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Influence of Deposition Pressure on the Film Morphologies, Structures, and Mobilities for Different-Shaped Organic Semiconductors

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journal contribution
posted on 03.07.2014, 00:00 by Yi Li, Shuang Chen, Qi Liu, Yun Li, Yi Shi, Xizhang Wang, Jing Ma, Zheng Hu
Four typical-shaped organic molecules including disk-, rod-, branch-, and sphere-like semiconductors are selected to investigate the influence of deposition pressure (Pdep) on the film morphologies, molecular packing, and mobilities. Different correlations of the microstructures and mobilities with Pdep are obtained, which are closely related with the corresponding molecular shapes. For disk-like F16CuPc and rod-like pentacene, higher Pdep leads to the lager interplanar spacing (D value) and grain sizes of the films which are beneficial to the charge transport and mobilities. For the branch-like TIPS-pentacene and sphere-like C60, the D values of the films keep unchanged and the grain sizes increase with increasing Pdep, presenting the unchanged or even decreased mobilities, respectively. The Pdep-dependence should be correlated with the interactions between the collisional N2 and organic molecules, the organic molecules and substrate, as well as among the organic molecules themselves, which is closely associated with the molecular shapes as partly understood by our theoretical simulations. This study suggests a convenient approach to optimize high-performance organic thin film transistors (OTFTs) according to the molecular shapes by regulating deposition pressure, and is also helpful for understanding the charge transport and performance of OTFTs.