IMEC's mechanically stacked GaAs/Ge cell

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鈥檚 novel technology to produce mechanically stacked, high-efficiency multijunction solar cells, aiming at efficiencies above 40%.

At the top of the stack is a one-side contacted GaAs top cell that is only 4碌m thick and that is transparent for . Its efficiency is 23.4%, which is close to the efficiency of standard GaAs cells. 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鈥檚 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鈥檚 Photovoltaics Program Director: 鈥淢echanical 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 . And they also enable an efficient way to try and use new combinations of materials. For this technology, we profit from IMEC鈥檚 expertise in 3D stacking, growing III-V layers, and solar cell processing.鈥�

Source: IMEC