Single planar heterojunction organic solar cells based on CuPc-C60
small molecule active layer have been optimised using ITO anode electrode
obtained by ion beam sputtering (IBS). The main interests in IBS process is
an easy control of layer thickness and light transmission, and a better
roughness of the anode compared to commercially available ITO, which can
allow a PEDOT-PSS layer thickness optimisation.
Comparison of two identical solar cells with commercially available ITO and
our ITO obtained by IBS leads to a power conversion efficiency enhancement
from 0.5% to 0.7%. Surprisingly, decreasing the serial resistance by
increasing ITO thickness does not lead to further improvements, and this
feature has been attributed to an increase of the ITO absorption and a
possible cathode breaking due to a too thick cell structure.
Better roughness of our ITO has permitted to decrease the PEDOT-PSS layer
thickness, leading to an enhancement of the power conversion efficiency up
to 1.3%.
Optimising the cathode by adding an exciton blocking layer (BCP or LiF) has
allowed us to decrease the active layer thickness, leading to a decrease of
the cell serial resistance and giving rise to near 1.9% power conversion
efficiency.