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=10 nm) as a sensing layer in a TPPy layer (80 nm) 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≃40 nm) of the source-drain electrodes and was independent of the gate bias voltage (Vg). Further, we observed that the EL external quantum efficiency (η_ext) significantly decreased as Vg increased, suggesting that excitons generated in a TPPy host layer by carrier recombination are quenched by the application of Vg.