Bis-Benzimidazole Analysis

2. Experimental details: The chemical structure of the naphthalene bis-benzimidazole (NBBI) is given in Fig. 1. The details of the naphthalene bis-benzimidazole synthesis, surface morphology and identification of molecular structure were described in our previous work in Ref. [34]. A scheme of the device structure was presented in Fig 2 (a) together with the chemical structure of the organic gate insulator divinyltetramethyldisiloxane-bis (benzo-cyclobutene) (BCB) (fig 2 (b)). All the OTFTs were fabricated with top contact/bottom gate geometry in order to sense visible light. All the NBBI-TFTs were constructed on the indium tin oxide (ITO) coated glass substrate. The ITO coated glass was patterned by etching with diluted HCl for

Fig. 3(a)–(d) shows the output characteristics (ID versus VD) of the NBBI-photoTFTs under dark and illumination conditions, which the white light intensity is ranging from 0mW to 80mW. The NBBI-photoTFTs exhibited a clear linear increase of the drain current at low drain voltages and saturation at larger drain voltages under dark and illumination conditions. From all electrical output characteristics, the linear and saturation regimes of the transistor were clearly observed that shown in Fig. 3 (a)-(d). The saturation regime was observed at positive gate voltages VG that demonstrate electron accumulation mode i.e. n-channel transistor is formed in the conductive channel at gate insulator–organic semiconductor interface. As shown in Fig. 3 (a)-(d), at off state (VG= 0V), there is an increase in ID by the white light intensity (IL). The reason of ID increment is the dissociation of light generated exciton to electron and hole charge carriers which transport in the active layer of the transistor via the gate and drain voltages as well as the trapping and de-trapping of minority mobile carriers