Estimation of carrier recombination and electroluminescence emission regions in organic light-emitting field-effect transistors using local doping method

To elucidate the electroluminescence (EL) mechanism of organic light-emitting field-effect transistors (OLEFETs), we determined the carrier recombination and EL emission regions using the local doping method. We demonstrated that the local doping method is a useful technique for estimating the width of these regions in OLEFETs. We inserted an ultrathin rubrene doped 1,3,6,8-tetraphenylpyrene (TPPy) layer (d=10nm) as a sensing layer in a TPPy layer (80nm) and measured the luminance-drain current-drain voltage characteristics and the EL spectra depending on the position of the sensing layer. We confirmed that the EL emission region expanded almost to the height (h≃40nm) of the source-drain electrodes and was independent of the gate bias voltage (Vg). Further, we observed that the EL external quantum efficiency (ηext) significantly decreased as Vg increased, suggesting that excitons generated in a TPPy host layer by carrier recombination are quenched by the application of Vg.