Effect of tube depth on the photovoltaic performance of CdS quantum dots sensitized ZnO nanotubes solar cells

High-density and vertically-aligned ZnO nanotubes (ZNTs) with different depth and ZnO nanorods (ZNRs) were used as photoelectrodes to assemble the CdS quantum dots sensitized solar cells (QDSSCs). In comparison with the CdS sensitized ZNRs solar cell, up to 170% enhancement in energy conversion efficiency was achieved for the CdS sensitized ZNTs under the white light illumination intensity of 100 mW/cm2. The investigation about the effects of tube depth on the photovoltaic performance of ZNTs/CdS electrodes revealed that at least two factors induce the enhancement of their conversion efficiency. One is that the higher surface-volume ratio of ZNTs can effectively increase the loading amount of CdS QDs, which can effectively absorb the light. The other is that the outer and inner wall of ZNTs can provide two transfer channels for photo-injected carriers, which can improve the efficiency of current collection.

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► ZnO nanotubes as photoanode can enhance the energy conversion efficiency.
► ZnO nanotubes with larger surface area can load more CdS QDs to absorb more light.
► ZnO nanotubes can provide two transfer channels for photo-injected carrier.