Electrical characteristics of pentacene-based thin film transistor with conducting poly(3,4-ethylenedioxythiophene) electrodes

This is a report on the fabrication and electrical characteristics of an all-organic-based thin film transistor that uses conducting poly(3,4- ethylenedioxythiophene) (PEDOT) as electrodes. The conducting PEDOT layers as source, drain, and gate electrodes were patterned by using photolithography. The poly(vinyl cinnamate) (PVCN) was spin coated and cross-linked as a gate insulator. The pentacene as an active layer was vapor deposited onto the PVCN layer. In order to compare the characteristics of the pentacene-based organic thin film transistor (OTFT) with PEDOT electrodes, we fabricated another pentacene-based OTFT using a Si-based pattern with Au electrodes. The electrical characteristics of the devices, such as charge carrier mobility (μ), threshold voltage (V_th), and on/off current ratio (I _on/off), were measured from its current-voltage (I-V) characteristic curves. The μ, V_th, and I_on/off of the pentacene-based OTFT with PEDOT electrodes were ∼2.3× 10^-3 cm²/V s, 4 V, and ∼100, respectively. We evaluated the activation energy (E _a) of the pentacene layer of the OTFT devices by analyzing the transfer characteristic curves measured in a temperature range from 10 to 300 K based on the multitrap and release model. The E_a of the OTFT with PEDOT electrodes was measured to be ∼0.33 eV, in the saturation region. This energy was larger than that of the OTFT with Au electrodes which was measured to be ∼0.13 eV. However, the μ's of both OTFTs were almost the same, in spite of the relatively lower electrical conductivity of the PEDOT and the larger E_a of the OTFT with the PEDOT electrodes. From the results of temperature dependence of current density based on the Schottky emission model, we analyze that the lower barrier height between the PEDOT electrode and the pentacene active layer resulted in easier charge injection from the PEDOT electrode into the active layer.