The performance of the QDSC could be improved by carrying
out the photovoltaic measurements using reduced illumination
light intensities. Fig. 5 (b) shows the I-V curves of the best cell
(sample No. 5) obtained under four different light intensities.
Table 2 lists the photovoltaic data. The data in Table 2 exhibit four
notable features: (1) an increase of Jsc; (2) an increasing of FF; (3)
an increase of PCE and (4) a decrease of Voc. The PCE increased
from 1.76% (100% sun) to 4.14% (10% sun), an enhancement of a
factor of 2.35. The improvement arose from two main parameters:
the FF increased from 30.8% (100% sun) to 50.5% (10%sun), an increase
of ~67%. In addition, Jsc also exhibited significant
improvement. Fig. 5 (c) shows the normalized Jsc (after normalizing
to a light intensity of 100% sun) as a function of light intensity.
Jsc increased from 10.9 mA cm2 (100% sun) to
20.0 mA cm2 (10% sun), an increase of 83%. In contrast, Voc
decreased steadily from 0.48 V (100% sun) to 0.41 V (10% sun). In
addition, in comparison to liquid-junction QDSCs (the only report
on Pb5Sb8S17 QDSC so far), the PCE of the present solid-state QDSC
(4.14%) is significantly larger than that (2.5%) of liquid-junction
QDSCs in Ref. [30].