Photocurrent generation by two-step photon absorption with quantum-well superlattice cell

We have assessed a possibility of using multiple quantum wells as an absorber for an intermediate-band solar cell. Photocurrent due to two-step photon absorption was observed using an InGaAs/GaAsP strain-balanced quantum-well superlattice cell, the barrier thickness of which was 3 nm. Upon infrared irradiation with a filtered AM 1.5 light source (λ>;1.4 μm), quantum efficiency was increased by 0.8% at the wavelength range corresponding to the absorption by the quantum wells. Such enhancement in quantum efficiency was not observed either for a conventional quantum-well solar cell with thick (11 nm) barriers or for a GaAs pin cell, suggesting that efficient separation between photo-generated electrons and holes in the superlattice is essential for this achievement of two-step photon absorption. The quantum efficiency of such two-step photocurrent generation can be enhanced by elaborate design of a superlattice layer structure, by which quantum-well superlattice will be a possible active region for an intermediate-band solar cell.