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Exciplex-type organic light-emitting diodes (OLEDs) are research focus at present, because of their high-efficiency luminescence at low cost due to the reverse intersystem crossing (RISC, EX1 ← EX3). Their microscopic processes usually exhibit intersystem crossing (ISC, PP1 → PP3) process dominated by polar pairs, leading the magneto-electroluminescence [MEL, MEL = (ΔEL)/EL × 100%] effect values and the magneto-conductance [MC, MC = (ΔI)/I × 100%] effect values to be both positive, the amplitude of MEL to be greater than that of MC at the same current, and the corresponding magnetic efficiency [Mη, Mη = (Δη)/η × 100%] values to be also positive due to the linear relationship EL
$ \propto \eta\cdot I $ within general current (I) range. Surprisingly, although the MEL value of the device coexisting with exciplex and electroplex is also greater than the MC value at low current, MEL value is less than MC value at high current. In other words, Mη value of this device undergoes a conversion from positive to negative with current increasing. In this work, to find out the reason why Mη value of exciplex-type OLED formed by TAPC and TPBi shows a negative value under high current and also to study the micro-dynamic evolution mechanism of spin-pair states in this device, three OLEDs are fabricated and their luminescence spectra and organic magnetic field effect curves are measured. The results indicate that the electroplex is produced in the exciplex-type OLED formed by TAPC and TPBi. Since the triplet exciton energy of monomers TAPC and TPBi is higher than those of triplet charge-transfer states of exciplex (CT${}_3^{\rm{ex}} $ ), and the CT${}_3^{\rm{ex}} $ energy is greater than the energy of triplet charge-transfer states of electroplex (CT${}_3^{\rm{el}} $ ), the CT${}_3^{\rm{ex}} $ energy can only be transferred to CT${}_3^{\rm{el}} $ through Dexter energy transfer (DET) process without other loss channels. The electroluminescence (EL) spectrum of this device shows that the luminescence intensity of exciplex is greater than that of electroplex, which indicates that the quantity of exciplex is more than that of electroplex. Besides, EL spectra at different currents prove that the formation rate of exciplex is faster than that of electroplex with current increasing. Owing to less quantity of exciplex at low current, the DET process from CT${}_3^{\rm{ex}} $ to CT${}_3^{\rm{el}} $ is too weak to facilitate the RISC process of charge-transfer states of electroplex (CTel). Therefore, the low field amplitude of Mη curve is positive at low current. The number of spin-pair states of exciplex increases with current increasing, which enhances the DET process. These processes of direct charge carriers trapped and energy transferred critically increase the number of CT${}_3^{\rm{el}} $ at high current, which greatly strengthens the RISC process of CTel. Therefore, the low field amplitude of Mη curve changes from positive to negative with current increasing. Furthermore, the Mη curves of this device are measured when only exciplex exists and only electroplex exists in the employing filter, respectively. As expected, the results confirm the accuracy of the mechanism of the negative value of the total Mη for this device. Obviously, this work contributes to the comprehension of the internal micro-physical mechanism in OLEDs and the law of interactions between excited states.[1] Godlewski J, Obarowska M 2007 Eur. Phys. J. -Spec. Top. 144 51Google Scholar
