The Influence of Recombination between Holes and Reduced Redox Ions on the Efficiency of Hole Injection from Electrolytic Contacts into Organic Insulator Crystals

The efficiency of hole injection from electrolytic contacts into organic insulator crystals is controlled by hole generation and hole destruction at the crystal surface through oxidized and reduced redox ions respectively and by hole escape into the crystal bulk which competes with hole destruction. By increasing the concentration of reduced redox ions from virtually zero in a suitable system the transition has been studied from the one extreme case where all the generated holes contribute to the injection current to the other extreme case where the majority of the generated holes recombines with reduced redox ions before they can escape into the crystal bulk. From the experiments one can deduce that the generated hole spends less than I O 1 0 s within the reaction distance of its reduced parent redox ion, at external field strengths 10 V/cm, but returns to the crystal surface during a much longer time, e .g . during about 10~ 8 s at an external field strength of 10V/cm, before it can escape finally into the crystal bulk.