Thickness Insensitive Organic Solar Cells with High Figure‐of‐Merit‐X Enabled by Simultaneous D/A Interpenetration and Stratification

Abstract Low cost and printing friendly fabrication of organic solar cells (OSCs) require thick‐film devices with simply structured photoactive molecules. Thus, achieving high power conversion efficiency (PCE) for non‐fused ring acceptor‐based devices with high thickness is of great significance. Herein, by transforming traditional blend casting method to emerging sequential deposition (SD) method, D18:A4T‐16 active blend exhibits large efficiency improvement from 8.02% to 14.75% in 300 nm thick devices. Systematic morphological and photophysical characterizations showcase the effectiveness of SD processing in achieving sufficient donor/acceptor interpenetration and vertical stratification, which eliminates the dilemma of charge generation/transport in blend casting films. Meanwhile, D18 bottom layer is proven helpful in realizing fast evaporation of postdeposited poor solvent, resulting in naturally thickened active layer with well‐regulated crystallization. Furthermore, a new index to emphasize thick‐film devices based on nonfused ring acceptors, called figure‐of‐merit‐X (FoM‐X), has been defined. The SD processed D18:A4T‐16 devices herein, with 300 nm, 500 nm, and 800 nm thicknesses possess leading FoM‐X values.