charge recombination rate due to the increased concentration
of photogenerated electrons. It is interesting to note
that the FF values are similar for each temperature even
though they can be decreased at higher cell temperatures
by the enhanced charge recombination rate due to reduction
in liquid electrolyte viscosity. This is because the series
resistance simultaneously decreases with increasing temperature;
consequently, these two contrasting effects can lead
to similar FF values at different operating temperatures.
The PCE of DSSCs is observed to steeply decrease with
increasing light intensity (6100 mW cm2), as can be
observed in Fig. 5d, while that of DSSCs at light intensities
greater than 100 mW cm2 exhibits a more gradual
decrease. The reduction in both Jsc and Voc values at high
operating temperatures results in decreasing PCE values at
different light intensities.
On the basis of photovoltaic performance parameter
measurements, one can expect to easily maintain the optimized
PCE value of DSSCs with very little temperature
influence at higher light intensities (>100 mW cm2). However,
in order to maintain the optimized PCE of DSSCs
that were measured at relatively low light intensities
(6100 mW cm2), it is necessary to either increase the light
intensity using a solar concentrator or lower the operating
temperature of DSSCs using a cooling system, or both. Our
findings provide a better understanding of the conditions
required for optimum DSSC performance.