InGaAs quantum well solar cells are demonstrated with record-high open circuit voltages. Higher open circuit voltages result from the use of a novel structure incorporating a wide band gap barrier layer within a heterojunction depletion region and a step-graded InGaAs well to suppress both non-radiative and radiative recombination. Analysis of the open circuit voltage as a function of well energy suggests these devices are operating in a regime that exceeds traditional radiative limits on the performance of photovoltaic devices.

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Photon absorption, and thus current generation, is hindered in conventional thin-film solar cell designs, including quantum well structures, by the limited path length of incident light passing vertically through the device structure. Optical scattering into lateral waveguide structures provides a physical mechanism to dramatically increase photocurrent generation through in-plane light trapping. However, the insertion of wells of high refractive index material with lower energy gap into the device structure often results in lower voltage operation, and hence lower photovoltaic power conversion efficiency. In this work, we demonstrate that the voltage output of an InGaAs quantum well waveguide photovoltaic device can be increased by employing a novel III-V material structure with an extended wide band gap emitter heterojunction. Analysis of the light IV characteristics from small area test devices reveals that nonradiative recombination components of the underlying dark diode current have been reduced, exposing the limiting radiative recombination component and providing a pathway for realizing solar-electric conversion efficiency of 30% or more in single-junction cells.