A Mixed‐Pure Planar Heterojunction Structure of Active Layers for Efficient Sequential Blade‐Coating Organic Solar Cells

Precise modulating the vertical structure of active layers to boost charge transfer is an effective way to achieve high power conversion efficiencies (PCEs) in organic solar cells (OSCs). Herein, efficient OSCs with a well-controlled vertical structure are realized by a rapid film-forming method combining low boiling point solvent and the sequential blade-coating (SBC) technology. The results of grazing incident wide-angle X-ray scattering measurement show that the vertical component distribution is varied by changing the processing solvent. Novel characterization technique such as tilt resonant soft X-ray scattering is used to test the vertical structure of the films, demonstrating the dichloromethane (DCM)-processed film is truly planar heterojunction. The devices with chloroform (CF) processed upper layer show an increased mixed phase region compared to these devices with toluene (TL) or -DCM-, which is beneficial for improving charge generation and achieving a superior PCE of 17.36%. Despite significant morphological varies, the DCM-processed devices perform slightly lower PCE of 16.66%, which is the highest value in truly planar heterojunction devices, demonstrating higher morphological tolerance. This work proposes a solvent-regulating method to optimize the vertical structure of active layers through SBC technology, and provides a practical guidance for the optimization of the active-layer microstructure.