Amorphous silicon/polyaniline heterojunction solar cells: Fermi levels and open-circuit voltages

We fabricated hydrogenated amorphous silicon/polyaniline n-i-p heterojunction solar cells incorporating a doped, hole conducting polyaniline (PANI) layer. The cells were prepared by spin-casting differing polyaniline dispersions corresponding to film conductivities ranging from 10^-2 to 10² S/m. The open-circuit voltages V_OC of the cells ranged from 0.5-0.7 V. While these open-circuit voltages are lower than for the best a-Si:H cells utilizing nanocrystalline Si or a-SiC:H p-layers, they illustrate well how open-circuit voltages are limited by the work function of the contacting material. They also give insight into the mechanism limiting V_OC for crystal silicon/PANI n/p solar cells, for which V_OC varies little for PANI conductivities greater than 10^-1 S/cm. The comparison excludes electrophoresis effects in the PANI as the limiting mechanism.