European thin film solar PV research organization Solliance along with partners has claimed to have achieved 28.7% combined efficiency for a perovskite and crystalline silicon tandem solar cell, and 27% for a perovskite and CIGS tandem cell. This has been made possible due to the team realizing a 18.6% efficient highly near infrared transparent perovskite solar cell, it explained.
Solliance's research partners for this work include Dutch research institute TNO, imec/EnergyVille from Belgium, and Eindhoven University of Technology.
The perovskite solar cell with 18.6% efficiency was combined with different architectures of bottom solar cells and different cell technologies, which the team claims demonstrates the wide applicability of the 4-terminal tandem approach. For their research, the team used a lab scale perovskite solar cell of 9 mm².
It was combined with a prototype c-Si Interdigitated Back Contact (IBC) silicon heterojunction (SHJ) solar cell of Panasonic leading to a tandem efficiency of 28.7%. When combined with a commercial c-Si Metal Wrap Through (MWT) SHJ cell of Choshu Industry and Co., developed by TNO, the tandem efficiency was 28.2%.
On the other hand, when used with a Solarlab Aiko Europe GmbH's commercial c-Si Passivated Emitter and Rear Contact (PERC) cell, the tandem efficiency was 27.7%.
Solliance described that when combined with a band-gap optimized flexible CIGS cell of MiaSole, a record tandem efficiency of 27% was realized.
According to Solliance, these results are more than 1.5% absolute efficiency improvements of earlier records achieved with its collaborators.
TNO/Solliance's Dr. Dong Zhang explained the team put together opto-electrical properties of the perovskite solar cell to better match the optical properties of the bottom cell, and determined the loss factors in the 4-terminal configuration, minimizing these step-by-step. They eventually maximized light absorption in the tandem solar cell.
"Currently, low-cost upscaling processes for large area modules and maintaining the same performance are being developed by the Solliance partners TNO and imec/EnergyVille," said Dr. Mehrdad Najafi of TNO/Solliance who stressed that the next step is to upscale the area and the processes.