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Geometrical optimization and contact configuration in radial pn junction silicon nanorod and microrod solar cells

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ABSTRACT

Electric charge transport simulations of symmetrically doped radial pn junction silicon nanorod solar cells were performed using the Technology Computer-aided Design software suite by Silvaco. Two schemes of electric contacting were applied, the first one consisting of a cathode wrapped around the cladding of the rod and the second one in a cathode located only on the top rod surface. In both cases, the anode was implemented just below the bottom end of the p-type rod core. P-type cores and n-type shells of the rods were assumed, with dopant densities of 1018 cm− 3 in both regions. The location of the pn junction was chosen such that well-formed space charge regions could be established with the outer end of the n-type depletion region being adjacent to the cylindric surface of the nanorod. Rod radii and rod lengths were varied and optimized in a three-step process for both types of contacting schemes. It was found that inhomogeneous carrier generation profiles diminish the open-circuit voltage in case of a wrapped cathode configuration. Most realistic is the usage of a top contact configuration with rod radii of 2 µm and lengths of around 100 µm, leading to a cell efficiency of about 15%. Further enhancement of performance is expected, if light trapping of the nanorod layer is taken into account and photonic light harvesting is applied. Copyright © 2012 John Wiley & Sons, Ltd.

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