• Publications
  • S. V. Dayneko, M. Rahmati, M. Pahlevani, G. C. Welch. Solution processed red organic light-emitting-diodes using an N-annulated perylene diimide fluorophore, 2020. (J. Mater. Chem. C)

    In this contribution we report on solution processed red OLEDs based upon an N-annulated perylene diimide dimer, namely tPDI2N-EH, a red-light emitting molecule. OLED devices with the architecture of glass/ITO/PEDOT:PSS/EML/LiF/Ag (EML = emitting layer) were fabricated with EMLs comprised of tPDI2N-EH neat and blended with poly(9,9-dioctylfluorene, PFO), all solution processed from non-halogenated solvents. The photophysical and electrophysical performance of PFO:tPDI2N-EH-blend films with different composition ratios were investigated. The PFO : tPDI2N-EH-based OLEDs with a 2 : 18 ratio exhibited the best performance. The PFO:tPDI2N-EH-based OLEDs gave red electroluminescence with the emission wavelength of 635 nm and the CIE (international commission on illumination) coordinates of (x = 0.672, y = 0.321). OLEDs with EMLs fabricated using roll-to-roll compatible methods are also demonstrated.
  • M. Rahmati, S. V. Dayneko, M. Pahlevani, G. C. Welch. Interlayer Engineering of Flexible and Large-Area Red Organic-Light-Emitting Diodes Based on an N-Annulated Perylene Diimide Dimer, 2019. (ACS Appl. Electron. Mater.)

    Flexible red OLEDs based on a quadruple-layer stack, in between electrodes, with 160 mm2 active area were fabricated in ambient air on PET via slot-die-coating. For the OLED structure PET/ITO/PEDOT:PSS/PVK/PFO:tPDI2N-EH/ZnO/Ag, the ink formulations and coating parameters for each layer were systematically evaluated and optimized. The air-stable red-light-emitting material tPDI2N-EH was successfully utilized as blended homogeneous film with PFO for the emitting layer. The use of an organic hole-transport layer (PVK) and inorganic electron injection layer (ZnO) significantly improved the brightness of the reference device from 4 to 303 cd/m2. Surface analysis using AFM measurements showed that the PVK interlayer reduced the surface roughness of the hole injection layer (PEDOT:PSS) from 0.45 to 0.17 nm, which improved the ability to form uniform emitting layers on top. In addition, the ZnO interlayer decreased surface roughness from 1.26 to 0.85 nm and reduced the turn-on voltage of the device from 5.0 to 2.8 V.
  • S. V. Dayneko, M. Pahlevani, G. C. Welch. Indoor Photovoltaics: Photoactive Material Selection, Greener Ink Formulations, and Slot-Die Coated Active Layers, 2019. (ACS Appl. Mater. Interfaces)

    Strong visible light absorption is essential to achieve high power conversion efficiency in indoor organic photovoltaics (iOPVs). Here, we report iOPVs that exhibit high efficiency with high voltage under excitation by low power indoor lighting. Inverted type organic photovoltaic devices with active layer blends utilizing the polymer donor PPDT2FBT paired with fullerene, perylene diimide, or ring-fused acceptors that are 6.5–9.1% efficient under 1 sun are demonstrated to reach efficiencies from 10 to 17% under an indoor light source. This performance transcends that of a standard silicon photovoltaic device. Moreover, we compared iOPVs with active layers both spin-cast and slot-die cast from nonhalogenated solvents and demonstrate comparable performance. This work opens a path towards high-efficiency iOPVs for low power electronics.
  • M. Rahmati, S. V. Dayneko, M. Pahlevani, Y. Shi. Highly Efficient Quantum Dot Light‐Emitting Diodes by Inserting Multiple Poly(methyl methacrylate) as Electron‐Blocking Layers, 2019. (Adv. Funct. Mater.)

    This work presents a new device architecture integrating multiple poly(methyl methacrylate) (PMMA) electron‐blocking layers (EBL) in quantum dot light‐emitting diodes (QD‐LEDs). The device utilizes red‐emitting CdSe/ZnS QD with a novel structure where multiple PMMA EBLs are sandwiched between a pair of QD layers. A systematic optimization of QD‐LED structures has shown that a device including two PMMA and three QD layers performs the best, achieving a current efficiency of 17.8 cd A−1 and a luminance of 194 038 cd m−2. Numerical simulation of a simplified model of the proposed QD‐LED structure verifies that the structure consisting of two PMMA and three QD layers provides significant improvement in electroluminescent intensity. The simulation provides further insight into the origin of the effect of the PMMA EBL by showing that the addition of PMMA EBL reduces the electron leakage from the active QD region and enhances electron confinement, leading to an increased electron concentration in the QD active layers and a higher radiative recombination rate. The experimental and theoretical studies presented in this work demonstrate that multiple layers of PMMA can act as efficient EBLs in the fabrication of QD‐LEDs of improved performance.
  • M. Abd-Ellah, J. Cann, S. V. Dayneko, A. Laventure, E. Cieplechowicz, G. C. Welch. Interfacial ZnO Modification Using a Carboxylic Acid Functionalized N-Annulated Perylene Diimide for Inverted Type Organic Photovoltaics, 2019. (ACS Appl. Electron. Mater.)

