Host‐Guest Active Layer Enabling Annealing‐Free, Nonhalogenated Green Solvent Processing for High‐Performance Organic Solar Cells†

Comprehensive Summary Recent advances in non‐fullerene acceptors (NFAs) like Y6 have pushed the power conversion efficiencies (PCEs) of organic solar cells (OSCs) above 19%. However, the harsh fabrication conditions, such as the use of the highly volatile chloroform ( CF ) solvent and the thermal annealing process, are not suitable for large‐area printing technologies and environmental standards. Here, a series of guest molecules, BT2O, BTO, and BT4O, are designed and synthesized with different numbers of oligo ethylene glycol (OEG) repeating units in side chains. All these guest molecules could tune the crystallization kinetics of the annealing‐free host‐guest active layers by inducing the self‐assembly of Y6 in non‐halogenated paraxylene ( PX ) solution. The increasing number of OEG repeating units in guest molecules could enhance the molecular assembly ability but molecular stacking steric hindrance simultaneously. Therefore, BTO with three OEG repeating units blended with PM6:PM7:Y6 delivers the highest PCE of 17.78%. Our results demonstrate controlling the crystallization kinetics via delicate side‐chain engineering of guest molecules is an effective way to achieve efficient OSCs in non‐halogenated solution.