At this week’s European Photovoltaic Solar Energy Conference, IMEC researchers are presenting a GaAs/Ge multijunction cell demo with potential >40% efficiency.
September 22, 2009 – At this week’s European Photovoltaic Solar Energy Conference, IMEC researchers are presenting a GaAs/Ge multijunction cell demo with potential >40% efficiency.
First, the group describes what it calls a demonstrator of mechanically stacked, high-efficiency InGaP/GaAs/Ge triple-junction solar cells. This multijunction cell starts with a one-side contacted GaAs top cell (4μm thick) transparent for infrared light, by itself 23.4% efficient (close to that of standard GaAs cells). This cell is then transferred onto a Ge bottom cell creating a mechanical stack; the separately-contacted Ge bottom cell has a 3%-3.5% efficiency, higher than Ge bottom cells in leading monolithically stacked InGaP/InGaAs/Ge cells, the researchers note. The goal is to have a working triple-junction cell in early 2010.
Expected conversion efficiencies of the whole thing are expected to be 1%-2% higher than what is obtainable today with monolithic triple-junction solar cells, or >40% using concentrated illumination. The new cells also show what IMEC calls “enhanced spectral robustness;” stacked solar cells made from different materials have been proven to capture and convert more of the light spectrum than just one material.
“Mechanical stacks are more complex to handle and interconnect [but] offer a way to increase the conversion efficiency and energy yield of high-efficiency solar cells, noted Jef Poortmans, IMEC’s PV program director, in a statement. They also represent a more efficient use of new material combinations — in this case, leveraging IMEC’s experience in 3D stacking, growing III-V layers, and solar cell processing, he added.
|IMEC’s mechanically stacked GaAs/Ge cell|