MIT-Masdar "step cell" offers 35% efficiency, low production cost
A silicon solar cell with silicon-germanium filter using a step-cell design (large) and a gallium arsenide phosphide layer on silicon step-cell proof-of-concept solar cell (small). Source: MIT News Office (news.mit.edu).
Researchers from the Massachusetts Institute of Technology (MIT) and the Masdar Institute have developed a two-layer solar cell with estimated practical efficiencies of about 35%.
Unlike other multijunction photovoltaic (PV) cells, the team’s “step cell” is also cheaper to make, the scientists say. There is a plan to form a startup company to commercialise the device.
The solar cell is made by growing a gallium arsenide phosphide (GaAsP) layer on top of silicon germanium, patterning it in an optimised geometric configuration, and bonding it to a silicon cell, MIT’s Eugene Fitzgerald explained. “Then we etched through the patterned channels and lifted off the silicon germanium alloys on silicon. What remains then, is a high-efficiency tandem solar cell and a silicon germanium template, ready to be reused,” the Professor said.
The two layers in the cell are arranged in a stepwise fashion, so that sunlight can reach both. The top GaAsP layer thus absorbs the high-energy photons (from blue, green, and yellow light), leaving the lower-energy photons for the bottom silicon layer. The silicon germanium template can be used again and again, reducing the manufacturing cost.
The step cells may be ready for roll-out within the next year or two, Fitzgerald says. He and Masdar Institute’s Ammar Nayfeh, principal investigators in the project, are thinking about setting up a startup company for “the promising solar cell”. Fitzgerald believes the step cell fits well in the existing gap between super high-efficiency and low-efficiency industrial applications in the solar market.
The initial proof-of-concept cell has been presented in June at the IEEE Photovoltaic Specialists Conference in Portland, Oregon.