||Magnetic Field Effect in Conjugated Polymer/Organic Molecules-Based Diodes
||Department of Photonics
Magnetic field effect
This dissertation presents the magnetic field effects (MFEs) in conjugated polymer/ organic molecules-based diodes, including the phenyl-substituted poly(p-phenylene vinylene) copolymer (super yellow, SY-PPV)-based polymer light-emitting diodes (PLEDs), tetracene- and pentacene-based diodes. For the first topics in the first part, the effect of device architecture (current injection through the diodes) and operating condition (the external applied bias) on magnetoconductance (MC) response was investigated and analyzed by the fitting analysis in SY-PPV-based PLEDs. Using the mathematical analysis to fit the curves with two empirical equations of a non-Lorentzian and a Lorentzian function, we are able to extract the hidden negative MC component from the positive MC resposes in charge-unbalance SY-PPV-based PLEDs. We attribute the negative MC component to the triplet excitons-charge reaction. The negative MC component can be further increase by increasing the concentration of free hole carriers in hole-blocking SY-PPV-based PLED. Thus, the negative MC component corresponds for the line shape broadening of MC curves. In the next part, we investigate the triplet-triplet annihilation (TTA) process in the charge-balanced SY-PPV-based PLEDs. We found that the temperature and current density may induce the TTA process in SY-PPV-based PLEDs. The TTA process may harvest the energy from triplet to singlet excitons in SY-PPY active layer and in part contribute the emission to fluorescence in PLEDs especially in the high current density regime.
In the second topics, we study the magnetic field effect in tetracene-based diodes. We found the singlet fission (SF) reaction occurs in tetracene-based diodes based on the magnetophotocurrent (MPC) and magnetophotoluminescence (MPL) characterization. By depositing the fullerene (C60) on the tetracene active layer to yield a planar heterojunction device, we found that the MPC response show the sign-change and the PL spectra of tetracene/C60 PHJ-based diode show almost completely quenched. It indicates that the charge separation by charge transfer (CT) complex states is more effective than the SF reaction. Consequently, the singlet fission reaction is suppressed by this charge separation of the opposite charge carriers at the donor/acceptor interfaces.
Finally, at the third topics, we investigate the MPC response of pentacene-based diodes in different magnetic fields orientation either perpendicular (90°) or parallel (0°) orientation. We found that the MPC magnitude is magnetic field-orientation dependent. We attribute the change of MPC magnitude under magnetic field-orientation to the interaction of polaron pair’s spins (dipole-dipole or exchange interaction). Depositing C60 on pentacene layer in addition to the change of MPC magnitude, it also narrows the MPC line shape. Due to the weaker exchange interaction in CT complex states from pentacene/C60 interface, the external applied magnetic field can modulate this interaction result in the modulation in MPC line shape. The MPC line shape narrowing is observed at low magnetic field regime (B < 300 Oe) in pentacene/C60-based diode by changing the magnetic field orientation from 90° to 0°. We contribute this MPC line shape narrowing to the suppression of hyperfine interaction to induce the intersystem crossing. Our experimental results strengthen the previous studies that the dipole-dipole, exchange or hyperfine interactions between polaron pairs or CT complex states are responsible for the magnetic field orientation dependence of organic magnetoresistance.
MAGNETIC FIELD EFFECT IN THE PHENYL-SUBSTITUTED POLY(P-PHENYLENE VINYLENE) COPOLYMER-BASED POLYMER LIGHT-EMITTING DIODES III
STUDY OF MAGNETIC FIELD EFFECT OF THE SINGLET FISSION REACTION IN TETRACENE-BASED DIODES XIII
ANGLE-DEPENDENT MAGNETO-PHOTOCURRENT RESPONSE IN PENTACENE-BASED DIODES XVIII
LIST OF TABLES XXXIII
LIST OF FIGURES XXXIV
CHAPTER ONE INTRODUCTION 1
1.1 Organic semiconductors devices 1
1.2 Organic light emitting diodes 3
1.2.1 Device structure 4
1.2.2 OLED working principle 5
1.3 Organic spintronics 8
1.4 Magnetic field effects 9
1.5 Dissertation motivation and outline 10
CHAPTER TWO THEORETICAL AND EXPERIMENTAL BACKGROUND 13
2.1 Electronic transition in organic molecules 13
2.1.1 Singlet and triplet excited states 16
