High power efficiency tandem organic light-emitting diodes based on bulk heterojunction organic bipolar charge generation layer

The significant enhancement in power efficiency of tandem organic light-emitting diodes (OLEDs) was achieved using bulk heterojunction organic bipolar charge generation layer (CGL), consisted of zinc phthalocyanine (ZnPc): fullerene (C₆₀) blend. In addition to a significant enhancement in luminance and current efficiency this work yielded a maximum power efficiency of 21 lm W^-1 for a tandem OLED, notably almost two times higher than that of a single-unit device, with a maximum power efficiency of 10.1 lm W ^-1. The enhancement in power efficiency at higher luminance is also over 50%. The remarkable enhancement in power efficiency has been attributed to the effective charge generation, transport and extraction due to the presence of interface-modified ZnPc: C₆₀ CGL in tandem OLEDs. Our results demonstrate that the bulk heterojunction, consisting of two matched n- and p-type organic semiconductors, is a promising bipolar CGL for high power efficiency tandem OLEDs.