This PDF file contains the front matter associated with SPIE Proceedings Volume 11365, including the title page, copyright information, table of contents, and author and conference committee lists.

Light-emitting electrochemical cells (LECs) are highly efficient, air-stable, low-cost, and single-layered lighting sources fabricated using up-scalable and sustainable solution-based techniques.[1] They consist of two electrodes sandwiching a thin film of electroluminescent material doped with ionic electrolyte, that allows for charge transport, recombination, and light-emission processes. In this context, white LECs (WLECs) still represents a challenge. Commonly, the active layer is constituted by a mixture of blue, green, red ionic transition metal complexes (iTMCs), or conjugated polymers, reaching efficacy of >10 cd/A, stability of tens of hours, and luminances of 10,000 cd/m2. Herein, the most recent advances in our group are described. Firstly, deep-red emitting Cu-iTMCs were reported. They featured high irradiances (>100 μW/cm2, long stabilities of > 20 h and excellent color stability (x/y 0.66/0.32).[3] By combining the best performing Cu-iTMC, featuring Xantphos as P^P ligand, with the high-bandgap hole transport material 4,4′-Bis(9-carbazolyl)-1,1′-biphenyl (CBP), proof-of-concept WLECs with x/y color coordinates of 0.32/0.31, and high CRI of 92 were achieved. These results open the way to fabricate all-Cu(I) based WLECs. Secondly, we reported on a hexa-peri-hexa-benzoborazinocoronene that gave rise to single-component WLECs luminances of 50 cd/m2, stabilities of 25 h and efficacy of 3.1 cd/A when driven at pulsed current of 5 mA, and with electroluminescence spanning the whole visible range – i.e., x/y CIE coordinates of 0.29-31/0.31-38 and average color rendering index (CRI) of 87.[4] We rationalized the electroluminescence behavior consisting of a ternary emission mechanism involving fluorescence and thermally activated dual phosphorescence. The latter is enhanced by both temperature, which can be as high as 80 °C upon device driving, and electric field. This represents the first example of ternary emission activated in lighting devices. [1] a) E. Fresta, R. D. Costa, J. Mater. Chem. C 2017, 5, 5643. b) R. D. Costa, Light-emitting electrochemical cells. Concepts, advances and challenges.; 1st ed.; Springer International Publishing: Basel, 2017. [2] E. Fresta, M. D. Weber, J. Fernández-Cestau, R. D. Costa, Adv. Opt. Mater. 2019, DOI: 10.1002/adom.201900830. [3] J. Dosso, J. Tasseroul, F. Fasano, D. Marinelli, N. Biot, A. Fermi, D. Bonifazi, Angew. Chem. Int. Ed. 2017, 56, 4483. [4] E. Fresta, J. Dosso, J. Cabanillas-Gonzalez, D. Bonifazi, R. D. Costa, Adv. Funct. Mater. 2019, under reviewer.

Quantum Dot Light Emitting Diodes (QDLEDs) are a promising alternative to the already established organic LEDs (OLEDs) in applications like automotive rear-lights. QDLEDs can exhibit higher luminance characteristics and superior operational stability. In order to be able to transfer the QDLEDs from their research state into market products, the oftenused Cadmium-containing QDs must be replaced by less toxic alternatives. Furthermore, the processing costs for the QDLEDs have to be minimized. We overcome both challenges by utilizing Indium Phosphide based QDs in the devices and applying inkjet-printing as a low-material consumption deposition technique. Inkjet-printing three layers of the stack design on top of each other proofs to be challenging concerning the layers homogeneity both macroscopically as well as microscopically. We present viable approaches for the ink formulation process, substrate-pretreatment steps and printing strategies to overcome wetting, dewetting and coffee-staining issues. The printed layers are investigated via topological and fluorescent tools and the successfully fabricated devices are examined via electrooptical measurements.

