  Bromothymol blue (BTB) with the molecular formula of C27H28Br2O5S was grown
onto p-Si substrate to fabricate heterojunction by spin coating technique. The
current voltage (I-V) measurements of diode were carried out in dark and under
different illumination intensity at room temperature. The photoelectrical
properties of heterojunction based on BTB were investigated using the
illumination intensity dependent I-V data. The results showed that photo
current of diode increases with the increase in light intensity. Also, the
electrical parameters of device were determined via I-V, and capacitance-
voltage (C-V), conductance-voltage (G-V) measurements at different frequencies.
It is observed that the excess capacitance is created at low frequencies due to
the contribution of interface states charge which can follow the alternative
current signal to capacitance. It is stated that, both the electrical
photoelectrical parameters of diode can be changed, and also the performance of
the device could be affected by the organic thin film interlayer.
