Study On Performance Of Organic Light Emitting Device Based On Exciton Adjusting Layer

Organic light-emitting devices(OLEDs)have drawn considerable interests for their broad applications in full-color flat-panel displays and solid state light sources.Along with the trend of OLEDs envolving into a mature technology in recent years,the voltage-controlled color-tunable OLEDs,which can generate two or more colors with a simple adjustment of bias voltage in one device,are of particular attention in the fields of decoration or agriculture industry due to their inherent advantages.The previous works to realize color-tunable OLEDs mainly focused on the innovation of device structure and the realization of novel functional materials,which are involved with the complicated device structure and timing consuming novel material design and synthesis.Alternatively,as low cost and simple structure are becoming more and more important in the consideration of designers,inserting an exciton adjusting layer(EAL)between two or more emitting layers(EMLs)to realize different color emissions in single device structure,which reduces the fabrication complexity and cost,is an easier and more effective way to fabricate color-tunable OLEDs.In this work,a series of color-tunable OLEDs with emission tunability including blue,yellow and white region were fabricated,by using four different EALs as the interlayer inserted between yellow and blue EMLs.The detailed content is as following:(1)A series of color-tunable OLEDs utilizing four different transport materials TPBi,mCP,TPD and TAPC as exciton adjusting layers have been fabricated.A wide color-tunable range covered with blue,white and yellow light has been achieved in OLEDs with the optimized thickness of EAL.In the devices using hole transport materials of mCP,TPD and TAPC as EALs,a wide range color emissions with the tuning sequences from blue,white,to yellow light is obtained,by varying the bias voltage from 6 to 10 V.For the device with an electron transport material of TPBi as EAL,a similar color-tunable range to that of hole transport materials is obtained.In contrast,the tunable sequence with the increase of voltages is opposite to the above three materials.(2)The color-tunable properties including color-tunable range,sequence and tuning voltage have been detailed studied by investigating the optical and electrical properties of these devices.The device performance is deeply affected by materials used as EAL with different charge carrier mobilities and energy levels.(3)The device performance was investigated by varying the film thickness of EALs.The results shows that the optimal EAL film thickness should be comparable to the triplet exciton diffusion length of corresponding material to efficiently harvest the excitons for color-tunable light emission.In summary,this work paves a way to quantitatively select the film thickness and the species of interlayer material for the development of color-tunable OLEDs and provides a guide to a simple device configuration design.