The Study On The Performance Of The Organic Cyclometalated Platinum(?) Complexes-based NIR-PLEDs And WPLEDs

Near infrared(NIR)luminescent materials(the wavelength range of 700-2500 nm)have unique advantages in sensing and information monitoring due to their good anti-interference characteristics in invisible light region.In recent years,with the rapid development of optical fiber communications,sensing,biological living detec-tion and medical imaging techniques,it has become a new developing goal of organic electroluminescence to tune emissive wavelength from visible light to NIR region for organic light-emitting diodes(OLEDs)and obtain warm white light illumination by combination of the complementary blue and NIR emitters.As cyclometalated platinum(II)complexes have an internal quantum efficiency(IQE)of 100% theoretically,they would exhibit highly efficient NIR emission in their NIR-emitting devices.To date,the maximum EQE values of the NIR-OLEDs were usually obtained under low current density.There is a serious luminous efficiency roll-off in these devices with increaseing current densities.NIR polymeric light emitting diodes(NIR-PLEDs)have recently received wide attention owing to their many advantages,such as simple processing technology,easy to implement flexible devices.However,the efficiency of NIR-PLEDs is still lower than that of NIR-OLEDs.In this paper,to solve the problem of low luminous efficiency and irradiation intensity,as well as to further extend the application of NIR materials in healthy solid state lighting for NIR-PLEDs,we carried out the study on the performance of NIR-PLEDs and NIR-WPLEDs by solution process.The main research contents and conclusions were summarized as follows:Firstly,NIR-PLEDs were fabricated by selecting a novel NIR luminescent material of(niq)2Pt2(?-C8PhOXT)2 as phosphor dopant,PFO [poly(9,9-dioctylfluorene)] or PVK [poly(vinylcarbazole)] as the host materials.The influence of the host chemical structure and device structure on device performance of NIR-PLEDs was researched.It is found that the(niq)2Pt2(?-C8PhOXT)2 based NIR-PLEDs showed best electroluminescent properties with a maximum EQE of 6.18%,a maximum radiant emittance of 903?W/cm2 under the optimized conditions using PFO:OXD-7 as the host and the dopant concentrations of 8 wt%.When the PVK:OXD-7 as the host,the dopant concentrations of 2 wt%,the(niq)2Pt2(?-C8PhOXT)2 based NIR-PLEDs only show a decreased EQE of 4.89% and a radiant emittanc of 684?W/cm2.Secondly,we achieved WPLEDs based on PVK host by choice the blue & NIR dual-color emitters,in which a sky-blue emitter of iridium(III)bis[(4,6-di-fluorophenyl)-pyridinato-N,C2](picolinate)(FIrpic)and a NIR emitter of(niq)2Pt2(?-C8-OXT)2 are employed as phosphor dopant.The dual-color WPLEDs demonstrated a maximum EQE of 9.49% with a CIE coordinate of(0.353,0.354)under a blending ratio of 20:0.6 between Firpic and(niq)2Pt2(?-C8OXT)2.The emissive colour is very close to the equi-energy white point(0.333,0.333).But the color quality of the above devices is unsatisfactory,with a relatively low color rendering index(CRI)of 42 and high correlated color temperature(CCT)of 4809 K,which were not meet the needs for indoor illumination application.In order to obtain high CRI and low CCT for WPLEDs,a yellow emitter of bis[2-(thieno[3,2-c]pyridin-4-yl)phenyl] iridium(III)(acetylacetonato)(PO-01)here was used as phosphor dopant with the above dual color emitters.While the doping ratio among FIrpic,PO-01 and(niq)2Pt2(?-C8OXT)2was 20:0.2:0.7,three-color WPLED acquired the maximum external quantum efficiency of 10.6% with low CCT of 3246 K and high CRI of 87.The resulting EL spectra cover nearly the whole visible light from 450 to 780 nm.In this system,a sky-blue emitter of FIrpic was selected to minimize the deep-blue-light damage and solve the problem of narrow spectral coverage of the sky-blue emtter-based WPLEDs.It is useful to achieve healthy warm white light for the solution-processed WPLEDs with high CRI.