Advanced electro-optical simulation of nanowire-based solar cells

The improvement of solar cell efficiency requires device optimization, including the careful design of contacts and doping profiles, and the development of light trapping strategies. In this context, electro-optical numerical simulation is essential to analyze the physical mechanisms that limit the cell efficiency and lead to design trade-offs. In this work we discuss the application of advanced electro-optical simulation to the analysis of nanowire-based solar cells. We demonstrate the possibility to combine two numerical tools to perform the electro-optical simulation in order to investigate critical issues and potentialities of nanowires for photovoltaic applications. Thanks to the adopted simulation methodology, requiring relatively low computational resources, analyses involving extended ranges of geometrical and physical parameters are performed. Nanowire-based (NW) solar cells are expected to outperform the thin-film counterparts in terms of optical absorptance. In this theoretical study we optimize the geometry of vertical crystalline-amorphous silicon core-shell NW arrays on doped ZnO:Al glass substrate by means of 3-D optical simulations in order to maximize the photon absorption. The optimized geometry is then analyzed by means of 3-D TCAD electrical simulation in order to calculate the ultimate efficiency and the main figures of merit. We show that optimized crystalline-amorphous silicon core-shell (c-Si/a-Si/AZO/Glass) NWs featuring height in the micrometer range can reach photogenerated current up to 22.94 mA/cm2, approximately 40 % larger than that of the planar counterpart with the same amount of absorbing material, and maximum conversion efficiency close to 14 %.