2.1.2 Intersystem crossing 18
2.2 Formation of excited states in organic molecules 20
2.2.1 Excitons 20
2.2.2 Polarons 22
2.2.3 Charge transfer complexes 25
2.3 Organic magnetoresistance (OMAR) effects 25
2.3.1 Definition 26
2.3.2 Experimental history of OMAR effect 27
2.3.3 OMAR effects in polymer-based devices 29
2.3.4 OMAR effects in organic molecules-based devices 31
2.4 General proposed mechanism of OMAR effects 32
2.4.1 Bipolaron model 33
2.4.2 Electron-hole pair model 35
2.4.3 Exciton polaron interaction model 37
2.4.4 Triplet-triplet annihilation 39
2.4.5 Singlet fission 42
2.5 Hyperfine interaction 44
2.6 Line shape 45
CHAPTER THREE EXPERIMENTAL AND MEASUREMENT METHODS 47
3.1 Materials 47
3.2 Device Fabrication 49
3.2.1 Substrate preparation 49
3.2.2 Spin coating process 50
3.2.3 Thermal evaporation 50
3.3 Magnetic field effect measurement 52
CHAPTER FOUR MAGNETIC FIELD EFFECT IN THE PHENYL-SUBSTITUTED POLY(P-PHENYLENE VINYLENE) COPOLYMER-BASED POLYMER LIGHT-EMITTING DIODES: 56
PART 1: MODULATING THE MC LINESHAPE IN DIFFERENT CHARGE INJECTION DEVICE 56
4.1 Introduction 56
4.2 Experimental section 57
4.3 MC responses under different applied bias 59
4.4 Extracting the negative MC component by fitting curve 62
4.5 MC responses in hole-blocking SY-PPV-based PLEDs 65
4.6 MC line shape narrowing in SY-PPV-based PLEDs 67
4.7 Summary 70
PART 2: THE TRIPLET-TRIPLET ANNIHILATION PROCESS IN SY-PPV-BASED PLEDS 71
4.8 Introduction 71
4.9 Experimental section. 73
4.10 MC and MEL responses under different external applied bias 73
4.11 Normalized MC and MEL curves 75
4.12 MEL responses of SY-PPV-based PLEDs under different current density and temperature 79
4.13 The contribution of TTA process to the EL of SY-PPV-based PLEDs 82
4.14 Summary 84
CHAPTER FIVE MAGNETIC FIELD EFFECT STUDY OF THE SINGLET FISSION REACTION IN TETRACENE-BASED DIODES 85
5.1 Introduction 85
5.2 Experimental Section 86
5.3 MPC responses of ITO/PEDOT:PSS/tetracene/BCP/Al device 87
5.4 MPC and MPL responses of SF reaction 88
5.5 MPC response of tetracene/C60 PHJ-based diode 91
5.6 PL spectra of the tetracene film and tetracene/C60 bilayer film 93
5.7 Summary 96
CHAPTER SIX ANGLE-DEPENDENT MAGNETO- PHOTOCURRENT RESPONSE IN PENTACENE-BASED DIODES 97
6.1 Introduction 97
6.2 Experimental Section 99
6.3 MPC responses of ITO/PEDOT:PSS/pentacene/LiF/Al device at different different magnetic field orientation 100
6.4 The proposed mechanism for magnetic field orientation dependence of MPC 104
6.5 MPC responses of ITO/PEDOT:PSS/pentacene/C60/LiF/Al device at different different magnetic field orientation 108
6.6 MPC curve fitting analysis 114
6.7 Summary 117
CHAPTER SEVEN CONCLUSION AND FUTURE WORK 119
7.1 Conclusion 119
7.2 Future work 121
LIST OF PUBLICATIONS 140
 H. Shirakawa, E. J. Louis, Alan G. MacDiarmid, C.-K. Chiang and A. J. Heeger, “Synthesis of electrically conducting organic polymers: halogen derivatives of polyacetylene, (CH)x,” J. Chem. Soc., Chem. Commun. 0, 578 (1977).
 S. Miyata, and H. S. Nalwa, “Organic electroluminescent materials and devices,” Overseas Publishers Association, Amsterdam, The Netherlands, ISBN 9782919875108 (1997).
 J. L. Brédas, J. P. Calbert, D. A. da Silva Filho, and J. Cornil, “Organic semiconductors: A theoretical characterization of the basic parameters governing charge transport,” PNAS 99(9), 5804 (2002).
 M. Pfeiffer, K. Leo, X. Zhou, J. –S. Huang, M. Hofmann, A. Werner, J. Blochwitz-Nimoth, “Doped organic semiconductors: Physics and application in light emitting diodes,” Org. Electron. 4, 89 (2003).
 D. Braun, and A. J. Heeger, “Visible light emission from semiconducting polymer diodes,” Appl. Phys. Lett. 58, 1982 (1991).
 J. Peet, J. Y. Kim, N. E. Coates, W. L. Ma, D. Moses, A. J. Heeger & G. C. Bazan, “Efficiency enhancement in low-bandgap polymer solar cells by processing with alkane dithiols,” Nat. Mater. 6, 497 (2007).
 J. Y. Kim , K. H. Lee, N. E. Coates, D. Moses, T. Q. Nguyen, M. Dante, A. J. Heeger, “Efficient Tandem Polymer Solar Cells Fabricated by All-Solution Processing,” Science 13, 222 (2007).
 Z. Bao, and J. Locklin, “Organic Field-Effect Transistors,” CRC Press, Boca Raton, ISBN 9780849380808 (2007).
 Z. -H. Xiong, D. Wu, Z. V. Vardeny, and J. Shi, “Giant magnetoresistance in organic spin-valves,” Nature 427, 821 (2004)
 R. Lin, F. -J. Wang, M. Wohlgenannt , C. -Y. He, X. -F. Zhai, and Y. Suzuki, “Organic spin-valves based on fullerene C60,” Synth. Met. 161, 553 (2011).
