Enhancing Quantum Efficiency of Thin Film Solar Cells via Joint Characterization of Radiation and Recombination

薄膜太阳能电池处于光伏技术创新的前沿。然而，薄膜太阳能电池的效率明显低于体电池，限制了其应用规模。基于结构修改的光捕获方案已被用于提高纳米级光伏器件的效率。这些方案以复杂的方式影响薄半导体的辐射和电学特性。这些影响既没有准确建模，也没有广为人知。这项研究通过模拟光捕获的辐射和电效应来填补这一知识空白。所提出的模型将是多样的、全面的和比现有文献更准确的。通过使用改进的模型，可以为太阳能电池设备设计新颖的架构，与对美国经济具有高度价值的最先进技术相比，具有更高的转换效率和更短的能源回收周期。此外，这项工作还有助于更好地理解纳米结构修饰的辐射效应，这在光伏以外的纳米级辐射应用中是必不可少的。本项目研究了系统提高纳米薄膜太阳能电池量子效率的方法。为此，我们研究了纳米尺度的光俘获影响辐射的基本原理。建立了用于解释非均匀半导体中的辐射以及载流子复合的解析模型。辐射模型是基于对存在伪周期金属介质表面和体图形时的局域态密度的改进估计，以及基于Mie散射改进的等离子体纳米粒子消光截面的精确估计，使用数学形状公式和数据拟合。在实际材料缺陷和物理缺陷的假设下，模拟了多种机制的叠加辐射效应，并与载流子输运模型相结合。这项工作利用改进的模型来设计宽带/角度光吸收超过遍历限制，量子效率接近块状电池限制的结构。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Thin film solar cells are at the forefront of innovation in photovoltaics technology. However, the efficiency of thin film solar cells is significantly lower than bulk cells, limiting the scale of their application. Light trapping schemes based on structural modifications have been used to improve the efficiency of nano-scale photovoltaic devices. These schemes affect both radiative and electrical characteristics of thin semiconductors in complex ways. These effects are neither accurately modeled nor well known. This research fills this knowledge gap by modeling the combined radiative and electrical effects of light trapping. The proposed models will be diverse, comprehensive and more accurate than the existing literature. By using the improved models, novel architectures can be designed for solar cell devices with enhanced conversion efficiencies and reduced energy payback periods compared to the state-of-the-art technology which is highly valuable to the US economy. Additionally, the work leads to better understanding of the radiative effects of nano-structural modifications which is imperative in nano-scale radiation applications beyond photovoltaics.This project investigates methods to systematically enhance the quantum efficiency of nano-scale thin film solar cells. To this end, fundamentals of light-trapping affected radiation at nano-scale are studied. Analytical models are formulated for explaining radiation in non-homogenous semiconductors along with electrical carrier recombination. The radiative models are based on improved estimations of the local density of optical states in the presence of pseudo-periodic Metallo-dielectric surface and bulk patterns, and accurate estimation of extinction cross-section in plasmonic nano-particles based on improvements of Mie scattering using mathematical shape formulations and data fitting. Overlaying radiative effects from multiple mechanisms are modeled and combined with carrier transport models under realistic material imperfections and physical defects assumptions. The work utilizes the improved models to design structures with broad-band/angle optical absorption beyond the ergodic limits, and quantum efficiencies approaching the limits of bulk cells.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.