Effects of rare earth ion modifications on the photoelectrochemical properties of ZnO-based dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated by using porous ZnO film electrodes derived from home-made ZnO nanoparticles. Electrochemical impedance spectroscopy and open-circuit voltage decay curve measurements were performed to investigate the photoelectrochemical characteristics of the ZnO films modified with different rare earth (La, Ce, Nd, Sm, and Gd) ions. The experimental results indicate that the rare earth oxides covered on the electrode surfaces can form energy barrier and maintain a lower charge recombination probability, and some rare earth ion modifications can passivate the surface states of ZnO electrode. Among these rare earth ions tested, the Nd-, Sm- and Gd-ion modifications can obviously enhance the open-circuit photovoltage and fill factor of the ZnO-based solar cell; whereas the La-, Ce-, Nd-, and Sm-ion modificaions lead to a decreased short-circuit photocurrent. The optimal conversion efficiency is obtained from the Gd-ion modified ZnO-based cells, with a 44.5% improvement in the efficiency as compared to the unmodified one, indicating this rare earth ion modification is promising in the ZnO-based solar cell.