Two dimensional graphitic-phase C3N4 (g-C3N4) was successfully coated as multifunctional protecting layer on ZnO nanoparticles via ultrasonic irradiation assisted monolayer dispersion. The as-prepared composites were applied as photoanode materials in dye-sensitized solar cells. Based on the optical and electrochemical measurements, the g-C3N4 stretches the absorption spectrum of the ZnO based photoanodes to visible region and enhances the harvesting of low energy photons. Moreover, the g-C3N4 with compatible band structure builds a stepwise energy gradient at the ZnO/C3N4/dye interface, which improves the injection efficiency of photo-generated electrons and leads to similar to 57% enhancement in the short-circuit photocurrent of Cell-ZnO-C3N4 (3%). Therefore, a high power conversion efficiency of 4.5% was demonstrated, indicating similar to 20% improvement compared with the pure ZnO based device (3.7%). (C) 2015 Elsevier B.V. All rights reserved.