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Anisotropic emission and photon-recycling in strain-balanced quantum well solar cells

Abstract : Strain-balanced quantum well solar cells (SB-QWSC) extend the photon absorption edge beyond that of bulk GaAs by incorporation of quantum wells in the i-region of a p-in device. Anisotropy arises from a splitting of the valence band due to compressive strain in the quantum wells, suppressing a transition which contributes to emission from the edge of the quantum wells. We have studied both the emission light polarized in the plane perpendicular (TM) to the quantum well which couples exclusively to the light hole transition and the emission polarized in the plane of the quantum wells (TE) which couples mainly to the heavy hole transition. It was found that the spontaneous emission rates TM and TE increase when the quantum wells are deeper. The addition of a distributed Bragg reflector (DBR) can substantially increase the photocurrent while decreasing the radiative recombination current. We have examined the impact of the photon recycling effect on SB-QWSC performance. We have optimized SB-QWSC design to achieve single junction efficiencies above 30%. I. Introduction The strain-balanced quantum well solar cell (SB-QWSC) is a GaAs p-in solar cell with quantum well (QW) layers incorporated into the i-region with InGaAs as well material and GaAsP as barrier material. The compressive strain in the InGaAs QW is matched by tensile strain in GaAsP barriers, overcoming the lattice-mismatch limitation. Using this strain-balancing technique, more than 65 quantum well layers have been grown without dislocations [1, 2]. The purpose of this design is to improve the spectral response of the cell in the energy region below the absorption edge of host material, in order to gain an extra photocurrent and therefore an increment in the short-circuit current. Under solar radiation, a drop in open circuit voltage (V oc) of a SB-QWSC is avoided, due to the inclusion of GaAsP with a higher bandgap than GaAs. This way the addition of short-circuit current (J sc) from the quantum wells leads to an increase of the solar cell conversion efficiency. Photo
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C. Cabrera, J. Rimada, L. Hernandez, James Connolly, A. Enciso, et al.. Anisotropic emission and photon-recycling in strain-balanced quantum well solar cells. Journal of Applied Physics, American Institute of Physics, 2014, 115 (16), pp.164502. ⟨10.1063/1.4873171⟩. ⟨hal-02635172⟩

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