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

Abstract

AbstractThis 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 (η) under one‐sun AM 1.5 G 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 900–930 nm. This resulted in a short‐circuit current density of 15.43 mA/cm2, an open‐circuit voltage of 2.54 V, a fill factor of 84.7%, and a η 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 © 2015 John Wiley & Sons, Ltd.