Local Chain Orientation and Alignment in All-Polymer Solar Cell

In recent years, all-polymer solar cell performance has accelerated, in part due to significant improvements in controlling microstructure by optimizing processing parameters. However, quantitative relationships between processing, microstructure, and performance remain weak. While charge generation in all-polymer blends is highly dependent on local chain orientation and local stacking structure, common microstructural characterization techniques only provide bulk average characteristics of film morphology. On the other hand, cryogenic High Resolution Transmission Electron Microscopy (cryo-HRTEM) has emerged as a promising method to image and quantify local polymer structure at sub-nanoscale resolutions.<br/><br/>In this study, we use cryo-HRTEM to analyze the structural organization of the fluorinated all-polymer blend PBDB-T-2F:F-N2200, and we show that donor microstructure can be selectively tuned with processing additives. By applying Fourier analysis and statistical methods, we map the local orientation of lamellar stacking, characterize donor/acceptor domains and interfaces, and quantify inter- and intra-species chain alignment. The results demonstrate how advances in quantitative analysis of cryo-HRTEM images can reveal new structural characteristics in polymer blends.