Estimation of carrier recombination and electroluminescenceemission regions in organic light-emitting field-effect transistorsusing 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 ( V g ) . Further, we observed that the EL external quantum efficiency ( η ext ) significantly decreased as V g increased, suggesting that excitons generated in a TPPy host layer by carrier recombination are quenched by the application of V g .