The present study shows for the first time the novel photoelectrochemical studies on nanohybrid films fabricated by blending regioregular polyhexylthiophene (RRPHTh) conducting polymer with nanodiamond (ND) nanoparticles. The photoelectrochemical properties of ND– RRPHTh nanohybrid films have been compared by blending RRPHTh with zinc oxide (ZnO) and titanium oxide (TiO2) nanoparticles deposited on indium tin oxide (ITO) coated glass plates, n-type silicon, and gold-coated glass substrates. The ND–RRPHTh film has revealed more promising morphological and photoelectrochemical properties than RRPHTh, ZnO–RRPHTh, and TiO–-RRPHTh nanohybrid films. The photoelectrochemical study has shown the photoinduced electron transfer in ND–RRPHTh nanohybrid films where RRPHTh acts as the donor and ND as the acceptor, providing a molecular approach to high-efficiency photoelectrochemical conversion properties. The photoelectrochemical properties of ND–RRPHTh deposited on either n-type silicon or ITO-coated glass plates in an electrolyte containing tetrabutylammonium tetrafluoroborate (TBATFB) is around 8–10 times higher in current density and energy conversion efficiencies compared to RRPHTh, ZnO–RRPHTh, and TiO2–RRPHTh nanohybrid films.