ZnSe: A Material to Improve Efficiencies for Current Solar Cell Multi-junction Stacks
Kyle H. Montgomery, Jong-Hyeok Jeon, Jerry M. Woodall, Qiang Zhang, Maria C. Tamargo
MRS Spring Meeting, San Francisco, CA, 2009.
Extended Abstract (pdf)
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Our current work focuses on the development of a high band gap solar cell based on the II-VI compound semiconductor ZnSe. Given that ZnSe is lattice-matched to GaAs, we are able to grow epitaxial layers by molecular beam epitaxy (MBE). Our particular growth is at 300°C on GaAs (100) substrates. The bandgap of ZnSe at room temperature is 2.7eV, which is a higher than the optimal band gap (2.4 eV) for 4 – 6 junction solar cells, but the blue response is sufficient to generate a noticeable increase in total efficiency without significantly degrading the response of the GaInP stack component cell. With a high absorption coefficient of about 105 cm-1 at the band edge, a total thickness of 500nm will be sufficient to absorb 99% of incident light. Due to difficulties in ohmic contact formation to p-type ZnSe, we have chosen to grow an n-type ZnSe layer over a p-type ZnSe layer, which is grown on a p-type GaAs substrate. Based on literature, we have chosen Au/Zn/Au contacts to the p-type GaAs and Ti/Pt/Au contacts to n-type ZnSe. As we have shown by x-ray diffraction and photoluminescence measurements, we are able to obtain high quality ZnSe with minimal defects. We will present our latest measurements of open circuit voltage, short circuit current, and external quantum efficiency.
solar, multijunctions, ZnSe, wide bandgap
K. H. Montgomery, J-H. Jeon, J. M. Woodall, Q. Zhang, and M. C. Tamargo. “ZnSe: A Material to Improve Efficiencies for Current Solar Cell Multi-junction Stacks.” presented at the Materials Research Society (MRS) Spring Meeting, San Francisco, CA, 2009.