Reciprocal Relation Between Intraband Carrier Generation and Interband Recombination at the Heterointerface of Two-Step Photon Up-Conversion Solar Cells

Abstract

Photon up-conversion processes are considered beneficial for energy-conversion devices. The recently proposed two-step photon up-conversion (TPU) solar-cell design employs an intermediate level with a high electron occupation probability. To understand the device physics, a quantitative evaluation of the different current-generation and loss mechanisms is required. In the present work, we use a TPU solar cell containing an $\mathrm{In}\mathrm{As}$/$\mathrm{Ga}\mathrm{As}$ quantum-dot layer located 10 nm in front of an ${\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$/$\mathrm{Ga}\mathrm{As}$ heterointerface. We study the relation between the photocurrent (PC), radiative recombination, and nonradiative recombination as a function of the bias voltage. The radiative interband recombination is evaluated by integrating the photoluminescence (PL) over the range from 1000 to 1300 nm. The magnitudes of the PC and PL signals generated via interband excitation of the $\mathrm{Ga}\mathrm{As}$ layer depend on the bias voltage; a higher forward bias reduces the PC and increases the PL intensity. We verify that, under additional infrared light illumination at 1319 nm, which induces intraband transitions, the PC density increases while the PL intensity significantly decreases. This PC enhancement exhibits a maximum at \ensuremath{-}0.6 V, which reflects the optimum internal electric field strength for maximizing the TPU efficiency.