High operational and environmental stability of high-mobility conjugated polymer field-effect transistors through the use of molecular additives.

Due to their low-temperature processing properties and inherent mechanical flexibility, conjugated polymer field-effect transistors (FETs) are promising candidates for enabling flexible electronic circuits and displays. Much progress has been made on materials performance; however, there remain significant concerns about operational and environmental stability, particularly in the context of applications that require a very high level of threshold voltage stability, such as active-matrix addressing of organic light-emitting diode displays. Here, we investigate the physical mechanisms behind operational and environmental degradation of high-mobility, p-type polymer FETs and demonstrate an effective route to improve device stability. We show that water incorporated in nanometre-sized voids within the polymer microstructure is the key factor in charge trapping and device degradation. By inserting molecular additives that displace water from these voids, it is possible to increase the stability as well as uniformity to a high level sufficient for demanding industrial applications.We gratefully acknowledge financial support from Innovate UK (PORSCHED project) and the Engineering and Physical Sciences Research Council though a Programme Grant (EP/M005141/1). I.N. acknowledges studentship support from FlexEnable Ltd. K.B. gratefully acknowledges financial support from the Deutsche Forschungsgemeinschaft (BR 4869/1-1). B.R., M.K.R., and J.L.B. thank the financial support from King Abdullah University of Science and Technology (KAUST), the KAUST Competitive Research Grant program, and the Office of Naval Research Global (Award N62909-15-1-2003 );This is the author accepted manuscript. The final version is available from Nature Publishing Group via https://doi.org/10.1038/nmat478

Heteroatom and bridged-ring π-conjugated polymers and their use in organic electronics

Organic semiconductors have attracted much interest over the last two decades for their potential to replace inorganic semiconductors in a range of applications. This work focuses on the design, synthesis, analysis and characterisation of new semiconducting polymers, and their use as the semiconducting layer in organic field effect transistors. This thesis reports and analyses fourteen novel semiconducting polymers. The substitution of thiophene for thiazole and has led to the synthesis and characterisation of isostructural thiazole containing polymers. We have observed that thiazole can induce extra crystallinity and molecular ordering, but have also noted that thiazole incorporation can lead to increased instability and disorder in polymers. The substitution of protons for fluorines has led to isostructural fluorinated polymers. We have observed that fluorination can stabilise energy levels and does not significantly impact disorder, the solid-state or optical properties. But fluorination does have an adverse impact on the charge transport properties. Through the synthesis of IDT-BT and other IDT copolymers, we have developed an understanding of how molecular design, purification, and annealing can affect its preferential disorder and morphological properties. Furthermore, we have the developed the idea that charge-transport along the rigid planar backbone of IDT-BT is a major charge transport pathway, and that by extending the bridged IDT motif with fused rings we could enforce even greater rigidity and planarity and reduce alkyl chain density along the polymer backbone. The idea increasing the bridge donor length has culminated with the synthesis of TIF. TIF-BT has achieved high charge carrier mobilities and high on-currents of 3.0 cm2 V-1 s-1 and 0.8 mA, respectively. TIF-BT was judiciously designed through applying molecular design criteria, which have been developed throughout this work by improving increasing our understanding of the relationship between chemical structure and charge-transport.Open Acces

The effect of thiadiazole out-backbone displacement in indacenodithiophene semiconductor polymers †

We describe the synthesis and characterisation of two new polymers consisting of an electron-rich backbone containing indacenodithiophene (IDT) and dithiophene (DT) with the electron-poor units benzothiadiazole (BT) and benzopyrazolothiadiazole (BPT) fused on top of DT. The effect of this substitution has been studied and discussed by optical, electrochemical and computational means. Despite having very similar molecular distribution as well as thermal and electrochemical properties, the addition of the stronger electron-withdrawing BPT unit leads to a substantial change on the absorption properties by promoting the intramolecular charge transfer (ICT) band alongside the p-p*. Furthermore, we also report organic field effect transistor and solar cells device results, giving hole mobilities of 0.07 cm 2 V À1 s À1 with low threshold voltage (<10 V) and power conversion efficiencies of up to 2.2%

Dithiopheneindenofluorene (TIF) Semiconducting Polymers with Very High Mobility in Field-Effect Transistors

