26 Mar 00:45
by Yuwei Xu,
Xiaoming Liang,
Xuehong Zhou,
Peisen Yuan,
Jiadong Zhou,
Cong Wang,
Binbin Li,
Dehua Hu,
Xianfeng Qiao,
Xiaofang Jiang,
Linlin Liu,
Shi‐Jian Su,
Dongge Ma,
Yuguang Ma
A pure‐blue fluorescent organic light‐emitting device (OLED) based on phenanthroimidazole−anthracene derivative obtains a maximum external quantum efficiency of 10.5% with excellent stability. Experimental investigations reveal that the high efficiency is attributed to triplet exciton harvesting by reverse intersystem crossing from the high‐lying triplet state. The results demonstrates that “hot exciton” channels represent a promising way to construct high‐performance fluorescent OLEDs.
Abstract
Purely organic electroluminescent materials, such as thermally activated delayed fluorescent (TADF) and triplet–triplet annihilation (TTA) materials, basically harness triplet excitons from the lowest triplet excited state (T1) to realize high efficiency. Here, a fluorescent material that can convert triplet excitons into singlet excitons from the high‐lying excited state (T2), referred to here as a “hot exciton” path, is reported. The energy levels of this compound are determined from the sensitization and nanosecond transient absorption spectroscopy measurements, i.e., small splitting energy between S1 and T2 and rather large T2–T1 energy gap, which are expected to impede the internal conversion (IC) from T2 to T1 and facilitate the reverse intersystem crossing from the high‐lying triplet state (hRISC). Through sensitizing the T2 state with ketones, the existence of the hRISC process with an ns‐scale delayed lifetime is confirmed. Benefiting from this fast triplet–singlet conversion, the nondoped device based on this “hot exciton” material reaches a maximum external quantum efficiency exceeding 10%, with a small efficiency roll‐off and CIE coordinates of (0.15, 0.13). These results reveal that the “hot exciton” path is a promising way to exploit high efficient, stable fluorescent emitters, especially for the pure‐blue and deep‐blue fluorescent organic light‐emitting devices.
19 Mar 02:22
by Jianqiu Wang,
Zhong Zheng,
Dongyang Zhang,
Jianqi Zhang,
Jiyu Zhou,
Jingchong Liu,
Shenkun Xie,
Yong Zhao,
Yuan Zhang,
Zhixiang Wei,
Jianhui Hou,
Zhiyong Tang,
Huiqiong Zhou
The molecular orientation and charge extraction of PEDOT:PSS‐based hole‐transporting layers are effectively modulated through fine tuning of the surface energy by introducing poly(styrene sulfonic acid) sodium salts or nickel formate dihydrate, which boosts the fill factor and eventual efficiency of organic solar cells based on fullerene and nonfullerene acceptors.
Abstract
Interface properties are of critical importance for high‐performance bulk‐heterojunction (BHJ) organic solar cells (OSCs). Here, a universal interface approach to tune the surface free energy (γS) of hole‐transporting layers (HTLs) in a wide range through introducing poly(styrene sulfonic acid) sodium salts or nickel formate dihydrate into poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is reported. Based on the optimal γS of HTLs and thus improved face‐on molecular ordering in BHJs, enhanced fill factor and power conversion efficiencies in both fullerene and nonfullerene OSCs are achieved, which is attributed to the increased charge carrier mobility and sweepout with reduced recombination. It is found that the face‐on orientation‐preferred BHJs (PBDB‐TF:PC71BM, PBDB‐T:PC71BM, and PBDB‐TF:IT‐4F) favor HTLs with higher γS while the edge‐on orientation‐preferred BHJs (PDCDT:PC71BM, P3HT:PC71BM and PDCBT:ITIC) are partial to HTLs with lower γS. Based on the surface property–morphology–device performance correlations, a suggestion to select a suitable HTL in terms of γS for a specific BHJ with favored molecular arrangement is provided. This work enriches the fundamental understandings on the interface characteristics and morphological control toward high‐efficiency OSCs based on a wide range of BHJ materials.
10 Jul 09:18
by Nicholas M. Randell, Chase L. Radford, Jinli Yang, Jesse Quinn, Dongliang Hou, Yuning Li, Timothy L. Kelly
Chemistry of Materials
DOI: 10.1021/acs.chemmater.8b02535
