Experimental measurement of restricted radiative emission in quantum well solar cells

We present the first experimental data showing a restriction of the radiative recombination in strain-balanced quantum well solar cells. This arises due to the combined effects of quantum confinement and strain splitting the valence band in the quantum wells into heavy and light hole sub-bands. Under increasing compressive strain, the light hole sub-band moves further in energy from the conduction band, suppressing the conduction-band-to-light-hole recombination which couples primarily to photons emitted in the plane of the quantum wells. As a solar cell fundamentally need only emit in the angular range of absorption, the strain-balanced quantum well solar cell operates more closely to this optimal regime than a bulk solar cell.