Abstract
The tantalizing prospect of harnessing the unique properties of graphene crumpled nanostructures continues to fuel tremendous interest in energy storage and harvesting applications. However, the paper ball-like, hard texture, and closed-sphere morphology of current 3D graphitic nanostructure production not only constricts the conductive pathways but also limits the accessible surface area. Here, we report new insights into electrohydrodynamically-generated droplets as colloidal nanoreactors in that the stimuli-responsive nature of reduced graphene oxide can lead to the formation of crumpled nanostructures with a combination of open structures and doubly curved, saddle-shaped edges. In particular, the crumpled nanostructures dynamically adapt to non-spherical, polyhedral shapes under continuous deposition, ultimately assembling into foam-like microstructures with a highly accessible surface area and spatially interconnected transport pathways. The implementation of such crumpled nanostructures as three-dimensional rear contacts for solar conversion applications realize benefits of a high aspect ratio, electrically addressable and energetically favorable interfaces, and substantial enhancement of both short-circuit currents and fill-factors compared to those made of planar graphene counterparts. Further, the 3D crumpled nanostructures may shed lights onto the development of effective electrocatalytic electrodes due to their open structure that simultaneously allows for efficient water flow and hydrogen escape.
Highlights
Made possible by the facile aerosol assembly
We demonstrate that electrostatically charged droplets generated through the scalable ElectroHydroDynamic (EHD) process can be used as freestanding nanoreactors to enable the formation of 3D crumpled nanostructures
The synergistic combination of electrostatic stabilization, and fission processes substantially suppresses the aggregation of reduced graphene oxide (rGO) sheets, preserving the materials properties that only exhibit in single layer configurations
Summary
Nanostructures for Efficient Solar received:19May2016 accepted: 14 November 2016. Hidetaka Ishihara1,*, Yen-Chang Chen1,2,*, Nicholas De Marco[1], Oliver Lin[2], Chih-Meng Huang[3], Vipawee Limsakoune[1], Yi-Chia Chou[3], Yang Yang4,5 & Vincent Tung[1]. The dimensions of crumpled nanostructures and the degree of crumpling as indicated by the density of ridges and vertices remained largely the same regardless of the increased concentrations of rGO in EHD-generated droplets This can be attributed to the synergistic effects of electrostatic charges and droplet fission that effectively suppresses the formation of overlapping sheets before dimensional transition takes place, reducing the possibility of forming thick rGO stacks that are known to be stiffer and harder to crumple. A combination of deposition time (~30 minutes), concentration of rGO (50 μg/mL, pH = 11), electric field (0.575 kV/cm), surrounding temperature of 155 °C and flow rate (4 μL/min) was found to deliver the most optimized coverage over the entire CFEs. Figure 4a,b together present a series of HRSEM images that demonstrate the uniformity, fidelity and reproducibility of the EHD deposition at different length scales as over 95% of the CFE (spraying area of 1 cm × 1 cm) is coated with crumpled nanostructures. The 3D crumpled nanostructures may shed lights onto the development of effective electrocatalytic electrodes due to their open structure that simultaneously allows for efficient water flow and hydrogen escape[18]
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