Polymer chain distribution reorganization for improving the power conversion efficiency of polymer solar cells

We investigate the influence of the post solvent evaporation time delay on the performance of polymer solar cell (PSC) devices employing a bulk heterojunction photoactive polymer layer of regioregular poly(3-hexylthiophene) as electron donor and polymer [6,6]-thienylC61 butyric acid methyl ester as an electron acceptor. Characterization of the fabricated solar cell devices clearly demonstrates balanced transport of electrons and holes in the blend and confirms increased surface roughness and crystallinity of the films when post solvent evaporation time delay is optimised. An optimum device performance is obtained with 72 hours of post solvent evaporation time delay, achieving a power conversion efficiency of 4.1%, which is 0.9% higher than similar devices made without enough time for polymer-chaindistribution reorganization

High contrast tandem organic light emitting devices employing transparent intermediate nano metal layers and a phase shifting layer

A high contrast-ratio organic light emitting device (OLED) is proposed and experimentally demonstrated. The OLED is implemented by stacking two organic phase tuning layers between composite metal layers and optimizing their thicknesses. Such a tandem device can increase the current efficiency by 120%, and reduce the operating voltage by 1.1 V, in comparison to conventional high contrast OLEDs. Measured reflection spectra validate the high-contrast capability of the OLED, and demonstrate experimentally an average reflectivity of 6% under ambient light illumination. This is the lowest reflectivity reported to date for OLEDs employing organic phase tuning layers

Simultaneous monitoring of singlet and triplet exciton variations in solid organic semiconductors driven by an external static magnetic field

The research field of organic spintronics has remarkably and rapidly become a promising research area for delivering a range of high-performance devices, such as magnetic-field sensors, spin valves, and magnetically modulated organic light emitting devices (OLEDs). Plenty of microscopic physical and chemical models based on exciton or charge interactions have been proposed to explain organic magneto-optoelectronic phenomena. However, the simultaneous observation of singlet- and triplet-exciton variations in an external magnetic field is still unfeasible, preventing a thorough theoretical description of the spin dynamics in organic semiconductors. Here, we show that we can simultaneously observe variations of singlet excitons and triplet excitons in an external magnetic field, by designing an OLED structure employing a singlet-exciton filtering and detection layer in conjunction with a separate triplet-exciton detection layer. This OLED structure enables the observation of a Lorentzian and a non-Lorentzian line-shape magnetoresponse for singlet excitons and triplet excitons, respectively

High-contrast tandem organic light-emitting devices employing semitransparent intermediate layers of LiF/Al/C60

The use of a black cathode with a metal-organic-metal structure is an attractive approach to achieving a high-contrast organic light-emitting device (OLED) for future-generation flat panel displays. However, the large reduction in OLED power efficiency is currently restricting the use of the black cathode for industrial applications. In this paper, a high-contrast, high-efficiency tandem OLED employing a black cathode is proposed and experimentally demonstrated. The OLED is implemented by stacking two organic phase tuning layers between a composite intermediate layer of LiF/Al/C60 and LiF/Al and optimizing their thicknesses. Electroluminescence spectra and brightness-current measurement reveal that the phase tuning layer emits photons. Such a tandem device can increase the current efficiency by 110% and reduce the operating voltage by 1.3 V, in comparison to the conventional high-contrast OLED. Measured reflection spectra validate the high-contrast capability of the OLED and demonstrate experimentally an average reflectance of 5.9% in the visible range from 400 to 750 nm, which is much lower than 20.3% for the conventional high-contrast OLED

Room-temperature spin-polarized organic light-emitting diodes with a single ferromagnetic electrode

In this paper, we demonstrate the concept of a room-temperature spin-polarized organic light-emitting diode (Spin-OLED) structure based on (i) the deposition of an ultra-thin p-type organic buffer layer on the surface of the ferromagnetic electrode of the Spin-OLED and (ii) the use of oxygen plasma treatment to modify the surface of that electrode. Experimental results demonstrate that the brightness of the developed Spin-OLED can be increased by 110% and that a magneto-electroluminescence of 12% can be attained for a 150 mT in-plane magnetic field, at room temperature. This is attributed to enhanced hole and room-temperature spin-polarized injection from the ferromagnetic electrode, respectively

High contrast tandem organic light emitting devices

A high contrast-ratio organic light emitting device (OLED) is proposed and experimentally demonstrated. The OLED is implemented by stacking two organic phase tuning (PT) layers between composite metal layers and optimizing their thicknesses. Such a tandem device can increase the current efficiency by 98%, and reduce the operating voltage by 1.04 V, in comparison to conventional high contrast OLEDs. Measured reflection spectra validate the high-contrast capability of the OLED, and demonstrate experimentally an average reflectivity of 6% under ambient light illumination. This is the lowest reflectivity reported to date for OLEDs employing organic phase tuning layers

Plasmonic Nanomaterials for Optical Sensor and Energy Storage and Transfer

Nanomaterials including noble metal nanomaterials and some metal oxide nanomaterials exhibit very strong lightmatter interactions under resonant excitation. Very large absorption and scattering at the localized wavelengths can been achieved. Because of their attractive optical properties, optical NPs and nanostructures have been commonly used in various fields from nanophotonics, analytical chemistry, biotechnology, and information storage to energy applications including photovoltaics and photocatalysisphotocatalysi

Magnetic field-modulated exciton generation in organic semiconductors: an intermolecular quantum correlation effect

Magnetoelectroluminescence (MEL) of organic semiconductor has been experimentally tuned by adopting blended emitting layer consisting of both hole and electron transporting materials. A theoretical model considering intermolecular quantum correlation is proposed to demonstrate two fundamental issues: (1) two mechanisms, spin scattering and spin mixing, dominate the two different steps respectively in the process of the magnetic field modulated generation of exciton; (2) the hopping rate of carriers determines the intensity of MEL. Calculation successfully predicts the increase of singlet excitons in low field with little change of triplet exciton population.Comment: 16 pages, 4 figure

Giant magneto-birefringence effect and tuneable colouration of 2D crystals' suspensions

One of the long sought-after goals in manipulation of light through light-matter interactions is the realization of magnetic-field-tuneable colouration, so-called magneto-chromatic effect, which holds great promise for optical, biochemical and medical applications due to its contactless and non-invasive nature. This goal can be achieved by magnetic-field controlled birefringence, where colours are produced by the interference between phase-retarded components of transmitted polarised light. Thus far birefringence-tuneable coloration has been demonstrated using electric field, material chirality and mechanical strain but magnetic field control remained elusive due to either weak magneto-optical response of transparent media or low transmittance to visible light of magnetically responsive media, such as ferrofluids. Here we demonstrate magnetically tuneable colouration of aqueous suspensions of two-dimensional cobalt-doped titanium oxide which exhibit an anomalously large magneto-birefringence effect. The colour of the suspensions can be tuned over more than two wavelength cycles in the visible range by moderate magnetic fields below 0.8 T. We show that such giant magneto-chromatic response is due to particularly large phase retardation (>3 pi) of the polarised light, which in its turn is a combined result of a large Cotton-Mouton coefficient (three orders of magnitude larger than for known liquid crystals), relatively high saturation birefringence (delta n = 2 x 10^-4) and high transparency of our suspensions to visible light. The work opens a new avenue to achieve tuneable colouration through engineered magnetic birefringence and can readily be extended to other magnetic 2D nanocrystals. The demonstrated effect can be used in a variety of magneto-optical applications, including magnetic field sensors, wavelength-tuneable optical filters and see-through printing.Comment: 10 pages, 4 figures. Nature Communications, 2020, Accepte