Electron spin resonance study of field-induced charge carriers in organic semiconductor devices

有机场效应器件作为21世纪低成本的电子器件备受关注。电子自旋共振（ESR）是一种强有力的技术，可以直接阐明带自旋的电荷载体的性质，从而体现这些器件的功能。高分子材料用ESR在具有最高载流子迁移率的导电聚合物聚烷基噻吩的金属-绝缘体-半导体（MIS）二极管中发现了场致极化子信号。在较低的电荷浓度下，我们发现自旋和电荷成比例，但在较高的电压下，自旋密度发生饱和，这表明极化子向无自旋双极化子转变。g值和线宽的角依赖性表明了聚合物链在基材上的边对边构型。基于理论极化子波函数，通过计算各向异性ESR谱，定量分析了聚合物链的角分布函数。我们还成功地观察到了富勒烯及其衍生物复合材料中的双极性载流子。在有机材料中，戊二烯薄膜（1cm2/Us）和rubrene单晶（10cm2/Us）的载流子迁移率最高。与日本东北大学Iwasa教授的团队合作，成功地观察到并五苯场效应晶体管（FHIi）的场致ESR。线宽表示电荷载流子在10个分子上的空间范围，提示带状输运。从g值和线宽来看，相对于衬底的pi-stacking分子构型在高迁移率下是较好的。并戊烯的诱导自旋密度与载流子密度成正比，这与区域规则型聚烷基酚形成鲜明对比。对于rubrene单晶，大阪大学的Takeya教授和日本东北的Iwasa教授的团队正在进行合作。ESR信号的运动变窄是良好的，表明rubrene单晶的高迁移率

Organic field-effect devices attract much attention as low-cost electronic devices of the 21st century. Electron spin resonance (ESR) is a powerful technique in caner to clarify directly the properties of charge carders with spins, which manifest the functionalities of those devices.1.Polymeric materialsField-induced polaron signals are found by ESR in Metal-Insulator-Semiconductor (MIS) diodes of regioregular polyalkylthiophenes, the conducting polymer with the highest charge carrier mobility. We found the proportionality of spins and charges at lower charge concentration At higher applied voltages, however, the saturation of the spin density occurred, which indicates the transformation of the polarons to spinless bipolarons. The angular dependence of g-values and line widths indicate the edge-on configuration of the polymer chain onto the substrata Then the angular distribution function has been quantitatively analyzed by calculating the anisotropic ESR spectra based on the theoretic … More al polaron wave functions. We also succeeded in observing the ambipolar carriers in the composites with fullerene and its derivatives.2.Molecular materialsPentacene thin film (1cm2/Us) and rubrene single crystal (10cm2/Us) possess the highest charge carrier mobility among organic materials. Collaborated with Prof. Iwasa's group in Tohoku University, field-induced ESR of pentacene field-effect-transistors (FHIi) is successfully observed. The linewidth indicates the spatial extent of charge carrier over ten molecules, suggesting the band-like transport. From the g-value and linewidth, pi-stacking molecular configuration with respect to the substrate is hind to be preferable fm the high mobility. In pentacene, the induced spin density is always proportional to the carrier density in Clear contrast with the regioregular polyalkyhlvophenes. For the rubrene single crystal, collaboration with Prof. Takeya in Osaka University and Prof. Iwasa's group in Tohoku is underway. Motional narrowing of the ESR signals is Sound, demonstrating the high mobility of the rubrene single crystals Less