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The design, fabrication, and characterization of optically switchable organic light-emitting diodes (OSOLEDs) based on the combination of the commercially available light-emitting polymer poly(9,9′-dioctylfluorene-alt-benzothiadiazole), F8BT, doped with a diarylethene derivative is reported. The photochromic activity of the dopant in the solid state has been investigated both via UV/vis absorption and photoluminescence spectroscopy, whereas the morphology of different blends is investigated via atomic force microscopy. OSOLEDs embedding dopant loadings of 1, 5, and 10 wt% exhibit optical responsivity with a maximum reversible optical threshold voltage shift of 4 V. The best performing devices containing 5 wt% dopant show a maximum current density and luminance ON/OFF ratio of ≈20 and ≈90, respectively. For the first time, the impact of the diarylethene isomerization on hole and electron transport has been decoupled and directly investigated, via the design, fabrication, and characterization of single-carrier switchable devices based on the same blends. Not only do these results confirm the photo-responsive trapping activity of the diarylethenes on both charge carriers, but they also demonstrate its asymmetry, with a predominant effect on electron transport that is over 3.4 times larger as compared to hole transport.

Visible light communication (VLC) is a wireless technology that relies on optical intensity modulation and is potentially a game changer for internet-of-things (IoT) connectivity. However, VLC is hindered by the low penetration depth of visible light in non-transparent media. One solution is to extend operation into the “nearly (in)visible” near-infrared (NIR, 700–1000 nm) region, thus also enabling VLC in photonic bio-applications, considering the biological tissue NIR semitransparency, while conveniently retaining vestigial red emission to help check the link operativity by simple eye inspection. Here, we report new far-red/NIR organic light-emitting diodes (OLEDs) with a 650–800 nm emission range and external quantum efficiencies among the highest reported in this spectral range (>2.7%, with maximum radiance and luminance of 3.5 mW/cm2 and 260 cd/m2, respectively). With these OLEDs, we then demonstrate a “real-time” VLC setup achieving a data rate of 2.2 Mb/s, which satisfies the requirements for IoT and biosensing applications. These are the highest rates ever reported for an online unequalised VLC link based on solution-processed OLEDs.

This paper investigates the use of organic polymer light emitting diodes (PLEDs) for the use in visible light communications (VLC). We prepared blue and green emitting PLEDs using commercial light-emitting polymers, and then characterised the device emission (spectrum and power), and extracted their circuit parameters for their electrical equivalent model for driving with small signals. In addition, we characterised the bandwidth (oldsymbol{B-{mod}}) of the devices over a period of continuous driving (∼ 4 h) and found that for the blue PLEDs the oldsymbol{B-{mod}} decreased from an initial 750 kHz to a steady state of ∼250 kHz. The green-emitting devices were found to benefit from an extended oldsymbol{B-{mod}} of ∼1.5 MHz at the beginning of the test, which then stabilised to ∼850 kHz. Furthermore, with the addition of a first order RC filter we show that, the steady state oldsymbol{B-{mod}} of the blue PLED cane be increased by a factor of ∼3, thus allowing > 1 Mbps non-return to zero on-off keying (NRZ OOK) data transmission in a complete VLC system.

Harnessing cost-efficient printable semiconductor materials as near-infrared (NIR) emitters in light-emitting diodes (LEDs) is extremely attractive for sensing and diagnostics, telecommunications, and biomedical sciences. However, the most efficient NIR LEDs suitable for printable electronics rely on emissive materials containing precious transition metal ions (such as platinum), which have triggered concerns about their poor biocompatibility and sustainability. Here, we review and highlight the latest progress in NIR LEDs based on non-toxic and low-cost functional materials suitable for solution-processing deposition. Different approaches to achieve NIR emission from organic and hybrid materials are discussed, with particular focus on fluorescent and exciplex-forming host-guest systems, thermally activated delayed fluorescent molecules, aggregation-induced emission fluorophores, as well as lead-free perovskites. Alternative strategies leveraging photonic microcavity effects and surface plasmon resonances to enhance the emission of such materials in the NIR are also presented. Finally, an outlook for critical challenges and opportunities of non-toxic NIR LEDs is provided.

Porous silicon (PSi) is a promising material for future integrated nanophotonics when coupled with guest emitters, still facing challenges in terms of homogenous distribution and nanometric thickness of the emitter coating within the silicon nanostructure. Herein, it is shown that the nanopore surface of a porous silicon oxide (PSiO2) microcavity (MC) can be conformally coated with a uniform nm-thick layer of a cationic light-emitting polyelectrolyte, e.g., poly(allylamine hydrochloride) labeled with Rhodamine B (PAH-RhoB), leveraging the self-tuned electrostatic interaction of the positively-charged PAH-RhoB polymer and negatively-charged PSiO2 surface. It is found that the emission of PAH-RhoB in the PSiO2 MC is enhanced (≈2.5×) and narrowed (≈30×) at the resonant wavelength, compared with that of PAH-RhoB in a non-resonant PSiO2 reference structure. The time-resolved photoluminescence analysis highlights a shortening (≈20%) of the PAH-RhoB emission lifetime in the PSiO2 MC at the resonance versus off-resonance wavelengths, and with respect to the reference structure, thereby proving a significant variation of the radiative decay rate. Remarkably, an experimental Purcell factor Fp = 2.82 is achieved. This is further confirmed by the enhancement of the photoluminescence quantum yield of the PAH-RhoB in the PSiO2 MC with respect to the reference structure. Application of the electrostatic nanoassembling approach to other emitting dyes, nanomaterials, and nanophotonic systems is envisaged.

