Amphiphilic conjugated molecules with multifunctional properties as efficient blue emitters and cathode interlayers for inkjet printed organic light-emitting diodes

A novel set of amphiphilic conjugated molecules consisting of highly emissive fluorene and pyrene species functionalized with phosphonate polar pendant groups, namely PEP and POEP, were designed and synthesized. The novel molecular design endows the resulting molecules with good solution processability, excellent thermal stability, and multifunctional optoelectronic properties, i.e. bright blue emission in films and efficient interfacial functionality, which contribute to effectively lowering the electron injection barriers for efficient electron injection from the cathode. As a result, by using the multifunctional amphiphilic conjugated molecules as both light emitters and cathode interlayers, inkjet-printed single-layer organic light-emitting diodes (OLEDs) with an ITO/PEDOT:PSS/PEP or POEP/Al configuration have been successfully constructed. Comparable or even superior device characteristics have been achieved in comparison with those of spin-cast devices. In particular, inkjet printed devices based on PEP exhibited a low turn-on voltage (Von) of 3.8 V, a maximum current efficiency (ηc,max) of 1.12 cd A−1 at 10.0 V (687.2 mA cm−2), and a high maximum brightness (Lmax) of 8850.1 cd m−2 at 11.0 V. According to these results, such a novel molecular design is beneficial for achieving high-performance inkjet-printed OLEDs with simplified device architecture, which can help in tackling the hurdle of conventional multilayer devices with high work-function electrodes.