Evaluation of work functions of organic semiconductors and electronic structures of organic/metal interfaces

用开尔文探针(KP)方法研究了分子半导体在空气中的能级结构。在真空升华膜中，与金属接触的金属组成了理想的肖特基势垒，它们分别是：酞菁(p-型)、卟啉(p-型和n-型)及其衍生物(n-型)。由肖特基-莫特规则计算出p型分子半导体的公共功函数为4.8±0.05 eV，n型分子半导体为4.1-4.3 eV。用KP法直接测量的功函数值强烈依赖于用作衬底的金属。这归因于在Kp组态的开路情况下，分子固体与金属之间的费米能级不对齐。对费米能量差的修正减少了对金属的依赖。结合分子半导体中O_2和/或H_2O的掺杂，讨论了费米能级不对准的可能原因。同样，肖特基-莫特规则也被成功地应用于计算va…的功函数更多的聚(3-芳基噻吩基)(PATS)。根据聚合物膜的阳极p掺杂和阴极n掺杂的起始电势估算了PAT膜的价带和导带的边缘。在此基础上，描述了PAT薄膜的电子结构及其在空气中与金属的界面。评价了聚[(乙氧基丙基硅烷基)五(2，5-亚硫烯)](MS5T-OEt)薄膜中正电荷载流子的近似迁移率。迁移率随着掺杂浓度的增加而单调下降，最高可达几个百分点，而之前报道的聚(3-甲基噻吩基)(PMT)薄膜的迁移率增加了四个数量级。这表明，π薄膜中的阳离子自由基二聚体和光电倍增管中的双极化子这两种抗磁性物种与电导的关系是完全不同的。原位电子自旋共振研究表明，在MS5T-OEt薄膜中存在一些低硫链段，在这些链段中，极化子被隔离，从而不形成π-二聚体。较少

Energy structures of molecular semiconductors are investigated in air on the basis of the Kelvin probe (KP) method. Vacuum sublimed films of phthalocyanines (p-type), porphyrins (p- and n-type) and perylene derivative (n-type) contacting metals form ideal Schottky-barriers. A common work function of 4.8±0.05 eV for p-type molecular semiconductors and 4.1-4.3 eV for n-type ones are evaluated from the Schottky-Mott rule. Work function values measured directly with the KP method strongly dependent on the metal used as substrate. This is ascribed to nonalignment of Fermi levels between a molecular solid and metal under the open-circuit situation of the KP configuration. Correction for the Fermi energy differences reduces the metal dependencies. Possible reasons for the nonalignment of Fermi levels are discussed in connection with incorporation of O_2 and/or H_2O into molecular semiconductors. Similarly, the Schottky-Mott rule has been successfully applied to evaluating work functions of va … More rious poly (3-arylthiophenes) (PATs). Edges of the valence and conduction bands of the PAT films are estimated from the onset potentials for anodic p-doping and cathodic n-doping of the polymer films. On these bases electronic structures of the PAT films and their interfaces with metals in air are depicted.Apparent mobilities of positive charge carriers in a poly [(ethoxypropylsilanylene) quinqe-(2,5-thienylene)] (MS5T-OEt) film are evaluated. The mobility decreases monotonously with the increase in doping level up to a few percents, in contrast to four order-of-magnitude increase of mobilities reported earlier for the poly (3-methylthiophene) (PMT) film. This indicates that the two kinds of diamagnetic species, cation radical π-dimers in the MS5T-OEt film and bipolarons in the PMT, are related to the electrical conduction in completely different manners. An in situ ESR study performed to characterize charge-carrying species in the MS5T-OEt film demonstrates that there are oligothienylene segments where polarons are isolated so as not to form π-dimers. Less