Low-Work-Function,
ITO-Free Transparent Cathodes for
Inverted Polymer Solar Cells
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Abstract
A low-work-function,
indium tin oxide (ITO)-free transparent cathode
having a tin oxide (SnO<sub>X</sub>)/Ag/SnO<sub>X</sub>/bismuth oxide
(Bi<sub>2</sub>O<sub>3</sub>) (SASB) structure is developed without
using annealing treatment. This represents the first time that Bi<sub>2</sub>O<sub>3</sub> has been introduced to lower the work function
of transparent electrodes. The SASB transparent cathode exhibits excellent
photoelectric properties with a maximum transmittance of ∼88%,
a low sheet resistance of ∼9.0 Ω·sq<sup>–1</sup>, and a suitable work function of 4.22 eV that matches the lowest
unoccupied molecular orbital level of the acceptor for exacting electrons
efficiently. The power conversion efficiency of the polymer solar
cell with the SASB electrode is 6.21%, which is comparable to that
of ITO-based devices. The results indicate that SASB is a good alternative
to ITO as transparent cathodes in optoelectronic devices