| Graphene is a promising conductive material due to its novel electrical properties, extraordinary mechanical property, flexibility, and high chemical and thermal stability, graphene-based conducting electrodes and their applications in organic optoelectronic are emerging as a new field of vital significance. Up to now, various approaches, mainly including vacuum filtration, spin coating, chemical vapor deposition, and expiaxial growth, have been proposed to prepare graphene-based films, much progress has been made toward their use as electrodes in organic solar cells, organic light-emitting diodes, and organic transistors. However, techniques for fabricating graphene films with high performance and low price, mechanisms, and related emerging organic semiconductor devices, are still in their infancy where a lot of challenges remain in fundamental research and practical applications. In this dissertation I introduce the field of fabrication of graphene-based films and related organic optoelectric diodes, progress in organic/polymer memory devices and their mechanisms have been reviewed. While great strides have been made toward the design and fabrication of emerging graphene-based conducting films and their organic electronics. Specially, detailed studies of the conductivity of redued graphene films (rGO) and device mechanisms have been explored. The completed works and the results are mainly summarized as follows:Based on the analysis of advantages and disadvantages of rGO films by chemical reduction, a scheme of hydrazine smearing at low temperature was proposed to reduce GO films. Herein, the hydrazine was smeared on the surface of GO film to avoid fragmentation and delamination of rGO film in hydrazine solution. In order to accelerate the reduction reaction, the hydrazine-smeared GO film was heated to 100°C (low temperature), thus many different polymers can be used as substrates. Moreever, a concept of the"effective reduction depth"for GO film was defined to assess the reduction effect and the reduction mechanism is proposed. The prepared rGO film has a lower sheet resistance (~160-500 ohm/sq) and higher conductivity (26 S/cm) as compared to other rGO films obtained by commonly used chemical reduction methods. The effective reduction can be attributed to the large"effective reduction depth"in the GO films (1.46μm) and the high C/O ratio (8.04). By combining reduction with smeared hydrazine at low temperature and the multilayer stacking technique, rGO film with a tunable thickness and sheet resistance are achievd.A facile approach for fabricating flexible rGO films on PET substrates by high temperature annealing (high reduction ability) and transfer technique was describled. By controlling the differential centrifugation, GO sheets with tunable laterial size have been separated and obtained to study the influence of GO size on the detachment feasibility of rGO film, with the average value of laterial size of ~4μm for large-size GO and ~1μm for small-size GO. GO size dependent the detachment feasibility of rGO films has been observed and rGO films from large-size GO is easily detached. Meanwhile, the concentration (2M) of NaOH etchant, as a critical factor of detachment efficiency, is optimized. The flexible rGO films show outstanding optic-electronic properties, possessing a sheet resistance of 8000 ohm/sq with a transmittance of ~80% at 550 nm. Moreover, by blending the large-size GO and SWNT-COOH directly, a higher conductive and transparent all-carbon hybrid film was solution processed under ambient condition, possessing a sheet resistance of 4500 ohm/sq with a transimittance of ~90% at 550 nm. Thus, combining the remarkable conductivity, high transparency, large-scale, and green production of these conducting films make them of tremendous potential in flexible electronics.The relationship between the conductivity of rGO film and its four contributions, including GO size, C/O ratio, film fabrication process, and effective reduction depth, has been systematically analysed, the effect of GO size, film thickness, and reduction method on the film morphology is investigated as well. By varying the fourth factor with other three factors restricted, measurement results show that the film conductivity is dependent on the four contributions. The conductivity increases with an increasing C/O ratio and tend to saturation finally. Furthermore, rGO films from large-size GO exhibit a higher conductivity with a value of 5P S/m, about two times than that from small-size GO. Moreover, great significance of the difference of conductivity induced by the microstructure of rGO film fabrication is obtained; the conductivity of rGO films with well stacked microstructures is about 10 times higher than that with random stacked microstructures. In addition, the GO films reduced completely and uniformly show a higher electrical property than that reduced partially due to the presence of effective reduction depth. From the point of view of film morphology, the roughness from large-size GO sheets is lower than that from small-size GO when their thickness are similar. Meanwhile, thin film has smooth surface relative to thick film. We also find the film morphology by thermal annealing show the highest quality compared to that by other reduction methods.A unique device structure with a configuration of rGO/P3HT: PCBM/Al has been designed for the polymer memory device, where the rGO film and bulk heterojunction concept are firstly applied as the electrodes and functional layer in organic memory, respectively. The current-voltage curves of the device show the electrical bistable behavior and WORM memory effect, with a high On/Off ratio (10P) and low switching threshold voltage (0.5-1.2 V), which are dependent on the sheet resistance of rGO electrode. Our experimental results confirm that the carrier transport mechanism in the Off and On states are dominated by the thermonic emission current and ohmic current. The polarization of PCBM domains and the localized internal electrical field formed among the adjacent domains are proposed to explain the electrical switching of the memory device. In addition, solution-processable GO: SWNT-COOH hybrid films are also introduced as electrodes in organic solar cells, the hybrid film favors the collection of dissociated hole due to its p-type semiconductor property. The solution-processable polymer solar cell with a configuration of GO: SWNT-COOH/PEDOT: PSS/P3HT: PCBM/Al has a shor-circuit current of 0.627 mA/cmP and open-circuit voltage of 0.52 V.The device function is dependent on its current-voltage characteristics; one of the strategies to tune current-voltage behanviors in organic diodes is to combine field-induced charge transfer with schottky barrier. According to this principle, a diode was fabricated utilizing a hybrid of post-functionalized polystyrene derivative covalently tethered with electron-donar carbazole moieties and electron-acceptor CdTe nanocrystals. Current-voltage curves show an electrical transition with some hysteresis is only observed under a negative bias, with three orders of On/Off ratio. Moreover, the device has rectifying effect with a rectification ratio of 6 and its maximum rectified output current is ~5×10~5P A. The asymmetric switching is interpreted as the result of both field induced charge transfer ad schottky barrier, capable of reducing the misreading of crossbar memory. Meanwhile, chemical doping of CdTe nanocrystals favor their uniform dispersion in matrix and stable operation of device. Based on above analysis, a diode with flexible rGO film as electrode and GO film as functional layer was designed and fabricated, with a configuration of rGO/GO/Al. Both hysteresis effect and rectifying effect are observed in device, with a rectification ratio of 3. Note that the low resistance state by hysteresis under the positive and negative sweeping will back to its initial state when the applied voltage is removed, promising the effect of random acess memory, which extends the scope of applications of GO film- based diodes in electrical memory.
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