To systematically study the thickness effect of copper phthalocyanine (CuPc) buffer layers on pentacene-based organic thin-film transistors, various-thick CuPc buffer layers deposited on pentacene channel layers with various deposition rates were designed and studied in the work. By considering the contrary effect of the lower conductivity and the bandgap difference reduction of a CuPc buffer layer inserted between the Au electrode and the pentacene channel layer, the optimal thickness of the CuPc buffer layer stacked on the 50-nm-thick pentacene channel layer of the thin-film transistors was 5 nm. Furthermore, by considering the molecule ordering and quality of pentacene channel layer, the optimal deposition rate of pentacene channel layer of the thin-film transistors was 1.5 Å/s. After measuring the organic thin-film transistors with the optimal parameters, the associated transconductance of 2.4 μS, effective carrier mobility of 0.23 cm2/Vs, threshold voltage of − 5.1 V, subthreshold swing of 1.46 V/dec., and on/off current ratio of 3.7 × 105 were obtained.
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