A group of scientists working with the University of Utah believe they’ve discovered a method of substantially boosting solar cell efficiencies, in a breakhrough that could significantly reduce the total cost per watt — if it can be successfully commercialized.

Traditionally, solar cell technology has struggled to overcome a significant efficiency problem. The type of substrate used dictates how much energy can be absorbed from sunlight — but each type of substrate (silicon, gallium arsenide, indium gallium arsenide, and many others) corresponds to capturing a particular wavelength of energy. Cheap solar cells built on inexpensive silicon have a maximum theoretical efficiency of 34% and a practical (real-world) efficiency of around 22%. Multijunction cells that use multiple substrates to capture a larger section of the sun’s spectrum can reach up to 87% efficiency in theory, but are currently limited to 43% in practice. What’s more, these types of multijunction cells are extremely expensive — wiring and laying out precise structures is far more difficult than a simple thin film silicon cell.


We have a vast array of cells, but all of the inexpensive, common designs are low-efficiency. Image courtesy of Wikipedia

What the team has developed is a polychromat layer that separates and sorts incoming light, redirecting it to strike particular layers in a multijunction cell. The test device used two layers — indium gallium phosphide (for visible light) and gallium arsenide for infrared light. According to the research team, “When the University of Utah polychromat was added, the power efficiency increased by 16 percent.” The team also ran simulations of a polychromat layer with up to eight different absorbtion layers and claim that it could yield an efficiency increase of up to 50%, but have not actually tested the technology.

The polychromat layer sits on top and splits energy wavelengths, aiming them at the layers where they'll be absorbed.

The polychromat layer sits on top and splits energy wavelengths, aiming them at the layers where they’ll be absorbed.

This is where the reporting gets a little tenuous. The University of Utah statement refers to single-junction solar panels but describes a multi-junction device. Furthermore, it states the gain as a percentage rather than “percentage points.” This implies that the sentence should be understood as a percent of a percent; if the original cell efficiency was, say, 30%, then a gain of 16% percent means that the new efficiency is 34.8% (30 percent * 1.16x). That’s still a huge gain for a polychromat layer that the researchers say could be stamped out using DVD-like technology, but it’s not quite the enormous advance it’s been depicted as.

Given that the biggest barrier to III-V multi-junction solar cell technology is manufacturing complexity and associated cost, anything that boosts cell efficiency on the front end without requiring any major changes to the manufacturing process is going to help with the long-term commercialization of the technology. Until now, most of the multijunction devices deployed go into space or are used by for military applications where cost is less of an issue and peak performance is essential. Advances like this could help make technologies cost effective for personal deployment and allow them to scale in a similar fashion to cheaper devices.