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The charge-carrier mobility of organic semiconducting polymers is known to be enhanced when the energetic disorder of the polymer is minimized. Fused, planar aromatic ring structures contribute to reducing the polymer conformational disorder, as demonstrated by polymers containing the indacenodithiophene (IDT) repeat unit, which have both a low Urbach energy and a high mobility in thin-film-transistor (TFT) devices. Expanding on this design motif, copolymers containing the dithiopheneindenofluorene repeat unit are synthesized, which extends the fused aromatic structure with two additional phenyl rings, further rigidifying the polymer backbone. A range of copolymers are prepared and their electrical properties and thin-film morphology evaluated, with the co-benzothiadiazole polymer having a twofold increase in hole mobility when compared to the IDT analog, reaching values of almost 3 cm2 V−1 s−1 in bottom-gate top-contact organic field-effect transistors

Crystal Engineering of Dibenzothiophenothieno[3,2-b]thiophene (DBTTT) Isomers for Organic Field-Effect Transistors

Three thiophene ring-terminated benzothieno[3,2-b]benzothiophene (BTBT) derivatives, C-C6-DBTTT, C-C12-DBTTT, and L-C12-DBTTT, were designed and synthesized, differing in the isomerization of alkyl chain position as well as aromatic core construction. A study of crystal structure and electronic properties combined with a theoretical investigation was performed to understand the structure–property relationships for the application of these molecules in organic field-effect transistors (OFETs). Different crystal packing structures were observed for these three isomers by single-crystal X-ray diffraction as a result of a crystal engineering molecular design approach. The highest charge-carrier mobility was observed for the isomer with a collinear core, L-C12-DBTTT. Preliminary results demonstrated a promising hole mobility of 2.44 cm2 V–1 s–1, despite the polymorphism observed in ambient conditions.info:eu-repo/semantics/publishe

Chalcogenophene Comonomer Comparison in Small Band Gap Diketopyrrolopyrrole-Based Conjugated Polymers for High-Performing Field-Effect Transistors and Organic Solar Cells

The design, synthesis, and characterization of a series of diketopyrrolopyrrole-based copolymers with different chalcogenophene comonomers (thiophene, selenophene, and tellurophene) for use in field-effect transistors and organic photovoltaic devices are reported. The effect of the heteroatom substitution on the optical, electrochemical, and photovoltaic properties and charge carrier mobilities of these polymers is discussed. The results indicate that by increasing the size of the chalcogen atom (S < Se < Te), polymer band gaps are narrowed mainly due to LUMO energy level stabilization. In addition, the larger heteroatomic size also increases intermolecular heteroatom–heteroatom interactions facilitating the formation of polymer aggregates leading to enhanced field-effect mobilities of 1.6 cm²/(V s). Bulk heterojunction solar cells based on the chalcogenophene polymer series blended with fullerene derivatives show good photovoltaic properties, with power conversion efficiencies ranging from 7.1–8.8%. A high photoresponse in the near-infrared (NIR) region with excellent photocurrents above 20 mA cm^–2 was achieved for all polymers, making these highly efficient low band gap polymers promising candidates for use in tandem solar cells

Isostructural, Deeper Highest Occupied Molecular Orbital Analogues of Poly(3-hexylthiophene) for High-Open Circuit Voltage Organic Solar Cells

We present the synthesis and characterization of two novel thiazole-containing conjugated polymers (<b>PTTTz</b> and <b>PTTz</b>) that are isostructural to poly­(3-hexylthiophene) (P3HT). The novel materials demonstrate optical and morphological properties almost identical to those of P3HT but with HOMO and LUMO levels that are up to 0.45 eV deeper. An intramolecular planarizing nitrogen–sulfur nonbonding interaction is observed, and its magnitude and origin are discussed. Both materials demonstrate significantly greater open circuit voltages than P3HT in bulk heterojunction solar cells. <b>PTTTz</b> is shown to be an extremely versatile donor polymer that can be used with a wide variety of fullerene acceptors with device efficiencies of up to 4.5%. It is anticipated that this material could be used as a high-open circuit voltage alternative to P3HT in organic solar cells