Origin of Hole-Trapping States in Solution-Processed Copper(I) Thiocyanate and Defect-Healing by I2 Doping |
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Authors: | Pimpisut Worakajit Pinit Kidkhunthod Thanasee Thanasarnsurapong Saran Waiprasoet Hideki Nakajima Taweesak Sudyoadsuk Vinich Promarak Adisak Boonchun Pichaya Pattanasattayavong |
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Affiliation: | 1. Department of Materials Science and Engineering, School of Molecular Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), Rayong, 21210 Thailand;2. Synchrotron Light Research Institute (Public Organization), 111 University Avenue, Muang, Nakhon Ratchasima, 30000 Thailand;3. Department of Physics, Faculty of Science, Kasetsart University, Bangkok, 10900 Thailand |
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Abstract: | Solution-processed copper(I) thiocyanate (CuSCN) typically exhibits low crystallinity with short-range order; the defects result in a high density of trap states that limit the device's performance. Despite the extensive electronic applications of CuSCN, its defect properties are not understood in detail. Through X-ray absorption spectroscopy, pristine CuSCN prepared from the standard diethyl sulfide-based recipe is found to contain under-coordinated Cu atoms, pointing to the presence of SCN− vacancies. A defect passivation strategy is introduced by adding solid I2 to the processing solution. At small concentrations, the iodine is found to exist as I− which can substitute for the missing SCN− ligand, effectively healing the defective sites and restoring the coordination around Cu. Computational study results also verify this point. Applying I2-doped CuSCN as a p-channel in thin-film transistors shows that the hole mobility increases by more than five times at the optimal doping concentration of 0.5 mol.%. Importantly, the on/off current ratio and the subthreshold characteristics also improve as the I2 doping method leads to the defect-healing effect while avoiding the creation of detrimental impurity states. An analysis of the capacitance-voltage characteristics corroborates that the trap state density is reduced upon I2 addition. |
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Keywords: | copper(I) thiocyanate defect healing doping hole transports thin-film transistors |
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