Abstract
N-doping is an effective way to increase the electron conductivity of organic semiconductors and achieve ohmic cathode contacts in organic electronics. To avoid the use of difficult-to-handle highly reactive n-dopants, air-stable precursors are widely used nowadays, which could decompose to release reactive species in a subtractive way though always with unwanted and even harmful byproducts during processing. Here, we show that air-stable metals, such as copper, silver and gold, could release free electrons readily in the presence of chelating ligands, as the irreversible coordination reaction between metal ions and the ligands would push the equilibrium between metals and metal ions to the forward direction. By using a well-designed multi-functional electron transport material with a strong nucleophilic quality, 4,7-dimethoxy-1,10-phenanthroline (p-MeO-Phen), silver could function as an n-dopant stronger than cesium and could be used to fabricate organic light-emitting diodes with higher performance than the cesium-doped control device.
Highlights
N-doping is an effective way to increase the electron conductivity of organic semiconductors and achieve ohmic cathode contacts in organic electronics
As calculated (Fig. 1a), the ionization energy of Ag is 8.0 eV ðAg ! Agþ þ eÀ; 8:0 eVÞ, but when Ag is doped into BPhen, its ionization energy would decrease rapidly to 4.4 eV ðAg þ o2BBfPPhcheenesniu!m!,1⁄2AÂdAguðgBeðPBhtPoehneÞnthÞþe2þÃþierþÀre;ev4Àe:r;4s2ieb:V7leÞeVcÞooowrrdhiinchaevtieoisnnlobw2eet:rw[7] eteheVnaðnAAtghgþa+t and BPhen and the formation of stable complexes (Agþ þ BPhen ! 1⁄2AgðBPhenÞþ; À3:6 eV and 1⁄2AgðBPhenÞþþ BPhen ! 1⁄2AgðBPhenÞ2þ; À1:7 eV)
Compared with standard Ag samples (Supplementary Fig. 1), we find that Ag atom is reduced to its oxidized form (Ag+) when doped into BPhen film, indicating the efficient n-doping process between Ag and BPhen
Summary
N-doping is an effective way to increase the electron conductivity of organic semiconductors and achieve ohmic cathode contacts in organic electronics. By doping air-stable metals in organic ligands with chelating cites, the strong coordination of organic ligands with metal ions would push the equilibrium between metals and metal ions to the forward direction with free electrons more-readily to be released. In this way, the ionization energy of air-stable metals could be remarkably reduced and with proper design of the ligand structures, airstable metals could function more efficiently as n-dopants than alkalis and improve the performance of OLEDs
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