Organic light-emitting diodes (OLEDs) possess many unique properties such as large-area emission, fabrication on flexible plastic films, adjustment of the emission spectrum and angular distribution by chemical and optical means, and structuring to high-density arrays with millions of pixels. While especially the latter contributed to commercialization of OLED displays in consumer electronics, the properties of OLEDs also make them highly attractive for biological applications. In this contribution, we present fluorescent blue OLEDs with electrically doped charge transport layers that reach more than 100,000 cd/m² at 5 V. We applied the light source in optogenetics to stimulate primary mouse hippocampal neurons and to evoke sensory response in Drosophila melanogaster larvae using micro-structured OLED pixels. Furthermore, by applying a distributed Bragg reflector, we narrowed the OLED spectrum down in order to enable imaging of neuronal activity using genetically encoded calcium indicators. Finally, we discuss our recent efforts on providing stable encapsulation of flexible OLEDs. These examples show how OLEDs may outperform traditional light sources applied in biophotonics by enabling conformable, bio-compatible, and bright illumination with unprecedented resolution.

By utilizing the room temperature phosphorescence (RTP) of organic materials, transparent and flexible optical tags with high resolutions up to 700 dpi are realized. Through masked ultraviolet (UV) illumination or laser ray writing, any phosphorescent pattern can be printed into the transparent device. With the help of infrared (IR) light, it is possible to fully erase the imprint again. This cycle is shown to be repeatable at least 40 times. The functional layer of these devices consists of different organic biluminescent emitters doped into a polymethylmethacrylate (PMMA) host matrix covered with an oxygen barrier layer. However, due to the sample preparation in ambient conditions, molecular oxygen is still present in the emissive layer. This leads to a full quenching of the phosphorescence and the generation of excited singlet oxygen due to triplet-triplet interactions involving the oxygen triplet groundstate. The singlet oxygen has a high chemical reactivity and thus is able to form a bond with the surrounding materials. Consequently, the molecular oxygen concentration decreases in the illuminated areas. The concurrently decreasing oxygen-quenching rate is at some point outcompeted by the radiative rate of the emitter, enabling locally resolved phosphorescence. This emission resembles the intended pattern. The oxygen permeability of the barrier layer is temperature dependent and increases with rising temperature, which can be realized using a hotplate or IR illumination. This enables an oxygen refilling of the functional layer and therefore increases the quenching rate to a value prior to the activation process, leading to the vanishing of the phosphorescent image. After a short cooling phase, new information can be printed into the device. In continuous wave illumination, fluorescence may limit the contrast between activated areas and those still containing oxygen. Hence, different material systems showing reduced fluorescence without losing the oxygen quenching ability of the phosphorescence, are developed and tested.

A significant challenge to achieving higher efficiencies in organic solar cells (OSCs) is increasing the open circuit voltage (Voc) relative to the absorption threshold. The reason why voltage losses in OSCs are higher than in other material systems has been attributed to the molecular heterojunction that is required to dissociate photogenerated excitons, which gives rise to electron-hole pairs bound across the donor-acceptor interface known as charge-transfer (CT) states. Whilst these CT states are crucial to charge separation, their decay to the ground state via energy transfer to vibrational modes is a significant non-radiative recombination pathway in the device, which has meant that non-radiative contributions to Voc losses are significantly larger in OSCs than in comparative solar cell technologies. Given the importance of CT-states in the charge generation process of OSCs, an understanding of the factors that govern CT-state recombination is crucial in designing higher efficiency systems, especially given the recent emergence of non-fullerene based systems that have managed to decrease non-radiative voltage losses to below 0.2 eV without affecting charge-generation efficiency. It has previously been suggested that the open circuit voltage (Voc) in OSCs is largely determined by the energy of the donor-acceptor CT state, since a higher overlap of the vibrational modes of the CT and ground states increases the rate of non-radiative recombination in accordance with the energy gap law. However, more recent studies have found that increasing the CT state energy does not always result in a reduction in the non-radiative voltage losses, which suggests that other properties of the CT state to ground state transition appear to affect the trend. Here, we present spectroscopic studies of CT-states to determine their impact on the Voc and the subsequent efficiency of OSCs. We present a model of recombination via CT-states in OSCs that shows how particular CT-state properties affect voltage losses, and specifically focus on the case where the energy difference between the exciton and the CT-state becomes very small, as has often been the case for many recently published high efficiency systems. In this case, hybridization between the CT and excited state may occur, leading to an increase in the radiative ability of the CT-state due to intensity borrowing. We show both experimentally and using our model that this leads to a decrease in non-radiative voltage losses, and further address the questions of what molecular parameters of the CT-state may be beneficial to further reduce voltage losses in low offset OSC blends.

