Abstract
The electrical and optoelectrical properties of naphthalene bis-benzimidazole (NBBI) based organic thin film phototransistors (photoTFTs) with divinyl tetramethyl disiloxane-bis (benzo-cyclobutene) (BCB) as a gate insulator layer were investigated in detail under dark and various white light illumination conditions. One of the most apparent effects on devices under illumination is the shifting of the threshold voltage from positive values to negative values with increasing the light intensity. The calculated values by the proposed expression of the threshold voltage under illumination are fitted well with the experimental data. The photoTFTs exhibited a photoconduction behavior with a high photosensitivity value of 5.45×104 under 80mWcm−2 in off-state (VG=0V) and a high responsivity value of 34.4 AW−1 under 50mWcm−2 in the on-state that demonstrate the NBBI is promising material to be used on the optoelectronic applications. The combination of illumination-induced effect and dipole layer has been also studied to see how DOS distribution changes. When the dipole moment increased from P=2D to P=6D, the DOS distribution is more broadened and the DOS decrease with increasing the white light intensity. The used model gives a good agreement between the measured current–voltage characteristics of the NBBI-photoTFTs and those modeled in all measurement conditions (in dark and under illumination).
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•Various performance metrics NBBI-photoTFTs in a wide range of illumination are extracted.•NNBI-photoTFTs shows a high photosensitivity value of 5.45 × 104 in off state and a high responsivity of 34.4 AW-1 in on state.•An analytical expression for threshold voltage under illumination is presented.•The combined of illumination and dipole layer effects on the DOS distribution are analyzed.•Additional information on the charge transport in naphthalene bis-benzimidazole can be obtained from the illumination and dipole layer-dependent density of state.•The analytical model results are in good agreement with the experimental data.