The energy gap law (EG-law) and aggregation quenching are the main limitations to overcome in the design of near-infrared (NIR) organic emitters. Here, we achieve unprecedented results by synergistically addressing both of these limitations. First, we propose porphyrin oligomers with increasing length to attenuate the effects of the EG -law by suppressing the non-radiative rate growth, and to increase the radiative rate via enhancement of the oscillator strength. Second, we design side chains to suppress aggregation quenching. We find that the logarithmic rate of variation in the non-radiative rate vs. EG is suppressed by an order of magnitude with respect to previous studies, and we complement this breakthrough by demonstrating organic light-emitting diodes with an average external quantum efficiency of ~1.1%, which is very promising for a heavy-metal-free 850 nm emitter. We also present a novel quantitative model of the internal quantum efficiency for active layers supporting triplet-to-singlet conversion. These results provide a general strategy for designing high-luminance NIR emitters.

Efficient charge photogeneration in conjugated polymers typically requires the presence of a second component to act as electron acceptor. Here, we report a novel low band-gap conjugated polymer with a donor/orthogonal acceptor motif: poly-2,6-(4,4-dihexadecyl-4H-cyclopenta [2,1-b:3,4-b′]dithiophene)-alt-2,6-spiro [cyclopenta[2,1-b:3,4-b′]dithiophene-4,9′-fluorene]-2′,7′-dicarbonitrile, referred to asPCPDT-sFCN. The role of the orthogonal acceptor is to spatially isolate the LUMO from the HOMO, allowing for negligible exchange energy between electrons in these orbitals and minimising the energy gap between singlet and triplet charge transfer states. We employ ultrafast and microsecond transient absorption spectroscopy to demonstrate that, even in the absence of a separate electron acceptor,PCPDT-sFCNshows efficient charge photogeneration in both pristine solution and film. This efficient charge generation is a result of an isoenergetic singlet/triplet charge transfer state equilibrium acting as a reservoir for charge carrier formation. Furthermore, clear evidence of enhanced triplet populations, which form in less than 1 ps, is observed. Using group theory, we show that this ultrafast triplet formation is due to highly efficient, quantum mechanically allowed intersystem crossing between the bright, initially photoexcited local singlet state and the triplet charge transfer state. Remarkably, the free charges that formviathe charge transfer state are extraordinarily long-lived with millisecond lifetimes, possibly due to the stabilisation imparted by the spatial separation ofPCPDT-sFCN's donor and orthogonal acceptor motifs. The efficient generation of long-lived charge carriers in a pristine polymer paves the way for single-material applications such as organic photovoltaics and photodetectors.

In this article, we experimentally demonstrate a novel expanded nonorthogonal multiband super-Nyquist carrier-less amplitude and phase (m-ESCAP) modulation for bandlimited organic visible light communication (VLC) systems. The proposed scheme has the same bandwidth requirement as the conventional m-CAP while breaking the orthogonality between subcarriers by purposely overlapping them. We compare m-ESCAP with the conventional m-CAP and a compressed nonorthogonal version of m-CAP (m-SCAP) in terms of measured bit error rate (BER) performance, bit rates, and spectral efficiencies. We show that the m-ESCAP system offers improvement in the bit rate of ∼10% and 20% compared to the m-CAP and m-SCAP, respectively, and in the spectral efficiency of ∼20% compared to m-CAP. These gains are achieved at the cost of increased BER, which, however, remains below the 7% forward error correction limit.

This work reports the first observation of circularly polarized electroluminescence (CPEL) in thin films of self-organized oligothiophenes. Four new 1,4-phenylene and 9H-carbazole-based oligothiophenes were ad hoc designed to ensure efficient spontaneous formation of chiral supramolecular order. They were easily synthesized and their chiroptical properties in thin films were measured. Circularly polarized luminescence (CPL) spectra revealed glum in the order of 10−2 on a wide wavelengths range, originating from their self-organized chiral supramolecular organization. These molecules have reasonable properties as organic semiconductors and for this reason they can constitute the active layer of circularly-polarized organic light-emitting diodes (CP-OLEDs). Thus, we could investigate directly their electroluminescence (EL) and CPEL, without resorting to blends, but rather in a simple multilayer device with basic architecture. This is the first example of a CP-OLED with active layer made only of a small organic compound.

