|Sunlight Concentration Properties of InAs/InAsSb Ultrahigh-Density Quantum-Dot Solar Cells|
|Keisuke Terada1, Takumi Togawa1, Fumiaki Ozeki1, Katsuyoshi Sakamoto1, Tomah Sogabe2,1, Koichi Yamaguchi1,2
1Department of Engineering Science, The University of Electro-Communications, Tokyo, Japan
/2Info-Powered Energy System Research Center, The University of Electro-Communications, Tokyo, Japan
The development of intermediate-band solar cells (IBSCs) using quantum dots (QDs) requires high-density QDs and high sunlight concentration to achieve high power conversion efficiency (PCE). In this study, in-plane ultrahigh-density (UHD) InAs/InAsSb QDs with 1.0×1012 cm-2 were introduced into the GaAs p+-n--n solar cell. Sunlight concentration properties of this InAs/InAsSb UHD-QD cell were measured and were compared with that of a GaAs reference cell without the QDs and a conventional InAs/GaAs QD cell with 2.0×1011 cm-2. In a case of 500-µm-separated comb electrodes, the fill factor (FF) of the GaAs reference cell and the InAs/GaAs QD cell drastically decreased with increasing the sunlight concentration. It could be explained by the lateral voltage drop between the electrodes. For the InAs/InAsSb UHD-QD cell, the degradation of FF under high sunlight concentration was effectively suppressed. It was considered that the lateral carrier transport through the UHD-QD layer played a role in lowering series resistance. The open-circuit voltage (Voc) of all cells increased logarithmically with increasing the sunlight concentration, however, the rate of increase of Voc with respect to the sunlight concentration was largest for the UHD-QD cell. That is, the diode ideal factor (n) was the lowest value (close to 1), and the carrier recombination was effectively suppressed because of the lateral carrier transport through the UHD-QD layer. The PCEs of the GaAs cell and the conventional InAs-QD cell decreased and saturated with increasing the sunlight concentration. In contrast, the PCE of the UHD-QD cell increased with increasing the sunlight concentration. When the sunlight concentration increased more than 4, the PCE of UHD-QD cell exceeded that of the GaAs reference cell.