Theoretical insights into molecular blending on charge transport properties in organic semiconductors based on quantum nuclear tunneling model

The effects of molecular blending on the charge transport properties of organic semiconductors are studied based on ab initio DFT calculation and quantum nuclear tunneling model coupled with kinetic Monte-Carlo simulation. Two model compounds, [(2,3,9,10-tetrachloropentacene-6,13-diyl)bis(ethyne-2,1-diyl)]bis(triisopropylsilane) (4Cl-TIPS-P) and [(1,2,3,4,8,9,10,11-octafluoropentacene-6,13-diyl)bis(ethyne-2,1-diyl)]bis(triisopropylsilane) (8F-TIPS-P), are blended homogeneously with different ratios, and the system is studied at a temperature ranging from 50 to 300 K. Our result shows that, at high temperature, blending leads to a smooth shift in mobility, whereas at a low temperature, one of the components tends to become traps, thus hamper the charge transport at low concentration. It is found that at 50 K, blending 0.995 mol. % of 4Cl-TIPS-P with 0.005 mol. % of 8F-TIPS-P, whose site energy is 48.1 meV lower than that of 4Cl-TIPS-P, would reduce the electron mobility by three orders of magnitude from that of pristine 4Cl-TIPS-P due to the trapping effect. The results are in agreement with the experimental observations.