Performance improvement of dye-sensitized solar cells by introducing a hierarchical compact layer involving ZnO and TiO2 blocking films

The novel hierarchical compact layer involving ZnO and TiO2 blocking films is used to improve the overall performance of dye-sensitized solar cells. The ZnO compact films are fabricated as a bottom layer to block the electrons injection to the conductive glass and improve the open-circuit voltage. The TiO2 compact layer is employed to suppress back electron transfer and avoid ZnO contacting the acid dyes directly. The short-circuit current density of the DSSC containing the hierarchical compact layer is improved by 30% compared to that of one with only ZnO as the compact layer. The open-circuit voltage is increased by 4% after introducing the additional TiO2 blocking layer between the ZnO compact layer and mesoporous TiO2 layer. Overall, the short-circuit current density, open-circuit voltage and solar energy conversion efficiency are enhanced by 15.3%, 3.7% and 29.6%, respectively, relative to the traditional DSSC without any blocking layers. The ZnO–TiO2 blocking layer has been characterized by electrochemical impedance spectroscopy, open-circuit voltage decay and dark current measurement to reveal the mechanism of short-circuit current density and open-circuit voltage improvement.