In this contribution, the optical losses and gains attributed to periodic nanohole array electrodes in polymer solar cells are systematically studied. For this, thin gold nanomeshes with hexagonally ordered holes and periodicities (P) ranging from 202 nm to 2560 nm are prepared by colloidal lithography. In combination with two different active layer materials (P3HT:PC61BM and PTB7:PC71BM), the optical properties are correlated with the power conversion efficiency (PCE) of the solar cells. A cavity mode is identified at the absorption edge of the active layer material. The resonance wavelength of this cavity mode is hardly defined by the nanomesh periodicity but rather by the absorption of the photoactive layer. This constitutes a fundamental dilemma when using nanomeshes as ITO replacement. The highest plasmonic enhancement requires small periodicities. This is accompanied by an overall low transmittance and high parasitic absorption losses. Consequently, larger periodicities with a less efficient cavity mode, yet lower absorptive losses were found to yield the highest PCE. Nevertheless, ITO-free solar cells reaching ~77% PCE compared to ITO reference devices are fabricated. Concomitantly, the benefits and drawbacks of this transparent nanomesh electrode are identified, which is of high relevance for future ITO replacement strategies.

Plasmonic nanomeshes: their ambivalent role as transparent electrodes in organic solar cells

This is a review on recent developments in the field of transparent conductive coatings (TCCs) for ITO replacement. The review describes the basic properties of conductive nanomaterials suitable for fabrication of such TCCs (metallic nanoparticles and nanowires, carbon nanotubes and graphene sheets), various methods of patterning the metal nanoparticles with formation of conductive transparent metallic grids, honeycomb structures and 2D arrays of interconnected rings as well as fabrication of TCCs based on graphene and carbon nanotubes. Applications of TCCs in electronic and optoelectronic devices, such as solar cells, electroluminescent and electrochromic devices, touch screens and displays, and transparent EMI shielders, are discussed.

Transparent conductors composed of nanomaterials

Organic light-emitting diodes (OLEDs) are remarkably promising display devices that can function in mechanically flexible configurations on a plastic substrate due to various compelling properties, including organic constituents, ultrathin and simple structure, and low-temperature fabrication. In spite of successful demonstrations of flexible OLEDs, some technical issues of containing relatively thick transparent electrodes made of ceramic materials and an unstable flexible encapsulation system have impeded reaching high levels of reliability and durability toward full commercialization. This review covers recent developments in structure designs for highly durable flexible OLEDs, ranging from alternative transparent electrodes to thin-film encapsulation layers, in which solution concepts for the existing critical issues of flexible OLEDs are addressed. Emerging unusual substrates and their application strategies are additionally introduced to find intimations of future display technologies and hence to disclose nonclassic flexible OLEDs.

A Review of Flexible OLEDs Toward Highly Durable Unusual Displays

Abstract Surface plasmon resonance (SPR) biosensor is a powerful tool for studying the kinetics of biomolecular interactions because they offer unique real-time and label-free measurement capabilities with high detection sensitivity. In the past two decades, SPR technology has been successfully commercialized and its performance has continuously been improved with lots of engineering efforts. In this review, we describe the recent advances in SPR technologies. The developments of SPR technologies focusing on detection speed, sensitivity, and portability are discussed in details. The incorporation of imaging techniques into SPR sensing is emphasized. In addition, our SPR imaging biosensors based on the scanning of wavelength by a solid-state tunable wavelength filter are highlighted. Finally, significant advances of the vast developments in nanotechnology-associated SPR sensing for sensitivity enhancements are also reviewed. It is hoped that this review will provide some insights for researchers who are interested in SPR sensing, and help them develop SPR sensors with better sensitivity and higher throughput.

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Recent advances in surface plasmon resonance imaging: detection speed, sensitivity, and portability

Photonic nanostructures, manipulating and confining light on the nanometer scale, provide new opportunities to improve the efficiency of solar energy conversion. Optical microcavities confine light to small volumes by resonant recirculation. Plasmonic metal nanostructures with surface plasmon resonances can act as antennas to localize optical energy and control the location of charge carrier generation. Photonic crystals can enhance the interaction of light with a semiconductor. Integrated photonic crystals and the plasmonic effects of micro-structural materials may have a superposition effect in controlling light. Some applications and practical examples with respect to improving the efficiency of solar energy conversion with photonic nanostructures have been reviewed, demonstrating how such structures can enhance light absorption and improve the generation and separation of photoexcited charge carriers in photocatalytic degradation, solar water splitting, photovoltaic devices and CO2 photoreduction. Distinct from other published reviews, we simultaneously discuss several different types of photonic nanostructures in order to show the similarities and differences of photonic structures for solar energy conversion. Furthermore, the combination of different types of photonic nanostructures for developing more efficient solar energy conversion systems is discussed and explored.

Photonic nanostructures for solar energy conversion

Interface engineering for efficient charge collection in Cu2O/ZnO heterojunction solar cells with ordered ZnO cavity-like nanopatterns

Large-scale periodic gold network electrodes were fabricated using the developed and versatile nanosphere lithography technique. The fabrication processes, structural characterizations and network formation mechanism were described in detail. An enhanced optical transmission peak was observed from the transmission spectrum, which could be assigned to the extraordinary transmission mediated commonly by (a) localized surface plasmon resonance (LSPR) and (b) surface plasmon polaritons. The effects of film thickness, sphere diameter (periodicity) and reactive ion etching time on their optical and electrical properties were also investigated. By controlling these three independent variables, we could tune the SPR peak position and their light transmission distributions flexibly. Our large-scale continuous gold network can serve as a transparent conductive electrode, while possessing the role of a surface plasmonic resonance component can make it very attractive for potential photo-electric device applications in a range from plasmon-enhanced broadband photovoltaics to SPR-based chemo- and biosensors.

Large-scale fabrication of a continuous gold network for use as a transparent conductive electrode in photo-electronic devices

We present the design and fabrication of large-scale gold nanohole arrays based on the versatile nanosphere lithography technique. The gold nanohole arrays exhibit two surface plasmonic resonance related transmission peaks and show a sensitive response to refractive index. The working wavelength and sensitivity can be tuned by changing the hole diameter and hole depth. A sensitivity of 125 nm/refractive index unit is obtained in the visible region. Our quasi-infinite gold nanohole arrays film can serve as an optical enhancing component while also can serve as a transparent conductive electrode for the opto-electric devices.

Qianqian Li

Papers

Interface engineering for efficient charge collection in Cu2O/ZnO heterojunction solar cells with ordered ZnO cavity-like nanopatterns

Large-scale fabrication of a continuous gold network for use as a transparent conductive electrode in photo-electronic devices

Large-scale fabrication of plasmonic gold nanohole arrays for refractive index sensing at visible region