Researchers from KAUST, TU Delft and LMU Munich have improved the performance of monolithic perovskite-silicon tandem solar cells by changing the physical structure at the front of the bottom heterojunction solar cell.
A research team from Delft University of Technology (TU Delft), King Abdullah University of Science and Technology (KAUST) and Ludwig-Maximilians-Universität Munich (LMU Munich) has shown that controlling nanoscale surface roughness at the recombination layer in perovskite-silicon tandem solar cells can improve performance.
The researchers noted that the influence of the surface roughness of the nanoscale crystalline silicon (c-Si) bottom cell has received much less attention than perovskite optimization. The researchers investigated the effects of surface modification of the silicon heterojunction (SHJ) bottom cell to understand the impact of surface nanoroughness on the performance of tandem devices.
“The main novelty of our study lies in demonstrating that the nanoroughness of the recombination compound can be deliberately designed to significantly improve the performance of perovskite-silicon tandem solar cells,” said Erkan Yadin, co-corresponding author of the study. pv magazine. “By systematically tuning the surface morphology at the nanoscale, we improved the quality of electrical contact and reduced recombination losses, leading to reproducible and higher efficiency results.”
“This provides a new design parameter that is compatible with existing silicon heterojunction technology,” Yadin said.
The team’s tandem optimization approach differs from approaches that focus on material composition, interface passivation or optical management. “Our design strategy complements these efforts by addressing the physical structure of the recombination junction itself. Importantly, this approach does not require new materials or complex processing steps, making it highly synergistic with established silicon heterojunction and perovskite fabrication routes,” said Yadin, adding that it provides a “scalable and manufacturable path to further improve tandem performance.”
In the study, the team investigated variations in thickness and plasma treatments of n-type(n) hydrogenated nanocrystalline silicon ((n)nc-Si:H) thin films. “We tailored the (n)nc-Si:H nanoroughness by (i) adjusting the thickness of the (n)nc-Si:H layers and (ii) applying plasma treatment using a hydrogen (H2) and carbon dioxide (CO2) gas mixture for different durations prior to the deposition of (n)nc-Si:H layers,” the report said.
Testing showed that both methods improve the conductivity and crystallinity of (n)nc-Si:H layers and increase surface nanoroughness, with plasma treatment allowing the efficient realization of apparent nanoroughness in thin (n)nc-Si:H (15 nm thick) layers.
The systematic variation of plasma treatment duration enabled controlled variation of the surface nanoroughness of textured c-Si bottom cells, promoting enhanced tin-doped indium oxide (ITO)/hole transport layer (HTL)/perovskite interfaces, which improved the performance of tandem devices, the study said.
“Our results show that the surface nanoroughness imposed by (n)nc-Si:H layers influences the anchoring of the self-assembled monolayer (SAM), leading to larger shifts in the work functions and improved SAM/perovskite interface quality, thus affecting the overall performance of tandem devices,” the researchers said.
“Specifically, tandem devices with higher nanoroughness bottom cells achieved higher fill factors, dominating the observed efficiency improvements of the tandems, with a peak efficiency of 32.6% enabled by a 30-second plasma treatment,” they concluded.
The new process has potential not only in perovskite-silicon tandems, but also in several other cell technologies. “Although our work is demonstrated in perovskite-silicon tandems, the concept is broadly applicable to silicon heterojunction devices and other crystalline silicon technologies that use similar thin films,” says Yadin.
The research is described in detail in “Tuning the nanoroughness of the recombination compound surface for high-performance perovskite-silicon tandem solar cells”, published by EES solar energy.
Looking ahead, each research group continues to explore key aspects of perovskite and silicon solar technologies. The LMU Munich team is currently working on how the interfaces can be further improved through surface treatments. “We are also investigating how nanoscale morphology, chemistry and mechanical stress interact in next-generation perovskite and tandem devices, with a strong focus on long-term stability and compatibility with industrial production,” says Yadin.
At TU Delft, the researchers will use state-of-the-art equipment in the PV Technology Center for future-oriented crystalline silicon technologies, said co-corresponding author Yifeng Zhao. pv magazine. The group uses advanced characterization and modeling techniques to design and manufacture innovative, stable and powerful solar cells.
The KAUST Photovoltaics lab (KPV lab) aims to bring emerging photovoltaic technologies closer to the market. “We are working on perovskite and silicon technologies in single-, dual- and triple-junction configurations for different applications. Tuning PV cell and module technologies for deployment in warm and sunny climates is of particular importance,” says Stefaan de Wolf, co-corresponding author. pv magazine.
This content is copyrighted and may not be reused. If you would like to collaborate with us and reuse some of our content, please contact: editors@pv-magazine.com.