 J. Shinar, and R. Shinar, “Organic light-emitting devices (OLEDs) and OLED-based chemical and biological sensors: an overview,” J. Phys. D: Appl. Phys. 41, 133001 (2008).
 R. H. Friend , R. W. Gymer, A. B. Holmes, J. H. Burroughes, R. N. Marks, C. Taliani, D. D. C. Bradley, D. A. Dos Santos, J. L. Brédas, M. Lögdlund, and W. R. Salaneck, “Electroluminescence in conjugated polymers,” Nature 397, 121 (1999).
 M. Pope, and C. E. Swenberg, “Electronic processes in organic crystals,” 2nd edition, Oxford university press, ISBN 9780195129632 (1999).
 A. Bernanose, “Electroluminescence of organic compound,” Br. J. Appl. Phys. 6, 64 (1955).
 M. Pope, H. P. Kallman, and P. Magnante, “Electroluminescence in organic crystal,” J. Chem. Phys. 38, 2042 (1963).
 W. Helfrich, and W. G. Schneider, “Recombination radiation in anthracene crystals,” Phys. Rev. Lett. 14, 229 (1965).
 C. -W. Tang, and S. A. VanSlyke, “Organic electroluminescent diodes,” Appl. Phys. Lett. 51, 913 (1987).
 J. Burroughes, D. Bradley, A. Brown, R. Marks, K. Mackay, R. Friend, P. Burns, and A. Holmes, “Light-emitting diodes based on conjugated polymers,” Nature 347, 539 (1990).
 M. A. Abkowitz, H. A. Mizes and J. S. Facci, “Emission limited injection by thermally assisted tunneling into a trap-free transport polymer,” Appl. Phys. Lett. 66(10), 1288 (1995).
 V. I. Arkhipov, E. V. Emelianova, Y. H. Tak, and H. Bässler, “Charge injection into light-emitting diodes: Theory and experiment,” J. Appl. Phys. 84, 848 (1998).
 J. C. Scott, “Metal-organic interface and charge injection in organic electronic devices,” J. Vac. Sci. Technol. A 21, 521 (2003).
 E. Frankevich, A. Lymarev, I. Sokolik, F. Karasz, S. Blumstengel, R. Baughman, and H. Hoerhold, “Polaron pair generation in poly(phenylene vinylenes),” Phys. Rev. B 46, 9320 (1992).
 J. Kalinowski, M. Cocchi, D. Virgili, P. Di Marco, and V. Fattori, “Magnetic field effects on emission and current in Alq3-based electroluminescent diodes,” Chem. Phys. Lett. 380, 710 (2003).
 T. D. Nguyen, Y. Sheng, J. Rybicki, and M. Wohlgenannt, “Magnetic field-effects in bipolar, almost hole-only and almost electron-only tris-(8-hydroxyquinoline) aluminum devices,” Phys. Rev. B 77, 235209 (2008).
 P. Desai, P. Shakya, T. Kreouzis, and W. P. Gillin, “Magnetoresistance in organic light-emitting diode structures under illumination,” Phys. Rev. B 76, 235202 (2007).
 Ö. Mermer, G. Veeraraghavan, T. L. Francis, and M. Wohlgenannt, “Large magnetoresistance at room-temperature in small-molecular-weight organic semiconductor sandwich devices,” Solid State Commun. 134, 631 (2005).
 N. J. Turro, “Modern molecular photochemistry,” Benjamin/Cummings Pub. Co., ISBN 9780805393538 (1978).
 M. Born, and R. Oppenheimer, “Quantum theory of molecules,” Ann. Phys. 84, 0457 (1927).
 A. P. Monkman, H. D. I. Burrows, Hamblett, S. Navarathnam, M. Svensson, and M. R. Andersson, “The effect of conjugation length on triplet energies, electron delocalization and electron-electron correlation in soluble polythiophenes,” J. Chem. Phys. 115, 9046 (2001).
 Guillet, “Polymer Photophysics and Photochemistry,” Cambridge University Press, ISBN 9780521235068 (1985).
 A. Kohler, J. S. Wilson, R. Friend, M. Al-Suti, A. Gerhard, and H. Bassler, “The singlet triplet energy gap in organic and Pt-containing phenylene ethynylene polymers and monomers,” J. Chem. Phys. 116, 9457 (2002).
 S. -S. Sun, and L. R. Dalton, “Introduction to Organic Electronic and Optoelectronic Materials and Devices,” CRC Press, ISBN 9780849392849 (2008).
 M. Fox, “Optical properties of solids,” Oxford University Press, ISBN 9780199573370 (2010).
 W. Su, J. Schrieffer, and A. Heeger, “Soliton Excitations in Polyacetylene,” Phys. Rev. B 22, 2099 (1980).
 V. Coropceanu, J. Cornil, D. A. da Silva Filho, Y. Olivier, R. Silbey, and J. L. Brédas, “Charge transport in organic semiconductors,” Chem. Rev. 107(4), 926 (2007).
