Near and Far-Field Plasmonic Enhancement From Thermally Evaporated Ag Nanostructures in Polymer Photovoltaic Cells: Simulation and Experimental Study

In this research, the plasmonic Ag nanostructures prepared by the thermal evaporation method in organic cells were investigated by 3-D finite-difference time-domain (3D-FDTD) simulation and experiment. For the more realistic FDTD modeling, suitable forms of Ag nanostructures that were close to the form of a very thin layer prepared by the thermal evaporation method were used. The experimental results showed that when the thermally evaporated Ag nanostructures are added at the interface of the buffer/active layer, the organic solar cell with 4-nm Ag nominal thickness has maximum enhancement. Then, a comprehensive 3D-FDTD simulation was carried out to determine the optical reasons. In fact, the cell has the potential to benefit from both near- and far-field effects simultaneously. But the simulations showed that the utility of the plasmonic structure in this regard is very challenging and this structure needs to be optimized for both near- and far-field enhancement. On the other hand, the nominal thickness of 4 nm could lead to an optimum size-shape distribution of the nanostructure, which is associated with improving organic cell operation with both near- and far-field effects. In this thickness, the efficiency of the cell was increased by a factor of 1.62 relatives to the organic cell without the Ag nanostructure. The dark J-V curves as well as the series resistance of the plasmonic organic cell revealed that it was important to consider electrical effect along with optical one, concurrently. Finally, the charge transport mechanisms in the more optimized cell were investigated and it was demonstrated that the trap-charge-limited-current model was dominant.