Visible Light Communications (VLC) is a promising new technology which could offer higher data transmission rates than existing broadband RF/microwave wireless technologies. In this paper, we show that a blend of semiconducting polymers can be used to make a broadband, balanced color converter with a very high modulation bandwidth to replace commercial phosphors in hybrid LEDs for visible light communications. The resulting color converter exploits partial Forster energy transfer in a blend of the highly fluorescent green emitter BBEHP-PPV and orange-red emitting MEH-PPV. We quantify the efficiency of the photoinduced energy transfer from BBEHP-PPV to MEH-PPV, and demonstrate modulation bandwidths (electrical-electrical) of ∼200 MHz, which are 40 times higher than commercially available phosphor LEDs. Furthermore, the VLC data rate achieved with this blend using On−Off Keying (OOK) is many times (∼35) higher than that measured with a commercially available phosphor color converter.

at high effi ciency and brightness, but the long excited state lifetime of the phosphors restricts modulation frequency and hence the transmission rate. [ 2 ] The photoluminescence (PL) lifetime typical of the phosphor materials used is on the microsecond timescale, which limits the system bandwidth to a few megahertz (MHz). [ 5,6 ] There is currently a strong need for alternative materials for fast color converters, which can combine high illumination performance with short PL lifetimes. This combination of properties implies that the key fi gure of merit for color converter materials is a short natural radiative lifetime.Organic semiconductors offer many potential advantages as a novel color converter for VLC due to their visible band gaps, short radiative lifetime, and high photoluminescence quantum yield (PLQY). They have been applied as a color converter in vacuum-evaporated OLEDs [ 7 ] and we recently demonstrated the use of a yellow emitting conjugated polymer as a fast additive color converter for VLC. [ 8 ] To achieve high-quality sources for good color rendering, suitable materials with green or red PL are also needed to mix with the blue emission from the LED.In this paper, we explore the potential of star-shaped organic semiconductors based on boron dipyrromethene (BODIPY) cores as red-conversion material for LEDs in VLC applications. We selected BODIPY as the core of the molecules because it is a red emitter of known stability. [ 10 ] We investigate the infl uence of different substitution patterns of the BODIPY core with oligofl uorene arms, leading to different shapes of the molecules (T-and Y-shaped). In particular, we study the photophysical properties of these materials, measure their modulation bandwidth, and demonstrate their potential for VLC by achieving a data rate ten times higher than measured with a conventional phosphor color converter. BODIPY (4,4-difuoro-4-bora-3a,4a-diaza-s-indacene)-based organic semiconductors have attracted signifi cant attention due to their electronic and optical properties with narrow absorption and emission bands, high PLQY, and good thermal stability. [ 9 ] Furthermore, they are solution-processable unlike previous red organic color converter materials. [ 7 ] They have been applied in many fi elds such as biology, [ 11 ] medicine, [ 12 ] solar energy, [ 13 ] and lasers [ 10 ] . BODIPYs can have red emission with lifetimes in the range of a few nanoseconds and can strongly absorb in the range of the GaN LEDs electroluminescence (≈450 nm) making them suitable candidates to be used in three-component additive coloration for VLC.

Organic optoelectronic devices combine high-performance, simple fabrication and distinctive form factors. They are widely integrated in smart devices and wearables as flexible, high pixel density organic light emitting diode (OLED) displays, and may be scaled to large area by rollto-roll printing for lightweight solar power systems. Exceptionally thin and flexible organic devices may enable future integrated bioelectronics and security features. However, as a result of their low charge mobility, these are generally thought to be slow devices with microsecond response times, thereby limiting their full scope of potential applications. By investigating the factors limiting their bandwidth and overcoming them, we demonstrate here exceptionally fast OLEDs with bandwidths in the hundreds of MHz range. This opens up a wide range of potential applications in spectroscopy, communications, sensing and optical ranging. As an illustration of this, we have demonstrated visible light communication using OLEDs with data rates exceeding 1 gigabit per second.

