Dithienylbenzothiadiazole-based donor-acceptor organic semiconductors and effect of end capping groups on organic field effect transistor performance

Donor-Acceptor-Donor (D-A-D) based conjugated molecules 4,7-bis(5-(4-butoxyphenyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (BOP-TBT) and 4,7-bis(5-(4-trifluoromethyl)phenyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (TFP-TBT) using thiophene-benzothiadiazole-thiophene central core with trifluoromethyl phenyl and butoxyphenyl end capping groups were designed and synthesised via Suzuki coupling. Optical, electrochemical, thermal, and organic field effect transistor (OFET) device properties of BOP-TBT and TFP-TBT were investigated. Both small molecules possess two absorption bands. Optical band gaps were calculated from the absorption cut off to be in the range of 2.06–2.25 eV. Cyclic voltammetry indicated reversible oxidation and reduction processes and the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels were calculated to be in the range of 5.15–5.40 eV and 3.25–3.62 eV, respectively. Upon testing both materials for OFET, trifluoromethylphenyl end capped material (TFP-TBT) shows n-channel behaviour whereas butoxyphenyl end capped material (BOP-TBT) shows p-channel behaviour. Density functional theory calculations correlated with shifting of HOMO-LUMO energy levels with respect to end capping groups. Vacuum processed OFET of these materials have shown highest hole carrier mobility of 0.02 cm2/Vs and electron carrier mobility of 0.004 cm2/Vs, respectively using Si/SiO2 substrate. By keeping the central D-A-D segment and just by tuning end capping groups gives both p- and n-channel organic semiconductors which can be prepared in a single step using straightforward synthesis

Carbon based materials for electronic bio-sensing

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A fluorenone based low band gap solution processable copolymer for air stable and high mobility organic field effect transistors

A fluorenone based alternating copolymer (PFN-DPPF) with a furan based fused aromatic moiety has been designed and synthesized. PFN-DPPF exhibits a small band gap with a lower HOMO value. Testing this polymer semiconductor as the active layer in organic thin-film transistors results in hole mobilities as high as 0.15 cm2 V-1 s-1 in air

A benzothiadiazole end capped donor-acceptor based small molecule for organic electronics

A benzothiadiazole end-capped small molecule 3,6-bis(5-(benzo[c][1,2,5] thiadiazol-4-yl)thiophen-2-yl)-2,5-bis(2-butyloctyl)pyrrolo[3,4-c]pyrrole-1, 4(2H,5H)-dione (BO-DPP-BTZ) using a fused aromatic moiety DPP (at the centre) is designed and synthesized. BO-DPP-BTZ is a donor-acceptor-donor (D-A-D) structure which possesses a band gap of 1.6 eV and exhibits a strong solid state ordering inferred from ∼120 nm red shift of the absorption maxima from solution to thin film. Field-effect transistors utilizing a spin coated thin film of BO-DPP-BTZ as an active layer exhibited a hole mobility of 0.06 cm 2 V-1 s-1. Solution-processed bulk heterojunction organic photovoltaics employing a blend of BO-DPP-BTZ and [70]PCBM demonstrated a power conversion efficiency of 0.9%

Accurate Field‐Effect Mobility and Threshold Voltage Estimation for Thin‐Film Transistors with Gate‐Voltage‐Dependent Mobility in Linear Region

Abstract The measurement of mobility and threshold voltage in thin‐film transistors (TFTs) in which the mobility is a function of gate voltage or carrier density is usually done inaccurately. Herein, accurate mobility calculations within the framework of the gradual channel approximation are described. Conventionally, the derivative of drain current with respect to gate voltage is often used to calculate mobilities in the linear region. This procedure often leads to errors when the mobility is not constant. Using a first‐order finite difference‐based calculations, it is shown how the correct field‐effect mobility can be extracted. The corrected mobility can be smaller than the conventionally calculated field‐effect mobility by up to a factor of 2. It is also shown that the corrected field‐effect mobility is identical to the average mobility. A threshold voltage that is independent of gate voltage value and suitable for disordered semiconductors is used for more accurate mobility calculations. The mobility and threshold voltage calculations are illustrated with experimental data from multiple TFTs with indium gallium zinc oxide, zinc tin oxide, and molybdenum disulfide channel layers