Vignesh Gowrishankar

Exciton splitting and carrier transport across the amorphous-silicon/polymer solar cell interface

The authors study exciton splitting at the interface of bilayer hybrid solar cells to better understand the physics controlling organic-inorganic device performance. 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 show photoresponse dominated by exciton production in the polymer. The a-Si:H∕P3HT devices are nearly as efficient as titania/P3HT cells. However, the a-Si:H∕MEH-PPV system has much lower photocurrent than a-Si:H∕P3HT, likely due to inefficient hole transfer back to the MEH-PPV after energy transfer from MEH-PPV to a-Si:H.

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

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 mechan...

Making Photovoltaic Power Competitive with Grid Power

Photovoltaic (PV) systems are currently too expensive to compete with grid power. After discussing the cost breakdown of currently available PV technology, we analyze the retail prices of PV necessary to become competitive with grid-power in various geographic and economic scenarios. We also address to what extents a tax on carbon emissions as well as inherent cost reductions in PV may influence and achieve PVs competitiveness with grid-power. The analyses focus on the US, but may be suitably extended to other locations

Harvesting excitons and improving charge transport in organic-inorganic hybrid photovoltaic cells

The authors describe the studies of exciton diffusion and charge transport in polymer-titania and polymer-alumina systems. We show that the exciton diffusion length is 12 nm in MDMO-PPV, the effective exciton diffusion length can be even larger if two polymers are used to promote efficient Forster energy transfer, and charge carrier mobilities higher than 10minus;3 cm2/Vs can be obtained in the relevant direction with regioregular poly(3-hexyl thiophene) by aligning the chains in nanopores

Improving exciton and charge transport in organic-inorganic hybrid photovoltaic cells

We have investigated the electronic processes that occur in organic-inorganic hybrid photovoltaic cells and show how exciton splitting and charge collection can be improved.