We obtained improved polythiophene / PCBM bulk heterojunction photovoltaic devices by doping with stable and highly electrically conductive Au nanoparticles (NPs). Figure 1 shows TEM images of thermally annealed polythiophene / PCBM films with Au nanoparticles (fig 1(a)) and without (fig.1(b)) Au nanoparticles. We can clearly observe the formation of nanodomains of polythiophene and PCBM. In addition, Au nanoparticles are dispersed homogeneously in the film even after thermal annealing at 140oC.
The Au nanoparticle doped hybrid devices showed improved efficiency. The improvement is mainly ascribed to the increased photocurrent density.
We suggest that a dominate mechanism for the efficiency enhancement of hybrid photovoltaic device is the improved electrical conductivity and enhanced optical strength due to the surface plasmon of the Au NPs. The detailed voltage-current density characteristics and wavelength dependence of external quantum efficiency of the hybrid solar cell will be discussed in detail.