Abstract
A comparative study on thermal stability of hybrid (organic / inorganic) electrolytes for dye-sensitized solar cells (DSSCs) in various ethylene oxide oligomers / silica based gelly matrices, containing also some efficiency-promoter additives is presented. Using thermogravimetry combined with two evolved gas analytical (EGA-FTIR and EGA-MS) techniques, the released gases and volatile decomposition products from the composite electrolytes during dynamic heating programs have been identified and monitored. First methanol (arising from condensation of tetramethoxysilane, TMOS) and acetonitrile (solvent) are evolved followed by elongated release of 4-tert-butylpyridine, than carbonyl sulfide, which is one of the degradation products of guanidinium thiocyanate, and various alkyl iodides, as well as iodine, later various oxidized species with >C=O groups (arising from oxidative degradation of oligo(ethylene glycolic) parts, ammonia (originated from guanidine) have been observed and traced during the accelerated heating tests, before final burning out of the organic residue with CO2 evolution. Thermal behavior of pure guanidinium thiocyanate, one of the most important additives improving thermal stability of Grätzel type solar cells (DSSCs), combined with identification of its eight gaseous decomposition products and their release pattern is also reported.
Highlights
The family of dye-sensitized solar cells (DSSCs) is one of the most promising low cost alternative for the effective conversion of light energy into electrical energy [1].The components of a DSSC are in most cases the following: a nanocrystalline TiO2 film deposited on a transparent conductive electrode, a complex ruthenium-dye adsorbed on TiO2 nanocrystallites, an electrolyte bearing the I- / I3- or other redox couple and a platinized counter electrode [2,3,4,5]
3 Results and discussion 3.1 Comparative thermogravimetric analysis (TG / DTG) of TMOS-based electrolyte samples incorporating either Triton X - 100 or poly(ethylene glycol) 200 (PEG 200) For all the three samples, we can separate at least three decomposition stages according to the TG and DTG curves, to our previous experiments with UreaSil based electrolytes [19]
The fine dynamical variations - observed on the DTG curves up to these temperatures - indicate already the release complexity of various volatile components studied by both FTIR and MS coupled evolved gas analysis (EGA)-methods
Summary
The family of dye-sensitized solar cells (DSSCs) is one of the most promising low cost alternative for the effective conversion of light energy into electrical energy [1].The components of a DSSC are in most cases the following: a nanocrystalline TiO2 film deposited on a transparent conductive electrode, a complex ruthenium-dye adsorbed on TiO2 nanocrystallites, an electrolyte bearing the I- / I3- or other redox couple and a platinized counter electrode [2,3,4,5]. First methanol (arising from condensation of tetramethoxysilane, TMOS) and acetonitrile (solvent) are evolved followed by elongated release of 4-tert-butylpyridine, than carbonyl sulfide, which is one of the degradation products of guanidinium thiocyanate, and various alkyl iodides, as well as iodine, later various oxidized species with >C=O groups (arising from oxidative degradation of oligo(ethylene glycolic) parts, ammonia (originated from guanidine) have been observed and traced during the accelerated heating tests, before final burning out of the organic residue with CO2 evolution.
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