[2] Pan Y Y, Li W J, Zhang S T, Yao L, Gu C, Xu H, Yang B, Ma Y G 2014 Adv. Opt. Mater. 2 510Google Scholar
[3] Crooker S A, Liu F, Kelley M R, Martinez N J D, Nie W, Mohite A, Nayyar I H, Tretiak S, Smith D L, Ruden P P 2014 Appl. Phys. Lett. 105 153304Google Scholar
[4] Uoyama H, Goushi K, Shizu K, Nomura H, Adachi C 2012 Nature 492 234Google Scholar
[5] Liu F L, Kelley M R, Crooker S A, Nie W Y, Mohite A D, Ruden P P, Smith D L 2014 Phys. Rev. B 90 235314Google Scholar
[6] Kalinowski J, Cocchi M, Virgili D, Marco P D, Fattori V 2003 Chem. Phys. Lett. 380 710Google Scholar
[7] Zhang T T, Holford D F, Gu H, Kreouzis T, Zhang S J, Gillin W P 2016 Appl. Phys. Lett. 108 023303Google Scholar
[8] Zhang L Cheah K W 2018 Sci. Rep. 8 8832Google Scholar
[9] Bera K, Douglas C J, Frontiera R R 2017 J. Phys. Chem. Lett. 8 5929Google Scholar
[10] 赵茜, 汤仙童, 潘睿亨, 许静, 屈芬兰, 熊祖洪 2019 科学通报 64 2514Google Scholar
Zhao X, Tang X T, Pan R H, Xu J, Qu F L, Xiong Z H 2019 Chin. Sci. Bull. 64 2514Google Scholar
[11] Doubleday C, Turro N J, Wang J F 1989 Acc. Chem. Res. 22 199Google Scholar
[12] 张勇, 刘亚莉, 焦威, 陈林, 熊祖洪 2012 61 117106Google Scholar
Zhang Y, Liu Y L, Jiao W, Chen L, Xiong Z H 2012 Acta Phys. Sin. 61 117106Google Scholar
[13] 陈秋松, 袁德, 贾伟尧, 陈历相, 邹越, 向杰, 陈颖冰, 张巧明, 熊祖洪 2015 64 177801Google Scholar
Chen Q S, Yuan D, Jia W Y, Chen L X, Zou Y, Xiang J, Chen Y B, Zhang Q M, Xiong Z H 2015 Acta Phys. Sin. 64 177801Google Scholar
[14] Xiang J, Chen Y B, Yuan D, Jia W Y, Zhang Q M, Xiong Z H 2016 Appl. Phys. Lett. 109 103301Google Scholar
[15] Zhang Y, Liu R, Lei Y L, Xiong Z H 2009 Appl. Phys. Lett. 94 083307Google Scholar
[16] Chen P, Song Q L, Choy W C H, Ding B F, Liu Y L, Xiong Z H 2011 Appl. Phys. Lett. 99 143305Google Scholar
[17] Wang Y F, Sahin-Tiras K, Harmon H J, Wohlgenannt M, Flatté M E 2016 Phys. Rev. X 6 011011Google Scholar
[18] Zhao X, Tang X T, Zhu H Q, Ma C H, Wang Y, Ye S N, Tu L Y, Xiong Z H 2021 ACS Appl. Electron. Mater. 3 3034Google Scholar
[19] Zhang T Y, Chu B, Li W L, Su Z S, Peng Q M, Zhao B, Luo Y S, Jin F M, Yan X W, Gao Y, Wu H R, Zhang F, Fan D, Wang J B 2014 ACS Appl. Mater. Interfaces 6 11907Google Scholar
[20] Gruenbaum W T, Sorriero L J, Borsenberger P M, Zumbulyadis N 1996 Jpn. J. Appl. Phys. 35 2714Google Scholar
[21] 雷俊峰, 郝玉英, 樊文浩, 房晓红, 许并社 2009 发光学报 30 590
Lei J F, Hao Y Y, Fan W H, Fang X H, Xu B S 2009 Chin. J. Lumin. 30 590
[22] Wei M Y, Gui G, Chung Y H, Xiao L X, Qu B, Chen Z J 2015 Phys. Status Solidi B 252 1711Google Scholar
[23] Deng J Q, Jia W Y, Chen Y B, Liu D Y, Hu Y Q, Xiong Z H 2017 Sci. Rep. 7 44396Google Scholar
[24] Sheng Y, Nguyen T D, Veeraraghavan G, Mermer Ö, Wohlgenannt M, Qiu S, Scherf U 2006 Phys. Rev. B 74 045213Google Scholar
[25] Yuan P S, Qiao X F, Yan D H, Ma D G 2018 J. Mater. Chem. C 6 5721Google Scholar
