Professor Martin Green compared tiny pyramids on silicon’s surface for improved sunlight absorption – and big performance gains

Professor Martin Green giving a plenary presentation at SNEC 2025, in Shanghai, on a promising frontier in photovoltaic innovation: reducing reflection and boosting light capture using ultra-fine, sub-micron surface structures.

At last year’s SNEC 2025 conference in Shanghai, ACAP founder and UNSW Scientia Professor Martin Green unveiled new insights showing that silicon still has room for big performance gains. His plenary talk focused on a promising frontier in photovoltaic innovation: reducing reflection and boosting light capture using ultra-fine, sub-micron surface structures.

For decades, researchers have worked to extract every additional fraction of a percent in efficiency from silicon. A key barrier has always been reflection – sunlight bouncing off the surface instead of being absorbed and converted into electricity. Traditional pyramid texturing has helped, but Professor Green’s latest work shows that much more is possible.

Using nanoscale surface features – pyramids smaller than a micrometre across – his team has demonstrated that silicon can support special “resonances”, or miniature echo chambers for light. These resonances dramatically reduce reflection and keep photons inside the cell for longer, increasing the likelihood they’ll be harvested for energy.

By refining the geometry and spacing of these pyramids, the researchers propose that the long-assumed theoretical efficiency limit for silicon, around 29.4%, is actually conservative.

Professor Green and co-author Dr Zibo Zhou calculated an efficiency of 30.1% is achievable in principle, with one of the schemes analysed, “Although we may obtain even better results in the future,” said Professor Green.

Crucially, the team is now exploring whether these benefits require perfectly periodic patterns or whether more irregular, lower-cost surfaces could achieve the same effect. If so, manufacturers could incorporate these advanced textures using scalable, industry-friendly processes – leading to cheaper modules with higher performance.

A slide from his presentation. The graph shows how different microscopic pyramid shapes etched onto a silicon solar cell’s surface affect how much sunlight is reflected, across the wavelenghs of the solar spectrum. These pyramids are far smaller than the width of a human hair, but their shape has a big impact on performance. Lower values mean less light is being reflected, and more can be converted into electricity.

The blue line is a pyramid with a base angle of 54.7° – similar to the angle used in the ancient pyramids at Giza – and already reduces reflection quite effectively. The red line is a slightly steeper pyramid with a 60° base angle, and performs even better. The green line is for a more complex, smoothly curved “quintic” shape, like that in the microscopic picture, and is the most effective at reducing reflection.

The sharp drops in reflection around 500 nanometres arise from optical resonances, where light becomes temporarily trapped by the tiny surface structures instead of being reflected away.

“Past work suggested that silicon cells needed to be over 100 microns thick for optimal performance, however, our work shows that a thickness around 60 µm microns may be the actual optimum,” added Professor Green. “With the additional advantage of reducing silicon wafer costs.”

While still in development, this research highlights a powerful message: silicon, already the most successful energy technology in history, still has untapped potential. By capturing more energy from sunlight, these innovations could deliver cleaner power at even lower cost, accelerating the transition to a renewable future.

Reference:

Green, M. A. (2025, June 11-13). Reduced Si reflection from sub-μm pyramid resonance [Plenary presentation]. SNEC 2025 International Photovoltaic Power Generation & Smart Energy Conference & Exhibition, Shanghai, China.