Reproducibility in Time and Space—The Molecular Weight Effects of Polymeric Materials in Organic Photovoltaic Devices

Abstract

The reproducibility issue is one of the major challenges for the commercialization of large-area organic electronic devices. It involves both the device-to-device variation and opto-electronic properties in different positions of a single thin film. Herein, the molecular weight effects in polymeric semiconductors with three widely used photovoltaic donor materials P3HT, PBDB-T, and PM6 are systematically investigated. A simple but effective method is proposed to evaluate the uniformity of large-area devices by adopting the micron-level grid electrodes in organic thin films. An interesting phenomenon is observed that the device is gradually improved uniformly with the Mw range lower than 100kg mol-1 . In neat films, both the mobility and energetic disorder values of hole carriers exhibit relatively lower coefficient of variation (cv ) in high molecular-weight systems. After blending with the electron-accepting materials, their bulk heterojunction films also enjoy more uniform hole transfer rates, fluorescence lifetimes, and power conversion efficiencies in single and different devices. This work not only proposes a facile approach to evaluate the electrical properties of large-area organic thin films, but also demonstrates the relationship between molecular weight and device reproducibility in polymer solar cells. This contribution provides a new insight into the commercial large-scale production of organic electronics.