Hierarchical ZnO Microspheres Embedded in TiO2 Photoanode for Enhanced CdS/CdSe Sensitized Solar Cells

Control of structural and compositional characteristics of photoanodes is a crucial step toward rapid transport of charges and high-efficiency loading of dye or quantum dots in the case of solar cell application. Hierarchical ZnO microspheres (ZMS) and TiO2 hybrid photoanode film were prepared for improved CdS/CdSe quantum dot sensitized solar cells (QDSCs). The addition of ZMS into TiO2 electrode films resulted in both increased short circuit current density (Jsc) and open circuit voltage (Voc). Such an improvement is ascribed to the increased light harvesting owing to scattering by ZMS and the reduced charge recombination due to the surface modification. TiO2/ZMS hybrid photoanode displays superior charge injection/transport performance due to the ZMS with unique hierarchical structure, providing charge transfer continuity and multiple electron transport channels for timely electron transport. As a result, the Jsc, Voc, and the photovoltaic conversion efficiency (PCE) were all remarkably enhanced with the insertion of hierarchical ZMS though varied appreciably with the amount of ZMS. Thus, the designed TiO2/ZMS heterostructure-based QDSCs with an optimizing ZMS ratio of 20 wt % achieved a PCE of 5.99%, which is about 35% increase of the efficiency for the devices without ZMS (4.45%)