| Popis: |
Energy consumption in the world is increasing rapidly and the supply of fossil fuels will not be able to keep up with the demand for too long. Fortunately, two emerging technologies, photovoltaic (PV) cells and concentrated solar power (CSP), can deliver a large portion of United States’ energy needs in the next 40 years if they are properly developed. In this chapter, first, fundamental mechanisms of how electricity is generated by these two technologies are described. Next, recent developments in the application of nanotechnology for enhancing PV cell performance are presented. Among inexpensive solar cell technologies, copper indium diselenide (CuInSe2 or CIS) based thin film solar cells have achieved solar to electrical conversion efficiency of 19.5 %. However, further improvement of efficiency is needed for them to become competitive with traditional energy sources. Two major efficiency limiting factors are, less than optimal energy band gap and short carrier diffusion length. In our group, we have used nanoscale engineering to develop device designs that would counter these two limiting factors. Specifically, vertically aligned nanowire arrays of CuInSe2 of controllable diameter and length were produced by simultaneously electrodepositing Cu, In, and Se from an acid bath into the pores of anodized aluminum oxide (AAO) formed on top of an aluminum sheet. Ohmic contact to CIS was formed by depositing a 100 nm thick gold layer on top and thus a Schottky diode device of the Au/CIS nanowires/Al configuration was obtained. Analysis of the current–voltage characteristics of these devices yielded higher resistivity than those reported for CIS thin films, as expected from the size-dependent effects. Capacitance–voltage measurements were performed on the diodes to get the estimates of space charge density and the junction potential. Based on these experimental results, a nanowire-based solar cell configuration is proposed and illustrated. |
