At the European Photovoltaic Solar Energy Conference (Hamburg, Germany),
IMEC presents a mechanically-stacked
GaAs/Ge multijunction solar cell. This is the first promising demonstrator of
IMEC's novel technology to produce mechanically stacked, high-efficiency
multijunction solar cells, aiming at efficiencies above 40%.
IMEC's mechanically stacked GaAs/Ge cell
At the top of the stack is a one-side contacted GaAs top cell that is only
4µm thick and that is transparent for infrared light. Its efficiency is
23.4%, which is close to the efficiency of standard GaAs cells. IMEC has succeeded
in transferring this GaAs top cell onto a Ge bottom cell, creating a mechanical
stack. In that stack, the Ge bottom cell is separately contacted. It has a potential
efficiency of 3-3.5%, which is higher than Ge bottom cells in state-of-the-art
monolithically stacked InGaP/(In)GaAs/Ge cells. Looking forward, Giovanni Flamand,
team manager at IMEC, expects to show a first working triple-junction cell beginning
of 2010.
This cell is a demonstrator of IMEC's innovative technology to produce
mechanically stacked, high-efficiency InGaP/GaAs/Ge triple-junction solar cells.
This includes manufacturing world-class thin-film III-V cells and Ge bottom
cells, and developing a technology to mechanically stack them. The expected
conversion efficiencies are 1-2% higher than those obtained today with monolithic
triple-junction solar cells (> 40% with concentrated illumination). In addition,
the new cells show an enhanced spectral robustness. Stacked solar cells combine
cells made from different materials to capture and converse a larger part of
the light spectrum than is possible with a single material.
Dr. Jef Poortmans, IMEC's Photovoltaics Program Director: "Mechanical
stacks are more complex to handle and interconnect. But they definitely offer
a way to increase the conversion efficiency and energy yield of high-efficiency
solar cells. And they also enable an efficient way to try and use new combinations
of materials. For this technology, we profit from IMEC's expertise in
3D stacking, growing III-V layers, and solar cell processing."