Fabrication and electrical characteristics of organic thin film transistor using π-conjugated dendrimer

We fabricated organic thin film transistors (OTFTs) by using soluble π-conjugated dendrimers of 4(HPBT)-benzene, 4(HPTT)-benzene, and 4(HPDTT)-benzene. Electrical characteristics such as current-voltage characteristic curves and their temperature dependence were measured for the dendrimer-based OTFT devices. The active layer using planar π-conjugated dendrimers was spin-coated, and thermally grown silicon dioxide layer was used as a dielectric layer. Through the measurements of source-drain currents with varying gate voltages, we obtained charge carrier mobility (μ), on/off current ratio (I_on/off), and threshold voltage (V_th). The 4(HPBT)-benzene and 4(HPTT)-benzene-based OTFT devices showed that the μ's were ∼6.2 × 10^-3 cm²/V s and ∼1.9 × 10^-3 cm²/V s, respectively. We measured temperature-dependent mobility and activation energy (E_a) of the dendrimer-based OTFTs by using Arrhenius fitting. The E_a's of 4(HPTT)-benzene and 4(HPDTT)-benzene-based OTFTs were estimated to be ∼0.39 eV and ∼0.13 eV, respectively. In case of 4(HPBT)-benzene-based OTFT, two trap levels were measured and the E_a's were estimated to be ∼0.027 eV and ∼0.22 eV.