NREL Researchers Outline Path Forward for Tandem Solar Cells

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Because the previous saying goes, two heads are higher than one. The identical is true on the subject of photo voltaic cells working in tandem.

Researchers on the U.S. Division of Vitality’s Nationwide Renewable Vitality Laboratory (NREL) have ready a roadmap on methods to transfer tandem photo voltaic cells—significantly those who mesh completely different photovoltaic applied sciences—nearer to commercialization.

Because the researchers identified in a recently published article within the journal Joulesignificantly extra solar energy have to be added globally past the at present put in 1 terawatt of capability. Due to the rising inhabitants and elevated electrification of all power sectors, specialists are predicting the world will want 75 terawatts of photovoltaics (PV) by 2050.

The overwhelming majority of photo voltaic modules in use immediately depend on a single junction, which is ready to soak up solely a fraction of the photo voltaic spectrum and thus are restricted to how environment friendly they are often. Tandem photo voltaic cells, which include two or extra junctions, maintain the potential to achieve a lot increased efficiencies. As a result of tandems are stacked on prime of one another, the full space a module requires decreases—in flip, elevating the effectivity and probably decreasing the full system value.

Kirstin Alberi, the lead creator of the journal article, titled “A Roadmap for Tandem Photovoltaics,” mentioned high-efficiency III-V multijunction photo voltaic cells have been accessible for many years however at small scales and primarily for house purposes reminiscent of to energy satellites. Alberi, director of the Supplies Science Middle at NREL, mentioned newer forms of hybrid tandem modules utilizing extra scalable PV applied sciences are actually in improvement by each main producers and startup corporations “but we are not aware of any that are being mass-produced and sold commercially.”

Alberi and her 17 coauthors from the Division of Vitality-funded laboratory are trying to spur researchers and producers to collaborate with a aim of constructing speedy progress towards mass manufacturing of tandems.

They spelled out the advances that have to be made:

• Enhance the effectivity of photo voltaic cells to file ranges, after which translate these efficiencies to modules and high-volume manufacturing
• Determine and tackle reliability and sturdiness points
• Work out the design of hybrid tandem PV modules and techniques to hurry deployment.

The roadmap focuses on hybrid tandems, the place two or extra completely different PV applied sciences are mixed to offer the utmost effectivity. With a large number of supplies designed to soak up daylight, the variety of combos to create tandems are plentiful. These supplies are divided into two teams: these greatest as prime cells and people greatest as backside cells. The proper match between the 2 junctions will increase the quantity of daylight that’s absorbed and transformed into electrical energy. A prime photo voltaic cell product of steel halide perovskites, for instance, may enhance the efficiency of a single junction silicon photo voltaic cell.

“Metal halide perovskites are viewed as an initial enabler of hybrid tandems from a cost and efficiency perspective,” Alberi mentioned. “They provide high enough efficiencies as a top cell and are also cost effective enough to incorporate that the tandem would have much higher efficiencies than the single-junction cells of either technology.”

The time period perovskite refers to a crystalline construction, somewhat than to a selected component reminiscent of silicon. Analysis continues into the long-term stability of perovskite photo voltaic cells, which have been proven to be tremendously environment friendly. Perovskites are additionally simpler and cheaper to fabricate than many different photo voltaic applied sciences.

The tandem roadmap advocates contemplating the potential of different supplies as a prime cell. Gallium arsenide (GaAs) and gallium indium phosphide (GaInP) are each candidates as they’ve the best effectivity of single-junction units. The principle downside to their use, nonetheless, is the expense to make. Researchers at NREL have been wanting into cheaper manufacturing strategies.

The plain materials for a backside cell, the researchers mentioned, is silicon, which dominates the photo voltaic trade. A tandem product of a prime steel halide perovskite cell and a backside silicon cell at present holds the file for effectivity.

A tandem comes with extra challenges, mentioned Emily Warren, a workers scientist within the Excessive-Effectivity Crystalline Photovoltaics group at NREL and a coauthor of the roadmap paper.

“For single-junction PV materials, modules are made by interconnecting individual cells laterally in series,” she mentioned. “For tandems, there are multiple options to interconnect the cells, which provides another layer of complexity to the design of tandem modules.”

Solely three single-junction PV applied sciences have efficiently been scaled to a minimum of a gigawatt of manufacturing. Along with silicon, inroads have been made by photo voltaic cells created from copper indium gallium diselenide (CIGS) and from cadmium telluride (CdTe). CIGS is appropriate for a backside cell and CdTe as a prime.

The researchers mentioned the distinction within the commercialization trajectories between silicon and the thin-film cells product of CIGS and CdTe gives perception into the challenges that have to be overcome to determine a gigawatt-scale tandem expertise. Silicon PV benefited from main investments by the semiconductor group, leading to shared information and standardized processes. Corporations specializing in CIGS and CdTe, nonetheless, have rigorously guarded their processes and deposition methods as they try to make headway in opposition to silicon PV.

The roadmap proposes a collaborative effort, reminiscent of a consortium just like these which were created to spice up the manufacturing of perovskites and of CdTe photo voltaic panels. This might convey trade and researchers collectively “to discuss common issues and share lessons learned,” in keeping with the roadmap paper. Some consortia are already engaged on perovskite-based tandems.

“Existing consortia have proven to be immensely helpful in the development and commercialization of single-junction PV technologies because they can help in information sharing, advocating for cross-cutting research that will help the field as a whole, and focusing larger sets of stakeholders to work together to solve problems that impact the entire field,” Alberi mentioned. “We think consortia could serve a similar role in the development of hybrid tandems, particularly because we are still early in the commercialization phase of this technology.”

Article from NREL | By Wayne Hicks | Study extra about solar and PV research at NREL.