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Solid-State Organic Photovoltaics: A Review of Molecular and Polymeric Devices
Published in Sun Sam-Shajing, Sariciftci Niyazi Serdar, Organic Photovoltaics, 2017
Arias et al. [107–109] reported the performance of photovoltaic devices based on blends of poly(9,9′-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)-bis-N,N′-phenyl-1,4-phenylenediamine) (PFB). Polyfluorene and its copolymers have emerged as leading candidates for polymer LEDs and displays due to attractive optical and chemical properties such as chemical tunability via copolymerization, high fluorescence quantum yield in neat films, and trap-free charge transport [110]. Polyfluorene also exhibits superior thermal stability and photostability vis-à-vis PPV, suggesting its use in solar cells where stability has been problematic. PFB is a copolymer with alternating fluorene and triphenylamine subunits that has been used as a hole-transporting layer. Triphenylamines have excellent hole transport properties and have been used in photoconductors and LEDs. Time-of-flight mobility measurements of PFB performed by Redecker et al. have shown hole mobilities of up to 2×10−3 cm2/Vs [111]. F8BT, on the other hand, has a high electron affinity (3.53 eV) [108]. Because of the large difference between the highest occupied molecular orbital (HOMO; 0.8 eV) and LUMO (1.24eV) levels of the two polymers, photoinduced charge transfer should be strong in a blend of PFB and F8BT.
Metal-Catalyzed Condensation Polymerization
Published in Samir H. Chikkali, Metal-Catalyzed Polymerization, 2017
Catalyst-transfer polymerization has been observed under Suzuki–Miyaura conditions. Boronate ester of iodo-substituted 3-hexylthiophene was polymerized at 0°C in the presence of CsF and 18-crown-6 in THF/water. P3HT with a narrow molecular weight distribution and very high head-to-tail regioregularity and low polydispersity was obtained while the Mn values increased in proportion to the monomer/catalyst feed ratio. Presence of phenyl ring at one end and a hydrogen atom at the other was confirmed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) technique. A block copolymer of polyfluorene and P3HT was also synthesized.50 The catalyst-transfer method was used to synthesize a star polymer with terrylene diimide (TDI) core and polyfluorene arms as a light-harvesting system by Suzuki–Miyaura coupling polymerization. Four iodophenyl rings on the TDI core were used as initiating sites for polymerization of bromo-substituted fluorine boronate ester using Pd(dba)2 as catalyst. It was proposed that aromatic core of TDI allowed chain walking of the catalyst promoting the catalyst-transfer mechanism.51 Polyfluorenes with a single amine or phosphonic acid at the end-group were synthesized by Pd-catalyzed Suzuki–Miyaura coupling polymerization. The polymers were used as stabilizing ligands for synthesis of cadmium selenide quantum dots to obtain inorganic nanocrystals with polyfluorene attached to the surface.52
Polymer Field-Effect Transistors
Published in Sam-Shajing Sun, Larry R. Dalton, Introduction to Organic Electronic and Optoelectronic Materials and Devices, 2016
Poly(3-hexylthiophene) (P3HT) is one of the most studied and most promising polymers for electronic applications, especially in its regioregular form [52]. The material is, however, sensitive to air and humidity and, for this reason, may not be suitable for large-scale applications even though less air sensitive grades have recently been developed. To minimize the effect of the environment, production devices will be encapsulated, which reduces the significance of the air sensitivity of the semiconductor material. To reduce the requirements on the encapsulation, the material properties must be optimized. A wide spectrum of derivatives of alkylthiophenes has been developed and new improved variants are frequently reported. Other promising and widely used materials are polyfluorenes and their derivatives.
