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 VOC 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 VOC for crystal silicon/PANI n/p solar cells, for which VOC varies little for PANI conductivities greater than 10−1 S/cm. The comparison excludes electrophoresis effects in the PANI as the limiting mechanism.