Success in integrating III-V compounds on silicon substrates can lead to affordable (cost-efficient) photovoltaic (PV) and thermophotovoltaic (TPV) systems, says Mantu Hudait.
“The biggest challenge for PV is drastically reducing the cost per watt to deliver solar electricity.” While power electronics researchers at Tech are enhancing conversion efficiency, Hudait is pursuing lowering the cost of highly efficient solar cells.
PV cells are usually made of a stack of up to 10 different materials of which the composition has to be minutely controlled — each being optimal at converting a different part of the solar light spectrum into electricity, he explains. Each layer of a cell, however, adds materials and processing cost as well as manufacturing time. Moreover, any single layer cannot exceed 30-percent efficiency according to the laws of physics as defined by the Shockley-Queisser limit. “Even a hypothetical cell with an infinite number of light-converting layers would have a conversion efficiency just under 70 percent,” he says.
“The real question is,” Hudait says, “if you want to buy energy, what is its cost per watt?” His solution is to use the compound III-V technology on silicon and to make the layers thinner, and use fewer layers to reduce the cost. “A 10 micron thickness has been demonstrated in the literature to achieve 41 percent efficiency. I propose we build a 5-micron thick active layer and accept 30-percent efficiency. We give up some efficiency for a much lower cost such that solar PV systems can become more acceptable.”