Ordering of semiconducting polymers in thin films from the nano to microscale is strongly correlated with charge transport properties as well as organic field-effect transistor performance. This paper reports a method to control nano to microscale ordering of poly{[N,N′-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)) thin films by precisely regulating the solidification rate from the metastable state just before crystallization. The proposed simple but effective approach, kinetically controlled crystallization, achieves optimized P(NDI2OD-T2) films with large polymer domains, long range ordered fibrillar structures, and molecular orientation preferable for electron transport leading to dramatic morphological changes in both polymer domain sizes at the micrometer scale and molecular packing structures at nanoscales. Structural changes significantly increase electron mobilities up to 3.43 ± 0.39 cm 2 V −1 s −1 with high reliability, almost two orders of enhancement compared with devices from naturally dried films. Small contact resistance is also obtained for electron injection (0.13 MΩ cm), low activation energy (62.51 meV), and narrow density of states distribution for electron transport in optimized thin films. It is believed that this study offers important insight into the crystallization of conjugated polymers that can be broadly applied to optimize the morphology of semiconducting polymer films for solution processed organic electronic devices.flexibility, unique electronic properties, and simple and cost effective printing processes. [1][2][3] Since charge transport in semiconducting polymer films depends mainly on charge hopping along both intramolecular and intermolecular π-orbitals, it is important to control crystalline grain size and connectivity at conjugated polymer grain boundaries to obtain high performance organic field-effect transistors (OFETs). [4][5][6][7] Several strategies have been reported to control conjugated polymer film morphology for high performance OFETs including the most widely used method being thermal annealing method. [8][9][10] Simple thermal annealing can improve the performance of almost all polymer transistors to some extent, but optimum morphology for efficient charge transport must still show precisely controlled grain sizes and boundaries. Several morphology control strategies to overcome this issue have been reported, including solvent engineering, which provides large ordered domains originating from interactions between solvent and conjugated polymers; [11,12] applying shear force to organic semiconductors using various printing methods; [13][14][15][16][17][18][19][20] and other shear alignment methods including off-center spin coating, which applies centrifugal force to substrate away from the spin coater axis. [12,[21][22][23][24] However, it is essential to understand the kinetics of drying from a deposited solution in
A molecular design strategy to achieve highly balanced ambipolar charge transport for donor–acceptor (D–A) isoindigo (IIG)‐based copolymer through systematic selection of fluorination positions is reported. To study fluorine substitution site effects on electronic and structural properties, two fluorinated IIG‐based copolymers (PIIG‐iFT2 and PIIG‐oFT2) are synthesized, which contain two fluorine atoms at the bithiophene (T2) inner and outer site and compare them with a nonfluorinated copolymer of IIG and T2 (PIIG‐T2) as the reference polymer. Fluorination at the outer site of T2 in PIIG‐oFT2 polymer effectively lowers molecular energy levels and increases molecular planarity more than fluorination at the T2 inner site. PIIG‐oFT2 organic field‐effect transistors show highly balanced ambipolar mobility, hole mobility (μh)/electron mobility (μe) = 1 by increasing electron mobility, whereas PIIG‐T2 (μh/μe = 9.0) and PIIG‐iFT2 (μh/μe = 2.4) exhibit unbalanced ambipolar transport. The ambipolar complementary‐like inverter is also demonstrated by simple one‐time coating of PIIG‐oFT2 with gain = 21.
In article number https://doi.org/10.1002/adma.201802379, Yong Xu, Myung‐Gil Kim, Yong‐Young Noh, and co‐workers develop room‐temperature solution‐processed, high‐performance, solution‐processible, and reliable copper iodide (CuI) thin‐film transistors (TFTs). These p‐type CuI TFTs with a ZrO2 dielectric show impressively high field‐effect mobility of 1.93 cm2 V−1 s−1 at a low operating voltage of 5 V. Transparent complementary inverters composed of the p‐type CuI and n‐type IGZO TFTs are demonstrated with clear inverting characteristics and voltage gain of >4.
Ultra‐thin and dense sol‐gel metal oxide films for gate dielectric layers in large‐area printed metal oxide and organic thin‐film transistors are reported by a simple wire bar coating method. Y.‐Y. Noh, M.‐H. Yoon, and co‐workers describe this method on page 5043.
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