Controlling Both Anode and Cathode Interfacial Properties of Nanocrystal LEDs by Combining Solution-Processed Semiconducting Polymer Interlayers

Light-emitting diodes (LEDs) based on colloidal semiconductor nanocrystals represent a promising technology for next-generation electroluminescence displays. While ongoing efforts focus on optimizing nanocrystal properties, device performance also critically depends on the LED architecture, particularly the design of interfacial layers. Efficient charge injection and balanced carrier transport toward recombination layers require careful alignment of energy levels between adjacent layers. In this study, we investigate the cooperative role of different hole-transporting (HT) and electron-injecting (EI) polymers in a multilayered all-solution-processed LED structure incorporating CdSe/CdZnS nanoplatelets as deep-red emitters. Three commercially available HT polymers, differing in hole mobility and energy levels, were combined with custom-designed EI polar polymers featuring varied conjugated backbones and tailored highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) levels. Particular attention is given to the EI/metal interface, whose properties are tuned via phosphonate-functionalized polymer side chains. Device performance is assessed under inert and ambient conditions (without encapsulation) and correlated to the electronic properties of the interfacial layers. Notably, specific HT/EI polymer pairings substantially influence key parameters of fabricated LEDs, enabling either a reduced turn-on voltage down to 1.7 V or enhanced external quantum efficiency up to 7%, depending on the selected combination.