Charge conduction mechanism and photovoltaic properties of 1,2-diazoamino diphenyl ethane (DDE) based schottky device

Abstract

The dark electrical, impedance and photovoltaic properties of 1,2-diazoamino diphenyl ethane (DDE) based schottky device were investigated. It is found that DDE behaves as an n-type organic semiconductor which forms the schottky barrier with ITO (high work function electrode) and ohmic contact with Al (low work function electrode) having ITO/DDE/Al configuration. The J– V characteristics of device reveal that the conduction mechanism for biasing voltage between 0.6 and 1.2 V can be described by modified Schockley equation. For the higher voltage (beyond 1.2 V), the current transport is due to the space charge limited current (SCLC) in the presence of exponentially distributed traps, however for voltage below 0.6 V, the conduction mechanism is determined on the basis of schottkey emission and Poole–Frenkel emission. The formation of Schottky barrier at ITO–DDE interface is also evidenced by the impedance analysis and comparison of photoaction spectra of the device with optical absorption spectra of DDE thin layer. The dependence of ac conductivity on temperature yields low activation energy in low temperature region which indicates the dominance of hopping conduction process in DDE thin film layer. It is also found that the slower relaxation process occurs at the interface, which limits the carrier injection across the ITO–DDE junction. The observation of high interfacial resistance and low electron mobility in DDE leads to the conclusion that most of the electron–hole recombination occurs at the ITO–DDE junction, thus increasing the diode ideality factor. The photogeneration mechanism of the charge carriers in the device has also been described in detail. The analysis of dark space charge limited current at high voltage region and exponential relation of the photocurrent with illumination intensity attributes an exponential trap distribution in the band gap of the film.