Towards high efficiency GaAsP solar cells on (001) GaP/Si

Abstract

We demonstrate metamorphic 1.66 eV GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.77</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.23</sub> solar cells grown by molecular beam epitaxy on exact (001) GaP/Si templates. Cascading such a cell with a 1.1 eV Si junction enables theoretical efficiencies of > 37% under the AM1.5G spectrum. We optimized the initial GaP growth on pseudomorphic GaP/Si templates to promote maximum strain relaxation with minimal nucleation of new threading dislocations. Electron beam-induced current studies of our cells reveal a threading dislocation density (TDD) of 7.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , about 18% lower than our prior results on GaP/Si. The lower TDD has contributed to a low bandgap-voltage offset (W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> =E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> /q-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> ) of 0.55 V, which is 40 mV lower than our previous report, and represents significant progress for GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y</sub> /GaP/Si metamorphic solar cells.