Probing electric field distribution in organic double-layer diode by electric field induced optical second harmonic generation

Analyzing spectroscopic optical properties of an organic double-layer diode comprised of α-NPD and Alq3 layers, we studied the selectively probing of electric field distribution in one of the two layers by using the microscopic electric field induced optical second harmonic generation (EFISHG) measurement. Spectroscopic SHGs from Indium–Zinc-Oxide/N,N-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine/tris(8-quinolinolato) aluminium/Al (IZO/α-NPD/Alq3/Al) diodes were measured. Results showed that the SHG peaks were generated at 940 and 1050 nm from the α-NPD and Alq3 layers, respectively, due to the EFISHG process, and the electric field in each layer can be selectively probed. The contribution of the accumulated charge at the double-layer α-NPD and Alq3 interface was also identified by the d.c. voltage dependence on the EFISHG intensity.