Our New Study in EES Solar Reveals Impact of Surface Nano-Roughness in Recombination Layers of Perovskite-Silicon Tandem Solar Cells

January 10, 2026

Engineering Nanoscale Surface Roughness Boosts Perovskite-Silicon Tandem Solar Cell Efficiency to 32.6%

Our latest study demonstrates that controlling nanoscale surface roughness in the recombination layer of perovskite-silicon tandem solar cells is a key lever for improving device performance.

Monolithic integration of perovskite top cells on textured crystalline silicon is a promising route for high-efficiency tandem solar cells, but the influence of the bottom cell’s surface morphology has often been overlooked. In this work, we systematically engineered the top surface nanoroughness of silicon heterojunction bottom cells to understand its impact on tandem device performance.

We used two approaches to tune surface nanoroughness:

1. Adjusting the thickness of (n)-type hydrogenated nanocrystalline silicon ((n)nc-Si:H) layers.

2. Applying a brief plasma treatment with hydrogen and carbon dioxide before depositing (n)nc-Si:H layers.

Both methods increased the conductivity and crystallinity of the (n)nc-Si:H layers and enhanced surface nanoroughness. Importantly, plasma treatment enabled distinct nanoroughness even in ultrathin (15-nm) layers.

Our findings reveal that the surface nanoroughness significantly affects self-assembled monolayer (SAM) anchoring, improving the SAM/perovskite interface quality and shifting work functions. These effects translated to measurable improvements in device performance: tandem cells with higher nanoroughness bottom cells exhibited higher fill factors, enabling a peak efficiency of 32.6% after a 30-second plasma treatment.

This international collaboration—between Delft University of Technology, KAUST, and Ludwig-Maximilians-Universität München—highlights the power of nanoscale surface morphology engineering as an underexplored strategy to complement existing perovskite optimization approaches. By controlling the bottom cell’s surface at the nanoscale, we can improve perovskite crystallization, interface quality, and overall tandem efficiency, opening a pathway for more scalable, high-performance photovoltaics.

Team contributions: Cem Yilmaz, Rik Hooijer, and Jian Huang.

These insights are broadly relevant to silicon heterojunction and other crystalline silicon technologies, emphasizing the importance of nanoscale engineering for next-generation solar cells.