Liaquid Phase Exfoliation Of Graphene-like Molybdenum Disulfide And Its Application In Organic Thin Film Transistors

Graphene-like molybdenum disulfide (MoS2) has attracted tremendous attention due to its excellent optoelectronic properties with unique microstructure and controllable bandgap. Exfoliation of MoS2 and its application in optoelectronic devices has become a research hot. Liquid exfoliation has been widely studied for achieving mass production. However, the solvents used in liquid exfoliation are limited in high boiling point solvents such as N-methylpyrrolidone. Though the method has been extended by the use of polymer in low boiling point solvents, the insulating polymer would block the further application. Chloroform, an organic solvent with low boiling point, has been commonly used in optoelectronic devices. Achieving MoS2 nanosheets dispersed in chloroform will accelerate the application in optoelectronic field.In this thesis, we adopted two materials, N-dodecanthiol and poly-3-hexylthiophene (P3HT), for successful exfoliation of MoS2 nanosheets in chloroform. The effect of MoS2 nanosheets on immediate aggregation of P3HT was also investigated and the organic thin-film transistors (OTFT) based on P3HT and MoS2 exhibited higher mobility.In Chapter 1, basic properties and common preparation of MoS2 are summarized, followed by the recent advance in surface modification and dispersion in low boiling point solvents. The applications of two-dimensional materials for P3HT-based FETs are also reviewed.In Chapter 2, we reported N-dodecanthiol exfoliation of MoS2. Since N-dodecanthiol will cause aggregations of MoS2 nanosheets, we extended to N-dodecanthiol/chloroform co-assisted liquid exfoliation of MoS2. The relationships between sonication time, solvent volume ratios and exfoliating effect were investigated, of which the volume ratio of 1:1 and the sonication time of 12 h are the best parameters. Through solvent exchange, the MoS2 nanosheets could be dispersed well in chloroform. We demonstrated the successful exfoliation of relatively disperse MoS2 nanosheets via TEM characterization.In Chapter 3, we reported conductive P3HT-assisted chloroform exfoliation of MoS2. TEM characterization has proven the ultrathin nanosheets. Based on this, we assumed the exfoliating mechanism. In addition, we successfully applied this method for liquid exfoliation of WS2 and MoSe2 nanosheets.In Chapter 4, we studied the influence of MoS2 on the immediate aggregation of P3HT solution and crystallinity of the related films. P3HT-MoS2 based OTFTs were constructed and the electric performances were investigated. The devices exhibited p-type characteristics with the best performance of 0.056 cm2V-1s-1 for hole mobility and 105 for on-off ratio. The effect of initial mass of MoS2 on device performances was also investigated and found that the suitable content of MoS2 was critical for achieving efficient OTFT performance.