**4. Summary**

We demonstrate efficient charge injection into solvent-free liquid organic semiconductors via cracked metal structures with a large number of edges leading to local electric field enhancement. For this work, the Ag thin films on the deformable FEP substrates were mechanically stretched to generate the cracks on the surfaces in a controlled manner, and subsequently transferred and welded onto other intact Ag films for avoiding increases in electrical resistance. Using the prepared Ag electrodes with varied crack densities, the charge injection properties into EHCz were investigated in low bias region (i.e., ohmic current region). It was found that the device with the highly cracked electrode dramatically increased the current density within the ohmic current region, indicating that efficient charge injection via local electric field enhancement can exert similar effects to the introduction of ionic dopants on J-V characteristics in terms of charge carrier concentrations. Although the hole-only devices were demonstrated in this work, these results still offer a wide range of possibilities for various device applications. Careful consideration of work functions of electrodes and cascade energy levels would be required for optimizing the device design or selection of device components. In addition, the field intensity within the device was calculated using COMSOL Multiphysics software, based on the experimental observation, and static analysis was also performed to reveal the spatial distribution of local electric fields. The calculation results were in good agreemen<sup>t</sup> with our experimental results, where charge injection properties were dramatically improved by the high-density cracks contributing to local electric field enhancement. We anticipated that these results will significantly contribute to the development and further refinement of various organic electronic and optoelectronic devices based on non-volatile liquid organic semiconducting materials.

**Author Contributions:** K.-H.K.: methodology, software, formal analysis, investigation, data curation, visualization, and writing—original draft preparation; M.-J.P.: methodology, software, resources, and supervision; J.-H.K.: conceptualization, methodology, validation, writing—original draft preparation, review and editing, supervision, project administration, funding acquisition. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Basic Science Research Program through the National Research Foundation of Korea (NRF-2018R1C1B6003122).

**Conflicts of Interest:** The authors declare no conflict of interest.
