Molecular Orientation‐Dependent Exciton Separation in Optimized Single‐Component Y6 Organic Solar Cells

The excitons are generally decomposed into free charges by the heterojunction due to the low dielectric constant of organic materials. Recent research indicates that owing to the low exciton binding energy, the pure Y6 film can directly and spontaneously generate free charge carriers after photoexcitation, even without the assistance of the donor/acceptor interface driving force. However, the serious bimolecular recombination and trap‐assisted recombination also limit the photovoltaic efficiency of single‐component Y6 devices. Herein, efficient exciton separation and charge collection by changing the buffer layer and using mixed solvents to control the active layer morphology of single‐component devices based on Y6 are achieved. It is found that the short‐circuit current is significantly increased by properly adjusting the proportion of face‐on and edge‐on direction of molecules. Eventually, the power conversion efficiency (PCE) of single‐component devices based on Y6 is increased from 0.15% to 1.41%. The corresponding dynamic process is revealed by ultrafast transient absorption spectroscopy and entropy effect on the exciton dissociation. Effective charge separation and collection in single‐component devices is not only critical to improving the PCE, but provides an in‐depth understanding for the further design of high‐performance multicomponent devices.