Nanostructured interfaces for optoelectronic and fluidic applications

Abstract

The research work presented in this dissertation consists of two parts: (1) a comprehensive study about effects of nanostructured interfaces on optoelectronic device performance including both light-absorbing and light-emitting devices based on perovskite materials; (2) the integration of nanostructured surfaces into metal-mesh Janus membranes (MM-JMs) with asymmetric wettability for efficient fog harvesting as a typical application of nanostructures in fluidics.

The first part investigates the ability of nanostructured interfaces to modulate light absorption of perovskite photodetectors (PePDs) and light extraction of perovskite light-emitting diodes (PeLEDs) through light-matter interactions. The perovskite thin films in PePDs are textured with nanostructures via blade-coating the perovskite precursor solution on pre-patterned plastic substrates fabricated by thermal nanoimprint lithography. The nanotexture endows the PePDs with enhanced light absorption while the perovskite film thickness remains unchanged, contributing to amplified detectivity and responsivity. Optical simulations reveal that the properly designed nanostructure results in electromagnetic hotspots in the light-absorbing material and thus increase light absorbance. While insightful optical analysis facilitates understanding and optimization of nanostructured PePDs, there is still a lack of dependable optical simulation methods for PeLEDs with corrugated emissive layers due to the missing information about the location and quantity of the electric dipole light source. A coupled electrical-optical modelling method is developed in this dissertation to address this issue, which integrates electrical modelling with optical calculation to make reliable predictions on device performance of nanostructured PeLEDs. Specifically, the electrical simulation supplies with accurate dipole distribution profiles, enabling the correct setting of light source in the optical analysis to obtain simulation results consistent with experimental observations. Apart from higher efficiencies, optoelectronic devices can also benefit from nanostructured transparent electrodes such as indium tin oxide (ITO) with selectively enhanced optical transmittance and strengthened mechanical flexibility. The morphological and electrical characterization of nanostructured ITO electrodes demonstrates that the introduction of nanostructures retards the crack development to improve the flexibility. Mechanical simulations elucidate the crack growth mechanism altered by the nanostructure, that nanostructures not only rearrange the stress distribution before crack initiation and thus change the onset position of cracks but also inhibit crack propagation with multiple discrete nano-cracks accommodating strains to some degree.

The second part demonstrates the employment of nanostructured surfaces in ultrathin MM-JMs to modify the surface wettability, aiming at improving the atmospheric water collection efficiency. A super-high water collection rate is achieved by the ultrathin hierarchical MM-JM, with the ultrasmall thickness accelerating the water transport speed and the more hydrophobic water-collecting surface decorated with nanostructures fastening the water removal process.