On Jan. 31, 2024, researchers from the Fraunhofer Institute for Photo voltaic Vitality Methods (Fraunhofer ISE) introduced that, alongside perovskite developer Oxford PV, that they had produced a full-sized perovskite tandem module with a conversion effectivity of 25%. At 421 W, the dual-glass module’s energy output is much from that achieved by the large-format modules manufactured by photo voltaic trade giants. Nonetheless, the end result was a strong demonstration of the steps being made towards commercializing what’s extensively thought of the following era of photo voltaic cell expertise.
When asserting the end result, the Fraunhofer ISE group famous that scientists from its CalLab PV Modules’ calibration laboratory used a “multispectral photo voltaic simulator” to measure each the crystalline silicon photo voltaic cell and perovskite cells. It allowed for various mild spectra to be utilized to the cell whereas underneath steady illumination. This required specialised measurement tools based mostly on LED mild sources that had been in a position to present illumination evenly throughout the module’s 1.68 m2 floor.
“The continual depth and spectral stability of the sunshine supply is of specific significance particularly for tandem units,” mentioned Johnson Wong, basic supervisor for the Americas at tools supplier Wavelabs. The researchers from Fraunhofer ISE used Wavelabs’ Sinus-3000 Superior LED module I-V tester for the Oxford PV module.
“Due to its optimized mild distribution over an extended working distance, the tester mild supply is designed to forged a light-weight area that very carefully mimics the solar at each level over the big module space,” Wong added. He mentioned the Sinus-3000 LED tester exceeds A+ class when it comes to “spectrum, mild uniformity, and stability over time, which play a vital position within the measurement accuracy.”
Correct characterization
The correct characterization of perovskite photo voltaic units requires not solely new tools but in addition novel processes. Longer illumination occasions are wanted; the temperature influence of the sunshine supply should be managed or corrected for; I-V sweeps must be considerably slower than in crystalline silicon cells; and, in tandem cells, their present should be aligned in order that the mixed energy output just isn’t restricted.
The PV analysis neighborhood, potential producers, and tools suppliers are making strides in overcoming the formidable challenges posed by perovskite photo voltaic units. New, collaborative analysis initiatives are being launched and measurement routines have gotten extra refined. Because of this, confidence is rising that as the potential PV perovskite producers develop their units towards maturity, the tools and processes might be prepared.
Sunny prospects
Karl Melkonyan, PV expertise analyst with S&P World Commodity Insights, mentioned that perovskite tandems have “the perfect possibilities for commercialization” amongst next-generation photo voltaic cell applied sciences. Perovskite PV cells could be coupled with both crystalline silicon (c-Si) or thin-film photo voltaic cells.
Early perovskite PV units achieved conversion efficiencies within the low single digits – 3.8% was recorded in 2008. Report efficiencies at the moment are set at common intervals and are nicely past 25%.
Perovskite tandem units are extraordinarily promising, primarily as a result of the thin-film perovskite cell plus the “base” c-Si, cadmium telluride, or copper indium gallium selenide layer can seize totally different mild wavelengths, leading to small-scale analysis cells with efficiencies past 30%.
Translating lab effectivity to bigger cells and modules is troublesome, nevertheless. “Whereas there are numerous document effectivity achievements of perovskite photo voltaic cells reaching 20% and above, the entire effectivity of a tandem construction could be a lot decrease than the sum of these particular person efficiencies,” mentioned Melkonyan. He famous that the explanation for that is usually a present mismatch between backside and high cells.
Measurement challenges
For a PV gadget to show its value, its energy output should be capable to be measured in a extremely correct, replicable, and standardized style. On the finish of the day, if a PV module is to be bought and put in, it’s important that its nameplate energy output could be trusted.
Right here, as famous within the current Fraunhofer ISE and Oxford PV end result, perovskite PV units current a bunch of latest challenges. “Sure, the facility measurement of a perovskite tandem or multi-junction cell presents challenges and may very well be fairly troublesome as a result of very particular spectrally-adjustable photo voltaic simulators are required,” mentioned Melkonyan. “Other than applicable stabilization strategies for various perovskite supplies, the processes ought to embody standardized protocols to measure underneath commonplace check situations.”
In late April 2024, Fraunhofer ISE, Oxford PV, Wavelabs, and the College of Freiburg wound up an 11-month investigation into how large-format perovskite tandem PV cells could be precisely characterised. Fraunhofer ISE’s Martin Schubert led the undertaking – abbreviated to “Katana” in German. He mentioned there are two main variations between the characterization of perovskite tandem units and common PV modules.
Two components
“One is that the effectivity could change throughout illumination,” mentioned Schubert, who leads the standard assurance, characterization and simulation group. “The rationale for that’s that there’s an ion migration within the perovskite cell during which some ions are shifting. The second complication is the tandem structure. By itself, which means we’ve got two photo voltaic cells – one on high of the opposite and with totally different spectral sensitivity. We have to take care that the highest cell will get the correct quantity of present and the underside cell will get the correct quantity of present.”
Ion migration inside the perovskite gadget whereas underneath steady illumination signifies that the measured effectivity can both enhance or lower over time. This “metastability” necessitates the lengthy illumination time wanted for stabilized energy output to be ascertained. Complicating issues additional, totally different perovskite PV compositions exhibit various ranges of metastability.
The necessity for lengthy mild publicity, to accommodate metastability, brings warmth, even when utilizing LEDs. Because of this the measurement of perovskite units is usually carried out at temperatures greater than commonplace check situations (STC).
The facility output of a photovoltaic gadget declines as its temperature will increase, an element described as a tool’s temperature coefficient. Completely different PV applied sciences imply differing temperature coefficients. c-Si photo voltaic merchandise, for instance, have a bigger temperature coefficient than skinny movie units. If that isn’t managed and accounted for, the result’s measurement uncertainty.
Testing tools with temperature management – primarily a chamber with air-con – can scale back this uncertainty in best-case situations. Such refined units, notably with ample scale to accommodate full modules, come at a price.
The influence of temperature could be corrected for utilizing mathematical fashions based mostly on correct temperature readings and may account for the uncertainty greater temperatures can convey. With tandem units, the temperature sensitivity of each the highest and backside cell should be accounted for – a fancy, if not inconceivable, equation.
Business implications
At current, the testing of perovskite units is carried out inside minutes, to account for metastability associated to ion migration within the perovskite cell, in order that slower I-V sweeps, with a number of energy level monitoring (MPPT), could be carried out. That is unsuitable for mass manufacturing, as many modules have to be rolling off manufacturing traces each minute.
Wavelabs’ Wong mentioned {that a} “extra pragmatic check routine” would possible first contain a preconditioning of the module utilizing mild soaking, from mass-production mild sources. That might then be adopted by “a quick I-V sweep utilizing top quality illumination that should match inside the specs of spectral match, uniformity, and stability,” mentioned Wong. “The quick I-V sweep will possible be completed within the order of 100 milliseconds to 1 second, throughout which the ions are ‘frozen in’ to their preconditioned distribution and don’t considerably redistribute.”
Fraunhofer ISE might be launching a three-year analysis undertaking in Could 2024 that may examine how “quick and exact measurements” could be developed and executed for perovskite units, together with tandems. The undertaking, abbreviated to “PERLE” in German, might be funded by Germany’s Federal Ministry of Financial Affairs and Local weather Motion. Fraunhofer ISE’s Schubert mentioned that it’s attainable that the primary findings from the undertaking might be printed by Could 2025.
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