Abstract:
In this work, chemical bath-deposited cadmium sulfide (CdS) thin films were employed as
an alternative hole-blocking layer for inverted poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric
acid methyl ester (PCBM) bulk heterojunction solar cells. CdS films were deposited by chemical
bath deposition and their thicknesses were successfully controlled by tailoring the deposition time.
The influence of the CdS layer thickness on the performance of P3HT:PCBM solar cells was systematically
studied. The short circuit current densities and power conversion efficiencies of P3HT:PCBM solar cells
strongly increased until the thickness of the CdS layer was increased to ~70 nm. This was attributed
to the suppression of the interfacial charge recombination by the CdS layer, which is consistent with
the lower dark current found with the increased CdS layer thickness. A further increase of the CdS
layer thickness resulted in a lower short circuit current density due to strong absorption of the CdS layer
as evidenced by UV-Vis optical studies. Both the fill factor and open circuit voltage of the solar cells
with a CdS layer thickness less than ~50 nm were comparatively lower, and this could be attributed
to the effect of pin holes in the CdS film, which reduces the series resistance and increases the charge
recombination. Under AM 1.5 illumination (100 mW/cm2
) conditions, the optimized PCBM:P3HT solar
cells with a chemical bath deposited a CdS layer of thickness 70 nm and showed 50% power conversion
efficiency enhancement, in comparison with similar solar cells with optimized dense TiO2 of 50 nm
thickness prepared by spray pyrolysis.
