High performance dye-sensitized solar cells based on platinum nanoparticle/multi-wall carbon nanotube counter electrodes: The role of annealing

A composite film is coated on the FTO using a solution, containing a synthesized dispersant, poly(oxyethylene)-segmented imide (POEM), dihydrogen hexachloroplatinate (H₂PtCl₆), and multi-wall carbon nanotube (MWCNT); the thus coated FTO is used as the counter electrode (CE) for a dye-sensitized solar cell (DSSC). The annealing temperature of the composite film, in the range of 110–580 °C, is found to be crucial for optimizing its catalytic ability to obtain the best possible performance for the DSSC. About 47% loss in mass for the POEM/H₂PtCl₆/MWCNT composite is observed from 110 to 390 °C, due to not only the progressive formation of PtNPs from H₂PtCl₆ but the decomposition of POEM. Therefore, the efficiencies (η) of DSSCs applying these CEs are enhanced from 1.28 ± 0.08% (110 °C) to 8.47 ± 0.21% (390 °C). The mass of the composite loses dramatically under heating above 390 °C, due to the decomposition of MWCNTs. The η decreases to 7.77 ± 0.15% at 450 °C because the decrease in surface roughness of film. PtNPs grow in sizes from 450 to 580 °C, resulting in the further decrease in catalytic ability of film and the observed η from 7.77 ± 0.15% to 7.19 ± 0.21%.