| 总结: | In this research work, a new bio-based polyurethane (PU) based on castor oil was
synthesized as host polymer in electrolytes for application in dye-sensitized solar cell
(DSSC). In the first stage of this work, castor oil based polyol was synthesized via
transesterification reaction under nitrogen gas atmosphere at room temperature. The
polyol possessed acid value of 3.0 mg KOH g−1, hydroxyl value of 190 mg KOH g−1 and
molecular weight of 2786 g mol−1, characteristics suitable for producing flexible PU. The
polyol was reacted with 4,4’-diphenylmethane diisocyanate at room temperature in
appropriate ratios to form flexible PU. The formation of urethane linkage was confirmed
using Fourier transform infrared analysis by the disappearance of NCO peak and
appearance of amine (secondary), carbonyl and ether group in PU chain. For the
preparation of PU polymer electrolytes, the PU was added with sodium iodide (NaI) and
lithium iodide (LiI) salts in different weight percentages to form PU-LiI and PU-NaI
systems respectively. 3-propyl-1-methylimidazolium iodide (PMII) ionic liquid was
added to the highest conducting sample of PU-NaI and PU-LiI systems to enhance the
conductivity as well as the efficiency of DSSC. The characteristics of polymer
electrolytes were analyzed using Fourier transform infrared spectroscopy, dynamic
mechanical analysis, electrochemical impedance spectroscopy, transference number
measurement and linear sweep voltammetry. Glass transition temperature of –15.8 °C of
PU decreased upon addition of salts. The lowest glass transition temperature of PU-NaI
system was –26.2 °C and PU-LiI system was –27.3 °C. The highest conductivity achieved
for the systems were 4.28 × 10−7 S cm−1 and 1.41 × 10−6 S cm−1, respectively. The
inclusion of PMII ionic liquid to the PU-NaI and PU-LiI enhanced the ionic conductivity
of the polymer electrolytes by one order of magnitude and also lowered the Tg value to
~ –33.0 °C. Ionic liquid is believed to act as plasticizer to soften the polymer backbone
iv
therefore increase the polymer segmental motion to ease ions migration which in turn
increased the ionic conductivity. The conductivity for all PU electrolyte films increased
with increase of temperature and follow the Arrhenius behaviour for PU-NaI, PU-LiI and
PU-NaI-PMII systems, and Vogel-Tamman-Fulcher behaviour for PU-LiI-PMII. The
calculation of activation energy, Ea from the gradient of Arrhenius and Vogel-Tamman-
Fulcher plots showed that the trend of conductivity was consistent with the trend of Ea,
i.e: the higher conducting sample possessed lower activation energy. The addition of ionic
liquid to the PU-salt also enhanced electrochemical stability window of the polymer
electrolytes. The electrochemical stability windows were ~ 2.0 V. DSSCs were fabricated
employing PU based polymer electrolytes with configuration of FTO/TiO2-dye/PU
electrolytes-I2/Pt/FTO. Photovoltaic parameters such as current density, open circuit
voltage, fill factor and efficiency were calculated from photocurrent–voltage
measurement. The highest efficiency employing PU-NaI and PU-LiI systems were 0.80%
and 0.83%, respectively, whereas for PU-NaI-PMII was 1.06% and PU-LiI-PMII was
1.92%. These results revealed that the new bio polymer electrolytes have potential for
application in DSSC.
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