| Summary: | 博士 === 國立成功大學 === 化學工程學系碩博士班 === 101 === A high efficient gel-state electrolyte was fabricated by using poly(acrylonitrile-co-vinyl acetate) (PAN-VA) as an novel gelator of a MPN-based liquid electrolyte and applied for dye-sensitized solar cells (DSSCs). The VA segaments play a role to dissolve the copolymer into the electrolyte, and the AN segaments form a gel-state structure. The electric conductivity of the gel-state electrolyte is close to that of the liquid electrolyte, attributed to the enhancement effect of AN segments to the dissociation of LiI and DMPII. This effect also leads to a slightly downward shift of TiO2 CB edge toward positive potentials. The energy conversion efficiency of the DSSC achieved by using this gel-electrolyte is 8.34%, which is 97 % the value of the liquid-state cell (8.6%).
However, one problem encountered in fabricating gel-state DSSCs is the high viscosity of gel-electrolytes which makes difficulty for the well penetration of gel-electrolytes into mesoporous TiO2 matrixes. This problem is especially serious on module cells which have large working area. By using PAN-VA as a gelator of an acetonitrile (ACN)-based liquid electrolyte and applied for preparation gel-state DSSCs. Due to the high interaction of PAN-VA to ACN, the gelation of the electrolyte performs slowly at room temperature, and several to hundreds hours are required to approach the gel-state, depend on the amounts of gelator and filler contained in the electrolyte. This property allows the injection of the electrolyte into DSSCs at the liquid state under room temperature. The injected liquid electrolyte then undergoes in-situ gelation inside the mesoporous matrix of a TiO2 film, making good contact to the electrode surface. Based on the advantage of this ACN-based electrolyte, the performance of the corresponding gel-state DSSC is higher than that obtained by the 3-methoxypropionitrile (MPN)-based electrolytes. For the ACN system, the energy conversion efficiency of a gel-state DSSC using PAN-VA can achieved a value (9.03%) nearly identical to that of a liquid-state cell (9.04%). Furthermore, by further introduction of TiO2 nanoparticles as fillers of the gel-electrolyte, an efficiency (9.46 %) higher than that of the liquid version can be achieved. It was also shown that the stability of a DSSC using ACN-based electrolyte can maintain efficiency 1000 hours at 50℃。
The effects of PAN-VA concentration on the gelation rate, gel-to-liquid transition temperature, and performance of gel-state DSSCs are studied. The results show that increasing the content of PAN-VA increases the phase transition temperature, but decreases the conductivity of the gel-state electrolytes. However, the energy conversion efficiencies of the gel-state cells do not significantly decrease due to the decrease of conductivity, but are strongly affected by the penetration of the electrolyte into the TiO2 film. For PAN-VA concentrations ≤ 15 wt%, the electrolyte can be easily injected at room temperature due to in-situ gelation. For higher PAN-VA concentrations, good penetration of the highly viscous electrolytes can be achieved by elevating the operation temperature. By using the proposed methods, energy conversion efficiencies of above 10% for gel-state DSSCs. The cell can maintain the initial efficiency above 93% at 60℃, 1000 hours.
Since the PGE with high PAN-VA content demonstrated good performance in terms of electric conductivity and energy conversion efficiency of DSSCs, it was used to fabricate solid-state electrolytes for DSSCs. TGA results show that the weight loss of the sample is only 3% before thermal degradation. By adjusting I2 concentration and introducing TiO2 as nanofiller for optimal potoanode thickenss to prepare solid-state DSSCs, conversion efficiency of 8.02% are achieved.
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