No abstract

No abstract

No abstract

Titanium dioxide (TiO 2 ), Zinc oxide (ZnO) and bilayer TiO 2 /ZnO (TZO) based cells have been developed and sensitized with five organic dyes and one cocktail dye composed of five dyes. Photovoltaic performance of TiO 2 and ZnO solar cell sensitized with six dyes is compared to that of bilayer TZO cells. The forward current is found to increase with applied voltage in the range V £ 0.4 V, which is dominated by thermionic emission, whereas in 0.4 £ V £ 0.7 V, the current transport is due to space charge-limited current controlled by exponential trap distribution in all devices. The combined properties of the materials enhance the efficiency of composite TZO cells. TiO 2 permits the formation of an energy barrier at the ZnO electrode/electrolyte interface, which reduces the back electron transfer from the conduction band of ZnO to I 3 À in the electrolyte. Also, due to the TiO 2 layer on the ZnO, the latter forms a compact layer between flourine-doped tin oxide (FTO)/TiO 2 which benefits the fast electron transfer from TiO 2 to ZnO to FTO glass. This reduces the charge recombination occurring at the ZnO/FTO interface leading to higher open circuit voltage (V oc ), higher short circuit current (J sc ), lower series resistance (R s ), and in turn higher efficiency in TZO solar cells as compared to ZnO cells. Among the six dyes, Eosin-Y and Rose Bengal dye gave the best performance as sensitizers with TZO.