Enhancing the Marangoni flow by inner side chain engineering in nonfullerene acceptors for reproducible blade coating-processed organic solar cell manufacturing

The industrial-scale, uniform film production of active layers is a prerequisite for high-performance, reproducible organic solar cells (OSCs), becoming a significant challenge. Blade coating, one of the most suitable protocols for industrial-scale OSC manufacturing, can be significantly affected by evaporation-driven convective flows (e.g., capillary and Marangoni flows), which directly influence film uniformity. Here, we present in-depth studies on how convective flows in blade coating-processed OSC fabrication depend on the inner side chain lengths of nonfullerene acceptors (L8-i-EB, L8-i-EH, and L8-i-BO). By analyzing the device performance in nine different regions in a blade-coated substrate, we find that the degree of variations in power conversion efficiency ranges from 15.61% to 16.85% (standard deviation (sigma) of 0.38%) for the L8-i-EB-based device, 15.31% to 17.20% (sigma of 0.57%) for the L8-i-EH-based device, and 13.92% to 16.66% (sigma of 0.97%) for the L8-i-BO-based device. This demonstrates that compared with the others, the L8-i-EB-based device with a shorter inner side chain enables higher reproductivity in blade coating-processed OSC fabrication, attributed to its superior film uniformity induced by the enhanced inward-directional Marangoni flow while counteracting the capillary flow. This study highlights the importance of the Marangoni flow effect and its contribution to realizing reproducible blade coating-processed OSCs.