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

Abstract

In this paper, a new electron-rich π-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 (Φb), series resistance (Rs), photosensitivity (S), photoresponsivity (R), photodetectivity (D*), open-circuit voltage (Voc), and short-circuit current (Isc), 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 (Vd) and carrier concentration are sensible to frequency changes.