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Organic semiconductor (OSC) devices based on manipulation of electron spin have attracted considerable attention since the discovery of long spin relaxation time and large transport distance in OSCs. For organic light-emitting devices (OLEDs), controlling the singlet to triplet ratio by spin-polarized electrodes is one of the effective ways to realize high luminescent efficiency. Based on the drift-diffusion equation, continuous equation and Langevin recombination theory, the spin injection, transportation and recombination properties of carriers in OLEDs are modeled in this paper. The density of polarized electrons and holes in OSCs are calculated, the singlet to triplet ratio is analyzed, and the influences of the electrical field, spin-related interfacial conductance, bulk conductivity and polarization of electrodes are accounted for. It is showed that opposite spin polarization of electrons and holes are in favor of increasing singlet to triplet ratio, and the higher spin polarization of injected carrier density is, the larger singlet to triplet ratio will be. Large spin-related interfacial resistance, large polarization of electrodes, matched bulk conductivity and high electrical field under forward bias favor spin polarization of carries density in OSCs. We can obtain obviously improved density polarization by optimizing the related parameters on the basis of essential injection efficiency. The optimized polarization ensures sufficient space for manipulating singlet to triplet ratio, hence the quantum efficiency of OLEDs.
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Keywords:
- organic light-emitting devices /
- spin-polarized injection /
- carriers recombination /
- singlet to triplet ratio
[1] ［1］Zhao J Q, Qiao S Z, Xu F Y, Zhang N Y, Pang Y T, Chen Y 2008 J. Semi. 29 418
[2] ［2］Zhang L J, Hua Y L, Wu X M, Wang Y, Yin S G 2008 Chin. Phys. B 17 3097
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[7] ［7］Xiong Z H, Wu D, Vardeny Z V, Shi J 2004 Nature 427 821
[8] ［8］Ren J F, Zhang Y B, Xie S J 2007 Acta. Phys. Sin. 56 4785 (in Chinese) ［任俊峰、张玉滨、解士杰 2007 56 4785］
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[11] ］Schmidt G, Ferrand D, Molenkamp L W, Filip A T, Van Wees B J 2000 Phys. Rev. B 62 R4790
[12] ］Rashba E I 2000 Phys. Rev. B 62 R16267
[13] ］Fert A, Jaffres H 2001 Phys. Rev. B 64 184420
[14] ］Ren J F, Fu J Y, Liu D S, Mei L M, Xie S J 2005 J. Appl. Phys. 98 074503
[15] ］Kikkawa J M, Awschalom D D 1999 Nature 397 139
[16] ］Malajovich I, Berry J J, Samarth N, Awschalom D D 2001 Nature 411 770
[17] ］D’Amico I 2004 Phys. Rev. B 69 165305
[18] ］Zhao J Q, Qiao S Z, Jia Z F, Zhang N Y, Ji Y J, Pang Y T, Chen Y, Fu G 2008 Chin. Phys. Lett. 25 4381
[19] ］Yu Z G, Flatte M E 2002 Phys. Rev. B 66 235302
[20] ］Ma Y N, Ren J F, Zhang Y B, Liu D S, Xie S J 2007 Chin. Phys. Lett. 24 1697
[21] ］Yu Z G, Flatte M E 2002 Phys. Rev. B 66 201202
[22] ］Zhao J Q, Qiao S Z, Zhang N Y, Xu F Y, Pang Y T, Chen Y 2009 Cur. Appl. Phys. 9 919
[23] ］Zutic I, Fabian J, Das Sarma S 2004 Rev. Mod. Phys. 76 323
[24] ］Hershfield S, Zhao H L 1997 Phys. Rev. B 56 3296
[25] ］Zhao J Q, Xie S J, Han S H 2003 Journal of Shan Dong University of Architecture and Engineering 18 10 (in Chinese) ［赵俊卿、解士杰、韩圣浩 2003 山东建筑大学学报 18 10］
[26] ］Albrecht J D, Smith D L 2002 Phys. Rev. B 66 113303
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[1] ［1］Zhao J Q, Qiao S Z, Xu F Y, Zhang N Y, Pang Y T, Chen Y 2008 J. Semi. 29 418
[2] ［2］Zhang L J, Hua Y L, Wu X M, Wang Y, Yin S G 2008 Chin. Phys. B 17 3097
[3] ［3］Kadashchuk A, Vakhnin A, Blonski I, Beljonne D, Shuai Z, Brédas J L, Arkhipov V I, Heremans P, Emelianova E V, Bssler H 2004 Phys. Rev. Lett. 93 066803
[4] ［4］Yin S W, Chen L P, Xuan P F, Chen K Q, Shuai Z 2004 J. Phys. Chem. B 108 9608
[5] ［5］Ding H J, Gao Y L, Cinchetti M, Wüstenberg J P, Sánchez-Albaneda M, Andreyev O, Bauer M, Aeschlimann M 2008 Phys. Rev. B 78 075311
[6] ［6］Wu Y, Hu B, Jane H, Li A P, Shen J 2007 Phys. Rev. B 75 075413
[7] ［7］Xiong Z H, Wu D, Vardeny Z V, Shi J 2004 Nature 427 821
[8] ［8］Ren J F, Zhang Y B, Xie S J 2007 Acta. Phys. Sin. 56 4785 (in Chinese) ［任俊峰、张玉滨、解士杰 2007 56 4785］
[9] ［9］Tsymbal E Y, Burlakov V M, Oleinik I I 2002 Phys. Rev. B 66 073201
[10] ］Smith D L, Silver R N 2001 Phys. Rev. B 64 045323
[11] ］Schmidt G, Ferrand D, Molenkamp L W, Filip A T, Van Wees B J 2000 Phys. Rev. B 62 R4790
[12] ］Rashba E I 2000 Phys. Rev. B 62 R16267
[13] ］Fert A, Jaffres H 2001 Phys. Rev. B 64 184420
[14] ］Ren J F, Fu J Y, Liu D S, Mei L M, Xie S J 2005 J. Appl. Phys. 98 074503
[15] ］Kikkawa J M, Awschalom D D 1999 Nature 397 139
[16] ］Malajovich I, Berry J J, Samarth N, Awschalom D D 2001 Nature 411 770
[17] ］D’Amico I 2004 Phys. Rev. B 69 165305
[18] ］Zhao J Q, Qiao S Z, Jia Z F, Zhang N Y, Ji Y J, Pang Y T, Chen Y, Fu G 2008 Chin. Phys. Lett. 25 4381
[19] ］Yu Z G, Flatte M E 2002 Phys. Rev. B 66 235302
[20] ］Ma Y N, Ren J F, Zhang Y B, Liu D S, Xie S J 2007 Chin. Phys. Lett. 24 1697
[21] ］Yu Z G, Flatte M E 2002 Phys. Rev. B 66 201202
[22] ］Zhao J Q, Qiao S Z, Zhang N Y, Xu F Y, Pang Y T, Chen Y 2009 Cur. Appl. Phys. 9 919
[23] ］Zutic I, Fabian J, Das Sarma S 2004 Rev. Mod. Phys. 76 323
[24] ］Hershfield S, Zhao H L 1997 Phys. Rev. B 56 3296
[25] ］Zhao J Q, Xie S J, Han S H 2003 Journal of Shan Dong University of Architecture and Engineering 18 10 (in Chinese) ［赵俊卿、解士杰、韩圣浩 2003 山东建筑大学学报 18 10］
[26] ］Albrecht J D, Smith D L 2002 Phys. Rev. B 66 113303
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