To improve the performance of organic photovoltaics (OPVs), it is useful to trap light by using the antireflection nanotexture such as moth eye structure. The finite-difference time-domain (FDTD) method is frequently used to analyze the optical properties of nanotexture. However, in the case that FDTD is applied to OPVs, the existence of a glass substrate generates a strong oscillation in optical response, which does not exist in the actual device. To remove such oscillatory components and accurately simulate optical response, we study an FDTD-based computational algorithm, which we call the envelope method. We compare this method with other possible methods, and demonstrate that the envelope algorithm is more accurate for estimating optical response and more robust against parameter variations than the other ones. We also apply this method to analyze the changes in the OPV performance associated with the changes in t he properties of m oth eye coati ng.
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