(Invited) Application of Carbon Nanotubes in CdTe Photovoltaics

Abstract

Single-wall carbon nanotube (SWCNT) films formed by spray deposition and membrane transfer processes are finding application in a wide variety of different solar cell device architectures. With a 1.45 eV band gap, a high absorption coefficient, high solar to electric conversion efficiency, and proven low-cost, high-volume manufacturing, CdTe-based photovoltaics are a fast growing technology. For CdTe photovoltaics, single-wall carbon nanotubes have been shown to provide a low-barrier back contact without the addition of Cu,1 protection against shunts and weak diodes,2 as well as the ability to grow devices in the substrate configuration.3 From a technology point of view, processes to form SWCNTs layers can be readily integrated with conventional CdTe manufacturing processes to provide both cost and performance advantages. Scientifically, the electronic properties of the interface between CdTe and SWCNTs are unusual and allow tunneling contacts to be formed. This allows flexibility in device design and offers the potential for monolithically integrated thin-film tandems. We will discuss the use of SWCNT layers in CdTe and other PV devices from both scientific and technology perspectives. (1) “Wiring-up Carbon Single Wall Nanotubes to Polycrystalline Inorganic Semiconductor Thin Films: Low-Barrier, Copper-Free Back Contact to CdTe Solar Cells”, Phillips, et al., Nano Lett., 2013, 13, pp 5224–5232. (2) “Simultaneous Shunt Protection and Back Contact Formation for CdTe Solar Cells with Single Wall Carbon Nanotube Layers”, Phillips, et al. Applied Physics Letters, in press. (3) “CdTe/CdS Thin Film Solar Cells in the Substrate Configuration on a Single-wall Carbon Nanotube Back Contact”, Khanal, et al., Proceedings of the 39th IEEE Photovoltaics Specialist Conference, pgs. 2013, pp. 1126–1130.