[26] Scharff T, Ratzke W, Zipfel J, Klemm P, Bange S, Lupton J M 2021 Nat. Commun. 12 2071Google Scholar
[27] Janssen P, Cox M, Wouters S H W, Kemerink M, Wienk M M, Koopmans B 2013 Nat. Commun. 4 2286Google Scholar
[28] 宁亚茹, 赵茜, 汤仙童, 陈敬, 吴凤娇, 贾伟尧, 陈晓莉, 熊祖洪 2022 71 087201Google Scholar
Ning Y R, Zhao X, Tang X T, Chen J, Wu F J, Jia W Y, Chen X L, Xiong Z H 2022 Acta Phys. Sin. 71 087201Google Scholar
[29] Liu W, Chen J X, Zheng C J, Wang K, Chen D Y, Li F, Dong Y P, Lee C S, Ou X M, Zhang X H 2016 Adv. Funct. Mater. 26 2002Google Scholar
[30] Zhang M, Liu W, Zheng C J, Wang K, Shi Y Z, Li X, Lin H, Tao S L, Zhang X H 2019 Adv. Sci. 6 1801938Google Scholar
[31] Chen P, Peng Q M, Yao L, Gao N, Li F 2013 Appl. Phys. Lett. 102 063301Google Scholar
[32] Sasabe H, Tanaka D, Yokoyama D, Chiba T, Pu Y J, Nakayama K, Yokoyama M, Kido J 2011 Adv. Funct. Mater. 21 336Google Scholar
[33] Liu X K, Chen Z, Zheng C J, Liu C L, Lee C S, Li F, Ou X M, Zhang X H 2015 Adv. Mater. 27 2378Google Scholar
[34] Hu B, Wu Y 2007 Nat. Mater. 6 985Google Scholar
[35] Bagnich S A, Niedermeier U, Melzer C, Sarfert W, von Seggern H 2009 J. Appl. Phys. 106 113702Google Scholar
[36] Fan Y X, Sun A H, Tian Y H, Zhou P C, Niu Y X, Shi Wei, Wei B 2022 J. Phys. D: Appl. Phys. 55 315103Google Scholar
[37] Xu Z, Gong Y B, Dai Y F, Sun Q, Qiao X F, Yang D Z, Zhan X J, Li Z, Tang B Z, Ma D G 2019 Adv. Opt. Mater. 7 1801539Google Scholar
[38] Wu Z B, Wang Q, Yu L, Chen J S, Qiao X F, Ahamad T, Alshehri S M, Yang C L, Ma D G 2016 ACS Appl. Mater. Interfaces 8 28780Google Scholar
[39] Mondal A, Paterson L, Cho J, et al. 2021 Chem. Phys. Rev. 2 031304Google Scholar
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[1] Godlewski J, Obarowska M 2007 Eur. Phys. J. -Spec. Top. 144 51Google Scholar
[2] Pan Y Y, Li W J, Zhang S T, Yao L, Gu C, Xu H, Yang B, Ma Y G 2014 Adv. Opt. Mater. 2 510Google Scholar
[3] Crooker S A, Liu F, Kelley M R, Martinez N J D, Nie W, Mohite A, Nayyar I H, Tretiak S, Smith D L, Ruden P P 2014 Appl. Phys. Lett. 105 153304Google Scholar
[4] Uoyama H, Goushi K, Shizu K, Nomura H, Adachi C 2012 Nature 492 234Google Scholar
[5] Liu F L, Kelley M R, Crooker S A, Nie W Y, Mohite A D, Ruden P P, Smith D L 2014 Phys. Rev. B 90 235314Google Scholar
[6] Kalinowski J, Cocchi M, Virgili D, Marco P D, Fattori V 2003 Chem. Phys. Lett. 380 710Google Scholar
[7] Zhang T T, Holford D F, Gu H, Kreouzis T, Zhang S J, Gillin W P 2016 Appl. Phys. Lett. 108 023303Google Scholar
[8] Zhang L Cheah K W 2018 Sci. Rep. 8 8832Google Scholar
[9] Bera K, Douglas C J, Frontiera R R 2017 J. Phys. Chem. Lett. 8 5929Google Scholar
[10] 赵茜, 汤仙童, 潘睿亨, 许静, 屈芬兰, 熊祖洪 2019 科学通报 64 2514Google Scholar
Zhao X, Tang X T, Pan R H, Xu J, Qu F L, Xiong Z H 2019 Chin. Sci. Bull. 64 2514Google Scholar
[11] Doubleday C, Turro N J, Wang J F 1989 Acc. Chem. Res. 22 199Google Scholar
[12] 张勇, 刘亚莉, 焦威, 陈林, 熊祖洪 2012 61 117106Google Scholar
Zhang Y, Liu Y L, Jiao W, Chen L, Xiong Z H 2012 Acta Phys. Sin. 61 117106Google Scholar
[13] 陈秋松, 袁德, 贾伟尧, 陈历相, 邹越, 向杰, 陈颖冰, 张巧明, 熊祖洪 2015 64 177801Google Scholar
