Role of simultaneous thermodynamic and kinetic variables in optimizing blade-coated organic solar cells

Abstract

Although not being established yet, the simultaneous understanding of the thermodynamic and kinetic mechanisms of film formation is very critical to enabling high power conversion efficiencies (PCEs) in the organic solar cells (OSCs) fabricated using the high-throughput printing technology of blade coating. Herein, using four rationally designed non-fullerene acceptors (NFAs) with different outer side-chain lengths (YC2, YC6, YC8, and YC11), regarded as the thermodynamic variable, a comprehensive study has been conducted on their correlation with different processing cosolvent compositions, which is regarded as a kinetic variable. The film formation process by blade coating consisted of step-by-step mechanistic pathways, namely the initial, propagation, and final film formation stages; the thermodynamics and kinetics of which highly depends on the NFA type and processing cosolvent composition. It is clear that both the outer side-chain length of the NFA and the processing cosolvent composition govern the crystalline behavior and/or self-aggregation of the active layers, which are crucial to realizing the optimized performances of the respective OSCs. Consequently, the thermodynamically and kinetically preferred YC2-based blade-coated OSCs with the optimal processing system delivered the best PCEs of 17.2% (4.2 mm2) and 15.2% (1.05 cm2). The relationship between the thermodynamics and kinetics of the active layer, established here for the first time, can contribute to large-area OSC performance advancements. The relationship between non-fullerene acceptor type and processing cosolvent composition in the blade coating process for active layer preparation is established to identify simultaneous thermodynamic and kinetic morphology toward large-scale organic solar cells.