Electron transfer properties of organic dye sensitized ZnO and ZnO/TiO2 photoanode for dye sensitized solar cells

The effect of using bilayer film on the efficiency of dye sensitized solar cells is investigated. ZnO, TiO2 and bilayer ZnO/TiO2 (ZTO) based cells are developed and sensitized with five organic dyes and one cocktail dye composed of five dyes. The electrical measurements such as steady state conductivity and transient photoconductivity are studied at different temperatures for understanding the electron transport and charge recombination mechanism in dye sensitized films. The photosensitivity of the dye sensitized film is higher than bare oxide film, while the carrier life time of dye sensitized metal oxide is smaller as compared to pure metal oxide films because of hole passivation effect. Photovoltaic performance of ZnO and TiO2 based solar cell sensitized with six dyes is compared to that of bilayer ZTO based cells. The current voltage characteristics of the cells show that ZnO modification improves open circuit voltage (Voc), but lowers short circuit current (Jsc), It is explained with help of charge trapping/detrapping and recombination mechanism. Among the six dyes, Rhodamine B (RhB) gives the best performance as sensitizer with TiO2 and ZTO. While Eosin Y (EY) dye gives highest efficiency with ZnO based solar cells. The comparison of conductivity measurements of the samples has emphasized the major role of surface states in recombination mechanism.