Influence of the film microstructure on the electronic properties and flicker noise in organic thin film transistors

In organic thin-film transistors (OTFTs) the intrinsic properties of the semiconductor are generally masked by structural defects which localize and trap the charge carriers and contact effects, which limit charge injection and cause deviation from ideal linear and square-law behavior. Thus, their electrical characteristics are strongly dependent on the fabrication conditions. We perform current-voltage (I-V) and low frequency noise (1/f) measurements to demonstrate a direct correlation between the thin film microstructure and the performance of OTFTs. Using fluorinated 5,ll-bis(triethylsilylethynyl) anthradithiophene as a model system, we show the relevance of the grain size and grain distribution in the changes in the electronic properties in an OTFT. We present a simple method to induce enhanced grain growth in solution-processed TFTs by room-temperature chemical modification of the source-drain contacts. This leads to improved device performance, and gives an unique thin film microstructure for fundamental studies concerning the effect of structural order on the charge transport. We present evidence that the 1/f flicker noise is sensitive to the microstructure of the organic semiconductor thin film in the transistor channel and can be a diagnostic tool for the quality of the devices.