 R. S. Mulliken, “Overlap integrals and chemical binding,” J. Am. Chem. Soc. 72, 4493 (1950).
 R. S. Mulliken, and W. B. Pearson, “Molecular Complexes,” Wiley Publishers, ISBN 9780471623700 (1969).
 R. Foster, “Charge Transfer Complexes,” Academic Press, ISBN 9780122626500 (1969).
 R. S. Mulliken, “Molecular compounds and their spectra. II,” J. Am. Chem. Soc. 74, 811 (1952).
 R. S. Mulliken, “Molecular compounds and their spectra. III. The interaction of electron donors and acceptors,” J. Phys. Chem. 56, 801 (1952).
 Ö. Mermer, G. Veeraraghavan, T. L. Francis, Y. Sheng, T. D. Nguyen, M. Wohlgenannt, A. Köhler, M. K. Al-Suti, and M. S. Khan, “Large magnetoresistance in nonmagnetic π-conjugated semiconductor thin film devices,” Phys. Rev. B 72, 205202 (2005).
 J. J. Martin, J. D. Bergeson, V. N. Prigodin, and A. J. Epstein, “Magnetoresistance for organic semiconductors: small molecule,oligomer, conjugated polymer, and non-conjugated polymer,” Synth. Met. 160, 291 (2010).
 A. H. Davis, and K. Bussmann, “Large magnetic field effect in organic light emitting diodes based on tris(8-hydroxyquinoline aluminium) (Alq3)/N,N-Di(naphthalen-1-yl)-N,N diphenyl-benzidine (NPB) bilayers,” J. Vac. Sci. Technol. A 22, 1885 (2004).
 F. J. Wang, H. Bӓssler, and Z. V. Vardeny, “Magnetic field effects in π-conjugated polymer-fullerene blends: evidence for multiple components,” Phys. Rev. Lett. 101, 236805 (2008).
 S. Yin, S. -J. Xie, K. Gao, and X. -R. Wang, “Temperature effect on spin relaxation in organic semiconductors,” Synth. Met. 165, 35 (2013).
 R. C. Johnson, R. E. Merrifield, P. Avakian, and R. B. Flippen, “Effects of magnetic fields on the mutual annihilation of triplet excitons in molecular crystals,” Phys. Rev. Lett. 19(6), 285 (1967).
 R. P. Groff, A. Suna, P. Avakian, and R. E. Merrifield, “Magnetic hyperfine modulation of dye-sensitized delayed fluorescence in organic crystals,” Phys. Rev. B 9(6), 2655 (1974).
 E. L. Frankevich, A. A. Lymarev, and I. A. Sokolik, “CT-excitons and magnetic field effect in polydiacetylene crystals,” Chem. Phys. 162, 1 (1992).
 J. Kalinowski, J. Szmytkowski, and W. Stampor, “Magnetic hyperfine modulation of charge photogeneration in solid films on Alq3,” Chem. Phys. Lett. 378, 380 (2003).
 Y. Wu, Z. Xu, B. Hu, and J. Howe, “Tuning magnetoresistance and magnetic-field-dependent electroluminescence through mixing a strong spin orbital coupling molecule and a weak spin orbital coupling polymer,” Phys. Rev. B 75, 035214 (2007).
 Y. Sheng, T. D. Nguyen, G. Veeraraghavan, Ö. Mermer, and M. Wohlgenannt, “Effect of spin-orbit coupling on magnetoresistance in organic semiconductors,” Phys. Rev. B 75, 035202 (2007).
 T. L. Francis, Ö. Mermer, G. Veeraraghavan, and M.Wohlgenannt, “Large magnetoresistance at room temperature in semiconducting polymer sandwich devices,” New J. Phys. 6, 185 (2004).
 Y. Sheng, T. D. Nguyen, G. Veeraraghavan, Ö. Mermer, M. Wohlgenannt, S. Qiu, and U. Scherf, “Hyperfine interaction and magnetoresistance in organic semiconductors,” Phys. Rev. B 74, 045213 (2006).
 S. Banerjee, D. Bülz, d. Reuter, K. Hiller, D. R. T. Zahn, and G. Salvan, “Light-induced magnetoresistance in solution-processed planar hybrid devices measured under ambient conditions,” Beilstein J. Nanotechnol. 8, 1502 (2017).
 B. Hu, and Y. Wu, “Tuning magnetoresistance between positive and negative values in organic semiconductors,” Nat. Mater. 6, 985 (2007).
 F. L. Bloom, W. Wagemans, M. Kemerink, and B. Koopmans, Correspondence of the sign change in organic magnetoresistance with the onset of bipolar charge transport, Appl. Phys. Lett. 93, 263302 (2008).
 F. L. Bloom, W. Wagemans, and B. Koopmans, “Temperature dependent sign change of the organic magnetoresstance effect,” J. Appl. Phys 103, 07F320 (2008).
 S. Majumdar, H. S. Majumdar, H. Aarnio, D. Vanderzande, R. Laiho, and R. Österbacka, “Role of electron-hole pair formation in organic magnetoresistance,” Phys. Rev. B 79, 201202(R) (2009).
