Simulation of a Square Mesh Fractal Topology Carbon Nanotube Photovoltaic Array

The use of carbon nanotubes (CNTs) represents a typical approach to reduce both cost and size and to improve the efficiency of photovoltaic (PV) devices. In order to concentrate the incident power in what is known as hot spots, an array spatial arrangement has been formed as a square mesh fractal topology. The interaction between electromagnetic waves from the sun and CNTs is simulated in order to calculate the amount of absorbed power. A home built simulator based on the self-consistent solution of Poisson’s equation and the semi-classical drift-diffusion equations is used to calculate the I-V characteristics of the device and hence its efficiency. INTRODUCTION Currently, CNTs based PV devices produce very small amounts of power. They could be used in self-powered nanosystems like wireless sensors, implantable biosensors, nanorobotics and wearable electronics (Wang, 2008). Since a single CNT delivers a very small current, the array format is advantageous because it can deliver much larger currents and have less noise, enabling the operation at high frequency (Ho et al, 2010). In earlier publications (Abdel Rahman et al, 2010), (Abdel Rahman & Kirah, 2010), we have introduced the use of fractal topologies (Peitgen et al, 2003) in implementing solar cells in order to improve the performance. Fractal-based arrangements are used to localize the energy at spatially-separated, high-intensity regions, called hotspots, where maximum power absorption occurs coinciding with the locations of the CNTs (Wong, 2007) A fractal is a fragmented geometric shape that can be subdivided into parts, each subdivision is approximately a reduced-size copy of the whole. Figure (1-a) shows the first four iterations of the Sierpinski triangle as an example of a mathematically generated pattern. In figure (1-b), we can see Broccoli which is an example of a naturally occurring fractal.