Formation of Single-Chain Anionic Bolaamphiphiles on Indium Tin Oxide Surfaces through Self-Assembly To Improve Optoelectronic Device Performance

The surface of indium tin oxide (ITO) was modified with bolaamphiphilic (BA) materials to tune the energy-level alignment of electrodes in optoelectronic devices (OEDs). Tuning the energy-level alignment of the electrode is crucial for enhancing OED efficiency by improving carrier injection. Although the dielectric properties of organic solvents influence the formation of BA self-assembled monolayers (SAMs), our study found that the intermolecular forces of the dissolved BA materials and the solution medium are more important for the formation of a well-ordered film on the electrode. Our results also showed efficient tunneling phenomenon between the electrode and the hole transport layer (HTL) using BA material. The holes were transported to the tunnel junctions where the Fermi energy was sufficiently close to the HOMO band of the BA. Therefore, the tunnel barrier height of the ITO/HTL of the OED was reduced, and favorable conditions for hole injection was created, resulting in a 2-3 times increase in luminance and current density. It is believed that the larger area of interface contact between electrode/BA/HTL and the formation of well-ordered BA layers are responsible for the improved performance of the BA-modified electrode surface and OED.