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21 February 2011Dilute nitride multi-quantum well multi-junction design: a route to ultra-efficient photovoltaic devices
The current high-efficiency triple junction (Al)InGaP (1.9eV)/GaAs(1.42eV)/ Ge(0.66eV) design for a solar cell can be
improved upon by the use dilute nitrides to include a sub-cell in the 1eV range. Addition of a small percentage of
nitrogen to III-V semiconductor alloys (such as GaAsN) enables us to achieve the required bandgap, however these bulk
dilute nitride structures suffer from a reduced minority carrier lifetime, decreasing the overall current output. The route
suggested herein is to include dilute nitride multi-quantum wells (with thicknesses much lesser than the minority carrier
diffusion length) within the intrinsic region of a GaAs subcell. Modeling has been done for this structure to obtain the
confined energies of the electrons and holes, as well as the absorption coefficient and thereby the spectral response of the
4-junction cell. The results show that it is possible to achieve with the appropriate current matching, a conversion
efficiency of ~40% under AM0 (1 sun) with up to ~18 mAcm-2 short circuit current.
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Gopi Krishna Vijaya, Andenet Alemu, Alex Freundlich, "Dilute nitride multi-quantum well multi-junction design: a route to ultra-efficient photovoltaic devices," Proc. SPIE 7933, Physics and Simulation of Optoelectronic Devices XIX, 79330G (21 February 2011); https://doi.org/10.1117/12.875239