Wide-Bandgap Metamorphic Solar Cells Grown By Molecular Beam Epitaxy

Speaker: 
Stephanie Tomasulo Department of Electrical Engineering, Yale University
Seminar Date: 
Friday, April 25, 2014 - 12:00pm
Location: 
BECTON SEMINAR ROOM See map
Prospect Street
New Haven, CT

For the past decade, III-V-based triple-junction solar cells have held the record for solar cell efficiency by collecting a broad portion of the solar spectrum. As this technology matures, the next step is to increase to 4- 6 junctions in order to collect a larger portion of the spectrum and surpass 50% efficiency. Maximizing efficiency in such designs requires a top junction with bandgap energy (Eg) of 2.0-2.2 eV. Here, we investigate InyGa1-yP (y=0.42-0.30) as an Al-free option that has a direct bandgap in the desired range. However, such compositions are lattice-mismatched to conventional substrates of GaAs and GaP. While mismatched growth introduces extended defects to the cells, it has been shown that minimal efficiency degradation occurs if the threading dislocation density (TDD) can be kept at or below mid-106 cm-2. After establishing high quality starting templates with appropriate TDD, we grew wide-Eg InyGa1-yP solar cells with Eg of 1.93-2.23 eV. Devices on GaAs with Eg of 1.93-2.06 eV possessed high Voc values of 1.37-1.49 V. We then grew novel InyGa1- yP (y=0.18-0.30) solar cells on GaP with Eg=2.12-2.23 eV, representing the widest-Eg InyGa1-yP solar cells to date. However, the Voc values of 1.42-1.46 V indicate significant non-radiative recombination that must be reduced to obtain higher efficiency. The results indicate that with continued growth and device optimization, metamorphic InyGa1-yP will be a promising candidate for the top cell in future 4-6 junction devices.

Host: 
Paul Fleury
Seminar Announcement Brochure: 

It appears your Web browser is not configured to display PDF files. Download adobe Acrobat or click here to download the PDF file.