Soluble Ruthenium Phthalocyanines as Semiconductors for Organic Thin-Film Transistors

Ruthenium phthalocyanine (RuPcs) are multipurpose compounds characterized by their remarkable reactivity and photoelectronic properties, which yield a broad synthetic scope and easy derivatization at the axial position. However, RuPcs have been underexplored for use in organic thin-film transistors (OTFTs), and therefore new studies are necessary to provide basic insight and a first approach in this new application. Herein, two novel RuPc derivatives, containing axial pyridine substituents with aliphatic chains (RuPc(CO)(PyrSiC6) (1) and RuPc(PyrSiC6)2 (2), were synthesized, characterized, and tested as the organic semiconductor in OTFTs. RuPc thin-films were characterized by X-ray diffraction (XRD), and atomic force microscopy (AFM) to assess film morphology and microstructure. 1 displayed comparable p-type device performance to other phthalocyanine-based OTFTs of similar design, with an average field effect mobility of 2.08×10−3 cm2 V−1 s−1 in air and 1.36×10−3 cm2 V−1 s−1 in nitrogen, and threshold voltages from −11 V to −20 V. 2 was found to be non-functional as the semiconductor in the device architecture used, likely as a result of significant differences in thin-film formation. The results of this work illustrate a promising starting point for future development of RuPc electronic devices, particularly in this new family of OTFT

Random controlled free radical copolymerization of acrylic acidstyrene and tert-butyl acrylatestyrene mixtures using nitroxide mediators

Controlled free radical polymerization facilitates the production of polymers with highly defined microstructures like traditional ionic polymerization; but in contrast allows for previously unattainable monomer combinations such as acrylic acid in its non-protected form. Incorporation of acrylic acid into styrene was done by random copolymerization of acrylic acid (directly and in its protected form as tert-butyl acrylate) with styrene. Styrene/tert-butyl acrylate (S/t-BuA) as well as styrene/acrylic acid (S/AA) mixtures were copolymerized to form tapered or gradient copolymers. Using an alkoxyamine unimolecular initiator, 2-[N- tert-butyl-2,2-(dimethylpropyl)aminooxy] propionic acid (BlocBuilder RTM), along with additional free nitroxide (SG1), the effect of acid protection on polymerization kinetics and copolymer composition was determined. Adding 4.5 mol% SG1/BlocBuilderRTM greatly improved the control of S/t-BuA copolymerization with low polydispersities (1.14-1.22) whereas the S/AA required higher levels of SG1 to produce polymers with low polydispersities that were comparatively still broader compared to the S/t-BuA system (polydispersities ∼ 1.3-1.4 at 9 mol% SG1/BlocBuilderRTM). S/AA copolymerization required higher SG1 concentrations to compensate for degradation of SG1 by attack from the acrylic acid monomer

Controlled and selective placement of boron subphthalocyanines on either chain end of polymers synthesized by nitroxide mediated polymerization

In previous studies, we synthesized the first organic light emitting diode (OLED) using boron subphthalocyanines (BsubPcs) based polymers. When designing new polymer materials for organic electronic applications such as OLEDs or organic photovoltaic (OPV) devices it is important to consider not only the contribution of each monomer but also the polymer chain ends. In this paper we establish a post-polymerization strategy to couple BsubPcs onto either the α- or the ω-chain end using chemically selective BsubPc derivatives. We outline how the chain ends of two representative polymers, poly(styrene) (PS) and poly(n-butylacrylate) (BA), synthesized by nitroxide mediated polymerization (NMP), using BlocBuilder-MA as the initiating species, can be chemically modified by the incorporation of BsubPc chromophores. The addition of the BsubPc chromophore was confirmed through the use of a photodiode array detector (PDA) connected in-line with a gel permeation chromatography (GPC) setup. These findings represent the first reported method for the controlled and selective placement of a BsubPc chromophores on either end of a polymer produced by NMP. This strategy will therefore be utilized to make next generation BsubPc polymers for OLEDs and OPV devices. The extremely high molar extinction coefficient of BsubPc also make these polymers ideally suited for dye-labelling of polymers

N‐Type Single Walled Carbon Nanotube Thin Film Transistors Using Green Tri‐Layer Polymer Dielectric

Abstract The proliferation of disposable, wearable, and implantable printable electronics requires the development of high‐performance biodegradable, and sustainable electronic components. Often green materials don't have the necessary properties for high‐performance electronics, therefore obtaining the ideal properties requires a combination of multiple green materials. A tri‐layer dielectric is reported using poly(lactic acid) (PLA), poly(vinyl alcohol)/cellulose nanocrystals (PVAc), and toluene diisocyanate terminated poly(caprolactone) (TPCL), which is integrated into semiconducting single‐walled carbon nanotube (sc‐SWCNT) based thin film transistors (TFTs) in a top gate bottom contact architecture. The PVA provides a high dielectric constant due to the hydroxy groups, the cellulose is used to optimize the viscosity, the TPCL layer provides a robust hydrophobic surface, and the PLA eliminates the interfacial charge traps present in the PVAc and improves the adhesion between PVAc and the substrate. This leads to a decrease in leakage currents and reduces the polarity at the dielectric/semiconductor interface. The TFTs fabricated using tri‐layer dielectrics led to air‐stable n‐type devices with higher overall performance when compared against the PVAc/TPCL bilayer devices

Silicon Phthalocyanines as Acceptor Candidates in Mixed Solution/Evaporation Processed Planar Heterojunction Organic Photovoltaic Devices

