Three organic devices with different quantum well period were fabricated. The potential barrier layer and well layer for electrons were made of N,N'-diphenyl-N,N'-bis(1-napthyl)-1,1'-biphenyl 1-4,4'-diamine(NPB) and 4,4,N,N'-dicarbazolebiphenyl(CBP). The photoluminescence quenching of these three devices under changed reverse voltages were studied. Results showed that photoluminescence quenching of NPB layer occurs more quickly than that of CBP layer in the authors' devices. This is because that the effective electric field in NPB layer is higher than that in CBP layer. The excitons in NPB and CBP layer were easily to be dissociated when the quantum well period increased under the same reverse voltage. Since these three devices are type II quantum well structure, the excitons in these devices are not very stable.