Triplet Harvesting with 100% Efficiency by Way of Thermally Activated Delayed Fluorescence in Charge Transfer OLED Emitters

被引:888
作者
Dias, Fernando B. [1 ]
Bourdakos, Konstantinos N. [1 ]
Jankus, Vygintas [1 ]
Moss, Kathryn C. [2 ]
Kamtekar, Kiran T. [2 ]
Bhalla, Vandana [2 ,3 ]
Santos, Jose [2 ]
Bryce, Martin R. [2 ]
Monkman, Andrew P. [1 ]
机构
[1] Univ Durham, Dept Phys, Durham DH1 3LE, England
[2] Univ Durham, Dept Chem, Durham DH1 3LE, England
[3] Guru Nanak Dev Univ, Dept Chem, Amritsar 143005, Punjab, India
基金
英国工程与自然科学研究理事会;
关键词
organic semiconductors; conjugated materials; organic light-emitting diodes; delayed fluorescence; LIGHT-EMITTING-DIODES; HOST MATERIALS; ORGANIC SEMICONDUCTORS; CARBAZOLE COMPOUNDS; DEEP BLUE; EMISSION; STATES; ENERGY; PHOTOPHYSICS; CONVERSION;
D O I
10.1002/adma.201300753
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Organic light-emitting diodes (OLEDs) have their performance limited by the number of emissive singlet states created upon charge recombination (25%). Recently, a novel strategy has been proposed, based on thermally activated up-conversion of triplet to singlet states, yielding delayed fluorescence (TADF), which greatly enhances electroluminescence. The energy barrier for this reverse intersystem crossing mechanism is proportional to the exchange energy (E-ST) between the singlet and triplet states; therefore, materials with intramolecular charge transfer (ICT) states, where it is known that the exchange energy is small, are perfect candidates. However, here it is shown that triplet states can be harvested with 100% efficiency via TADF, even in materials with E-ST of more than 20 kT (where k is the Boltzmann constant and T is the temperature) at room temperature. The key role played by lone pair electrons in achieving this high efficiency in a series of ICT molecules is elucidated. The results show the complex photophysics of efficient TADF materials and give clear guidelines for designing new emitters.
引用
收藏
页码:3707 / 3714
页数:8
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