Abstract
GaInP/GaAs/Ge triple-junction concentrator solar cells with significant efficiency enhancement were demonstrated with antireflective ZnO nanoneedles. The novel nanostructure was attained with a Zn(NO3)2-based solution containing vitamin C. Under one sun AM 1.5G solar spectrum, conversion efficiency of the triple-junction device was improved by 23.7% via broadband improvement in short-circuit currents of 3 sub-cells after the coverage by the nanoneedles with a graded refractive index profile. The efficiency enhancement further went up to 45.8% at 100 suns. The performance boost through the nanoneedles also became increasingly pronounced in the conditions of high incident angles and the cloudy weather, e.g. 220.0% of efficiency enhancement was observed at the incident angle of 60°. These results were attributed to the exceptional broadband omnidirectionality of the antireflective nanoneedles.
Highlights
Promising potential for single- and multi-junction solar cells[22,23]
The ZnO nanostructures synthesized by the hydrothermal process are displayed by the scanning electron microscopy (SEM) images, as shown in the dotted line section of Fig. 1(a)
Since ZnO has a nearly-zero extinction coefficient and the refractive index of around 2.0227, the oxide nanostructure is expected to act as an effective AR medium
Summary
Promising potential for single- and multi-junction solar cells[22,23]. The enhanced omnidirectionality of these nanostructured AR coating can further slash the cost of concentrator solar cells by making them less dependent on the pricy tracking system[7,8]. Since the nanoscale features become less resolvable in the long-wavelength solar spectrum, the nanostructured surface behaves as a transition layer from air to the device, breaking the abrupt transition of refractive index and facilitating optical transmission through the interface[24]. It has been shown that GaAs single-junction solar cells covered with syringe-like ZnO nanorod arrays exhibit a 30% enhancement in conversion efficiency[25]. The excellent omnidirectionality and heat sustainability demonstrated here bring promising potential for multi-junction concentrator solar cells
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