Carbon Nanotube Based Transparent Contacts for Photovoltaics: Abstract No. EM-MoA6

Transparent electrical contacts are an integral part of photovoltaic (PV) devices, and the transparent conducting oxide (TCO) films currently in use are not ideal for all PV applications. Nanostructured bundles of single wall carbon nanotubes (SWCNT) can be solution deposited to form highly conductive and transparent thin films. The films consist of entangled bundles of SWCNTs with a largefraction of void space. The optoelectronic properties of the SWCNT films approach those of commonly used TCO films. Unlike ZnO and other traditional TCOs, however, the SWCNT film has little absorption in the visible or near infra-red. Furthermore, in stark contrast to other available TCO materials, the SWCNT films appear essentially p-type due to the intrinsic p-type conductivity of the SWCNTs.In this paper, we demonstrate the utility of SWCNT based transparent contacts on several different types of thin-film solar cells. Firstly, they were successfully used to replace i-ZnO/ZnO:Al in high-efficiency CIGS devices. Secondly, the SWCNT coating was used to replace ITO and PEDOT:PSS in bulk- heterojunction organic devices, resulting in an exceptionally high efficiency for a device withoutindium or PEDOT:PSS. These coatings work well in excitonic devices because the large void fraction allows for interpenetration of the active polymer at the nanoscale. They are also highly amenable to use on flexible substrates.