Heterojunction n-Al 0.25 Ga 0.75 As 0.02 Sb 0.98 /p-In 0.16 Ga 0.84 As 0.04 Sb 0.96 thermophotovoltaic (TPV) cells were grown by molecular-beam epitaxy on n-GaSb-substrates. In the spectral range from 1 μm to 2.1 μm these cells, as well as homojunction n-p-In 0.16 Ga 0.84 As 0.04 Sb 0.96 cells, have demonstrated internal quantum efficiencies exceeding 80%, despite about a 200 meV barrier in the conduction band at the heterointerface. Estimation shows that the thermal emission of the electrons photogenerated in p-region over this barrier can provide high efficiency for hetero-cells if the electron recombination time in p-In 0.16 Ga 0.84 As 0.04 Sb 0.96 is longer than 10 ns. Keeping the same internal efficiency as homojunction cells, hetero-cells provide a unique opportunity to decrease the dark forward current and thereby increase open circuit voltage ( V oc ) and fill factor at a given illumination level. It is shown that the decrease of the forward current in hetero-cells is due to the lower recombination rate in n-type wider-bandgap space-charge region and to the suppression of the hole component of the forward current. The improvement in V oc reaches 100% at illumination level equivalent to 1 mA/cm2 and it decreases to 5% at the highest illumination levels (2–3 A/cm2), where the electron current component dominates in both the homo- and heterojunction cells. Values of V oc as high as 310 meV have been obtained for a hetero-cell at illumination levels of 3 A/cm2. Under this condition, the expected fill factor value is about 72% for a hetero-cell with improved series resistance. The heterojunction concept provides excellent prospects for further reduction of the dark forward current in TPV cells.


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    Title :

    A novel approach for the improvement of open circuit voltage and fill factor of InGaAsSb/GaSb thermophotovoltaic cells



    Conference:

    Space technology and applications international forum - 1998 ; 1998 ; Albuquerque,New Mexico (USA)


    Published in:

    AIP Conference Proceedings ; 420 , 1 ; 1400-1409


    Publication date :

    1998-01-15


    Size :

    10 pages





    Type of media :

    Conference paper


    Type of material :

    Electronic Resource


    Language :

    English



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