3D stacked solar collector cell tops 44% efficiency

July 13, 2017 // By Nick Flaherty
US researchers at the George Washington University in Washington, DC, have developed a prototype for a new solar cell that integrates multiple cells stacked into a single device capable of 44.5% efficiency in a solar collector.


The approach is different from the solar panels as it uses concentrator photovoltaic (CPV) panels with lenses to concentrate sunlight onto tiny, micro-scale solar cells. Because of the small size of the energy converter, most expensive materials can be used and still be cost effective.

Current GaInP/GaInAs/Ge cells on a silicon substrate have a verified efficiency of 34.5%, while InGaP/GaAs/InGaAs multijunction devices for the same PVC collector-style systems are showing an efficiency of 37.9% in the latest rankings published by Progress in Photovoltaics. Cells using lower cost perovskite materials for PVC applications are currently at 23.6% efficiency.

The stacked cell developed at GWU uses gallium antimonide (GaSb), which are usually found in applications for infra-red lasers and photodetectors. The cell is assembled in a stacked structure along with high efficiency solar cells grown on conventional substrates that capture shorter wavelength light. The stacking procedure also uses transfer-printing, which enables three dimensional assembly of the stack with precision without using a semiconductor process.

The cell has specialized materials in each layer absorbing the energy of a specific set of wavelengths. By the time the light is funneled through the stack, just under half of the available energy has been converted into electricity.

“Around 99 percent of the power contained in direct sunlight reaching the surface of Earth falls between wavelengths of 250 nm and 2500 nm, but conventional materials for high-efficiency multi-junction solar cells cannot capture this entire spectral range,” said Matthew Lumb, lead author of the study and a research scientist at the GW School of Engineering and Applied Science. “Our new device is able to unlock the energy stored in the long-wavelength photons, which are lost in conventional solar cells, and therefore provides a pathway to realizing the ultimate multi-junction solar cell.” 

The study, “GaSb-based Solar Cells for Full Solar Spectrum Energy Harvesting,” was published in Advanced Energy Materials.

Despite the current costs of the materials used in