DC electrical and photovoltaic studies on Schottky barrier devices using the tetra aza difurazano decalin (TADFD) thin films

Abstract

1, 4, 5, 8 tetra aza difurazano-(3, 4-c) (3, 4-h) decalin (TADFD) a fused ring system, was synthesised by 2:1 condensation of diaminofurazan with glyoxal in warm hydrochloric acid (HCl). Absorption spectra were recorded between 200 and 800 nm in dimethyl formamide (DMF). The electronic transition in this molecular system is n-π ∗ transition. The electrical and photovoltaic effects observed with the thin films of TADFD sandwiched between indium tin oxide (ITO) and Al electrodes are explained in terms of the P-type semiconducting behaviour of the organic film and its formation of a blocking contact (Schottky barrier) with Al electrode. At low voltages, the dark current in forward bias corresponding to a negative potential at Al electrode, varies exponentially with voltage, and Ohm's law is followed. The thermally activated hole concentration p 0 = 10 16m −3 and hole mobility μ p = 2.5×10 −5cm 2/V s and room temperature conductivity σ 0 = 4.0×10 −8(Ω m) −1 were obtained. At high voltage there is a space-charge-limited conductivity (SCLC) controlled by a single trap level. The derived trap level parameters are for e.g. the total trap concentration N t = 2.0×10 20 m −3, under reverse bias current, are identified with the Schottky emission over a potential barrier of 1.09 eV. The low-frequency capacitance-voltage ( C- V) characteristics have been employed to characterise the Schottky barrier device. The width of the depletion layer decreases with the increase of the temperature of the device. On illumination through ITO electrode with monochromatic light of wavelength 600 nm and light intensity P i = 10 mW/cm 2, the typical photovoltaic parameters were calculated. The action spectra were also explained in detail.