Reverse- and forward-bias current-voltage (I-V) data of the Au/(P3DMTFT)/n-GaAs Schottky barrier diodes (SBDs) were measured in dark and at under various illumination levels (from 50 to 200 W with steps of 25 W) for the purpose of examining the change in electrical parameters such as zero-bias barrier height (phi(bo)), ideality factor (n), reverse saturation current (I-o), series resistance (R-s) and shunt resistance (R-sh) with illumination. The values ofn,phi(bo)andI(o)were determined usingI-Vdata in dark as 1.34, 0.91 eV and 7.25 x 10(-12) A, respectively. On the other hand, these parameters were obtained as 1.85, 0.80 eV and 5.11 x 10(-10) A, respectively, when the SBD is exposed to 200 W illumination. The values of shunt resistance (R-sh) and series resistance (R-s) were determined from Ohm's law and shown asR(i)-Vplots. Additionally, Cheung's and modified Norde's functions were also utilized for the extraction ofR(s)in dark and under various illumination levels. The energy density distribution profiles of interface states (N-ss) were investigated for various illumination levels. The dependency of the energy density distribution profiles of interface states (N-ss) on illumination levels was investigated. Obtained results suggest that these electrical parameters are sensitive to illumination. Moreover, Au/(P3DMTFT)/n-GaAs SBDs shows remarkable photovoltaic performance with the values of short-circuit current (I-sc) of 1.45 x 10(-6) A, open-circuit voltage (V-oc) of 0.37 V and fill factor of 0.65 under 200 W illumination.