The spin mixing process between singlet and triplet in polymer light-emitting devices consisting of exciton and charge-transfer states

Abstract

The radiative deexcitation processes of excitons and charge-transfer states exist simultaneously in the emitting material PFOPV. In this work, polymer light-emitting devices based on PFOPV were fabricated, the two kinds of microscopic processes were investigated via magnetic field effects (MFEs) on electroluminescence (magneto-electroluminescence, MEL) and current (magnetoconductance, MC). At room temperature, the MEL of balanced device presented negative effects, compared with the positive MEL values of the unbalanced device; at low temperatures, the sign of MEL turned from negative to positive with the increasing injection current in the balanced deice. However, under all driving voltages, the sign of MC was always negative. These dependences of MFEs on temperature and driving voltage can be attributed to the competition between the two different emission processes in devices. Analysis shows that MFEs differences of the two emission processes are caused by the combined effects of intersystem crossing and reverse intersystem crossing induced by hyperfine interaction. This study reveals that charge-transfer states are important in improving the luminous efficiency of fluorescent organic light-emitting devices.