Aggregation Engineering of Toluene-Processed Acceptor Layer Enables Over 19% Efficiency of Air-Blade-Coated Organic...

Understanding the unique features of photovoltaic materials in high-performance blade-coated organic solar cells (OSCs) is critical to narrow the device performance difference between spin-coating and blade-coating methods. In this work, it is clarified that the molecular packing of acceptor and molecule-solvent interaction plays an essential role in determining the photovoltaic performance of blade-coated layer-by-layer OSCs. It is demonstrated that the unique dimer packing feature of L8-BO-4Cl can lead to lower excited energy (∆E_S1) and dominant J-aggregates in the blade-coated film compared to the analogs of Y6 and L8-BO. Meanwhile, the weaker molecule-solvent interaction between L8-BO-4Cl and toluene is in favor of forming prominent J-aggregation in blade-coated film, contributing to a more compact π-stacking than Y6 and L8-BO. Additionally, the blade-coated D18/L8-BO-4Cl film shows more defined interpenetrating networks with clearer donor-acceptor interfaces than D18/Y6 and D18/L8-BO, facilitating improved charge extraction and suppressed charge recombination. As a result, the air-blade-coated layer-by-layer device based on D18/L8-BO-4Cl yields a remarkable power-conversion efficiency (PCE) of 19.31% without any additive and post-treatment, while much lower PCEs of 7.01% and 16.47% are obtained in the device based on D18/Y6 and D18/L8-BO, respectively. This work offers an effective approach to developing highly efficient air-blade-coated layer-by-layer OSCs.