Amorphous-Silicon / Polymer Solar Cells and Key Design Rules for Hybrid Solar Cells

Hybrid solar cells combine the advantages of organic and inorganic materials. We report on the fabrication and performance of hydrogenated amorphous silicon (a-Si:H)/poly(3-hexylthiophene) (P3HT) and a-Si:H/poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV) solar cells. The a-Si:H/P3HT system is found to be almost as efficient as titania/P3HT systems. However, the a-Si:H/MEH-PPV system exhibits poorer efficiency vis-a-vis a-Si:H/P3HT and titania/MEH-PPV. This is hypothesized to be due to enhanced energy transfer from MEH-PPV to a-Si:H, coupled with inefficient backward hole transfer, due to the small offset between the highest occupied molecular orbital (HOMO) of MEH-PPV and the valence band edge of a-Si:H, and the extended valence bandtail states in a-Si:H