 P. A. Bobbert, T. D. Nguyen, F. W. A. van Oost, B. Koopmans, and M. Wohlgenannt, “Bipolaron mechanism for organic magnetoresistance,” Phys. Rev. Lett. 99, 216801 (2007).
 V. N. Prigodin, J. D. Bergeson, D. M. Lincoln, and A. J. Epstein, “Anomalous Room Temperature Magnetoresistance in Organic Semiconductor,” Synth. Met. 156, 757 (2006).
 M. N. Bussac, and L. Zuppiroli, “Bipolaron singlet and triplet states in disordered conducting polymers,” Phys. Rev. B 47, 5493 (1993).
 F. L. Bloom, M. Kemerink, W. Wagemans, and B. Koopmans, “Sign inversion of magnetoresistance in injection limited organic devices,” Phys. Rev. Lett. 103, 066601 (2009).
 W. J. Baker, D. R. McCamey, K. J. van Schooten, J. M. Lupton, and C. Boehme, “Differentiation between polaron-pair and triplet-exciton polaron spin-dependent mechanisms in organic light-emitting diodes by coherent spin beating,” Phys. Rev. B 84, 165205 (2011).
 T. D. Nguyen, B. R. Gautam, E. Ehrenfreund, and Z. V. Vardeny, “Magnetoconductance Response in Unipolar and Bipolar Organic Diodes at Ultrasmall Fields,” Phys. Rev. Lett. 105, 166804 (2010).
 V. N. Prigodin, and A. J. Epstein, “Spin dynamics control of recombination current in organic semiconductors,” Synth. Met. 160, 244 (2010).
 W. Wagemans, and B. Koopmans, “Spin transport and magnetoresistance in organic semiconductors,” Phys. Status Solidi B 248(5), 1029 (2011).
 S. A. Bagnich, U. Niedermeier, C. Melzer, W. Sarfert, and H. von Seggern, “Electron-hole pair mechanism for the magnetic field effect in organic light emitting diodes based on poly(paraphenylene vinylene),” J. Appl. Phys. 106, 113702 (2009).
 P. Desai, P. Shakya, T. Kreouzis, W. P. Gillin, N. A. Morley, M. R. J. and Gibbs, “Magnetoresistance and efficiency measurements of Alq3-based OLEDs,” Phys. Rev. B 75, 094423 (2007).
 V. Ern, and R. E. Merrifield, “Magnetic field effect on tripet exciton quenching in organic crystals,” Phys. Rev. Lett. 21, 609 (1968).
 B. Hu, L. Yan, and M. Shao, “Magnetic-field effects in organic semiconducting materials and devices,” Adv. Mater. 21, 1500 (2009).
 Z. Xu, and B. Hu, “Photovoltaic processes of singlet states in organic solar cells,” Adv. Funct. Mater. 18, 2611 (2008).
 R. Johnson, and R. E. Merrifield, “Effects of magnetic fields on the mutual annihilation of triplet excitons in anthracene crystals,” Phys. Rev. B 1, 896 (1970).
 R. E. Merrifield, “Theory of magnetic field effects on the mutual annihilation of triplet excitons,” J. Chem. Phys. 48, 4318 (1968).
 J. Schellekens, W. Wagemans, S. P. Kersten, P. A. Bobbert, and B. Koopmans, “Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors,” Phys. Rev. B 84, 075204 (2011).
 Y. Zhang, and S. R. Forrest, “Triplets contribute to both an increase and loss in fluorescent yield in organic light emitting diodes.” Phys. Rev. Lett. 108, 267404 (2012).
 Y. Zhang, R. Liu, Y. -L. Lei, and Z. -H. Xiong, “Low temperature magnetic field effects in Alq3-based organic light emitting diodes,” Appl. Phys. Lett. 94, 083307 (2009).
 S. Singh, W. Jones, W. Siebrand, B. Stoicheff, and W. Schneider, “Laser generation of excitons and fluorescence in anthracene crystals,” J. Chem. Phys. 42, 330 (1965)
 C. Swenberg, and W. Stacy, “Bimolecular radiationless transitions in crystalline tetracene,” Chem. Phys. Lett. 2, 327 (1968).
 N. Geacintov, M. Pope, and F. Vogel, “Effect of magnetic field on the fluorescence of tetracene crystals: exciton fission,” Phys. Rev. Lett. 22, 593 (1969).
 J. Kalinowski, and J. Godlewski, “Magnetic field effect on recombination radiation in tetracene crystal,” Chem. Phys. Lett. 36, 345 (1975).
 A. Suna, “Kinematics of exciton-exciton annihilation in molecular crystals,” Phys. Rev. B 1, 1716 (1970).
 R. P. Groff, P. Avakian, and R. E. Merrifield, “Coexistence of exciton fission and fusion in tetracene crystals,” Phys. Rev. B 1, 815 (1970).
