ABSTRACT
Modification of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with sodium-poly(styrenesulfonate) leads to a ca. 0.3 eV increase in the work function and 15 times enhancement in the photoluminescence intensity of the overlying perovskite layer, which is closely correlated with the formation of a highly PSS-enriched top layer. As a direct result, the hybrid halide perovskite light-emitting devices with a modified PEDOT:PSS layer show the maximum external quantum efficiency of 7.2% and power efficiency of 19.0 lm W-1, which are 14-20 times those of the analogous devices using a pristine PEDOT:PSS layer and among the best reported values for the light-emitting devices using a neat perovskite emission layer. Our results illustrate that insufficient hole injection and luminescence quenching at the PEDOT:PSS anode are among the most important factors limiting the external quantum efficiencies of inverted perovskite light-emitting devices.
ABSTRACT
Low-dimensional organometallic halide perovskites are actively studied for the light-emitting applications due to their properties such as solution processability, high luminescence quantum yield, large exciton binding energy, and tunable band gap. Introduction of large-group ammonium halides not only serves as a convenient and versatile method to obtain layered perovskites but also allows the exploitation of the energy-funneling process to achieve a high-efficiency light emission. Herein, we investigate the influence of the addition of ethylammonium bromide on the morphology, crystallite structure, and optical properties of the resultant perovskite materials and report that the phase transition from bulk to layered perovskite occurs in the presence of excess ethylammonium bromide. On the basis of this strategy, we report green perovskite light-emitting devices with the maximum external quantum efficiency of ca. 3% and power efficiency of 9.3 lm/W. Notably, blue layered perovskite light-emitting devices with the Commission Internationale de I'Eclairage coordinates of (0.16, 0.23) exhibit the maximum external quantum efficiency of 2.6% and power efficiency of 1 lm/W at 100 cd/m2, representing a large improvement over the previously reported analogous devices.
ABSTRACT
We report tandem polymer light emitting devices by using the PEDOTâ¶PSS/ZnO/PEIE charge generation layer (CGL) and investigate the influences of the conductance and thickness of PEDOTâ¶PSS layer on the properties of the devices. The results indicate that the conductance and thickness of PEDOTâ¶PSS layer have marginal impact on the J-V characteristics of the devices, while significant influences of device efficiency upon utilization of different PEDOTâ¶PSS specimens mainly come from their different strengths on exciton quenching. Luminance efficiency of TOLEDs with the PEDOTâ¶PSS thickness of 60 nm in CGL is better than TOLEDs with the PEDOTâ¶PSS thickness of 30 nm in CGL, the reason is that PEDOTâ¶PSS thickness of 60 nm the surface topography is more even . Luminance efficiency and driving voltage of the tandem devices match the sum of the luminance efficiency and driving voltage of the component light-emitting units, respectively, indicating that charges generated in the CGL can be injected efficiently into the adjacent light-emitting units. Incorporation of a V2O5 layer into the CGL structure only slightly affects the J-V and LE-I characteristics of the tandem devices, suggesting that the utilization of the PEDOTâ¶PSS/ZnO/PEIE CGL enables the simplification of the CGL structure without compromising device performance. The luminescence spectra of TOLEDs obviously involves two light emitting unit of spectrum, which shows that two light emitting unit in TOLEDs is normal work. Measurements on the capacitance-voltage characteristics of the CGL-based devices confirm that under negative bias (ITO anode) charges are accumulated and displaced in the CGL, which is totally in line with the full operation of light emitting units in the tandem devices. PEDOTâ¶PSS/ZnO/PEIE layer is evidenced the effective CGL. On this basis, for the first time we report tandem polymer light emitting devices containing three SY-PPV light-emitting unitsï¼which show the mixture of luminance efficiency and external quantum efficiency of 21.7 cd·A-1 and 6.95%, similar to the total luminance efficiency and external quantum efficiency of constituent LEUs. At 5 000 cd·m-2, the luminance efficiency and external quantum efficiency of the tandem devices are 20.5 cd·A-1 and 6.6%. Thus, the increase in the number of light emitting units leads to almost no performance losses, implying the robustness of the PEDOTâ¶PSS/ZnO/PEIE CGL. Tandem polymer light emitting devices containing three SY-PPV light-emitting units of the luminescent spectra is close to the light emitting unit. Further efforts on the optimization of hole injection layer in the CGL to minimize exciton quenching are underlying to promote the luminance efficiency of tandem polymer light emitting devices.
