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Significance Although graphene shows great promise as a generational flexible transparent electrode (FTE), its development has been severely limited by the intrinsic trade-off between electrical conductance and transparency with the performance metrics inferior to that of the state-of-the-art ITO electrodes. We report a straightforward approach to break previous limit in graphene FTEs and yield an unprecedented performance that rivals the best commercial ITO electrode. Using the tailored monolayer graphene FTE, we further demonstrate high-performance flexible green organic light-emitting diodes (OLEDs) with the efficiencies outperforming all comparable flexible OLEDs and surpassing that with rigid ITO anode. This simple strategy will boost the development of next-generation flexible optoelectronics beyond the dominant rigid platforms., Graphene has emerged as an attractive candidate for flexible transparent electrode (FTE) for a new generation of flexible optoelectronics. Despite tremendous potential and broad earlier interest, the promise of graphene FTE has been plagued by the intrinsic trade-off between electrical conductance and transparency with a figure of merit (σDC/σOp) considerably lower than that of the state-of-the-art ITO electrodes (σDC/σOp

In this review, the primary focus is the recent advances in the development of freestanding inorganic crystalline semiconductors and their manipulation technology for flexible optoelectronic applications. We firstly cover the details of the growth and processing techniques of freestanding inorganic crystalline semiconductors in various dimensions and their material property under strain condition. Finally, fabrication processes and opto-electrical properties of flexible optoelectronics are introduced. Future research directions are also discussed, including further enhancement of device performance, building more types of optoelectronic devices on flexible substrates, and process integration for the advanced optoelectronic circuits and systems. Nanyang Technological University Published version This work was supported by the National Science Foundation (Grant number: ECCS-1809077) and partially by KSEA Young Investigator Grants by Korean American Scientists and Engineers Association and the Start-up Grant (PI: Prof. Munho, Kim) of Nanyang Technological University (NTU), Singapore.

Top-emitting OLEDs (TOLEDs) represent a promising technology for the development of next-generation flexible and rollable displays, thanks to their improved light outcoupling and their compatibility with opaque substrates. Metal thin films are the most used electrodes for the manufacturing of TOLEDs, but they show poor resistance to mechanical deformation, which compromises the long-term durability of flexible devices. This paper reports the exploitation of a dielectric mirror (DBR) based on seven pairs of TiO2 and SiO2 combined with a polymeric electrode as an alternative to the bottom metal electrode in flexible TOLEDs. The DBR showed a maximum reflectivity of 99.9% at about 550 nm, and a stop-band width of about 200 nm. The reflectivity remained unchanged after bending and treatment with water and solvents. Green TOLED devices were fabricated on top of DBRs, and demonstrated good stability in terms of electro-optical and colorimetric characteristics, according to varying viewing angles. These results demonstrate that the combination of the flexible DBR with the polymeric anode is an interesting strategy for improving the durability of flexible TOLEDs for display applications, implemented on different kinds of free-standing ultra-thin substrates.

Controlled growth of heterostructured nanowires and mechanisms of their formation have been actively studied during the last decades due to perspectives of their implementation. Here, we report on the self-catalyzed growth of axially heterostructured GaPN/GaP nanowires on Si(111) by plasma-assisted molecular beam epitaxy. Nanowire composition and structural properties were examined by means of Raman microspectroscopy and transmission electron microscopy. To study the optical properties of the synthesized nanoheterostructures, the nanowire array was embedded into the silicone rubber membrane and further released from the growth substrate. The reported approach allows us to study the nanowire optical properties avoiding the response from the parasitically grown island layer. Photoluminescence and Raman studies reveal different nitrogen content in nanowires and parasitic island layer. The effect is discussed in terms of the difference in vapor solid and vapor liquid solid growth mechanisms. Photoluminescence studies at low temperature (5K) demonstrate the transition to the quasi-direct gap in the nanowires typical for diluted nitrides with low N-content. The bright room temperature photoluminescent response demonstrates the potential application of nanowire/polymer matrix in flexible optoelectronic devices.

