一种新的基于频域有限差分方法的小周期有机太阳能电池的光电特性

由MoO₃/Ag/MoO₃ （MAM）组成的多层膜结构非常有希望替代ITO作为有机太阳能电池中的透明阳极.然而，基于MAM结构的有机太阳能电池光吸收能力较弱.为此，引入了一种小周期短节距金属光栅，利用表面等离子激元增强活性层的光吸收.借助于频域有限差分方法求解麦克斯韦方程和半导体方程，探讨了有机太阳能电池结构的光学和电学性质.分析结果表明：与平面结构相比，活性层中的光吸收大大提高；同时，当凹槽宽度为4 nm，能量转换效率提高了49%.相关结果有助于更好地开发和利用无ITO层的有机太阳能电池.

Optical and electrical properties of short-pitch solar cells with finite-difference frequency-domain method

Organic solar cells (OSCs) have attracted intensive attention in recent years due to their distinct advantages of rich material resources, easy fabrication, and good flexibility. The standard structure of OSCs consists of an anode, an active layer and a cathode. Indium tin oxide (ITO) is often used as a transparent anode. However, the indium in ITO is not only very low in content, but also can penetrate into other layers of OSCs and affect the battery life. The ITO is not suitable for flexible OSCs because of its brittleness. Therefore, researchers have been trying to find alternatives to ITO, which should have transparent and flexible electrodes. The multilayer film consisting of MoO₃/Ag/MoO₃ is a very promising candidate as an alternative of ITO to work as the transparent anode in OSCs. However, in MoO₃/Ag/MoO₃ based thin OSCs structure, the absorption of light is quite poor. Here, we introduce a short-pitch metallic grating in which there are used the surface plasmon polaritons (SPPs) to enhance the light absorption of the active layer. The finite-difference frequency-domain method is used to solve the Maxwell's equations and semiconductor equations for revealing the optical and electrical properties of OSCs. As is well known, the contradiction between the long light absorption path and the short exciton diffusion length results in a relatively low power conversion efficiency (PCE) of the OSCs. Metallic gratings can be introduced into conventional OSCs for improving the light absorption due to the surface plasmon resonance. The light absorption can be enhanced compared with that in the conventional OSCs without metallic gratings. At the same time, the small periodic structure is introduced into the MoO₃/Ag/MoO₃ anode-based OSCs. The small spacing between gratings creates a strong interaction between two adjacent metal nanowalls. These nanostructures and metal nanostructures will further enhance the light absorption. In this work, it is proposed that short-pitch metallic gratings be introduced into the MoO₃/Ag/MoO₃ anode-based OSCs for improving the light absorption and PCE. It is found that the light absorption of plasmonic structure with short-pitch metallic gratings can be greatly enhanced compared with standard structure without metallic gratings. Meanwhile, with an optimal groove width of 4 nm, PCE is improved by 49% compared with the case with the planar structure. These results contribute to better developing the ITO free OSCs.