Investigation of interfaces between insulator and active layer, and between active layer and electrodes in n-type organic field-effect transistors

The interface effects of insulator/active layer and active layer/electrode in solution-processed n-type organic field-effect transistors (OFETs) using [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were investigated. Cesium fluoride (CsF) insertion at the active layer/electrode interface induces a large threshold voltage shift, and realizes low-gate-voltage operation. The threshold voltage shift followed by the insertion of CsF is mainly caused by the efficient electron injection due to the coexistence of CsF and a metal electrode. We also investigated the characteristics of OFETs using poly(psilsequioxane) (PSQ) derivatives, which contain various amounts of phenol groups with OH in the side chain of their molecular structures. It is found that the field-effect mobility increases with decreasing phenol group ratio in their side chain. The mobility of the device with PSQ containing a phenol group ratio in a half of the side chain of molecular structures is 0.024 cm(2) V-1 s(-1), which is twice of that in all side chains.