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Threshold Voltage Control in Organic Field-Effect Transistors by Surface Doping with a Fluorinated Alkylsilane
摘要： Doping is a powerful tool to control the majority charge carrier density in organic field-effect transistors and the threshold voltage of these devices. Here, a surface doping approach is shown, where the dopant is deposited on the prefabricated polycrystalline semiconducting layer. In this study, (tridecafluoro-1,1,2,2-tetrahydrooctyl)-trichlorosilane (FTCS), a fluorinated alkylsilane is used as a dopant, which is solution processable and much cheaper than conventional p-type dopants, such as 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). In this work, the depositions from the gas phase and from solution are compared. Both deposition approaches led to an increased conductivity and to a shift in the threshold voltage to more positive values, both of which indicate a p-type doping effect. The magnitude of the threshold voltage shift could be controlled by the FTCS deposition time (from vapor) or FTCS concentration (from solution); for short deposition times and low concentrations, the off current stayed constant and the mobility decreased only slightly. In the low doping concentration regime, both approaches resulted in similar transistor characteristics, i.e., similar values of shift in the threshold and turn-on voltage as well as mobility, ION/IOFF ratio and amount of introduced free charge carriers. In comparison with vapor deposition, the solution-based approach can be conducted with less material and in a shorter time, which is critical for industrial applications.
关键词： self-assembled monolayers,fluorinated alkylsilanes,organic field-effect transistors,surface doping,p-type doping
更新于2025-09-23 15:23:52
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Growth mechanisms of F4-TCNQ on inorganic substrates and nanostructures
摘要： The organic semiconductor tetrafluorotetracyanoquinodimethane (F4-TCNQ) is a promising candidate for the doping of organic semiconductors, two-dimensional materials and inorganic compounds, such as ZnO, and also to enhance the charge carrier injection at contacts in organic electronics. In order to evaluate its applicability as a functionalization material or as an electrically active part in devices, we present a systematic study on the growth mode of F4-TCNQ beyond the first few monolayers on different inorganic substrates that cover a broad variety regarding their physical, chemical and morphological surface properties. The materials used are silicon, silicon carbide, graphene on silicon, sapphire, nanocrystalline diamond, as well as gallium nitride (GaN) layers and nanowire arrays. While the surface termination influences the shape and morphology of the islands of F4-TCNQ which form on all substrates investigated, no significant dependence of the growth mode on the substrate doping type and concentration is observed. GaN nanowires are found to act as nucleation sites for F4-TCNQ islands and to be covered by few monolayers of F4-TCNQ forming a closed coaxial shell. In conclusion, F4-TCNQ is identified to nucleate via Stranski-Krastanov growth consisting of monolayers and islands of different size and shape. The findings in this work provide basic growth information for the implementation of F4-TCNQ as functionalization material for nanowire-based applications.
关键词： GaN nanowires,surface functionalization,growth mode,organic semiconductors,organic electronics,surface doping,F4-TCNQ
更新于2025-09-23 15:21:01
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Unsymmetrical Small Molecules for Broadband Photoresponse and Efficient Charge Transport in Organic Phototransistors
摘要： Organic photosensitizers have been investigated as effective light sensing elements that can promote strong absorption with high field-effect mobility in organic phototransistors (OPTs). In this study, a novel organic photosensitizer is synthesized to demonstrate broadband photoresponse with enhanced electrical performance. An unsymmetrical small molecule of a solubilizing donor(Dsol)-acceptor(A)-dye donor(Ddye) type connected with twisted conjugation system is designed for broadband detection (ranging from 250 nm to 700 nm). This molecule has high solubility, thereby facilitating the formation of uniformly dispersed nanoparticles in an insulating polymer matrix, which is deposited on top of OPT semiconductors by a simple solution process. The broadband photodetection shown by the organic photosensitizer is realized with improved mobility by close to an order of magnitude and high on/off current ratio (~105) of the organic semiconductor. Furthermore, p-type charge transport behavior in the channel of the OPT is enhanced through the intrinsic electron-accepting ability of the organic photosensitizer, caused by the unique molecular configuration. These structural properties of organic photosensitizers contribute to an improvement in broadband photosensing systems with new optoelectronic properties and functionalities.
关键词： Photosensitizer,Surface doping,Broadband detection,Phototransistor,Charge trap
更新于2025-09-23 15:19:57
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Surface modification of TiO2 photoanodes with In3+ using a simple soaking technique for enhancing the efficiency of dye-sensitized solar cells
摘要： Indium-doped TiO2 photoanode for dye-sensitized solar cells are prepared using a simple surface-doping technique by soaking the TiO2 film in acidic In3+ solution at 70oC for 30, 45 and 60 minutes followed by sintering at 450oC. Structural characterization of In-doped TiO2 films by SEM, TEM, EDX, XRD and Raman spectroscopy revealed the successful attachment of Indium to the surface of TiO2 and that the amount of In dopant is proportional to the soaking time. The PCE of the devices fabricated from In-doped TiO2 with a soaking time of 30 minutes produced an increase of 18.0 % compared to the undoped cells. Charge extraction analysis at open-circuit revealed that surface-doping with indium shifts TiO2 band edge downward. However, the increase in VOC was found as the net effect of negative movement of CB and retarded recombination caused by TiO2 surface passivation via the In dopant.
关键词： Recombination reactions,Surface-doping,Photovoltage decay,X-ray spectroscopy
更新于2025-09-19 17:13:59
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Construction of Interface Dipoles by Surface Doping and Their Role in the Open Circuit Voltage in Polymer Solar Cells
摘要： A kind of dipolar interface is realized by surface doping of poly-(3,4-ethylenedioxythiophene) (PEDOT) with tetrafluoro-tetracyano-quinodimethane (F4TCNQ). PEDOT is in situ synthesized by electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) on an indium tin oxide (ITO) electrode, and then F4TCNQ is spin-coated atop the PEDOT layer. Because the LUMO of F4TCNQ is lower than the HOMO of PEDOT, the spontaneous electron transfer from PEDOT to F4TCNQ results in a bilayered structure of PEDOT cations and F4TCNQ anions. Thus, a permanent interfacial dipole is formed in the surface-doping system. The surface doping not only enhances the conductivity of PEDOT, but also increases the surface work function of the electrode. The dipolar film is applied as the anode interface in polymer solar cells (PSCs), and the results show that such an interface dipole plays a very important role in the open circuit voltage (Voc) of the PSCs.
关键词： interfaces,dipoles,surface doping,charge transfer,solar cells
更新于2025-09-19 17:13:59