Abstract
In this study, we aim to develop a simple, low temperature process tofabricate the Pt counter electrodes for dye-sensitized solar cells (DSSCs) basedon electrochemical deposition techniques including electroless deposition(ELD), electrodeposition (ECD) and surface modification of self-assembledmonolayers (SAMs).By electroless deposition, a cost-effective and low- temperature wetprocess to coat Pt on counter electrode has been developed with superiorcoating selectivity by means of self-assembly monolayers modification andelectroless deposition techniques. Images of fluorescent test and atomic forcemicroscope measurements demonstrated that 3-(2-Aminoethylamino)propylmethyl- dimethoxysilane (Me-EDA-Si) was homogeneously grafted onFTO surface and XPS result proves that the palladium deposited on the FTOsurface initiates the electroless deposition. The Pt deposit so obtained exhibitsrough morphology and increased active sites. This method makes it easy todeposit a Pt thin-film under ambient condition without the need for highvacuum chamber. Moreover, the so-prepared DSSC exhibits improvedperformance compared to the DSSC with a sputtered Pt counter electrode.In the case of electrodeposition, Pt counter electrodes with lowcharge-transfer resistance (Rct), low Pt loading and high active surface area canbe obtained within 30s by using the direct-current deposition in the presence of3-(2-Aminoethylamino) propyl -methyldimethoxysilane (Me-EDA-Si) as anIIadditive. The addition of Me-EDA-Si can not only enhance the currentefficiency but also inhibit the growth of semicircle-like grains, thus resulting inPt electrode with high active surface area. Consequently, the dye-sensitizedsolar cells (DSSCs) fabricated with so-prepared Pt electrodes exhibited cellefficiency of 7.39% while 0.01 vol% Me-EDA-Si was added, which is muchsuperior to that with sputtered-Pt electrodes under the same assemblyconditions.In the last part, we would like to know how additive affects the Ptnucleation and growth mechanism on the FTO surface since the additiveseemingly acts as an accelerator during Pt electrodeposition by studying theFESEM images of electrodeposited-Pt electrode fabricated from a plating bathcontaining Me-EDA-Si. According to the current-time transients experimentsand S-H theory model simulation, we found that Me-EDA-Si functions asaccelerator to promote nucleation with low concentration of additive underhigh precursor concentration. By contrast, excess additive tends to influencethe nucleation of Pt deposition towards to progressive mechanism.