In this study, three different poly(vinyl alcohol) (PVA) films doped with weight percentages of 0.05, 0.10 and 0.20 coumarin were coated on p-Si wafer via spin-coating method for the purpose of investigating the interaction of coumarin dopant with polymer host at molecular level. Therefore, metal-polymer-semiconductor (MPS) structures were formed and their current-voltage (I-V) and admittance measurements were taken to compare the main electrical parameters of the MPS structures with different film thicknesses. The values of ideality factor (n), barrier height (phi(b)), rectification ratio (RR = I-F/I-R), series resistance (R-s) and energy-dependent profiles of surface states (N-ss) were calculated using the forward bias I-V data. There exists increasing trend for N-ss values from mid-gap energy of Si toward the bottom of conductance band. The highest values of RR and photosensitivity (I-photo/I-dark) were found as 4.62 x 10(4) at +/- 4 V for the MPS structure with 0.10 wt% coumarin doping level, respectively. The photoresponse of the structures was also analyzed using relation, and the value of m was obtained from the slope of ln(I-ph)-Ln(P) plot for each diode as 1.48, 1.27 and 1.57, respectively. Experimental results suggest that 0.10% coumarin-doped PVA caused MPS structure to reveal better performance considering higher RR and lowest N-ss, and so it can be considered as an alternative interfacial layer material for replacing traditional insulators.