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We show that organic photovoltaics (OPVs) are suitable for high-speed optical wireless data receivers that can also harvest power. In addition, these OPVs are of particular interest for indoor applications, as their bandgap is larger than that of silicon, leading to better matching to the spectrum of artificial light. By selecting a suitable combination of a narrow bandgap donor polymer and a nonfullerene acceptor, stable OPVs are fabricated with a power conversion efficiency of 8.8% under 1 Sun and 14% under indoor lighting conditions. In an optical wireless communication experiment, a data rate of 363 Mb/s and a simultaneous harvested power of 10.9 mW are achieved in a 4-by-4 multiple-input multiple-output (MIMO) setup that consists of four laser diodes, each transmitting 56 mW optical power and four OPV cells on a single panel as receivers at a distance of 40 cm. This result is the highest reported data rate using OPVs as data receivers and energy harvesters. This finding may be relevant to future mobile communication applications because it enables enhanced wireless data communication performance while prolonging the battery life in a mobile device.

This letter presents a novel technique to achieve high-speed visible light communication (VLC) using white light generated by a blue GaN µLED and a yellow fluorescent copolymer. We generated white light suitable for room illumination by optimising the ratio between the blue electroluminescence of the µLED and yellow photoluminescence of the copolymer colour converter. Taking advantage of the components' high bandwidth, we demonstrated 1.68 Gb/s at a distances of 3 cm (at 240 lx illumination). To the best of our knowledge, This is the fastest white light VLC results using a single blue LED/colour converter combination.

Organic semiconductors are an important class of optoelectronic material that are widely studied because of the scope for tuning their properties by tuning their chemical structure, and simple fabrication to make flexible films and devices. Although most effort has focused on developing displays and lighting from these materials, their distinctive properties also make them of interest for visible light communications (VLCs). This article explains how their properties make them suitable for VLC and reviews the main uses that have been explored. On the transmitter side, record white VLC communication has been achieved by using organic semiconductors as colour converters, while direct modulation of organic light-emitting diodes is also possible and could be of interest for display-to-display communication. On the receiver side, organic solar cells can be used to harvest power and data simultaneously, and fluorescent antennas enable fast and sensitive receivers with large field of view. This article is part of the theme issue ‘Optical wireless communication’.

Copyright © and Moral Rights are retained by the author(s) and/ or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s). The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders.This document is the author's post-print version, incorporating any revisions agreed during the peer-review process. Some differences between the published version and this version CURVE is the Institutional Repository for Coventry University may remain and you are advised to consult the published version if you wish to cite from it. They are broadband visible emitters whose emission can be tuned by changing the chemical structure, and can have high photoluminescent quantum yields (PLQY) of up to 90% in undiluted films 5,9,10 . This combined with simple and low cost solution processing techniques make them attractive materials for optoelectronic devices.An emerging application area for organic semiconductors is in the field of visible light communications (VLC).Increasing demand for wireless communications has driven research into improving data transmission concepts 3The oligofluorene arms have a substituent effect on the BODIPY core and therefore the increase in the number of arms influences the photophysics of the material.Solid state colour converters were spin-coated from solution to make thin films on quartz substrates for the photophysical studies. Films of thickness ca. 100 nm were deposited from solutions at concentrations of 10 and 20 mg/ml for photophysical and communications measurements respectively. These were spin-coated at 1500 rpm for 60 seconds. Figure 1 (bottom) shows the absorption and PL spectra of the films for each molecule. The absorption spectra show peaks at 450 and 620 nm for Y1; 350, 473 and 626 nm for Y2; 350, 477 and 625nm for Y3; and 366, 480 and 625nm for Y4. The absorption band below 400 nm is attributed to the fluorene arms and increases in intensity with arm length. Y1 has a peak in absorption at 450 nm matching well the emission of the blue LEDs used for lighting, and this feature shifts slightly to longer wavelengths for longer arms as seen in Figure 1. The peak emission wavelengths were in the red region of the spectrum, 663, 679, 682, 682 nm for Y1, Y2, Y3and Y4 respectively. The red PL emission comes from an extended conjugation across the BODIPY core and adjacent fluorene units as has been described previously 24 . The bathochromic shift from Y1 to Y2 is also evident in solution 23,24 and indicates that there is a further delocalisation of the excited state across the BODIPY and neighbouring fluorene units.Time-resolved fluorescence measurements were conducted using the time correlated single photon counting (TCSPC) technique, exciting the materials at 375 nm and detecting at the corresponding peak PL...