Department of Electrical & Computer Engineering & the Ilse-Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 8410501, Israel.
Nanoscale. 2017 Oct 19;9(40):15707-15716. doi: 10.1039/c7nr05172g.
Decorating the top surface of silicon solar cells with nanopillar arrays of subwavelength periodicity is a promising path toward low-cost thin-film photovoltaics with enhanced solar radiation absorption due to the inherent light trapping capabilities of nanopillar arrays. Common practice and knowledge for the efficient carrier extraction from the excited nanopillars is the formation of ultra-shallow radial p-n junctions that provide both short carrier collection lengths, and also ensure that the volume of the photo inactive emitter is as small as possible. In the current manuscript, both finite-difference time-domain simulations and three-dimensional device simulations are used to examine carrier extraction from nanopillar arrays that are geometrically optimized in terms of array periodicity and nanopillar diameter to provide maximum absorption of the solar spectrum. The discussion is limited to nanopillars with heights of 2 μm in line with what is currently available with leading top-down fabrication technologies for the formation of nanopillars with smooth sidewalls and radial uniformity. The examination considers both radial and axial homojunctions for various junction depths. It is shown that, contrary to common practice and knowledge, the ultra-shallow junctions are detrimental to the photovoltaic performance of such systems while the radial configuration with a junction depth of ∼50 nm is the most efficient. Furthermore, the open circuit voltage is highest for axial junctions with a junction depth of 100 nm. Also, it is shown that the axial junction is preferable in the low dopant concentration regime and that overall, the axial junction is less sensitive to variations in junction depth.
在硅太阳能电池的上表面装饰亚波长周期性的纳米柱阵列是一条很有前途的途径，可以实现低成本的薄膜光伏，因为纳米柱阵列具有固有的光捕获能力，可以增强太阳辐射吸收。从受激发的纳米柱中高效提取载流子的常见做法和知识是形成超浅的径向 p-n 结，这不仅提供了短的载流子收集长度，而且还确保了非活性发射体的体积尽可能小。在当前的手稿中，使用有限差分时域模拟和三维器件模拟来研究从纳米柱阵列中提取载流子，这些纳米柱阵列在阵列周期性和纳米柱直径方面进行了几何优化，以最大限度地吸收太阳光谱。讨论仅限于高度为 2 μm 的纳米柱，这与目前领先的自上而下制造技术形成具有光滑侧壁和径向均匀性的纳米柱的技术相匹配。该研究考虑了不同结深的径向和轴向同质结。结果表明，与常见的做法和知识相反，超浅结对这种系统的光伏性能不利，而具有约 50nm 结深的径向配置是最有效的。此外，结深为 100nm 的轴向结具有最高的开路电压。此外，还表明轴向结在低掺杂浓度范围内更优，并且总体而言，轴向结对结深的变化不太敏感。