Silicon phthalocyanines (SiPc) are showing promise as both ternary additives and non-fullerene acceptors in organic photovoltaics (OPVs) as a result of their ease of synthesis, chemical stability and strong absorption. In this study, bis(3,4,5-trifluorophenoxy) silicon phthalocyanine ((345F)2-SiPc)) and bis(2,4,6-trifluorophenoxy) silicon phthalocyanine ((246F)2-SiPc)) are employed as acceptors in mixed solution/evaporation planar heterojunction (PHJ) devices. The donor layer, either poly(3-hexylthiophene) (P3HT) or poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), was spin coated followed by the evaporation of the SiPc acceptor thin film. Several different donor/acceptor combinations were investigated in addition to investigations to determine the effect of film thickness on device performance. Finally, the effects of annealing, prior to SiPc deposition, after SiPc deposition, and during SiPc deposition were also investigated. The devices which performed the best were obtained using PCDTBT as the donor, with a 90 nm film of (345F)2-SiPc as the acceptor, followed by thermal annealing at 150 °C for 30 min of the entire mixed solution/evaporation device. An open-circuit voltage (Voc) of 0.88 V and a fill factor (FF) of 0.52 were achieved leading to devices that outperformed corresponding fullerene-based PHJ devices

One-step synthesis of perfluorinated polyphenylenes using modified Ullmann coupling conditions

Fluorinated compounds have attracted attention in both the pharmaceutical industry and materials science due to the small size and strong electron-withdrawing property of the fluorine atom. In materials science, perfluorinated polyphenylenes play an important role as electron transport layers in organic electronics. While various strategies for the preparation of fluorinated arenes have been reported, the number of synthetic methods available for perfluorinated arenes remains limited, mainly due to the change in reactivity of reagents and substrates at the reaction site upon the introduction of additional fluorine atoms. Given the important applications of perfluorinated polyphenyl-based compounds, this article describes the one-step synthesis of the dendrimer perfluoro-3,3’5,5’-tetrakisphenyldiphenyl-1,1’, which to date no example of a targeted synthesis has been reported in literature, and the synthetic methodology for the direct preparation of linear perfluorinated para-sexiphenyl. Both strategies use starting materials that are either commercially available or can be easily accessed using standard literature methods.</p

Solution-Processable n-Type Tin Phthalocyanines in Organic Thin Film Transistors and as Ternary Additives in Organic Photovoltaics

Tin phthalocyanines have shown promise in both organic thin film transistors (OTFTs) and organic photovoltaics (OPVs); however, no examples of solution processable axial derivatives have been reported. We synthesized and characterized tin phthalocyanines (SnPcs) with tributylsilane and trihexylsilane axial functional groups and examined their performance in OTFTs and in poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) OPV devices as ternary additives. We also report the OTFT performance of the previously studied trialkylsilane silicon phthalocyanines for comparison. In polycrystalline OTFTs the tin derivatives show higher electron mobilities than their silicon counterparts due to increased molecular interactions. As a ternary additive in OPV devices, similar to the SiPc analogues, both SnPc derivatives show an EQE contribution &gt;20% in the range 650–750 nm. These results suggest soluble SnPcs show potential as active materials in OTFTs and OPVs, justifying further investigation into additional derivatives of SnPcs

Organic Thin Film Transistors Incorporating Solution Processable Thieno[3,2-b]thiophene Thienoacenes

Bottom-gate bottom-contact organic thin film transistors (OTFTs) were prepared with four novel star-shaped conjugated molecules containing a fused thieno[3,2-b]thiophene moiety incorporated either in the core and/or at the periphery of the molecular framework. The molecules were soluble in CS2, allowing for solution-processing techniques to be employed. OTFTs with different channel geometries were characterized in both air and vacuum in order to compare environmental effects on performance. Blending the small molecules with poly(styrene), an insulating polymer, facilitated the formation of an even semiconducting film, resulting in an order of magnitude increase in device mobility. The highest field-effect mobilities were in air and on the order of 10−3 cm2/Vs for three of the four molecules, with a maximum mobility of 9.2 × 10−3 cm2/Vs achieved for the most conjugated small molecule. This study explores the relationship between processing conditions and OTFT devices performance for four different molecules within this new family of materials, resulting in a deeper insight into their potential as solution-processable semiconductors

Molecular Engineering of Silicon Phthalocyanine to Improve the Charge Transport and Ammonia Sensing Properties of Organic Heterojunction Gas Sensors

Abstract Novel organic heterostructures fabricated with a bilayer consisting of an axially substituted silicon phthalocyanine (R2‐SiPc) derivative and lutetium bis‐phthalocyanine (LuPc2) are investigated for their ammonia sensing properties. Surface and microstructure characterization of the heterostructure films reveal either compact or highly porous surface topography in (345F)2‐SiPc and Cl2‐SiPc‐based heterostructures, while electrical characterization reveals a strong influence of the axial substituent in R2‐SiPc on NH3 sensing capabilities. Electrical characterization further demonstrates an apparent energy barrier for interfacial charge transport, which is higher in the (345F)2‐SiPc/LuPc2 heterojunction device. In‐depth charge transport studies by impedance spectroscopy further reveal a resistive interface in (345F)2‐SiPc/LuPc2 and faster bulk and interfacial charge transport in Cl2‐SiPc/LuPc2 heterojunction devices. Different interfacial charge transport capabilities and surface topographies affect NH3 sensing properties of the two heterojunction devices, in which (345F)2‐SiPc/LuPc2 reveals a fast and non‐linear response with a limit of detection (LOD) of 310 ppb, while Cl2‐SiPc/LuPc2 exhibits a slow, and linear response to NH3 with LOD of 100 ppb. Finally, different metrological parameters of the two sensors are correlated to the respective gas‐material interactions, in which adsorption and diffusion regimes are modulated by the surface topography and hydrophobicity of the sensing layer