Voltage dependence of two-step photocurrent generation in quantum dot intermediate band solar cells

We studied in detail the voltage dependence of two-step photocurrent generation through a two-step process of absorbing sub-band gap photons of different photon energies in a GaAs/AlGaAs quantum dot Intermediate Band Solar Cell. Our experiments revealed that two-step photocurrent generation is largely dependent on voltage, and exhibits a maximum at -0.3 V. A notable feature is a monotonic decrease in two-step photocurrent in the forward bias region, where the operating point of the solar cell lies. Using a model of rate equations, we extracted the voltage dependence of the individual escape and recombination rates, and found that the decrease in two-step photocurrent in the forward bias region is related to a monotonic increase in recombination rate in the quantum dots with increasing bias. (C) 2014 Elsevier B.V. All rights reserved.