Hybrid antireflection structure with moth eye and multilayer coating for organic photovoltaics

We propose a hybrid antireflection structure (ARS), which integrates moth eye texturing and multilayer interference coating, to improve efficiency of organic photovoltaic (OPV) solar cells. We perform nearly global optimization of the geometric parameters characterizing the hybrid ARS, by using optical simulations based on the finite-difference time-domain method. The proposed optimization algorithm consists of two steps: in the first step, only the moth eye structure is globally optimized and, in the second step, the whole hybrid structure is optimized efficiently based on the results of the first step. Thus, the optimal moth eye structure is additionally obtained as an intermediate result. By applying this optimization method to an organic thin film solar cell, we show that the short-circuit current density (J _SC) is increased by 8.90% with the moth eye structure and by 9.89% with the hybrid ARS. We also study the sensitivity of photocurrent to the geometric parameters of hybrid ARS, and the change in the spatial distribution of electric field intensity by the ARS. The results show that the hybridization of the two types of light trapping techniques is effective to reduce the inhomogeneity in the electric field distribution and obtain higher electric intensity in almost the whole active layer. The design concept of the hybrid ARS is quite useful for improving light trapping in OPVs and allows for extending the options available for broadband antireflection.