Date

6-2015

Degree Name

BS in Materials Engineering

Department

Materials Engineering Department

Advisor(s)

Linda Vanasupa

Abstract

The top contact electrode layers of nine organic photovoltaic cells were prepared with two varying factors: three Silver nanowire (AgNW) densities deposited on a conductive polymer doped with three concentrations. Silver’s low sheet resistance of 20-Ω/sq is hypothesized to lower the sheet resistance of the anode layer and thus enhance the overall efficiency of the cell. Four-point probe measurements indicated that increasing AgNW density in the top contact electrode layer of an organic photovoltaic cell significantly reduces sheet resistance from 52.2k-Ω/sq to 18.0 Ω/sq. Although an increase in doping concentration of the conductive polymer reduced sheet resistance in low AgNW density samples from 52.2k-Ω/sq to 5.10k-Ω/sq, only a minor decrease from 34.7-Ω/sq to 29.2-Ω/sq was found in the higher AgNW density samples. To explain these patterns, we propose a transition in charge carrier conduction mechanism from one of resistors in series (AgNW and polymer matrix), controlled by the resistance of the conductive polymer, to that of a parallel circuit, with resistance controlled by the resistance of silver. Proposed models are supported by the number of disjoints between AgNWs found in Scanning Electron Microscope characterizations at 20,000X magnification. The number of disjointed AgNWs within 2.8 µm x 3.2-µm sections on the electrode surface decreased from an average of two to zero with increasing AgNW density. Atomic Force Microscopy characterizations portrayed increased RMS roughness due to AgNW agglomeration, ring shaped wire orientation and a random distribution of particles that potentially raise sheet resistance with increased contact resistance.