Researchers from Delft University of Technology (TU Delft), King Abdullah University of Science and Technology (KAUST), and Ludwig-Maximilians-Universität München (LMU Munich) have found a novel way to boost the performance of perovskite - silicon tandem solar cells, by tuning the nanoscale surface roughness of the silicon bottom cell.
Image from: EES Solar
While most efforts to improve tandem devices have focused on materials composition or optical design, the team chose to concentrate on the physical structure of the recombination junction - the interface where the perovskite top cell meets the silicon base. Their findings show that controlled surface nanoroughness can significantly enhance electrical contact quality, reduce recombination losses, and yield more efficient and reproducible devices.
By varying the thickness of n-type hydrogenated nanocrystalline silicon ((n)nc-Si:H) layers and applying a hydrogen–carbon dioxide plasma treatment before deposition, the researchers were able to systematically tailor the surface morphology of the silicon heterojunction (SHJ) bottom cell. Plasma treatment in particular proved effective, enabling distinct nanoroughness even in ultra-thin (15 nm) layers.
This engineered roughness improved the anchoring of molecular self-assembled monolayers (SAMs) and enhanced the quality of the perovskite interface, leading to higher fill factors and efficiency gains. Devices with optimized plasma treatment reached a peak efficiency of 32.6% after just 30 seconds of processing - highlighting both performance and scalability.
Beyond perovskite - silicon tandems, the approach offers a versatile and manufacturable route for improving a broad range of silicon heterojunction technologies. By showing that morphology control at the nanoscale can serve as a new design lever for tandem integration, the research opens the door to faster industrial adoption and next-generation high-efficiency PV architectures. The work exemplifies how small structural adjustments can deliver big leaps in solar performance.
