Controlling device properties in Organic Thin Film Transistors (OTFTs) by the application of Organic Photoreactive Interfacial Layers
The charge carrier mobility and the threshold voltage are crucial device parameters of Organic Thin Film Transistors (OTFTs). In this presentation, we present an approach to photochemically tune those properties using photoreactive polymers between the SiO2 surface and the active organic semiconductor layer. By depositing the polymeric photo acid generator Poly(bicyclo[2.2.1]hept-5-ene-2,3-(2-nitrobenzyl)dicarboxylate) (PPAG) and illuminating it prior to pentacene deposition the final grain size of the pentacene film can be controlled. This allows tuning the effective hole mobility over more than an order of magnitude. A different effect is observed when illuminating the OTFT through the active layer after deposition of pentacene and the gold source and drain contacts. Then, the acid generated in the photoreaction of the PPAG layer dopes the channel region. As a consequence, the threshold voltage (Vth) is shifted to large positive values and the magnitude of the shift can be controlled by the illumination time. The results obtained for the PPAG interfacial layer are compared to those obtained with those obtained with different other polymers. In particular, we focus on the magnitude of the Vth-shift and its stability when operating the device.