One of the key areas of study in organic photovoltaics is the development of so-called 'nonfullerene acceptors’ (NFAs), which enjoy several benefits over older, fullerene-based acceptors, including: low open circuit voltage losses, low cost, high absorptivity, and broad tuneability. However, these advantages come at the expense of light harvesting efficiency. Recent reports demonstrated conversion efficiencies up to 17% in donor acceptor blends of conjugated polymers and ‘small’ electron accepting molecules. In order to understand the processes underlying this remarkable efficiency, we performed ultrafast transient absorption and optical control (pump-push and pump-push-probe) studies on the broad range of donor:acceptor blends. For many systems we observe that relatively long-lived excitons form at the acceptor regardless of whether the donor or acceptor is pumped, suggestive of rapid energy transfer from the donor to the acceptor followed by slow charge separation. A distinct change in exciton decay characteristics was observed at longer timescales in tandem with spectral drift in the acceptor localised excitonic peak. We use global analysis methods to elucidate the mechanism behind this feature as well as 3-pulse ”Pump-Push-Probe” spectroscopy to track the dissociation of interfacial charge transfer states within the material. Our results will help to shed light on the remarkable efficiency of this material and aid the development of more efficient and effective non fullerene acceptors.

Organic semiconductor materials such as planar conjugated small molecules are of great interest to the photovoltaic community [1, 2]. In thin films, the exciton and charge carrier dynamics, which are crucial to photovoltaic device operation, depend in a non-trivial way on the organic molecular structure and on the molecular organization in the solid state. [3, 4] Several recent studies have established that the exciton diffusion strongly depends on the crystalline order of the organic films. [5, 6] Our work presents the study of the exciton dynamics in an innovative class of molecular semiconductors able to present high crystalline order. This family of molecules has a “dumbbell-shaped” structure based on triazatruxene units that act as a π-stacking platform. [7] Such molecules with different side-chain have been found to self-assemble into various crystalline and liquid crystalline phases. We have studied exciton dynamics of molecular with different side-chain: in solution and in thin films for different solid state phases. In solution, the lifetime corresponds to the reference value that can be obtained without intermolecular interaction. In thin films, we measured the exciton lifetime for different molecular structures in order to correlate the exciton diffusion length with the intermolecular stacks. The results reveal a significant increase in exciton lifetime with structural order. [1] Y. Lin et al., Chem. Soc. Rev. 2012, 41, 4245. [2] S. D. Collins et al., Adv. Energy Mater. 2017, 7, 1602242. [3] J. A. Bartelt et al., Adv. Energy Mater. 2013 , 3 , 364. [4] J. T. Bloking et al., Adv. Energy Mater. 2014, 4, 201301426. [5] R. R. Lunt et al., Adv. Mater., 2010, 22, 11, 1233-1236. [6] A. T. Haedler et al., Nature, 2015, 523,196–199. [7] I. Bulut et al., J. Mater. Chem. A, 2015, 3, 6620.

