Computational Analysis of Thermal Energetic Disorder in a Pentacene Crystal: Temperature Dependence of Trap Levels and Possible Novel Thermoelectric Contribution

Abstract

In organic semiconductors, the sudden appearance of deep traps (30 -100 meV) below 100 -200 K is frequently observed experimentally even in highly crystalline films and single crystals. We analyzed this phenomenon by molecular dynamics combined with semi-empirical quantum chemical calculation, and found that defect levels are concealed by thermal disorder at high temperatures but appear as hole traps at low temperatures. We propose that the thermal energetic disorder may lead to a considerably large thermoelectric effect in organic semiconductors.--

Crystal growth of doped organic semiconductors

“…It is also promising in the application of high efficiency solar cells because exciton mean free path might be elongated by orders of magnitudes compared with the ordinary amorphous semiconductors [1]. Thermoelectricity is another one of the promising applications of doped organic semiconductors [2]. In order to explore these possibilities, it is highly desirable to prepare doped organic semiconductor single crystals to enhance the electronic conductivity.…”

Bulk crystal growth of organic semiconductors for thermoelectric applications

“…We have predicted that organic semiconductor crystals with several percent carrier doping might show a considerable thermoelectric effect caused by transition in conduction mechanism from hopping to band-like [1]. Figure 1 shows the simulated density of states of thin-film phase pentacene which shows narrowing of HOMO states as the temperature is lowered due to decreased thermal motion of the molecule.…”

Giant Seebeck effect in pure fullerene thin films

“…Shimada et al pointed out that a thermal disorder of molecular alignment provides additional thermoelectricity. 27) This effect is no larger than tens of µV=K in α and simultaneously suppresses the electrical conductivity because of the unfavorable disorder for the electron transfer. A similar influence is also predicted on the basis of the percolation theory for organic semiconducting polymers.…”