Three-Bandgap Absolute Quantum Efficiency in GaSb/GaAs Quantum Dot Intermediate Band Solar Cells

Abstract

In this work, we study type-II GaSb/GaAs quantum-dot intermediate band solar cells (IBSCs) by means of quantum efficiency (QE) measurements. We are able, for the first time, to measure an absolute QE which clearly reveals the three characteristic bandgaps of an IBSC; E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> , E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> , and E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> , for which we found the values 1.52, 1.02, and 0.49 eV, respectively, at 9 K. Under monochromatic illumination, QE at the energies E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> and E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> and 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> , respectively. These low values are explained by the lack of efficient mechanisms of completing the second sub-bandgap transition when only monochromatic illumination is used. The addition of a secondary light source (E = 1.32 eV) during the measurements produces an increase in the measured QE at E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> of almost three orders of magnitude.