Persistent room-temperature phosphorescence (pRTP) under ambient conditions is attracting attention due to its strong potential for state of art bioimaging and security applications because materials with pRTP can be utilized for high contrast emission imaging independent of autofluorescence using small-scale and low-cost photo-detectors. To extract efficient pRTP, the control of the radiative rate from the lowest triplet excited state (T1) (kp), the nonradiative rate of intramolecular vibrational relaxation at room temperature (RT) from T1 (knr(RT)), and the triplet quenching rate at RT caused by interactions with the ambient surroundings (kq(RT)) is crucial. In the last six years, knr(RT)+kq(RT) have been suppressed in a variety of heavy atom-free molecular materials under ambient conditions, which has allowed electrons in T1 to partly access the pRTP pathway with small kp. However, a key strategy to suppress knr(RT) and kq(RT) as well as increase kp for the efficient persistent RTP is not found yet. Here, we investigate kp, knr(RT), and kq(RT) of heavy atom-free molecular materials showing pRTP. Cooperative analysis using microscope and quantum chemical calculation indicated that no appearance of pRTP of many heavy atom-free molecules are mostly caused by kq(RT) while minimization of the intermolecular triplet energy transfer using appropriate design of materials could largely decreased kq(RT). For knr(RT), analysis using vibrational spin–orbit coupling at RT indicates that knr(RT) of many heavy atom-free molecules is intrinsically small and approaches the small kp. To increase kp independent of knr(RT), the control of electronic structure of the high order excited state is highly important. This is first overall analysis of kp, knr(RT), and kq(RT) of heavy atom-free molecules, which will be important for realizing efficient pRTP from a variety of heavy atom-free molecular materials. In symposium, intrinsic characteristics of pRTP that general long persistent emitters could not reach are also explained.

The aim of the LaPOF research project is to develop and define the technological basis for the preparation of innovate laser-active polymer-optical fibers (LaPOF). The sub-project BINNOPTA (integrated innovation management to optimize the adoption potential) is investigating areas with high application potential for this innovative laser technology in close cooperation with commercial enterprises.

Material and functional stability remains a major issues in field of perovskite photovoltaics. To achieve a long device lifetime, it is crucial that we understand and optimize the lifetime of the material itself. One-step antisolvent processing is a facile method to enhance stability. Herein, we report that changes in the degradation process of perovskite films is modified by the antisolvent treatment in comparison to the conventional film without the process which we measure by monitoring the emission. Perovskite films prepared with anti-solvent processing have improved film morphology and reduced evolution of surface metallic lead, which correlated with improved film lifetimes.

The current photovoltaic module market is dominated by silicon solar cells, whose development is limited by high costs of manufacturing processes. The search for easy low temperature fabrication techniques has spurred the development of solar cells based on organic semiconductor polymers. Recent studies have reported polymer based solar cells with comparable power conversion efficiencies to those of commercially available silicon solar cell modules. In the face of these advances, higher efficiencies are still desirable to better utilize the available solar energy for power generation. Organic semiconducting polymers have a high coefficient of absorption, but short carrier path lengths which necessitates the fabrication of thin layers for optimal power generation. The introduction of plasmonic effects in these organic solar cells leads to an increase in the optical path length of the incident light in the active layer, thereby increasing the short circuit current density. In this work, an organic solar cell is presented which contains metal-dielectric core-shell plasmonic nanoparticles. Finite difference time domain (FDTD) modelling has been used to simulate the models of light interaction with the organic solar cells containing different metal@dielectric nanoparticle composites. The different parameters of the nanoparticle composites in the organic solar cells were varied to the study the absorption enhancement in the active layer medium. The results, thus obtained for enhanced performance, were used for the chemical synthesis of the metal@dielectric nanoparticle composites and fabrication of organic solar cells with high power conversion efficiency.