 H. Bouchriha, V. Ern, J. L. Fave, C. Guthmann, and M. Schott, “Magnetic field dependence of singlet exciton fission and fluorescence in crystalline tetracene at 300 K,” J. de Physique 39(3), 257 (1978).
 G. Klein, and R. Voltz, “Formation and decay of superexcited states in dense organic matter under high energy radiation,” Int. J. Radiat. Phys. Chem. 7, 155 (1975).
 M. Hanna, and A. Nozik, “Solar conversion efficiency of photovoltaic and photoelectrolysis cells with carrier multiplication absorbers,” J. Appl. Phys. 100, 074510 (2006).
 J. Zirzlmeier, D. Lehnherr, P. B. Coto, E. T. Chernick, R. Casillas, B. S. Basel, M. Thoss, R. R. Tykwinski, and D. M. Guldi, “Singlet fission in pentacene dimmers,” PNAS 112, 5325 (2015).
 N. Monahan, and X. -Y. Zhu, “Charge transfer-mediated singlet fission,” Ann. Rev. Phys. Chem. 66, 601 (2015).
 U. E. Steiner, and T. Ulrich, “Magnetic field effects in chemical kinetics and related phenomena,” Chem. Rev. 89, 51 (1989).
 T. D. Nguyen, G. Hukic-Markosian, F. Wang, L. Wojcik, X.-G. Li, E. Ehrenfreund, and Z.V. Vardeny, “Isotope effect in spin response of π-conjugated polymer films and devices,” Nat. Mater. 9, 345 (2010).
 N. Rolfe, P. Desai, P. Shakya, T. Kreouzis, and W. P. Gillin, “Separating the roles of electrons and holes in the organic magnetoresistance of aluminum tris(8-hydroxyquinoline) organic light emitting diodes,” J. Appl. Phys. 104, 083703 (2008).
 P. Bobbert, T. D. Nguyen, W. Wagemans, F. van Oost, B. Koopmans, and M. Wohlgenannt, “Spin relaxation and magnetoresistance in disordered organic semiconductors,” Synth. Met. 160, 223 (2010).
 A. J. Schellekens, “Exploring spin interactions in organic semiconductors,” Master’s thesis, Eindhoven University of Technology (2010).
 S. P. Kersten, A. J. Schellekens, B. Koopmans, and P. A. Bobbert. “Magnetic-field dependence of the electroluminescence of organic light-emitting diodes: A competition between exciton formation and spin mixing,” Phys. Rev. Lett. 106, 197402 (2011).
 M. Vogel, S. Doka, Ch. Breyer, M. Ch. Lux-Steiner, K. Fostiropoulos, “On the function of a bathocuproine buffer layer in organic photovoltaic cells,” Appl. Phys. Lett. 89, 163501 (2006).
 P. J. Jadhav, P. R. Brown, N. Thompson, B. Wunsch, A. Mohanty, S. R. Yost, E. Hontz, T. V. Voorhis, M. G. Bawendi, V. Bulović and M. A. Baldo, “Triplet exciton dissociation in singlet exciton fission photovoltaic,” Adv. Mater. 24, 6169 (2012).
 W. -S. Huang, T. -H. Lee, T. -F. Guo, J. C. A. Huang, and T. -C. Wen, “Identifying the magnetoconductance responses by the induced charge transfer complex states in pentacene-based diodes,” Appl. Phys. Lett. 101, 053307 (2012).
 T. D. Nguyen, Y. Sheng, J. Rybicki, G. Veeraraghavan, and M. Wohlgenannt, “Magnetoresistance in π-conjugated organic sandwich devices with varying hyperfine and spin–orbit coupling strengths, and varying dopant concentrations,” J. Mater. Chem. 17, 1995 (2007).
 T. Reichert, and T. P. I. Saragi, “Photoinduced magnetoresistance in organic field-effect transistors,” Appl. Phys Lett. 98, 063307 (2011).
 T. -H. Lee, B. Hu, C. -L. Tsai, R. -S. Guan, T. -C. Wen, T. -F. Guo, and J. C. A. Huang, “The magnetoconductance responses in polymer photovoltaic devices,” Org. Electron. 11, 677 (2010).
 W. P. Gillin, S. Zhang, N. J. Rolfe, P. Desai, P. Shakya, A. J. Drew, and T. Kreouzis, “Determining the influence of excited states on current transport in organic light emitting diodes using magnetic field perturbation,” Phys. Rev. B 82, 195208 (2010).
 P. Desai, P. Shakya, T. Kreouzis, and W. P. Gillin, “The role of magnetic fields on the transport and efficiency of aluminium tris(8-hydroxyquinoline) based organic light emitting diodes,” J. Appl. Phys. 102, 073710 (2007).
 Y. -L. Lei, Q. -L. Song, Y. Zhang, P. Chen, R. Liu, Q. -M. Zhang, and Z. -H. Xiong, “Magnetoconductance of polymer-fullerene bulk heterojunction solar cells,” Org. Electron. 10, 1288 (2009).
 J. D. Bergeson, V. N. Prigodin, D. M. Lincoln, and A. J. Epstein, “Inversion of magnetoresistance in organic semiconductors,” Phys. Rev. Lett. 100, 067201 (2008).
