Nano-Templating of Iron Oxide for Solar Cells

Abstract

Electricity production by solar cells is currently expensive due to the materials and processes used in their fabrication. Novel types of solar cells such as dye sensitized and organic and organic/inorganic hybrid bulk heterojunction solar cells may in the future serve as cheaper alternatives with complementary areas of use. One approach to producing hybrid bulk heterojunction solar cells is filling a porous metal oxide semiconductor with an organic hole conducting and photo active material. The performance of the resulting solar cell is greatly dependent on the porous nanostructure of the metal oxide. This thesis work is focused on the fabrication of nanoporous iron and iron oxide films that may be used for solar cells, but also have many other possible applications. The films are produced by electrodeposition through a porous block-copolymer template. The template is fabricated by swelling the polymer, polystyrene-block-poly(2-vinyl pyridine), in a solvent which makes it porous. The control of the pore size and pore-to-pore distance was investigated by varying the swell time. It was shown that nanoporous iron films with thickness ranging from 100 to 800 nm can be produced on indium tin oxide (ITO) in acidic conditions if a thin seed layer is present. The pore size (20 􀀀 30 nm) as well as the pore-to-pore distance (70 nm) were found to differ only slightly for various swell times of the block-copolymer template. To obtain iron oxide, the films were then annealed; and this was observed to deform the porous structure. Nanoporous iron oxide films, however, could be fabricated in a basic electrolyte without a seed layer. Compared to the iron films, the pores size was found to be slightly larger while the pore-to-pore distance was equal.