Abstract
Recently there have been worldwide interests in the research of next generation solar cells by novel nanostructures and nanomaterials. Because of their near-wavelength-scale geometry, the Si nanostructure arrays have broadband low reflection and therefore strong absorption from near IR to visible region, which can be applied as an antireflection layer without further coating processes. Moreover, the high aspect ratio of nanostructure allows enhancing optical absorption while simultaneously decreasing the carrier diffusion length through the fashion of core-shell nanowires. In this study, first we fabricated a p-type single-crystal (sc) Si nanostructure arrays as the base by statistic electroless metal deposition (SEMD) method. The morphology control of the Si nanostructures on Si substrate by four major factors was discussed in SEMD process. Next, we employed a spin-on-dopant (SOD) method to form a uniform n-type emitter on our Si nanostructures, which is suitable for the dense and high aspect ratio arrays with a super-hydrophilic surface. The thin layer of emitter facilitates to construct the core-shell structure arrays for radial p-n junction solar cell that decouples the incoming light route and carrier diffusion path into orthogonal directions. This architecture benefits to the light absorption as well as the carriers collection by allowing lateral diffusion of minority carriers to the p-n junction rather than many microns away as in Si bulk solar cells. At last, we investigated relative reflection and photovoltaic parameters of four kinds of Si nanostructure based solar cells such as nanopores, nanowires, nanotips, and nanohills. The Si nanowires (SiNWs) based solar cell possesses the lowest total reflection (~ 1%) within the range of wavelength from 530 to 1030 nm. It also improves the conversion efficiency up to more than 25% in contrast to planar sc-Si solar cell under identical condition. In addition, the issues of length and electrode contact of SiNWs based solar cell were discussed, and several guidelines for optimizing such SiNWs based photovoltaic device were further suggested. The proposed novel design of solar cell by incorporating SiNW array revolutionizes the current architecture of solar cells, promising niche points of (1) better absorption, (2) self-antireflection, and (3) cost-effective fabricated process.