Carbon films prepared from pyrolyzation of spin-casted polyacrylonitrile (PAN) thin films display high electrical conductivity (>600 S/cm, at 1000 °C carbonization), low sheet resistance (about 100 Ω/square at the PAN film thickness of 70 nm) and partial transmittance. These pyrolyzed PAN (PPAN) films were patterned as bottom electrodes by photolithography, and utilized as drain and source electrodes to fabricate organic field-effect transistor (OFET) devices with a p-type semiconductor (P3HT) and an n-type semiconductor (DPP-containing quinoidal small molecule) through a spin-coating procedure. The results showed that the devices with the PAN electrodes exhibited almost the same excellent performance without any further modification compared to those devices with traditional Au electrodes. Since these PPAN films had the advantages of low-cost, high performance, easier for large-area fabrication, thermal and chemical stability, it should be a promising electrode material for organic electrodes.
The coordination polymer poly(nickel-ethylenetetrathiolate)(poly(Ni-ett)), formed by nickel(II) and 1,1,2,2-ethenetetrathiolate(ett), is the most promising N-type organic thermoelectric material ever reported; it is synthesized via potentiostatic deposition,and the effect of different applied potentials on the optimal performance of the polymers is investigated. The optimal thermoelectric property of poly(Ni-ett) synthesized at 0.6 V is remarkably greater than that of the polymers synthesized at 1 and 1.6 V, exhibiting a maximum power factor of up to 131.6 μW/mK^2 at 360 K. Furthermore, the structure-property correlation of poly(Ni-ett) is also extensively investigated. X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) analyses revealed that the larger size of crystalline domains and the higher oxidation state of poly(Ni-ett) synthesized at 0.6 V possibly results in the higher bulk mobility and carrier concentration in the polymer chains, respectively, accounting for the enhanced power factor.
Organic semiconductors are inherently soft,making it possible to increase their mobilities by strains.Such a unique feature can be exploited directly in flexible electronics for improved device performance.The 2,7-dioctyl[1]benzothieno[3,2-b][1]-benzothiophene derivative,C8-BTBT is one of the best small-molecule hole transport materials.Here,we demonstrated its band structure modulation under strains by combining the non-equilibrium molecular dynamics simulations and first-principles calculations.We found that the C8-BTBT lattice undergoes a transition from monoclinic to triclinic crystal system at the temperature below 160 K.Both shear and uniaxial strains were applied to the low-temperature triclinic phase of C8-BTBT,and polymorphism was identified in the shear process.The band width enhancement is up to 8%under 2%of compressive strain along the x direction,and 14%under 4%of tensile strain along the y direction.The band structure modulation of C8-BTBT can be well related to its herringbone packing motifs,where the edge to face and edge to edge pairs constitute two-dimensional charge transport pathways and their electronic overlaps determine the band widths along the two directions respectively.These findings pave the way for utilizing strains towards improved performance of organic semiconductors on flexible substrates,for example,by bending the substrates.
We introduce here a work package for a National Natural Science Foundation of China Major Project. We propose to develop computational methodology starting from the theory of electronic excitation processes to predicting the opto-electronic property for organic materials, in close collaborations with experiments. Through developing methods for the electron dynamics, considering superexchange electronic couplings, spin-orbit coupling elements between excited states, electron-phonon relaxation, intermolecular Coulomb and exchange terms we combine the statistical physics approaches including dynamic Monte Carlo, Boltzmann transport equation and Boltzmann statistics to predict the macroscopic properties of opto-electronic materials such as light-emitting efficiency, charge mobility, and exciton diffusion length. Experimental synthesis and characterization of D-A type ambipolar transport material as well as novel carbon based material will provide a test ground for the verification of theory.
