Planar Black Silicon: disentangling optical and electrical properties of textured interfaces using transformation optics

对太阳能电池的吸收材料进行纳米织构可以增强对入射太阳光的强吸收和光谱宽带吸收。然而，对界面进行纳米加工会同时降低光电子器件的电学性能。这否定了吸收改进的完全收获，并且不允许将其转化为设备EFfi效率的可比改进。为了解决这个问题，我们建议利用变换光学的概念来设计光子结构，该结构保留了吸收材料的几何fl属性，使其在电上保持不变，同时在光学上表现为具有优化的抗反射和散射性能的纹理界面。在变换光学过程之后，可以利用麦克斯韦方程的不变性来推导出材料分布，该材料分布以与模板表面纹理完全相同的方式调节光flow，例如传统的黑硅。通过这样做，我们有效地推导出了一个不均匀的平面层，当放置在吸收体层的顶部时，它可以提供减反射和光捕获，从而增强吸收，相当于模板的表面纹理而不会产生电子退化。我们将致力于介电梯度折射率光管理结构的实验实现，并演示其在太阳能电池中的集成。作为构建块，我们将利用介电高折射率纳米结构和不同材料的薄film层，通过先进的原子层沉积技术。据我们所知，我们用变换光学推导光管理结构的方法是开创性的。我们的设计方法偏离了目前常见的变换光学应用，并将开辟变换光学概念在各种实际器件的结构设计中的应用。太阳能转换是最明显也是最重要的应用，它将直接受益于该项目的fifi。然而，这里将要开发的方法也可能有助于在其他光学fi领域中开发新的概念。例如，人们还可以推导出发光二极管(LED)中的替代光出耦合结构，这与我们这里的主要目标相反。

Nanotexturing a solar cell’s absorber material leads to a strong and spectrally broadband absorption enhancement of incident sun light. However, nanotexturing the interfaces degrades simultaneously the electronic properties of the optoelectronic device. This denies the complete harvest of the absorption improvement and does not allow to translate it to a comparable improvement in device efficiency. In contrast, external light management structures that leave the absorber material undamaged are optically far from optimum and they provide substantially weaker absorption enhancement.To solve this problem, we propose to capitalize on the notion of transformation optics to design photonic structures that preserve the geometrical flatness of the absorber material, to leave it electrically intact, while acting optically like a textured interface with optimized antireflection and scattering properties. Following transformations optics procedures, the invariance of Maxwell’s equations can be exploited to deduce a material distribution that regulates the light flow in exactly the same way as a template surface texture, e.g. conventional black silicon, would do. By doing so, we are effectively deducing an inhomogeneous planar layer that, when placed on top of the absorber layer, can provide antireflection and light trapping, thus absorption enhancement, equivalent to the template surface texture without its electronic degradation. We will pursue the experimental realization of the dielectric graded refractive index light management structures and demonstrate its integration into a solar cell. As building blocks, we will utilize dielectric high refractive index nanostructures and thin film layers of different materials conformally deposited by an advanced atomic layer deposition technique.Our approach of deducing light management structures with transformation optics, to the best of our knowledge, is pioneering. Our design approach is a departure from currently common transformation optics applications and will open up applications of transformation optics concepts in designing structures for various real devices. Solar energy conversion is the obvious and most important application that would directly benefit from the findings of this project. However, the methods to be developed here may also contribute to the development of novel concepts in other fields of optics. For example, one can also deduce alternative light outcoupling structures in light emitting diodes (LEDs), which is the inverse of what we mainly aim to do here.