Optical and electrical characteristics of high-efficiency InGaP/InGaAs/Ge triple-junction solar cell incorporated with InGaAs/GaAs QD layers in the middle cell

This study presents high efficiency InGaP/InGaAs/Ge triple-junction (3-J) solar cells incorporated in the middle cell with layers of InGaAs/GaAs quantum dots (QDs) grown by metal organic chemical vapor deposition to achieve 33.5% conversion efficiency () under one-sun AM 1.5G illumination. We investigated the epitaxial structure and optical and electrical properties of InGaP/InGaAs/Ge 3-J solar cells with and without layers of QDs. We then measured X-ray diffraction (XRD), photoluminescence (PL), optical reflectance, dark and photovoltaic current-voltage (I-V) characteristics, external quantum efficiency (EQE) response, and capacitance-voltage (C-V) as a function of frequency under dark and illuminated conditions at room temperature. The use of 50 pairs of In0.7Ga0.3As (QD)/GaAs (Barrier) QD structure produced an impressive 35% enhancement in EQE at wavelengths of 900-930nm. This resulted in a short-circuit current density of 15.43mA/cm(2), an open-circuit voltage of 2.54V, a fill factor of 84.7%, and a of 33.5%. The 3-J cell with the proposed layers of QDs also demonstrated a 1.0% absolute gain in efficiency compared with a reference cell without QDs. Our XRD, PL, and C-V results revealed that highly stacked InGaAs/GaAs QD layers of high quality can be grown with very little degradation in crystal quality and without the need for strain compensation techniques. Copyright (c) 2015 John Wiley & Sons, Ltd.