The nature of electronic and carrier transport properties of M-(quinolate)(2) complexes (M = Be, Mg, Ca, and Sr): A computational study

Abstract

A series of metal-quinolate (MQ(2)) materials (M = Be2+, Mg2+, Ca2+, and Sr2+) were theoretically investigated to understand their electronic and charge transport properties as an application of electron injection layer (EIL) and additive material to electron transporting layer (ETL). It was found that the Be2+, Mg2+, and Ca2+ are tetragonally coordinated to the quinolate ligands whereas the Sr2+ is planarly coordinated. The analyses of electronic properties indicated that the stable lowest unoccupied molecular orbital (LUMO) energy level of these materials relative to LiQ is expected to improve the electron injection from cathode and enhance the electron transport in ETL. In perspective of electrochemical reactivity, the chemical hardness values of MQ(2) materials showed that hole and electron carriers can be easily facilitated in order of BeQ(2) < MgQ(2) < CaQ(2) < SrQ(2). In particular, the results of charge carrier transport properties clearly showed that k(e) of SrQ(2) is 64% higher than that of LiQ, which is an advantage for both EIL and ETL additive. Comprehensive analyses showed that SrQ2 is superior to LiQ as a replacement in perspective of electron injection and transport properties.