Study of interface layer effect in organic solar cells by electric-field-induced optical second-harmonic generation measurement

By using electric-field-induced optical second-harmonic generation (EFISHG) measurement, we studied the effect of the use of bathocuproine (BCP) interface layer. The EFISHG measurements of indium–zinc–oxide (IZO)/C₆₀/Al diodes showed that the BCP layer inserted between C₆₀ and Al formed an electrostatic field |E_i| = 2.5 × 10⁴ V/cm in the C₆₀ layer, pointing in a direction from the Al to the IZO. Accordingly, in the IZO/pentacene/C₆₀/BCP/Al organic solar cells (OSCs), holes (electrons) move to the IZO (Al) electrode, enhancing the short-circuit current. The EFISHG measurement is capable of directly probing internal fields in the layers used for OSCs, and is helpful for studying the contribution of the interface layer in OSCs. - Highlights: • Internal field in organic solar cells (OSCs) were directly probed. • Interface layer formed internal electric field, enhancing the OSC performance. • Maxwell–Wagner effect accounts for the internal electric field formation