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The new efficiency applies to a solar cell with an area of 1.081 cm².
Size matters in solar physics. Scientists in Germany may have just unlocked the next generation of clean energy by generating record-breaking power on a piece of material larger than a postage stamp.
A research team from the Helmholtz-Zentrum Berlin (HZB) and Humboldt-Universität zu Berlin has set a certified new record. Interestingly, the custom-built tandem solar cell converted 25.5 percent of sunlight into electricity. It shatters their own previous record of 24.6 percent set last year.
The victory lies in the size of the device. The cell measures 1.081 cm².
While that sounds tiny, crossing the 1 cm² threshold is a massive hurdle in the solar community. In fact, standard industry charts, such as the NREL table, list microscopic cells as small as 0.001 cm².
However, the prestigious Solar Cell Efficiency Tables, known globally as the “Green Tables”, are strict. The table refuses to list any technology unless it proves itself on an area larger than 1 cm². In crossing this line, the Berlin team has vaulted from a theoretical laboratory gimmick into the definitive ledger of scalable photovoltaics.
Rather than using a single material, tandem solar cells stack two different materials on top of each other, like a sandwich.
To achieve the milestone, the team stacked two different thin-film materials. A copper, indium, gallium, and selenium (CIGS) layer was used as a base. And it was then topped with perovskite, which is a highly adaptable crystalline structure. Each material is tuned to catch a different part of the light spectrum.
The top perovskite layer catches the high-energy blue light and turns it into electricity efficiently. The rest of the light passes right through it to the bottom CIGS layer, which catches the lower-energy red and infrared light.
The engineering required extreme precision. Dr. Guillermo Farias Basulto adjusted the CIGS base to vary its band gap to capture light more effectively.
“To push past our previous milestone within the framework of the European project SOLMATES, we employed CIGSe-bottom cells with different band gaps (i.e. 1.05 eV and 1.1 eV) and two different thicknesses of aluminium doped zink oxides with similar characteristics,” explained Basulto.
Meanwhile, chemist Wuai Zhang systematically screened atomic coatings to prevent electricity from leaking at the internal boundaries. Zhang even regulated the evaporation rate of “buckyballs” (Buckminsterfullerene) onto a microscopic, 1-nanometer passivation layer to streamline the current. It worked.
Can this leave the lab? The team is already proving it can.
Working with the University of Applied Sciences in Berlin (HTW), the researchers successfully scaled the exact same material stack into a 2.25 cm² mini-module. It retained a highly efficient 19.7 percent.
The scientists are confident this is just the beginning. According to Farias-Basulto, internal testing of modified architectures has already reached efficiencies as high as 27.5 percent. The physics suggests that the 30 percent barrier is well within reach.
“The physics embedded in our current cell architecture suggests that 25.5 percent is merely a stepping stone, given that our in-house testing of similar architectures has already reached efficiencies of 27.5 percent,” the researcher noted.
The thin-film CIGS and perovskite materials are lightweight and flexible. This unique combination allows the tandem solar cells to be applied to curved surfaces, integrated into building windows, or mounted on vehicle roofs where standard, rigid panels are impractical.
The findings were published in the journal Joule.
Mrigakshi is a science journalist who enjoys writing about space exploration, biology, and technological innovations. Her work has been featured in well-known publications including Nature India, Supercluster, The Weather Channel and Astronomy magazine. If you have pitches in mind, please do not hesitate to email her.
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