Abstract Upconversion of sub-band-gap photons constitutes a promising way for improving the efficiency of silicon-based solar cells beyond the Shockley-Queisser limit. 1500 nm to 980 nm upconversion by trivalent erbium ions is well-suited for this purpose, but the small absorption cross section hinders real-world applications. We employ tailored gold nanostructures to vastly improve the upconversion efficiency in erbium-doped TiO 2 thin films. The nanostructures are found using topology optimization and parameter optimization and fabricated by electron beam lithography. In qualitative agreement with a theoretical model, the samples show substantial electric-field enhancements inside the upconverting films for excitation at 1500 nm for both s- and p-polarization under a wide range of incidence angles and excitation intensities. An unprecedented upconversion enhancement of 913 ± 51 is observed at 1.7 W cm−2. We derive a semi-empirical expression for the photonically enhanced upconversion efficiency, valid for all excitation intensities. This allows us to determine the upconversion properties needed to achieve significant improvements in real-world solar-cell devices through photonic-enhanced upconversion.

中文翻译：

---

通过定制的金纳米结构强烈增强三价铒离子的上转换：迈向高效的硅基光伏

摘要 子带隙光子的上转换是提高硅基太阳能电池效率超过肖克利-奎瑟极限的一种有前途的方法。三价铒离子的 1500 nm 至 980 nm 上转换非常适合此目的，但小吸收截面阻碍了实际应用。我们采用定制的金纳米结构来极大地提高掺铒 TiO 2 薄膜的上转换效率。使用拓扑优化和参数优化发现纳米结构，并通过电子束光刻制造。与理论模型定性一致，样品显示出在 1500 nm 处激发的上转换薄膜内部的显着电场增强，用于在很宽的入射角和激发强度范围内进行 s 和 p 偏振。在 1.7 W cm-2 下观察到前所未有的 913 ± 51 上转换增强。我们推导出光子增强上转换效率的半经验表达式，适用于所有激发强度。这使我们能够确定通过光子增强上转换实现实际太阳能电池设备显着改进所需的上转换特性。