Chen Q S, Yuan D, Jia W Y, Chen L X, Zou Y, Xiang J, Chen Y B, Zhang Q M, Xiong Z H 2015 Acta Phys. Sin. 64 177801Google Scholar
[14] Xiang J, Chen Y B, Yuan D, Jia W Y, Zhang Q M, Xiong Z H 2016 Appl. Phys. Lett. 109 103301Google Scholar
[15] Zhang Y, Liu R, Lei Y L, Xiong Z H 2009 Appl. Phys. Lett. 94 083307Google Scholar
[16] Chen P, Song Q L, Choy W C H, Ding B F, Liu Y L, Xiong Z H 2011 Appl. Phys. Lett. 99 143305Google Scholar
[17] Wang Y F, Sahin-Tiras K, Harmon H J, Wohlgenannt M, Flatté M E 2016 Phys. Rev. X 6 011011Google Scholar
[18] Zhao X, Tang X T, Zhu H Q, Ma C H, Wang Y, Ye S N, Tu L Y, Xiong Z H 2021 ACS Appl. Electron. Mater. 3 3034Google Scholar
[19] Zhang T Y, Chu B, Li W L, Su Z S, Peng Q M, Zhao B, Luo Y S, Jin F M, Yan X W, Gao Y, Wu H R, Zhang F, Fan D, Wang J B 2014 ACS Appl. Mater. Interfaces 6 11907Google Scholar
[20] Gruenbaum W T, Sorriero L J, Borsenberger P M, Zumbulyadis N 1996 Jpn. J. Appl. Phys. 35 2714Google Scholar
[21] 雷俊峰, 郝玉英, 樊文浩, 房晓红, 许并社 2009 发光学报 30 590
Lei J F, Hao Y Y, Fan W H, Fang X H, Xu B S 2009 Chin. J. Lumin. 30 590
[22] Wei M Y, Gui G, Chung Y H, Xiao L X, Qu B, Chen Z J 2015 Phys. Status Solidi B 252 1711Google Scholar
[23] Deng J Q, Jia W Y, Chen Y B, Liu D Y, Hu Y Q, Xiong Z H 2017 Sci. Rep. 7 44396Google Scholar
[24] Sheng Y, Nguyen T D, Veeraraghavan G, Mermer Ö, Wohlgenannt M, Qiu S, Scherf U 2006 Phys. Rev. B 74 045213Google Scholar
[25] Yuan P S, Qiao X F, Yan D H, Ma D G 2018 J. Mater. Chem. C 6 5721Google Scholar
[26] Scharff T, Ratzke W, Zipfel J, Klemm P, Bange S, Lupton J M 2021 Nat. Commun. 12 2071Google Scholar
[27] Janssen P, Cox M, Wouters S H W, Kemerink M, Wienk M M, Koopmans B 2013 Nat. Commun. 4 2286Google Scholar
[28] 宁亚茹, 赵茜, 汤仙童, 陈敬, 吴凤娇, 贾伟尧, 陈晓莉, 熊祖洪 2022 71 087201Google Scholar
Ning Y R, Zhao X, Tang X T, Chen J, Wu F J, Jia W Y, Chen X L, Xiong Z H 2022 Acta Phys. Sin. 71 087201Google Scholar
[29] Liu W, Chen J X, Zheng C J, Wang K, Chen D Y, Li F, Dong Y P, Lee C S, Ou X M, Zhang X H 2016 Adv. Funct. Mater. 26 2002Google Scholar
[30] Zhang M, Liu W, Zheng C J, Wang K, Shi Y Z, Li X, Lin H, Tao S L, Zhang X H 2019 Adv. Sci. 6 1801938Google Scholar
[31] Chen P, Peng Q M, Yao L, Gao N, Li F 2013 Appl. Phys. Lett. 102 063301Google Scholar
[32] Sasabe H, Tanaka D, Yokoyama D, Chiba T, Pu Y J, Nakayama K, Yokoyama M, Kido J 2011 Adv. Funct. Mater. 21 336Google Scholar
[33] Liu X K, Chen Z, Zheng C J, Liu C L, Lee C S, Li F, Ou X M, Zhang X H 2015 Adv. Mater. 27 2378Google Scholar
[34] Hu B, Wu Y 2007 Nat. Mater. 6 985Google Scholar
[35] Bagnich S A, Niedermeier U, Melzer C, Sarfert W, von Seggern H 2009 J. Appl. Phys. 106 113702Google Scholar
[36] Fan Y X, Sun A H, Tian Y H, Zhou P C, Niu Y X, Shi Wei, Wei B 2022 J. Phys. D: Appl. Phys. 55 315103Google Scholar
[37] Xu Z, Gong Y B, Dai Y F, Sun Q, Qiao X F, Yang D Z, Zhan X J, Li Z, Tang B Z, Ma D G 2019 Adv. Opt. Mater. 7 1801539Google Scholar
[38] Wu Z B, Wang Q, Yu L, Chen J S, Qiao X F, Ahamad T, Alshehri S M, Yang C L, Ma D G 2016 ACS Appl. Mater. Interfaces 8 28780Google Scholar
[39] Mondal A, Paterson L, Cho J, et al. 2021 Chem. Phys. Rev. 2 031304Google Scholar
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