The present invention provides an improved 
redox couple for electrochemical and optoelectronic devices. The 
redox couple is based on a complex of a first row 
transition metal, said complex containing at least one mono-, bi-, or 
tridentate ligand comprising a substituted or unsubstituted ring or ring 
system comprising a five-membered N-containing heteroring and / or a six-membered ring comprising at least two heteroatoms, at least one of which being a 
nitrogen atom, said five- or six-membered heteroring, respectively, comprising at least one 
double bond. The invention also relates to electrolytes and to the devices containing the complex, and to the use of the complex as a 
redox couple. The invention further provides electrochemical and / or optoelectronic devices comprising a first and a second 
electrode and, between said first and second 
electrode, a charge 
transport layer, said a charge 
transport layer comprising tetracyanoborate ([B(CN)4]−) and a cationic 
metal complex functioning as redox-couple.