Influence of the hole transport layer on spectral stability in the white phosphorescent organic light emitting diode with non-doped structure

High-Efficiency Simplified Orange and White Organic Light-Emitting Devices Based on a Platinum(II) Complex

“…White light emission can be obtained by doping multiple dyes into one single EML or by using multiple EMLs [ 24 , 25 , 26 , 27 , 28 ]. However, doping is a sophisticated device fabrication process where it is difficult to precisely control the relative concentration of guest/host doping, especially for white OLEDs.…”

Recent progress on organic light-emitting diodes with phosphorescent ultrathin (<1nm) light-emitting layers

“…In general, holes and electrons mainly recombine in the organic layer between HTL (hole transporting layer) and ETL (electron transporting layer), which is structured by doping emitters into hosts in conventional host-guest system-based OLEDs. For UEMLs-based OLEDs, instead of doping emitter, phosphorescent UEML is directly inserted into common host materials such as TCTA ( Zhao et al., 2013a ; Tao et al., 2017 ; Zhang et al., 2017a ), CBP ( Liu et al., 2013b ; Xue et al., 2015a , 2015b ), and mCP ( Tan et al., 2015 ; Xue et al., 2015c ; Wang et al., 2019a , 2020 ; Yu et al., 2011 ; Yang et al., 2018 ) etc. Some work have been carried out for investigating the spatial distribution of excitons, and further revealed the effects of the thickness and position of UEMLs on the device performance in UEMLs-based OLEDs ( Tan et al., 2015 ; Zhao et al., 2018b ).…”

“…However, hole and electron transport materials forming mixed spacer usually have different response on charge transport with increasing voltage, makes that the shift of carrier recombination zone with increasing voltage still exist in mixed spacer-based devices ( Xue et al., 2015b ; Yang et al., 2018 ). This will inevitably lead to the spectral changes and deterioration of spectra stability for white devices ( Luo et al., 2018 ).…”

“…Such an exciplex-spacer system is beneficial to dilute the excitons density in UEMLs and subsequently reduces the efficiency roll-off. Besides, exciplex spacer also provides an improved long-range coupled Fo ¨rster energy transfer which also contributes to the realization of high efficiency (Tang et al, 2018;Wu et al, 2017;Tian et al, 2018;Shih et al, 2018). For example, in 2019, Sebastian Reineke et al employ the exciplex of mCP:B3PYMPM(1:1, 5 nm) as mixed spacer, and the fabricated green-UEMLs-based and red-UEMLs-based OLEDs achieve the maximum external quantum efficiency (EQE) of 23.2 and 15.6%, and still remains at high values of 22.5 and 15.0% at 1000 cd m À2 , respectively, which confirmed the advantage of exciplex spacers in developing high efficiency and low roll-off OLEDs (Liu et al, 2019).…”

“…Owing to the intrinsic nature of sub-monolayer, the introduction of ultrathin light-emitting layers (<1 nm, UEMLs) don't significantly affect the carrier behavior of devices. Hence, UEMLs were utilized as probe layer initially, and the approximate excitons distribution was obtained by varying the location of it and checking the electroluminescence (EL) spectra of corresponding devices (Tan et al, 2015;Tang et al, 2018;Miao et al, 2018b;Ma et al, 2014). Then, the structural characteristics of UEMLs are studied in-depth.…”