Incorporation of carbon nanotubes in a hierarchical porous photoanode of tandem quantum dot sensitized solar cells

The incorporation of multi-walled carbon nanotubes (MWCNT) in quantum dot (QD) sensitized solar cells (QDSC) based on CdSe QDs and quantum rods (QRs) is investigated. The composite hierarchical porous photoanode of titania/CNT is synthesized by sol-gel induced phase separation and QDs/QRs are prepared by the modified solvothermal method. The QDs and QRs form a tandem structure on the hierarchical porous photoanode after deposition by the electrophoretic method. Incorporation of MWCNT in the QDSC photoanode in optimum content (0.32 wt%) causes appreciable enhancement in cells efficiency (about 41% increase). This improvement in efficiency mainly emerges from the beneficial role of MWCNTs in charge injection and collection. The MWCNTs result in longer electron lifetime and higher electron diffusion length, which is confirmed by electrochemical impedance spectroscopy.