In this work, high-performance inverted indium tin oxide (ITO)-free
semitransparent polymer solar cells are comprehensively investigated using a novel
polymer/metal hybrid transparent electrode. The electrical and optical characteristics
of hybrid electrodes are significantly enhanced by introducing UV/ozone plasma
treatment on the polymer poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-
alt-2,7-(9,9-dioctylfluorene)] (PFN), which is functioned as both a seed layer
for ultrathin Ag metal electrode and an optical spacer for transparent devices. The
optimized sheet resistance of PFN/Ag (12 nm) hybrid electrode is only half of the
commercial ITO (9.4 vs 20.0 Ω sq−1) and the high wavelength-dependent reflectance
of hybrid electrode helps to increase the ITO-free device short-circuit current density.
Furthermore, the interface property between PFN and ultrathin Ag is analyzed in
detail and the optical field distribution is calculated for comparison. A high power
conversion efficiency of 5.02%, which is increased by 35% compared to that of the
ITO-based device, is achieved in the ITO-free semitransparent device in conjunction
with an excellent average visible transmittance above 28% that is higher than the benchmark of 25% for power-generating
window, indicating its great potential in building integrated photovoltaic systems in the future. Furthermore, the strategy is
successfully developed for other polymer systems, suggesting the universal applicability for plastic electronics.