    This study reports the modification of the zinc oxide cathodic interlayer with an N-annulated perylene diimide molecule functionalized with a carboxylic acid, namely, (HOOC5-triazole) PDIN-hex, referred to as IL-1, for the improvement of inverted-type organic photovoltaics. The new interlayer “IL-1” was synthesized using “click” chemistry and incorporated into the photovoltaic device structure using solution processing methods. The organic modified zinc oxide layer was characterized using optical absorption spectroscopy, contact angle measurements, and Kelvin probe force microscopy. IL-1 was retained on the zinc oxide surface and lowered the electrode work function from 4.5 to 4.1 eV, the low work function is crucial for any cathodic interlayer to match with the LUMO energy levels of acceptor materials for better charge extraction and electron collection properties. Bulk heterojunction organic photovoltaic devices utilizing this interlayer (compared to only zinc oxide) exhibited increases in power conversion efficiency ranging from 20% to 33% for those with active layer blends based on both fullerene and non-fullerene acceptors.
  • S. V. Dayneko, A. D. Hendsbee, J. Cann, C. Cabanetos, G. C. Welch. Ternary organic solar cells: using molecular donor or acceptor third components to increase open circuit voltage, 2019. (New J. Chem.)

    This report demonstrates that the open circuit voltage (VOC) and power conversion efficiency (PCE) of polymer:fullerene (PBDB-T:PC60BM) organic solar cells can be simultaneously enhanced by introducing a molecular π-conjugated donor or acceptor as a third component, thus affording high performance ternary blend devices. The use of a PDI-based acceptor “tPDI2N-hex” or benzothioxanthene-based donor “tBTI-IDT” as a third component leads to VOC increases of 60 to 150 mV without significant loss in power conversion efficiency (PCE). The best solar cell PCE of 8.8% was achieved by doping the PBDB-T:PC60BM system with 10% by weight of tPDI2N-hex.
  • A. Labrunie, G. Londi, S. V. Dayneko, M. Blais, S. Dabos-Seingnon, G. C. Welch, D. Beljonne, P. Blanchard, C. Cabanetos. A triazatruxene-based molecular dyad for single-component organic solar cells, 2018. (Chemistry Squared)

    The synthesis, characterization and use of a new donor-acceptor molecular dyad in single component organic solar cells are reported. The dyad, composed of a triazatruxene-based push-pull 'donor' unit linked to a C60 'acceptor' unit through a non-conjugated σ connector, led to promising power conversion efficiencies of 0.6% when embedded in simple devices exhibiting the architecture: indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT:PSS)/dyad/Al.
  • M. Vespa, J. Cann, S. V. Dayneko, O. A. Melville, A. D. Hendsbee, Y. Zou, B. H. Lessard, G. C. Welch. Synthesis of a Perylene Diimide Dimer with Pyrrolic N–H Bonds and N‐Functionalized Derivatives for Organic Field‐Effect Transistors and Organic Solar Cells, 2018. (Eur. J. Org. Chem.)

    This study reports on the new and optimized synthesis of an N‐annulated perylene diimide dimer with functional N–H moieties. The presence of two N–H moieties renders the dimer relatively insoluble in most organic solvents. The dimer is easily functionalized with electron donating hexyl chains or electron withdrawing tert‐butyloxycarbonyl (tBOC) groups to yield highly soluble materials. The tBOC groups can be thermally cleaved in the thin film to give the parent dimer. The N–H bonds are acidic and interact with volatile organic bases. Deprotonation results in a color change from red to blue. All compounds have utility as electron transport materials in organic field‐effect transistors and green solvent, air processed organic solar cells. Electron mobilities were on the order of about 2–7 × 10–6 cm2/V s. Solar cell power conversion efficiency reached 2 % for those using the tBOC functionalized dimer, 3 % for those using the H‐atom functionalized dimer, and 6 % for those using the hexyl chain functionalized dimer. The performance of the latter is quite impressive considering the simple materials synthesis and greener solar cell processing.
  • S. V. Dayneko, A. D. Hendsbee, G. C. Welch. Combining Facile Synthetic Methods with Greener Processing for Efficient Polymer‐Perylene Diimide Based Organic Solar Cells, 2018. (Small Methods)

    Through ease of scalability and facile synthetic methods, eight N‐annulated perylene diimide dimers with different aliphatic chains are synthesized and evaluated as non‐fullerene acceptors in organic solar cells (OSCs). Optical absorption and emission spectroscopy, and cyclic voltammetry are used to characterize the materials. Variation of the length and topology of the aliphatic chains attached at the pyrrolic N‐position is shown to have minimal effect on properties in solution. As films, the use of a branched aliphatic chains results in the dimer exhibiting a low energy shoulder in the absorption spectrum and a narrower emission band. OSCs are fabricated and tested in air, at room temperature, using an inverted architecture. The polymer PTB7‐Th is used as the donor and all active layers are processed from 2‐methyltetrahydrofuran. OSC power conversion efficiencies are shown to vary from 3.7%–5.4% for OSCs. The dimer with 2‐ethylhexyl aliphatic chains is selected for optimization because of a high organic solvent solubility and excellent film formation properties. Use of the solvent additive 1,8‐diiodooctane during film formation lead to an increase in efficiency to 6.6%, while halogen‐free processed OSCs reach 6%. This result offers a simple method for materials side‐chain engineering for the development of OSCs processed in air from eco friendly solvents.