2.2. DSSC characterization
The light intensity was controlled by placing neutral
density (ND) filters and a condenser lens in the illumination
path. The condenser-lens-based solar concentrator
employed in this study had a diameter of 30 mm, a center
thickness of 2 mm, an edge thickness of 1.46 mm, and an
effective focal length of 30 mm. The condenser lens was
supported by a homemade vertical holder, and the focal
length was varied by adjusting the rotating gauge (see
Fig. 2, Choi et al., 2011). The operating temperature of
the DSSCs was controlled using a Peltier cell (9501, Ferrotec
Co., Ltd., Korea) in the temperature range from 4 to
60 C. We measured the temperature of top and bottom
sides of DSSCs by using a thermocouple. Here, the top side