Synthesis of electron-rich thiophene triphenylamine based organic material for photodiode applications

In this paper, a new electron-rich pi-conjugated organic material, 4,4'-(thiophene-3,4-diyl)bis(N,N-diphenylaniline) (bisTPAT), which contain thiophene skeleton as the central core with bistriphenylamine side groups as the electron-rich unit and/or donor groups at the 3-and 4-positions, was designed for photodiode application. The bisTPAT was efficiently synthesized via the Pd-catalyzed Suzuki coupling reaction between 3,4-dibromo-thiophene (3) and (4-(diphenylamino)phenyl)boronic acid 4. Structural, optical, and chemical features of the bisTPAT material and thin film form-was characterized by NMR, FTIR, HRMS, UV-Vis spectroscopy, and SEM/EDX analysis techniques. Subsequently, bisTPAT/n-Si device fabrication was carried out by using the spin coating method. Current-voltage (I-V) measurements were performed to determine the characteristic properties of the device under different operating conditions. According to I-V measurements taken under illumination conditions, the fabricated device has photoresponse characteristics in the reverse bias region. Therefore, the fabricated device can be employed as a photodiode for optoelectronic applications. Additionally, the photodiode parameters, such as ideality factor (n), barrier height (phi(b)), series resistance (R-s), photosensitivity (S), photoresponsivity (R), photodetectivity (D*), open-circuit voltage (V-oc), and short-circuit current (I-sc), were analyzed under the light intensity of 100 mWcm(-2). Finally, capacitance-voltage (C-V) measurements were carried out to obtain important information about the diode's interfacial characteristics at different frequencies. The results show that the calculated parameters such as diffusion potential (V-d) and carrier concentration are sensible to frequency changes.