Tandem organic light-emitting diodes with buffer-modified C₆₀/pentacene as charge generation layer

Abstract

Buffer-modified C₆₀/pentacene as charge generation layer (CGL) is investigated to achieve effective performance of charge generation. Undoped green electroluminescent tandem organic light-emitting diodes (OLEDs) with multiple identical emissive units and using buffer-modified C₆₀/pentacene organic semiconductor heterojunction (OHJ) as CGL are demonstrated to exhibit better current density and brightness, compared with conventional single-unit devices. The current density and brightness both can be significantly improved with increasing the thickness of Al. However, excessive thickness of Al seriously decreases the transmittance of films and damages the interface. As a result, the maximum current efficiency of 1.43 cd·A^-1 at 30 mA·cm^-2 can be achieved for tandem OLEDs with optimal thickness of Al. These results clearly demonstrate that Cs₂CO₃/Al is an effective buffer for C₆₀/pentacene-based tandem OLEDs.