Single-layer homojunctional organic light-emitting diodes based on tris-(8-hydroxylquinoline)-aluminum(Alq

3

)as emitting layer were fabricated using vacuum deposition method.The device structure is:indium-tin-oxide(ITO)/Alq

3

(x nm)/Mg:Ag.According to trapped charge limited current(TCLC)theory

the current conduction regime in OLEDs devices with different thin film thicknesses was investigated systematically by varying the thickness of organic functional layer.A fitting analysis of device current via TCLC theory was adopted to study the relationship between experimental data and theoretical prediction

.The results demonstrated that the current of single-layer device with Alq

3

thin film has a change from ohmic conduction region

TCLC region to TCLC-SCLC transition region;while the current of device with relatively thick film has no SCLC region due to the increase of traps in the Alq

3

layer.The numerical fitting is very beneficial for Alq

3

film thickness optimization during device fabrication process.