A path to further increase the power conversion efficiency of perovskite solar cells is maximizing sunlight absorption by using patterned substrates with enhanced light trapping capabilities. However, to be competitive with traditional solar cells, especially in niche markets, low cost texturing methods need to be developed. In this work, we present as a proof‐of‐concept a roll‐to‐roll hot embossing method to pattern flexible PET foils. The cylindrical mold for the embossing process was structured with periodic grooves by picosecond Direct Laser Interference Patterning (DLIP). The optical characterization of the textured PET shows a tenfold increase in the haze factor (diffuse to global transmittance ratio) compared to flat PET due to the high intensity diffracted beams. Flexible triple cation perovskite cells deposited onto these patterned substrates show on average an 8 % (relative) higher efficiency than similar devices deposited on a reference flat PET substrate. This enhancement can be attributed to the increase in the light trapping provided by the textured substrate. Finally, a cost analysis model shows that the additional cost of integrating the proposed hot embossing step into a perovskite solar module manufacturing facility would represent less than 0.35 % of the initial fabrication cost. Fil: Soldera, Marcos Maximiliano. Technische Universität Dresden; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentina Fil: Wang, Qiong. Helmholtz Zentrum Berlin für Materialien und Energie; Alemania Fil: Soldera, Flavio Andres. Universitat Saarland; Alemania Fil: Lang, Valentin. Technische Universität Dresden; Alemania Fil: Abate, Antonio. Helmholtz Zentrum Berlin für Materialien und Energie; Alemania Fil: Lasagni, Andrés Fabián. Technische Universität Dresden; Alemania. Fraunhofer Institute For Material And Beam Technology; Alemania

Quasi-one-dimensional nanoribbons (NRs) are promising candidate materials for flexible optoelectronics with high device density. The optical properties of nanomaterials are strongly influenced by excitons, and it is important for flexible devices to explore how excitons behave under strain. In this work, we investigate the electronic and excitonic properties of bent black phosphorus (BP) NRs via density-functional theory and many-body Green's function methods. We find that inhomogeneous strain fields affect not only the first excitonic energy and thus the optical gap, but also the spatial distribution of the excitons. In particular, excitonic funnels can occur in bent black phosphorus nanoribbons (BPNRs), which drive higher-energy excitons toward lower energy locations. The funnels can be effectively tuned by the intensity and sign (compressed to tensile) of the strain field. Another critical factor is anisotropy: the funnel effect is much more pronounced in armchair BPNRs than in zigzag BPNRs. In addition, we find that the excitonic funnel effect in two-dimensional monolayer BP differs from that in multilayer BP films.

We report the pronounced effects of oxygen growth pressure (0.13 Pa–40 Pa) on the surface morphology, hydrophobicity, structural, optical and electrical properties of ZnO and aluminium-doped ZnO (AZO) thin films deposited by room temperature pulsed-laser deposition on the low water-absorbing polymer Zeonor. Significant changes were observed for oxygen growth pressures below ~ 10 Pa. In this pressure range, the morphology changed from nanocrystalline to that of a continuous film with a shift of the growth orientation of the crystalline fraction of the deposit from c-plane to m-plane. The appearance of valley-shaped surface cracks caused a significant increase of rms surface roughness, reduced hydrophobicity and shift to hydrophilicity at 0.13 Pa. The visible optical transmittance of the film reduced from an average of 90% to 65% and the orange/red deep level emission was quenched. The electrical properties showed decreasing resistivities (105 Ω cm to 10− 3 Ω cm) and Hall mobilities (35 cm2/V-s to 3 cm2/V-s) and increasing carrier concentrations (1011 cm− 3 to 1021 cm− 3). These significant changes of the films physical characteristics were related to the morphological and structural changes induced by the change of oxygen growth pressure. The observed effects are interesting for applications in flexible optoelectronics and briefly discussed in this context.

Heterogeneous integration between silicon (Si), III-V group material and Germanium (Ge) is highly desirable to achieve monolithic photonic circuits. Transfer-printing and stacking between different semiconductor nanomembranes (NMs) enables more versatile combinations to realize high-performance light-emitting and photodetecting devices. In this paper, lasers, including vertical and edge-emitting structures, flexible light-emitting diode, photodetectors at visible and infrared wavelengths, as well as flexible photodetectors, are reviewed to demonstrate that the transfer-printed semiconductor nanomembrane stacked layers have a large variety of applications in integrated optoelectronic systems.

Cataloged from PDF version of article. Proof-of-concept, first metal-semiconductor-metal ultraviolet photodetectors based on nanocrystalline gallium nitride (GaN) layers grown by low-temperature hollow-cathode plasma-assisted atomic layer deposition are demonstrated. Electrical and optical characteristics of the fabricated devices are investigated. Dark current values as low as 14 pA at a 30 V reverse bias are obtained. Fabricated devices exhibit a 15× UV/VIS rejection ratio based on photoresponsivity values at 200 nm (UV) and 390 nm (VIS) wavelengths. These devices can offer a promising alternative for flexible optoelectronics and the complementary metal oxide semiconductor integration of such devices. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE).