Electron Clouding Effect for Improvement of Electron Injection in a Solution-Processed Organic Diode with Dipolar Self-Assembled Monolayers

Low charge injection in solution-processed organic semiconductor devices is an important issue in organic electronics. The injection barrier, which originates from an energy level mismatch between the semiconductor and electrode material, severely degrades electrical performance. In this work, we describe a method to enhance the electron injection in n-type organic diodes by tuning the metal work function with dipolar self-assembled monolayers. When Ag electrodes are treated with thiophenol, we observed that the on-current increases by a factor of six, and the turn-on voltage decreases by a factor of more than three compared to those with pristine Ag electrodes in an organic planar diode structure. We also observed a high electron density in the near-electrode-side semiconductor from numerical simulations performed by controlling the work function of the metal electrodes. The device with thiophenol-treated Ag electrodes exhibits an electron density of 4.45 × 10¹⁹ cm⁻³, whereas that with pristine Ag electrodes shows an electron density of 1.74 × 10¹⁰ cm⁻³.