Page 413 - Polymer-based Nanocomposites for Energy and Environmental Applications

370 Polymer-based Nanocomposites for Energy and Environmental Applications

of HF for 30 s to separate the glass substrate by dissolving the glass from glass/TiO 2
interface. Further on, they coated an 80 nm-thick TiN layer onto the transferred TiO 2
as back contact via magnetron sputtering. Using similar preparation method, they pro-
duced and transferred Pt/carbon electrode on the top of another PEN substrate. The
electric conductivity of this layer is improved by annealing the Pt/carbon layer. Sche-
matic presentation and real image of flexible electrodes are given in Fig. 13.5. This
high-temperature annealed mesoporous layer on TCO-free plastic-substrate-based
DSC (5.76%) showed lower efficiency than 500°C annealed TCO-glass-based
(6.84%) and 500°C annealed TCO-free glass-based ones (6.09%), which was attrib-
uted to the higher series resistance of TiN layer than that of TCO. On the other
hand, the obtained results were found to be higher than a conventional, low-
temperature-prepared flexible electrode-based DSC (4.20%) as a result of the stronger
interconnection of TiO 2 particles with high-temperature sintering.
Yang et al. [34] prepared flexible DSC constructed by friction transfer of high-
temperature annealed TiO 2 on ITO-PEN substrate. Firstly, they produced 15 μm-thick
mesoporous TiO 2 layer on a ceramic tile by doctor blade and annealing at 500°C. At
the same time, they also prepared an underlying TiO 2 layer (28 μm) for the friction-
transfer process by spraying TiO 2 precursor paste (prepared by using certain amount
of P25 powders, tetrabutyl titanate (TBT), and ethanol) onto ITO-PEN and calcination
at 125°C. Further on, the TiO 2 layer prepared on the ceramic tile and the TiO 2 layer
prepared on the plastic substrate were brought face-to-face, and the film on the
ceramic tile was transferred onto the plastic by applying frictional force. After com-
pression under pressure of 100 kgf cm 2 and post treatment with TBT/n-butanol mix-
ture at 90°C for 15 min, strong connection of these layers was achieved, and all the
possible defects were fixed. Fig. 13.6 describes the friction-transfer method steps and
shows SEM micrographs of the obtained layer. For the preparation of flexible CE, they
used chemical reduction (CR) method to obtain Pt layer on ITO-PEN at low temper-
ature. For comparison, they also produced flexible DSC by using low-temperature
sintering and compression techniques. According to the results, fully flexible DSC

Fig. 13.5 Schematic of a TCO-free flexible DSSC device structure (left). Photographs of the
fabricated WE and CE (5 5 cm) under bending (right).
Reproduced with permission from Yoo K, Kim J-Y, Lee JA, Kim JS, Lee D-K, Kim K, et al.
Completely transparent conducting oxide-free and flexible dye-sensitized solar cells fabricated
on plastic substrates. ACS Nano 2015;9:3760–71.