A dianiline derivative of a symmetric donor-acceptor-donor diketopyrrolopyrrole-based dye is employed for the two-sided covalent functionalization of liquid exfoliated few layers graphene flakes, through a direct arylation reaction. The resulting nanohybrid features the properties of a polymeric species, being solution-processed into homogeneous thin films, featuring a pronounced red-shift of the main absorption band with respect to the model dye unit and energy levels comparable to those of common diketopyrrolopyrrole-based polymers. A good electrical conductivity and the absence of radical signals generated after intense white light illumination, as probed through electron paramagnetic resonance, suggest a possible future application of this composite material in the field of photoprotective, antistatic layers with tunable colors.

In this paper we experimentally demonstrate, for the first time, staggered carrier-less amplitude and phase (sCAP) modulation for visible light communication systems based on polymer light-emitting diodes emitting at ∼639 nm. The key advantage offered by sCAP in comparison to conventional multiband CAP is its full use of the available spectrum. In this work, we compare sCAP, which utilises four orthogonal filters to generate the signal, with a conventional 4-band multi-CAP system and on-off keying (OOK). We transmit each modulation format with equal energy and present a record un-coded transmission speed of ∼6 Mb/s. This represents gains of 25% and 65% over the achievable rate using 4-CAP and OOK, respectively.

Visible light communication systems often suffer from high frequency attenuation when transmitting out-of-band. This effect has been ameliorated by multi-band modulations such as multi-band carrier-less amplitude and phase (m-CAP), which minimises the effect of decreased high frequency magnitude and maximises signal-to-noise ratio-per-sub-band. On the other hand, in the pass-band region, super-Nyquist CAP (SCAP) can offer throughput improvements with no additional complexity at the receiver, at the cost of bit error rate. We propose, for the first time, a new hybrid SCAP modulation format that takes advantageous of both SCAP (i.e. overlapped sub-bands within the modulation bandwidth) and conventional m-CAP (orthogonally spaced bands outside the modulation bandwidth) while maintaining isolation between noise sources. We show higher baud rates within the passband region whilst supporting out-of-band transmission at lower error vector magnitudes.

We investigate, for the first time, the effect of signal clipping on multi-band carrier-less amplitude and phase (m-CAP) modulation in visible light communications based on PLEDs. We experimentally demonstrate a Q-factor improvement up to ~2.25 dB can be obtained with a clipping level of 50%.

We present the synthesis of a novel diphenylanthracene (DPA) based semiconducting polymer. The polymer is solubilised by alkoxy groups attached directly to a DPA monomer, meaning the choice of co-monomer is not limited to exclusively highly solubilising moieties. Interestingly, the polymer shows a red-shifted elecroluminescence maximum (510 nm) when compared to its photoluminescence maximum (450 nm) which we attribute to excimer formation. The novel polymer was utilised as a host for a covalently-linked platinum(ii) complexed porphyrin dopant. Emission from these polymers was observed in the NIR and again showed almost a 100 nm red shift from photoluminescence to electroluminescence. This work demonstrates that utilising highly aggregating host materials is an effective tool for inducing red-shifted emission in OLEDs.

The aggregation-induced emission (AIE) phenomenon provides a new direction for the development of organic light-emitting devices. Here, we present a new class of emitters based on 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY), functionalized at different positions with tetraphenylethylene (TPE), which is one of the most famous AIE luminogens. Thanks to this modification, we were able to tune the photoluminescence of the BODIPY moiety from the green to the near-infrared (NIR) spectral range and achieve PL efficiencies of ~50% in the solid state. Remarkably, we observed an enhancement of the AIE and up to ~100% photoluminescence efficiencies by blending the TPE-substituted BODIPY fluorophores with a poly[(9,9-di-n-octylfluorene-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,7-diyl)] (F8BT) matrix. By incorporating these blends in organic light-emitting diodes (OLEDs), we obtained electroluminescence peaked in the range 650–700 nm with up to 1.8% external quantum efficiency and ~2 mW/cm2 radiance, a remarkable result for red/NIR emitting and solution-processed OLEDs.

Due to the so-called energy-gap law and aggregation quenching, the efficiency of organic light-emitting diodes (OLEDs) emitting above 800 nm is significantly lower than that of visible ones. Successful exploitation of triplet emission in phosphorescent materials containing heavy metals has been reported, with OLEDs achieving remarkable external quantum efficiencies (EQEs) up to 3.8% (peak wavelength > 800 nm). For OLEDs incorporating fluorescent materials free from heavy or toxic metals, however, we are not aware of any report of EQEs over 1% (again for emission peaking at wavelengths > 800 nm), even for devices leveraging thermally activated delayed fluorescence (TADF). Here, the development of polymer light-emitting diodes (PLEDs) peaking at 840 nm and exhibiting unprecedented EQEs (in excess of 1.15%) and turn-on voltages as low as 1.7 V is reported. These incorporate a novel triazolobenzothiadiazole-based emitter and a novel indacenodithiophene-based transport polymer matrix, affording excellent spectral and transport properties. To the best of knowledge, such values are the best ever reported for electroluminescence at 840 nm with a purely organic and solution-processed active layer, not leveraging triplet-assisted emission.