Non-capped gold nanoparticles (AuNPs) with a diameter of 9-13 nm were electrochemically deposited on an ITO electrode, and poly(3-hexylthiophene-2,5-diyl) (P3HT) was spin-coated on the AuNP-deposited electrode. The degree of photocurrent enhancement exceeded unity when the coverages of AuNPs were below 14%, but were lower above 14%. The plasmonic effect was verified to be the major contribution at lower coverages, while the quenching effects became predominant at higher coverages. The spatial optimization (1-2 nm) between AuNP and P3HT was crucial and has been successful at 18%.