Recent progress at the interface between nanomaterial chirality and liquid crystals
Published in Liquid Crystals Reviews, 2021
Diana P. N. Gonçalves, Marianne E. Prévôt, Şenay Üstünel, Timothy Ogolla, Ahlam Nemati, Sasan Shadpour, Torsten Hegmann
Finally, we will consider how multidomain cholesteric emitting layers can combine semiconducting and photonic functionalities to make OLEDs emitting CP electroluminescence (CPE). OLEDs can emit circularly polarized electroluminescence (CPEL) when the emitting organic material is chiral and of one handedness only. Friend and team exploited a chiral and enantiomerically pure substituted polyfluorene copolymer poly(fluorene-alt-benzothiadiazole) (c-PFBT) used as emitting layer in the OLEDs (Figure 20) [151]. The polymer contained a fluorene-benzothiadiazole donor–acceptor repeat unit forming the conjugated backbone, with chiral centres attached to the fluorene moiety. Thermal annealing led to the self-assembly of the polymer into a multidomain N*-LC film. CPEL with up to 40% excess of right-handed polarization was reached under pulsed voltage bias operation ( = − 0.8) and 30% ( = − 0.6) under constant voltage bias. CPEL originated from circular selective scattering and birefringence in such multidomain films (Figure 20b).
Temperature-dependent UV absorption of biphenyl based on intra-molecular rotation investigated within a combined experimental and TD-DFT approach
Published in Liquid Crystals, 2018
Adriana Pietropaolo, Concetta Cozza, Zhaoming Zhang, Tamaki Nakano
On raising the temperature, a decrease in intensity and blue shifts occur in UV absorbance spectra of biphenyl in hexane. We observed a similar behaviour in polyfluorene derivaties on irradiation with Circularly Polarised Light (CPL) [44] where hypochromism and blue-shift were both predicted within TD-DFT with the B97D [45] functional for the 2,2ʹ-difluorenyl while it should be noted that hypochromism is contributed not only by the change in dihedral angle but also by π-stacking between polymer chains. Remarkable hypochromism has been observed for poly(dibenzofulvene) and its derivatives having a tightly π-stacked conformation [46–51].
Thermoelectric properties of sorted semiconducting single-walled carbon nanotube sheets
Published in Science and Technology of Advanced Materials, 2019
Wenxin Huang, Eriko Tokunaga, Yuki Nakashima, Tsuyohiko Fujigaya
Recently, various conductive polymers [7] such as poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT/PSS) [8], and acid-doped polyaniline [9–11], together with carbon nanotubes (CNTs) [12] have attracted attention as TE materials due to their electrical conductivity, lightness, flexibility, low toxicity, abundance, and production scalability [13]. In particular, semiconducting single-walled carbon nanotubes (s-SWNTs) have attracted strong attention as a promising TE material because of their large Seebeck coefficient over 1000 μV K−1 at room temperature [14–17], which is much higher than inorganic semiconducting materials [18]. In reality, most SWNTs are produced as a 1:2 mixture of metallic (m-) and s-SWNTs [19,20] and need to be extracted or sorted to use s-SWNTs. Recently, various methods such as gel chromatography [21], polyfluorene (PFO)-based polymer wrapping [22,23], DNA recognition [24], density gradient ultracentrifugation (DGU) [25,26] and two-phase separation [27,28] allow us to obtain s-SWNTs and to study their TE properties including their Seebeck coefficient, electrical conductivity, and thermal conductivity. Nakai et al. prepared s-SWNT sheet (thickness; 50–130 μm) using DGU technique and found that the s-SWNT sheet with 100% s-SWNT purity1 had a large Seebeck coefficient of 170 μV K−1, which was much higher than that of m-SWNT sheet (<25 μV K−1) and comparable to that of inorganic semiconducting materials [29]. They revealed that the Seebeck coefficient was increased as the purity of s-SWNT increased [29], which was also systematically studied by Piao et al. [30]. For the s-SWNT sheets, it was demonstrated that Seebeck coefficient was further increased by optimizing the doping level chemically [14,16,31,32] or electrochemically [33–35] and, quite importantly, the higher purity of s-SWNT leads to a larger increase of Seebeck coefficient [29], thus the value reached to 2000 μV K−1 [14].