Optimal design of ITO/organic photonic crystals in polymer light-emitting diodes with sidewall reflectors for high efficiency

Abstract

This study aims to achieve large extraction of light emission from polymer light emitting diodes (PLEDs) via optimizing photonic crystals (PCs) and sidewall angle reflectors. Both PCs and sidewall reflectors can be resulting in increasing light emission in useful directions and reducing refection loss. The optimization is achieved through the optical modeling using a 3D finite-difference time-domain (FDTD) method and the intelligent numerical optimization technique, genetic algorithm (GA). The optimal design of PCs and sidewall angle reflectors are presented in details. To accurately predict light extraction of the PLED, the numerical simulation tool, the FDTD method is employed. Based on the FDTD simulation, the optimal sidewall angle which can increase maximum light extraction efficiency (LEE) in our designed PLED structure is 35A degrees. With the optical modeling of optimal sidewall angle reflectors via FDTD computation and the next step is using GA optimization to seek optimal pitch and radius of photonic crystals. According to the GA optimal result, the ratio of pitch to wavelength is 0.47 times and the ratio of radius to pitch is 0.25 times. GA is a powerful tool to cope with a complicated optimization problem with multiple variables to optimize. The PLEDs with optimized PCs and angle of sidewall reflectors would increase extraction of light emission from 20 to 26 % and the 3D FDTD calculation was conducted to explain this result.