PCBM-doped electro-optic materials: investigation of dielectric, optical and electro-optic properties for highly efficient poling
Fullerenes are ubiquitously popular in organic electronic materials and devices. The high electron affinity, electron mobility and percolated networks for electron transport of fullerene derivatives, such as PCBM, have established them as excellent electron acceptors and transport materials in organic solar cells and electronic devices. It is intriguing to utilize these electronic properties and molecular three-dimensional networks to explore their potential applications in new electronic or optical devices. In this work, PCBM was doped into organic electro-optic (EO) materials and their surface morphology, photophysical properties, dielectric properties as well as optical properties (refractive index) were systematically investigated. It was found that the dielectric constant and refractive index of the doped materials were significantly enhanced. Based on temperature-dependent dielectric constant measurements, the relation between relative microscopic dipole moment and dielectric properties was established. It revealed that, at the poling temperature, the dipole moment of chromophores in the PCBM-doped film P1/PCBM was higher than that of the conventional EO film P1. This enhanced microscopic property of chromophores in P1/PCBM well accounted for the improved poling results in electric field induced poling. A larger EO coefficient (197 pm V−1versus 133 pm V−1) and figure-of-merit n3r33 (1002.9 versus 632.2), as well as a higher order parameter (15.7% versus 10.6%) and birefringence were achieved for the PCBM-doped film P1/PCBM, demonstrating the significant potential of PCBM to be used in organic EO materials and devices.