Abstract:
Hybrid nanocrystalline titanium dioxide (TiO2)/polymer solar cells draw intense interest due to the
potential advantages of nanocrystalline TiO2. The poly(styrenesulfonate)-doped poly(ethylenedioxy
thiophene) (PEDOT:PSS) layer spin-coated below the top electrode in these solar cells had shown
enhanced performance in previous studies, which motivated to explore the dependence of the thick ness of the PEDOT:PSS layer on its performance. This study focused on the characterization of
solar cells fabricated with poly(3-hexylthiophene) (P3HT) polymer with a silver electrode and differ ent PEDOT:PSS layer thicknesses, in the dark and under AM 1.5 stimulated illumination with the
intensity varying from 10 to 100 mW/cm2. The variations in the photovoltaic parameters, particu larly the open-circuit voltage, proved that the PEDOT:PSS layer significantly affects the photovoltaic
parameters through the characteristic changes in the morphology as well as the electrical proper ties. Discussed herein is the possible influence wielded by the thickness of the PEDOT:PSS layer
on different factors, such as the series and shunt resistances, the mode of recombination, the
reduction of the energy barrier, and the diffusion of silver. The optimum power conversion efficiency
was observed for the as-prepared devices with 50-nm-thick PEDOT layers. The optimum power
conversion efficiency, however, shifted to that corresponding to the 80 nm thick PEDOT:PSS layer
about 30 weeks after the fabrication. A sublinear variation of the short-circuit current density with
the intensity was found in the aged cells with relatively lower PEDOT:PSS layer thicknesses, sup porting the view of dominant recombination contributed from bimolecular recombination in the cells
with lower PEDOT:PSS thicknesses. The significantly increased open-circuit voltage and the more
stable current density in the aged devices are the main causes of the improved performance of the
cells generally with above 60 nm thick PEDOT:PSS layers. These, along with the long-term stability
found in the cells with reasonably thick PEDOT:PSS layers, may be a figure of merit, most probably
attributable to the comparatively minimized diffusion of silver nanoparticles.
