Effect of CuS nanocrystalline particles on counter electrodes of multi-wall carbon nanotubes for QDSCs

CuS nanocrystalline particles are deposited into the acid-treated multi-wall carbon nanotubes (MWCNTs) film on the fluorine-doped tin oxide glass substrate through the successive ionic layer adsorption and reaction combined with spin-coating technology to form MWCNTs/CuS composite counter electrode (CE). The CuS adding amount is changed in different cycles to discuss its effect mechanism on the photoelectric properties of MWCNTs/CuS composite CE based quantum dot sensitized solar cells (QDSCs). The TiO2 photoanodes are prepared by the electrospinning technique with CdS and ZnS as co-sensitizer. QDSCs are assembled with photoanodes, the polysulfide electrolyte and abovementioned CEs. The CEs are characterized by X-ray diffraction, transmission electron microscope and energy dispersed X-ray detector, which verifies CuS nanocrystalline particles are attached to MWCNTs successfully. The photoelectric properties are analyzed by Nyquist, Tafel and J-V curves. The results show that the introduction of CuS nanocrystalline particles can promote reduction rate of polysulfide species and the short circuit current density (Jsc) to improve catalytic activity, leading to a higher power conversion efficiency (PCE). The MWCNTs based CE with deposition CuS in eight cycles exhibits the best photoelectric performance within all CE samples and the electrical conductivity of MWCNTs/8CuS CE is superior to that of Pt CE according to Nyquist and Tafel curve analysis. PCE of QDSCs with MWCNTs/8CuS CE is up to 5.186%, which is a little lower than that of Pt CE (5.250%), but it possesses a higher Jsc value (18.028mA cm(-2)) than that of Pt CE (16.057mA cm(-2)). The low-cost MWCNTs/CuS composite CE with simple preparation is more suitable than Pt CE for commercial application of QDSCs.