Efficient white polymer light-emitting diodes (WPLEDs) based on covalent-grafting of [Zn2(MP)3(OAc)] into PVK

Abstract

Using [Zn2(MP)3(OAc)]-grafted polymer as a single emitting layer, record-high efficiencies and weak (ca. 25%) efficiency roll-off are realized for cost-effective and large-area flexible WPLEDs.

All-Solution-Processed Multilayered White Polymer Light-Emitting Diodes (WPLEDs) Based on Cross-Linked [Ir(4-vb-PBI)2(acac)]

“…420 nm) and the [Ir­(4-vb-PBI) 2 (acac)] -centered greenish-yellow light (516 nm) emissions are also ruled by the λ ex adjustment for the three cross-linked Ir 3+ polymer films, the relative deficiency of the PVK-based blue light allows for the dichromatic-integrated color waving from yellowish-green ( II-A–D , Figure b; x = 0.306–0.311, y = 0.476–0.481; CCTs = 6095–6233 K; and CRIs = 54–59) to green ( III-A–D , Figure c; x = 0.277–0.282, y = 0.415–0.425; CCTs = 7188–7446 K; and CRIs = 63–64; IV-A–D , Figure d; x = 0.274–0.281, y = 0.398–0.411; CCTs = 7341–7547 K; and CRIs = 65–67). Convincingly, the residual yet non-neglectful peak emission at 420 nm confirms the allowance of PVK-based blue light after the saturation of that energy transfer . Interestingly, through a comparable combination for the cross-linked Ir 3+ polymer film poly­(NVK- co -[Ir­(4-vb-PBI) 2 (acac)]- co -NVK) (250:1), all of the resulting dichromatic-integrated color coordinates ( V-A–D ( x = 0.272–0.278, y = 0.319–0.324); Figure a) locate within the desirable white-light regime, covering a broad range 350–750 nm emission with 11 017–12 088 K of the CCTs and 76–80 of the CRIs.…”

“…Noticeably, except for the feeding of 50:1 with a shorter phosphorescent lifetime (5.9 μs) due to aggregation-caused quenching (ACQ), the [Ir­(4-vb-PBI) 2 (acac)] -centered greenish-yellow light species decay with an almost constant lifetime (ca. 6.8 μs), whose dependence on both the other feeding (100:1–300:1) and the excitation wavelength (310–340 nm) should be attributed to the excess amount of PVK with the saturated Förster energy transfer . Thus, the facilitated molecular dispersion of the [Ir­(4-vb-PBI) 2 (acac)] chromophores within the PVK backbone, in avoidance of unexpected self-quenching, is realized especially for the cross-linked Ir 3+ polymer film (250:1).…”

“…To direct the cross-linked Ir 3+ polymer components from [Ir­(4-vb-PBI) 2 (acac)] , cross-linked Ir 3+ polymer films (40 nm thickness) poly­(NVK- co -[Ir­(4-vb-PBI) 2 (acac)]- co -NVK) (also Scheme ) with the stipulated feeding (50:1, 100:1, 150:1, 200:1, 250:1, or 300:1) were synthesized by AIBN-initiated copolymerization of NVK and [Ir­(4-vb-PBI) 2 (acac)] . As a matter of fact, the PVK matrix with higher-energy-state blue light can also function as both a compensation color and an energy donor to the greenish-yellow emissive [Ir­(4-vb-PBI) 2 (acac)] , from which effective Förster transfer energy (deduced from the significant spectral overlap between the emission of PVK and the absorption of [Ir­(4-vb-PBI) 2 (acac)] ; also shown in Figure ) and desirable dichromatic-integrated white light should be expectable for their cross-linked Ir 3+ polymer films.…”

“…Considering the junction (also Figure ) between the LLCT/MLCT absorption of [Ir­(4-vb-PBI) 2 (acac)] and the excitation of PVK, the λ ex = 310–340 nm with every 10 nm step size was adopted as the suitable excitation regime to realize their simultaneous and effective emissions. At 50:1 feeding, photoexcitation gives rise to the dominated greenish-yellow lights ( I-A–D , Figure a; x = 0.295–0.299, y = 0.475–0.483; CCTs = 6410–6527 K; and CRIs = 53–54) of [Ir­(4-vb-PBI) 2 (acac)] , and the PVK-based blue light is almost quenched with the preferential energy transfer . By increasing the feeding ratio to 100:1, 150:1, and 200:1, although both the PVK-based blue light (ca.…”

“…After the turn-on voltage ( V on at 1 cd/m 2 ) of 8.5 V, their comparative combination gives the stable white lights (CIE coordinates x = 0.266–0.275, y = 0.316–0.333, CCTs of 7420–8037 K, and CRIs of 70–73; Figure c) within the illuminating 9.0–18.0 V range. Undoubtedly, in contrast to the λ ex -dependent (310–340 nm) photoexcited white lights (CIE coordinates x = 0.272–0.278, y = 0.319–0.324, CCTs of 11 017–12 088 K, and CRIs of 76–80; Table S3) of poly­(NVK- co -[Ir­(4-vb-PBI) 2 (acac)]- co -NVK) (250:1), the electroluminescent warmer (significantly lower CCTs) white lights of WPLED-I should reflect concurrently conducted Förster energy transfer and carrier-trapping mechanisms. As shown in Figure d, with an increase of the applied bias voltage, both the luminance ( L , cd/m 2 ) and the current density ( J , mA/cm 2 ) monotonously increase, and an L Max of 315 cd/m 2 and a J Max of 17.9 mA/cm 2 at 18.0 V are observed.…”