PC70BM n-type Thin Film Transistors: Influence of HMDS Deposition Temperature on the Devices Properties

This study investigates the influence of the deposition temperature of hexamethyldisilazane (HMDS) on the performances of organic thin film transistors (OTFTs) using the [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) as semiconductor. N-type OTFTs have been fabricated using this fullerene derivative, deposited from solution by drop casting technique on HMDS self-assembled monolayer (SAM) deposited at three different temperatures, 7 °C, 25 °C and 60 °C, in order to evaluate the influence of these deposition conditions on the morphology of PC70BM films and on the electrical responses of fullerene derivative-based OTFTs. The effect of the treatments of the surfaces was observed through contact angle measurements. AFM imaging of the deposited material has been used to analyse its structure and morphology. The transistors performances have been evaluated through I vs. V static characterization and parameters extraction. Contact angle vs. HMDS deposition temperature shows the minimum value at 60 °C, instead here field effect mobility presents a maximum. It has been observed that the lower hydrophobicity of the surface of the SAM induces the formation of more homogeneous surface of the PC70BM film, resulting in an increase of the OTFTs performances.