According to simulated calculations, in our bottom emitting OLED devices, the outcoupling efficiency (ηOUT) is limited to only 17% of light escaping into free space due to light lost as substrate guided (22%), organic waveguided (12%) and evanescent modes (31%) and the air/substrate, substrate/organic and organic/metal interfaces respectively [1]. To extract substrate guided modes, our previous work showed that OLEDs fabricated over sample glass patterned substrates, can simultaneously enhance the ηOUT and reduce view angle dependency [1]. This represents an improvement on past research efforts, wherein some outcoupling structures tended to induce strong viewing angle dependence [2] and those intended suppress this, had no effect on ηOUT [3]. Previous research for extracting organic waveguides, however, may involve complex nm-scale fabrication techniques resulting in 20-25% enhancement in ηOUT [4-5]. In this work, we demonstrate that a novel pattern of ITO-coated glass substrate can extract up to 30.8% of organic waveguided modes, by micrometer-scale patterning of both the ITO and glass beneath the ITO. Using the simulation programme, Setfos, existing patterns at the air/substrate interface were first replicated and then manually optimized in terms of depth, diameter, edge-to-edge distance, the shape of holes and their packing arrangement. A combination of the most optimized dimensions then resulted in a maximum enhancement in ηOUT by 30.36%. Devices fabricated with similar pattern dimensions at the air/substrate interface (albeit slight differences) showed a 27.3% enhancement as a result of extracted substrate guided modes. The substrate/organic side of the device was also patterned with similar dimensions as mentioned above and resulted in a 30.8% enhancement of ηOUT due to extracted organic waveguided modes being redirected as leaky modes, wherein light is then able to escape into the forward viewing direction.

Herein, results from the investigation of ultrafast photophysical and third-order nonlinear optical properties of newly synthesized Zn phthalocyanine, namely [Zinc (II) 2,10,16,24tetrakis(2,6-dichloropyridin-3-yl) phthalocyanine, PyCl₂PC] molecule are presented. The photophysical properties were studied using femtosecond transient absorption spectroscopy while the NLO properties were measured using the single beam Z-scan and degenerate four-wave mixing (DFWM) techniques. The transient absorption spectra were obtained at 400 nm photoexcitation and a white light continuum probed the corresponding dynamics from (440-780 nm) in the solution phase. The obtained transient absorption spectra were globally fitted using a kinetic model which yielded the different photophysical constants after photoexcitation such as (i) internal conversion from higher electronic excited state (S_n) to lower electronic state (S₁) happening in 1 ps (ii) Vibrational relaxation (6.25 ps) occurring within the S₁ states (III) Intersystem crossing (1.78 ns) (IV) relaxation from the triplet states to ground state (0.11 μs). Nonlinear absorption properties were measured at 800 nm wavelength utilizing ~70 fs, 1 kHz laser pulses in the solution phase. A large two-photon absorption coefficient (β) of ~8×10^-13 cm/W was obtained and the corresponding cross-section was estimated to be 659 GM. Time-resolved degenerate four-wave-mixing measurements revealed a large magnitude and an ultrafast response of χ⁽³⁾.

In this work, we report a novel method of mask-less doping of graphene channel in field-effect transistor configuration by local inkjet printing of organic semiconducting molecules. Graphene-based transistor was fabricated via large-scale technology, allowing for upscaling electronic device fabrication and lowering the device cost. The altering of functionalization of graphene was performed through local inkjet printing of semiconducting molecules: N,N′-Dihexyl- 3,4,9,10-perylenedicarboximide (PDI-C6), 5,5′′′-Dihexyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (HEX-4T-HEX) and polyalanine (PANI). We found the effect of UV treatment on fabrication of graphene/organic junctions because of change in graphene hydrophobic properties. We demonstrated the high resolution (about 50 μm) and accurate printing of organic ink on UV treated chemical vapor deposited (CVD) graphene. The PANI/graphene junction demonstrate more stable photoresponse characteristic for 470 nm diode illumination. The characteristics of PDI/graphene junction demonstrate the saturation for high diode power because of organic crystals degradation. The photoresponse of 1 mA/W was demonstrated for PANI/graphene junction at 0.3 V bias voltage. The developed method opens the way for local functionalization of on-chip array of graphene by inkjet printing of different semiconducting organic molecules for photonics and electronics application.