Luminescent Cu(I) NHetPHOS complexes are highly efficient emitters used in organic light-emitting diodes (OLEDs). This work addresses key questions regarding Cu(I) complexes. Utilizing soft x-ray spectroscopy at the N K edge, ultraviolet photoelectron spectroscopy, and inverse photoemission spectroscopy, the study investigates the electronic structure, focusing on the occupied and unoccupied molecular orbitals formed from Cu- and N-atom binding, as well as the HOMO and LUMO energies. Additionally, new red-emitting Cu(I) complexes were developed. The principal structure of a non-crystallizable NHetPHOS complex with a bridging bisphosphine ligand was determined through x-ray spectroscopy at the Cu K edge, achieving a new quantum efficiency record for both solution- and vacuum-processed OLEDs with Cu(I) complexes as emitters. This advancement represents a significant breakthrough for the cost- and energy-efficient processing of organic light-emitting diodes from solution, including methods like printing techniques. Overall, the findings contribute to the understanding and development of Cu(I) complexes for enhanced OLED performance.
