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Abstract 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. 

Resonant soft X-ray scattering (RSoXS) is a powerful tool for chemically and orientationally resolved nano-to-mesoscale characterization of complex molecular materials. Through its development over the past 15 years, its use has been extended to uniquely characterize structures, not only dry, thin films for devices, coatings, photolithography, and liquid crystalline ordering, but also solvated nanostructures in biology for therapeutics and hydrated membranes for filtration or biosensing. Here, we review progress in this exciting and maturing technique with an eye toward the materials scientist or engineer who has little experience with RSoXS but would like to know more about how the technique would fit into their toolset.