Exciton harvesting, charge transfer, and charge-carrier transport in amorphous-silicon nanopillar/polymer hybrid solar cells

Abstract

We report on the device physics of nanostructured amorphous-silicon (a-Si:H)/polymer hybrid solar cells. Using two different polymers, poly(3-hexylthiophene) (P3HT) and poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV), we study the exciton diffusion, charge transfer, and charge-carrier transport in bilayer and nanostructured a-Si:H/polymer systems. We find that strong energy transfer occurs in the a-Si:H/MEH-PPV system. However, inefficient hole transfer from the a-Si:H to the polymers renders negligible photocurrent contribution from the a-Si:H as well as very small currents in the a-Si:H/MEH-PPV devices. These results suggest that a-Si:H may be unsuitable for use in polymer-based hybrid cells. Nanosphere lithography and reactive ion etching were used to fabricate nanopillars in a-Si:H. The nanostructured a-Si:H/P3HT devices showed improved efficiency and almost perfect charge-carrier extraction under short-circuit conditions. By modeling these nanostructured devices, the loss mechanisms were identified and solutions for higher efficiencies are suggested.