锥形二维光子晶体太阳电池数值模拟

采用时域有限差分方法,模拟研究在本征吸收层引入锥形二维光子晶体(2D PC)后,其结构参数变化对单结微晶硅电池各膜层吸收的影响规律.研究表明,2D PC的纵横比(高度与周期之比)对电池本征吸收具有决定性影响.周期小于1μm时,本征吸收随着纵横比的增大先上升后下降,纵横比为1时达到最大值;周期大于1μm时,本征吸收达到最大值的纵横比小于1,且周期越大,实现本征吸收最大化的纵横比越小.当周期为0.5μm,纵横比为1时,锥形2D PC电池的本征吸收达到峰值,短路电流密度为27.8 mA/cm2;与平面结构相比,短路电流密度提升5.8 mA/cm~2,相对增加27%.该研究突破了以往认为绒面陷光效果主要取决于绒面形貌横向特征尺寸的观点,对实验获取最佳的周期或随机绒面陷光结构具有指导意义.

Numerical study on conical two-dimensional photonic crystal in silicon thin-film solar cells

To further improve the absorption of thin-film silicon solar cells (TFSSCs), it is essential to understand what kind of texture morphology could present the best light trapping effect, or rather, which structural parameter plays the most important role, and offers the required lateral feature size, height or others. In this paper, the influences of structural parameters of conical two-dimensional photonic crystal (2D PC) on each-layer absorption of the microcrystalline silicon thin film solar cells are numerically studied by using the finite-difference time-domain method when 2D PC is introduced into the intrinsic layer. The results show that both the intrinsic absorption and parasitic absorption are significantly enhanced via introduction of 2D PC into the intrinsic layer. The parasitic absorption is mainly caused by the ITO layer, and the intrinsic absorption shows a sinusoidal fluctuation with the increase of period. It is found that the aspect ratio (height/period) of the 2D PC has a decisive influence on the cell intrinsic absorption. When the period of the 2D PC is less than 1μm, the intrinsic absorption first increases and then decreases with the increase of the aspect ratio, and reaches a maximum value with an aspect ratio of 1. For the case of period larger than 1μm, the aspect ratio needed to obtain the maximum result is smaller than 1. What is more, the larger the period, the smaller the aspect ratio for maximizing the intrinsic absorption will be. The peak intrinsic absorption can be obtained when a 2D PC with a period of 0.5μm and an aspect ratio of 1 is introduced. Compared with that of the flat cell, the short-circuited current density of the above optimized 2D PC cell can be significantly enhanced by 5.8 mA/cm²(from 21.9 to 27.8 mA/cm²), corresponding to a relative enhancement of 27%. In order to improve antireflection performance, it is critical to adopt a textured front-surface morphology where the aspect ratio is higher than 1/2. In addition, the intrinsic absorption increases with the increasing fill factor, and reaches a maximum value when the fill factor of the 2D PC is close to 0.9. The research results of this paper break through the traditional viewpoint of light trapping mechanism which points out that the light trapping effect is mainly dependent on the lateral feature size of the texture, and provide an important guide for obtaining optimized random or periodic texture via experiment.