Understanding the High Performance of over 15% Efficiency in Single‐Junction Bulk Heterojunction Organic Solar Cells

The highly efficient single‐junction bulk‐heterojunction (BHJ) PM6:Y6 system can achieve high open‐circuit voltages (VOC) while maintaining exceptional fill‐factor (FF) and short‐circuit current (JSC) values. With a low energetic offset, the blend system is found to exhibit radiative and non‐radiative recombination losses that are among the lower reported values in the literature. Recombination and extraction dynamic studies reveal that the device shows moderate non‐geminate recombination coupled with exceptional extraction throughout the relevant operating conditions. Several surface and bulk characterization techniques are employed to understand the phase separation, long‐range ordering, as well as donor:acceptor (D:A) inter‐ and intramolecular interactions at an atomic‐level resolution. This is achieved using photo‐conductive atomic force microscopy, grazing‐incidence wide‐angle X‐ray scattering, and solid‐state 19F magic‐angle‐spinning NMR spectroscopy. The synergy of multifaceted characterization and device physics is used to uncover key insights, for the first time, on the structure–property relationships of this high‐performing BHJ blend. Detailed information about atomically resolved D:A interactions and packing reveals that the high performance of over 15% efficiency in this blend can be correlated to a beneficial morphology that allows high JSC and FF to be retained despite the low energetic offset. The high‐performing single‐junction organic solar cell blend, PM6:Y6, is examined to obtain an in‐depth understanding of the voltage losses, and charge recombination and extraction dynamics. The devices exhibit remarkable extraction coupled with moderate recombination losses. This behavior can most likely be credited to a beneficial morphology as evidenced by atomically resolved 19F magic‐angle‐spinning solid‐state NMR analysis.