 Y. -L. Lei, Q. -M. Zhang, L.- J. Chen, X. -H. Yang, and Z. -H. Xiong, “Identifying the roles of the excited states on the magnetoconductance in tris-(8-hydroxyquinolinato) aluminium,” Appl. Phys. Lett. 102, 113301 (2013).
 S. -J. Zhang, N. J. Rolfe, P. Desai, P. Shakya, A. J. Drew, T. Kreouzis, and W. P. Gillin, Modeling of positive and negative organic magnetoresistance in organic light-emiting diodes,” Phys. Rev. B 86, 075206 (2012).
 M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson, and S. R. Forrest, “Highly efficient phosphorescent emission from organic electroluminescent devices,” Nature 395, 151 (1998).
 Q. -S. Zhang, J. Li, K. Shizu, S. Huang, S. Hirata, H. Miyazaki, and C. Adachi, “Design of efficient thermally activated delayed fluorescence materials for pure blue organic light emitting diodes,” J. Am. Chem. Soc. 134(3), 14706 (2012).
 H. Uoyama, K. Goushi, K. Shizu, H. Nomura, and C. Adachi, “Highly efficient organic light-emitting diodes from delayed fluorescence,” Nature 492(7428), 234 (2012).
 H. Tanaka, K. Shizu, H. Miyazaki, and C. Adachi, “Efficient green thermally activated delayed fluorescence (TADF) from a phenoxazine-triphenyltriazine (PXZ-TRZ) derivative,” Chem. Commun. 48, 11392 (2012).
 A. Endo, M. Ogasawara, A. Takahashi, D. Yokoyama, Y. Kato, and C. Adachi, “Thermally activated delayed fluorescence from Sn4+-porphyrin complexes and their application to organic light emitting diodes – A novel mechanism for electroluminescence,” Adv. Mater. 21, 4802 (2009).
 H. Sternlicht, G. C. Nieman, and G. W. Robinson, “Triplet-triplet annihilation and delayed fluorescence in molecular aggregates,” J. Chem. Phys. 3, 1326 (1963).
 J. Wilkinson, A. H. Davis, K. Bussmann, and J. P. Long, “Evidence for charge-carrier mediated magnetic-field modulation of electroluminescence in organic light-emitting diodes,” Appl. Phys. Lett. 86, 111109 (2005).
 P. Chen, Q. -L. Song, W. C. H. Choy, B. -F. Ding, Y. -L. Liu, and Z. -H. Xiong, “A possible mechanism to tune magnetoelectroluminescence in organic light-emitting diodes through adjusting the triplet exciton density,” Appl. Phys. Lett. 99, 143305 (2011).
 V. Jankus, E. W. Snedden, D. W. Bright, V. L. Whittle, J. A. G. Williams, and A. Monkman, “Energy upconversion via triplet fusion in super yellow PPV films doped with palladium tetraphenyltetrabenzoporphyrin: A comprehensive investigation of exciton dynamics,” Adv. Funct. Mater. 23, 384 (2013).
 Z. -H. Xu, Y. Wu, and B. Hu, “Dissociation processes of singlet and triplet excitons in organic photovoltaic cells,” Appl. Phys. Lett. 89, 131116 (2006).
 O. V. Mikhnenko, P. W. M. Blom, and T. Q. Nguyen, “Exciton diffusion in organic semiconductors,” Energy Environ. Sci. 8, 1867 (2015).
 T. Khan, and A. Datta, “Enhanced fluorescence with nanosecond dynamics in the solid state of metal ion complexes of alkoxy salophens,” Phys. Chem. Chem. Phys. 19, 30120 (2017).
 Y. Yamada, H. Yasuda, T. Tayagaki, and Y. Kanemitsu, “Temperature dependence of photoluminescence spectra of nanodoped and electron-doped SrTiO3: Crossover from Auger recombination to single-carrier trapping,” Phys. Rev. Lett. 102, 247401 (2009).
 H. Schömig, S. Halm, A. Forchel, G. Bacher, J. Off, and F. Scholz, “Probing individual localization centers in an InGaN/GaN quantum well,” Phys. Rev. Lett. 92, 106802 (2004).
 K. Szendrei, M. Speirs, W. Gomulya, D. Jarzab, M. Manca, O.V. Mikhnenko, M. Yarema, B.J. Kooi, W. Heiss, and M.A. Loi, “Exploring the origin of the temperature-dependent behavior of PbS nanocrystal thin films and solar cells,” Adv. Funct. Mater. 22, 1598 (2012).
 P. Chen, Z -H. Xiong, Q. -M. Peng, J. W. Bai, S. -T. Zhang, and F. Li, “Magneto-electroluminescence as a tool to discern the origin of delayed fluorescence: Reverse intersystem crossing or triplet-triplet annihilation?,” Adv. Opt. Mater. 2, 142 (2016).
 R. Liu, Y. Zhang, Y. -L. Lei, P. Chen, and Z. -H. Xiong, “Magnetic field dependent triplet-triplet annihilation in Alq3-based organic light emitting diodes at different temperatures,” J. Appl. Phys. 105, 093719 (2009).
