Abstract
Transparent and colorless solar cells are attractive new photovoltaic devices as they could bring new opportunities to harness sunlight energy and particularly for their integrations in windows. In this work, a new zinc phthalocyanine was synthesized and investigated as sensitizer in dye sensitized solar cell (DSSC) for this purpose. The zinc phthalocyanine features a benzoic acid anchoring group and six thio(4-tertbutylphenyl) substituents in position alpha of the phtalocyanine. The dye was characterized by absorption and emission spectroscopy and by electrochemistry. The physico-chemical properties show that the dye fulfills the criteria for such an application. A detailed computational study indicates that the electronic communication with TiO2 conduction is weak owing to the absence of overlapping of the wavefunctions of the dye with those of the TiO2 semiconductor. The photovoltaic performances of the zinc phthalocyanine were measured in TiO2 based DSSC and revealed inefficient electron injection and certainly explained by the weak electronic coupling of the 2 dye with TiO2 that limits electron injection efficiency. Strategy is proposed to make better performing sensitizers.
Highlights
Finding sustainable and environmentally friendly strategies to generate energy represents a huge challenge for modern society because of the inevitable depletion of widely used fossil fuels and the pollution they generate
The theoretical results indicate that the electron injection could occur from L+2 to the semiconductor because it is completely centered on the benzoic acid, but it would require an energy of 3.4 eV (365 nm), very high (UV region) to be an attractive compound to be used in dyesensitized solar cell (DSSC)
Detailed computational calculations enable a deeper understanding of the electronic properties of this sensitizer and that the presence of bulky thio-aryl substituents does not hinder the approach of the dye on the surface and do not perturb its chemisorption on TiO2 surface
Summary
Finding sustainable and environmentally friendly strategies to generate energy represents a huge challenge for modern society because of the inevitable depletion of widely used fossil fuels and the pollution they generate. Among the NIR absorbing dyes in DSSC, such as cyanines [23,24,25] and squaraines [26,27,28], phthalocyanine derivatives represent suitable candidates due to an intense absorption close to NIR region of the solar spectrum, a high molar extinction coefficient and a high fluorescence quantum yield, a great stability and proved efficiency in DSSCs [29] This is especially true since the seminal work of Ikeuchi et al when highly bulky groups were tethered to the macrocycle in order to limit deleterious aggregation, leading to a very significant jump in the photoconversion efficiencies, reaching 6% [30]. The performances of the DSSC remain weak because of a weak electron injection driving force that can be solved by changing the spacer linking the anchoring group and the phthalocyanine unit
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