Optimization and simulation of a carbon nanotube arrangement for transparent conductive electrodes with record-high direct current to optical conductive ratios

Abstract

Carbon nanotube (CNT) meshes have optical and electrical properties that make them suitable for use in next-generation transparent conductive electrodes (TCEs). Although circuit modeling of CNT meshes has been studied widely, very few researchers have modeled the optical properties of the horizontally and regular arrangement of CNT arrays. The behavior of light propagating through a CNT mesh is complex, with no straightforward rules established to provide simple analytical solutions. In this study, we used the three-dimensional finite difference time domain (3D-FDTD) method to model the optical properties of regular arrays of CNTs, based on the calculated refractive indices and extinction coefficients of multi-walled CNTs (MWCNTs). One-dimensional regular arrays of CNTs displayed strong anisotropic optical behavior. Moreover, by adjusting the spacing and arrangement of two-dimensional regular arrays of CNTs, we could identify the optimal structure for a CNT-based TCE displaying excellent optical and electrical performance. We have also developed the concept of the “optical threshold,” which defines the most effective charge transport channels possessing sufficiently open areas. This concept solves the trade-off between the two key parameters—the light transmittance and the sheet resistance—in TCEs. The optimal geometry provided a CNT mesh with not only the most effective charge transport channels but also very high optical transmittance, CNT network with a diameter of 10 nm (specific conductivity of 0.385 Ω−1 nm−1) has light transparency and low sheet resistance T > 90% and Rs < 1.6 Ω/sq, such that the ratio of the direct current conductivity to the optical conductivity (σDC/σop) reached as high as 2077. This value is far greater than previously reported simulated and experimental values for TCEs based on various materials.