David S. Ginley

Improvement of interfacial contacts for new small-molecule bulk-heterojunction organic photovoltaics.

The influence of protonation reactions between poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and a thiadiazolo[3,4-c]pyridine small-molecule donor are reported; these result in poor solar-cell performance due to a barrier for charge extraction. The use of a NiO(x) contact eliminates such deleterious chemical interactions and results in substantial improvements in open-circuit voltage, fill factor, and an increased power conversion efficiency from 2.3% to 5.1%.

Nanostructured TCOs (ZnO, TiO2, and Beyond)

Transparent conducting oxide (TCO) materials are traditionally used in applications as thin films, however there are a number of emerging technologies that require TCO materials in different form factors. This chapter will explore some three dimensional TCO nanostructures and their applications in hybrid photovoltaic devices. Additionally, we will look at the modification of TCO properties to allow for higher efficiency devices as well as novel materials, such as carbon nanotube assemblies, that might improve upon those properties. In many cases the nature of the TCO interface is constrained by the type of device. For example in hybrid organic–inorganic photovoltaic devices, poor exciton and charge carrier transport in the organic layer requires the distance to be short between the organic film and the TCO contact. In this case this distance is less than 10 nm necessitating a nanometer scale topology in a successful device. Similarly for solar cell and even display applications it is important to control the reflectance of the TCO surface through methods such as the etching facets in the surface as has been done in ZnO. This can, in fact, be accomplished simultaneously through the use of the TCO as the contact [1–8]. TCO nanofibers grown as a nanocarpet or incorporated in a composite can add conductivity without adversely affecting the optical properties [9–13]. In this chapter we review some of the more recent synthesis of nanostructured TCO materials and look at some of their emerging applications.