ポリ3ヘキシルチオヘン薄膜の構造と移動度

Abstract

Low-cost organic field-effect transistors (OFETs) were fabricated with soluble and crosslinkable poly (4-vinylphenol)(PVP) as the gate insulator and poly(3-hexylthiophene)(P3HT) as the active semiconductor which was cast by spin-coating or drop-casting method. The substrate was glass or poly (ethylene naphthalate)(PEN). As a comparison, OFETs with vacuum deposited pentacene film and polycarbonate (PC) gate insulator were also fabricated and investigated. We get the following conclusion. Aggregation states and charge transfer mechanisms in the P3HT films were studied in OFETs. Both regioregular and regiorandom P3HT (RRa-P3HT) were studied and also the oligomer acenes of pentacene. Pentacene films were deposited by the physical vapor deposition (PVD) method on the gate insulator of PC. RRa-P3HT films showed mobilities one or two orders lower than those of RR-P3HT films because they were amorphous in both spin-coated and drop-cast films. Experimental results also revealed a correlation between the mobility and the aggregation states that the larger aggregate size and number can result in the higher mobility. Pentacene films (in herringbone structure) displayed mobilities about two orders higher than RR-P3HT (in lamellar structure), because it formed polycrystalline films with crystal size being much larger than those in RR-P3HT semicrystalline films. For RR-P3HT films, aggregation with the π-π stacking interaction was found to assist the planarization of the polymer backbones, however, the alkyl side-chain interactions could result in chain folding within one polymer, and hence decrease the crystallinity and mobility greatly. Multiple π-π^* absorption peaks for RR-P3HT thin films were ascribed to the vibronic progression with the in-plane ring breathing mode assisted by polymer aggregation but not to the typical Davydov splitting; and this explanation coincide well with the relatively poor crystallinities and low mobilities in semicrystalline P3HT thin films. These results imply that there are still many spaces to increase the mobility of π-conjugated polymer films if larger π-π stacked crystal size can be obtained. The performances of the OFETs can be further improved by optimizing the structure and morphology of organic semiconductor film, the properties of the gate insulator layer, and the configuration of the OFETs. For real applications of all-polymer transistors, their stability should also be enhanced. Insertion of an isolation layer or a vacuum package is recommended to prevent ambient humidity, oxygen, and unintended doping.