Enhanced Efficiency of Tandem Organic Light-Emitting Diodes via Manipulating Heterojunction Composition of Charge Generation Unit

摘要

Tandem organic light-emitting diodes (OLEDs) with an organic photovoltaicheterojunction (OPV-HJ) as a charge generation unit (CGU), consisting of fullerence(C_(60)) and copper phthalocyanine (CuPc), are fabricated. The devicestructures are ITO/EL unit/C_(60)–CuPc HJ/MoO_3/EL unit/Al, where EL unit iscomposed of NPB/Alq_3/LiF. The efficiency improvement of tandem OLEDs isachieved by manipulating the structure and composition of C_(60)–CuPc HJs. Thecharge generation and transport characteristics of CGUs are strongly dependenton the detailed structures of C_(60)–CuPc HJs and the optimized CGU is 0.5:1 C_(60):CuPc bulk-HJ. The improved efficiency of the tandem device with 0.5:1 C_(60):CuPcbulk-HJ as CGU demonstrates to be the result of better charge carrier balanceinduced by the optimal charge transport and charge generation of C_(60):CuPc bulk-HJs according to their surface morphology and absorption spectra. These resultsshed light on that C_(60):CuPc OPV-HJ-based CGU is a promising connection unitfor the fabrication of high-efficiency tandem OLEDs.