have efficiencies of over 45%. The top cell produces electricity from high-energy photons (e.g., the ultraviolet range), while cells lower down the order interact with photons in the visible or infrared range of light. These cells can be connected in series or parallel, with series-connected multijunction devices limited by the current produced by the lowest current-producing cell. Multijunction solar cells are currently space grade and not commercially available; such solar cells lose their efficiency when scaled up, and this is the biggest hurdle for the industry. On the contrary, tandems, especially perovskite tandems, are zealously pursued in the industry as they can be scaled up. Most of the research activity is focused on developing perovskites or advanced silicon solar cells, which can be used in tandems rather than tandems themselves, as depicted by the somewhat-quiet growth in patents. Organic solar cells (OPV): Organic solar cells or OPV technologies use polymers as the absorber layer and the electron collection medium to generate power when exposed to sunlight. OPV is mostly characterized by conversion efficiencies in the single-digit range, while 15% efficiencies have also been reported. These solar cells also have similar properties to perovskites, can be tuned optically to meet user requirements, and are best suited for applications such as solar windows or indoor power generation from ambient light. Their reduced toxicity also makes them good competitors of other thin-film candidates. Research in OPV is trying to mitigate problems related to cell degradation and scale-up; however, research output has been low compared to other technologies, with German firm Merck leading the way. Large players in the PV industry will continue chasing after advanced c-Si technologies as they can be produced with existing manufacturing equipment, albeit with a few alterations. Perovskites and tandem solar cells are a hot topic among startups that are trying to disrupt the space with high-efficiency devices but still need to research how they can commercialize them. Multijunction solar cells and thin films will not gather any momentum anytime soon, and they will remain dormant for the foreseeable future. Overall, clients should expect advanced silicon technologies, perovskite solar cells, and tandems to pave the way in the advanced PV space as other concepts play catchup.

The École Polytechnique Fédérale de Lausanne (EPFL) hit a conversion efficiency of 29.2% by depositing a perovskite material on top of a "fully textured" silicon surface, which was certified by the Fraunhofer Institute. In addition to the textured surface implemented to reduce light reflection, the researchers claimed that the performance was obtained thanks to an "enhanced crystallization" of the perovskite cell and the implementation of transparent buffer layers to reduce parasitic light absorption. The current record obtained by Helmholtz-Zentrum Berlin (HZB) implements a "nanostructured" silicon surface and a dielectric reflector on the back part of the solar cell; EPFL claims that the efficiency they have recorded is a world record. While we cannot comment on which technology has better performance metrics, we continue to observe constant improvements in perovskite efficiencies. Expect lab-scale samples to surpass the 30% mark, but commercialization will depend on the development of suitable manufacturing techniques.

The École Polytechnique Fédérale de Lausanne (EPFL) developed a solvothermal method to deposit uniform "single-crystalline" TiO2 particles on top of a perovskite absorber layer. According to the researchers, the TiO2 particles showed lower "lattice" mismatches, resulting in a lower number of defects and enhanced electron flow. The deposition technique was used first on a "small-size" solar cell that achieved a conversion efficiency of 24.05%. Afterward, it was deposited on a 24-cm2 cell that achieved an efficiency of 22.72%. According to EPFL, it "represents the highest efficiency module with the lowest loss in efficiency when scaling up." TiO2 is used as the electron transport layer in perovskite solar cells. However, this material generally shows low electron mobility thanks to its high defect density. Clients should monitor the stability and reproducibility of the new deposition method and assess whether it can maintain this level of electrical performance.