 R. E. Merrifield, P. Avakian, and R.P. Groff, “Fission of singlet excitons into pairs of triplet excitons in tetracene crystals,” Chem. Phys. Lett. 3(3), 155 (1969).
 R. E. Merrifield, “Magnetic effects on triplet exciton interactions,” Pure and Appl. Chem. 27(3), 481 (1971).
 T. -C. Wu, N. J. Thompson, D. N. Congreve, E. Hontz, S. R. Yost, T. V. Voorhis, and M. A. Baldo, “Singlet fission efficiency in tetracene-based organic solar cells,” Appl. Phys. Lett. 104, 193901 (2014).
 D. Vacar, E. S. Maniloff, D. W. McBranch, and A. J. Heeger, “Charge-transfer range for photoexcitations in conjugated polymer/fullerene bilayers and blends,” Phys. Rev. B 56, 4573 (1997).
 H. L. Stern, A. Cheminal, S. R. Yost, K. Broch, S. L. Bayliss, K. Chen, M. Tabachnyk, K. Thorley, N. Greenham, J. M. Hodgkiss, J. Anthony, M. H. Gordon, A. J. Musser, A. Rao, and R. H. Friend, “Vibronically coherent ultrafast triplet-pair formation and subsequent thermally activated dissociation control efficient endothermic singlet fission,” Nat. Chem. 9, 1205 (2017).
 S. R. Yost, J. Lee, M. W. B. Wilson, T. Wu, D. P. McMahon, R. R. Parkhurst, N. J. Thompson, D. N. Congreve, A. Rao, K. Johnson, M. Y. Sfeir, M. G. Bawendi, T. M. Swager, R. H. Friend, M. A. Baldo, and T. V. Voorhis, “A transferable model for singlet-fission kinetics,” Nat. Chem. 6, 492 (2014).
 J. Li, Z. -H. Chen, Y. -L. Lei, Z. -H. Xiong, and Y. Zhang, “Competition between singlet exciton fission, radiation, and dissociation measured in rubrene-doped amorphous films,” Synth. Met. 207, 13 (2015).
 C. A. Nelson, N. R. Monahan, and X. -Y. Zhu, “Exceeding the Shockley–Queisser limit in solar energy conversion,” Energy Environ. Sci. 6, 3508 (2013).
 R. Wiltschko, and W. Wiltschko, “The Magnetite-based receptors in the beak birds and their role in avian naviation,” J. Comp. Physiol. A 199, 89 (2013).
 A. Günther, A. Einwich, E. Sjulstok, R. Feederlem P. Bolte, K. W. Koch, I. A. Solov’yov, and H. Mouritsen, “Double-cone localization and seasonal expression pattern suggest a role in magnetoreception for European Robi Crytochrome 4,” Current Biology 28, 211 (2018).
 G. Veeraraghavan, T. D. Nguyen, Y. Sheng, Ö. Mermer, and M. Wohlgenannt, “An 8 x 8 pixelarray pen-input OLED screen based on organic magnetoresistance,” IEEE Trans. Electron. Devices 54, 1571 (2007).
 W. Wagemans, A. J. Schellekens, M. Kemper, F. L. Bloom, P. A. Bobbert, and B. Koopmans, “Spin-spin interactions in organic magnetoresistance probed by angle-dependent measurement,” Phys. Rev. Lett. 106, 196802 (2011).
 T. D. Nguyen, E. Ehrenfreund, and Z. V. Vardeny, “Organic magneto-resistance at small magnetic fields; compass effect,” Org. Electron. 14, 1852 (2013).
 W. -S. Huang, Z. -R. Xu, K. -C. Chen, T. -F. Guo, J. C. A. Huang, and T. -C. Wen, “Modulations in the line shapes of magnetoconductance curves for diodes of pentacene:fullerene charge transfer complexes,” Org. Electron. 15, 3076 (2014).
 W. Chang, D. N. Congreve, E. Hontz, M .E. Bahlke, D. P. McMahon, S. Reineke, T. -C. Wu, V. Bulović, T. V. Voorhis, and M.A. Baldo, “Spin-dependent charge transfer state design rules in organic photovoltaics,” Nat. Commun. 6, 6415 (2015).
 L. He, M. -X. Li, A. Ubas, and B. Hu, “Magnetophotoluminescence line-shape narrowing through interactions between excited states in organic semiconducting materials,” Phys. Rev. B 89, 155304 (2014).
 M. Radaoui, M. A. Saidani, A. B. Fredj, S. Romdhane, M. Havlicek, D. A. Egbe, N. S. Sariciftci, and H. Bouchriha, “Role of recombination, dissociation, and competition between exciton-charge reaction in magnetoconductance of polymeric semiconductor device,” J. Appl. Phys. 116,183901 (2014).
 N. J. Harmon, and M. E. Flatté, “Effect of spin-spin interactions on magnetoresistance in disordered organic semiconductors,” Phys. Rev. B 85, 245213 (2012).