Interfacial Charge Transfer States in Condensed Phase Systems

Literature Cited

1. Walzer K, Maennig B, Pfeiffer M, Leo K. 1.  2007. Highly efficient organic devices based on electrically doped transport layers. Chem. Rev. 107:1233–71 [Google Scholar]
2. Lüssem B, Riede M, Leo K. 2.  2013. Doping of organic semiconductors. Phys. Status Solidi A 210:9–43 [Google Scholar]
3. Verhoeven J. 3.  1996. Glossary of terms used in photochemistry (IUPAC recommendations 1996). Pure Appl. Chem. 68:2223–86 [Google Scholar]
4. Jenekhe SA. 4.  1995. Excited-state complexes of conjugated polymers. Adv. Mater. 7:309–11 [Google Scholar]
5. Morteani AC, Dhoot AS, Kim JS, Silva C, Greenham NC. 5.  et al. 2003. Barrier-free electron–hole capture in polymer blend heterojunction light-emitting diodes. Adv. Mater. 15:1708–12 [Google Scholar]
6. Turro NJ. 6.  1991. Modern molecular photochemistry Sausalito, CA: Univ. Sci. Books [Google Scholar]
7. Mulliken RS. 7.  1952. Molecular compounds and their spectra. III. The interaction of electron donors and acceptors. J. Phys. Chem. 56:801–22 [Google Scholar]
8. Brédas JL, Norton JE, Cornil J, Coropceanu V. 8.  2009. Molecular understanding of organic solar cells: the challenges. Acc. Chem. Res. 42:1691–99 [Google Scholar]
9. Deibel C, Strobel T, Dyakonov V. 9.  2010. Role of the charge transfer state in organic donor–acceptor solar cells. Adv. Mater. 22:4097–111 [Google Scholar]
10. Liu Y, Zhao J, Li Z, Mu C, Ma W. 10.  et al. 2014. Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells. Nat. Commun. 5:5293 [Google Scholar]
11. Che X, Xiao X, Zimmerman JD, Fan D, Forrest SR. 11.  2014. High-efficiency, vacuum-deposited, small-molecule organic tandem and triple-junction photovoltaic cells. Adv. Energy Mater. 4181400568 [Google Scholar]
12. Goris L, Haenen K, Nesládek M, Wagner P, Vanderzande D. 12.  et al. 2005. Absorption phenomena in organic thin films for solar cell applications investigated by photothermal deflection spectroscopy. J. Mater. Sci. 40:1413–18 [Google Scholar]
13. Goris L, Poruba A, Hodákova L, Vaněček M, Haenen K. 13.  et al. 2006. Observation of the subgap optical absorption in polymer–fullerene blend solar cells. Appl. Phys. Lett. 88:052113 [Google Scholar]
14. Vandewal K, Gadisa A, Oosterbaan WD, Bertho S, Banishoeib F. 14.  et al. 2008. The relation between open-circuit voltage and the onset of photocurrent generation by charge-transfer absorption in polymer: fullerene bulk heterojunction solar cells. Adv. Funct. Mater. 18:2064–70 [Google Scholar]
15. Loi MA, Toffanin S, Muccini M, Forster M, Scherf U, Scharber M. 15.  2007. Charge transfer excitons in bulk heterojunctions of a polyfluorene copolymer and a fullerene derivative. Adv. Funct. Mater. 17:2111–16 [Google Scholar]
16. Hallermann M, Haneder S, Da Como E. 16.  2008. Charge-transfer states in conjugated polymer/fullerene blends: below-gap weakly bound excitons for polymer photovoltaics. Appl. Phys. Lett. 93:053307 [Google Scholar]
17. Tvingstedt K, Vandewal K, Gadisa A, Zhang F, Manca J, Inganäs O. 17.  2009. Electroluminescence from charge transfer states in polymer solar cells. J. Am. Chem. Soc. 131:11819–24 [Google Scholar]
18. Jarzab D, Cordella F, Gao J, Scharber M, Egelhaaf HJ, Loi MA. 18.  2011. Low-temperature behaviour of charge transfer excitons in narrow-bandgap polymer-based bulk heterojunctions. Adv. Energy Mater. 1:604–9 [Google Scholar]
19. Vandewal K, Albrecht S, Hoke ET, Graham KR, Widmer J. 19.  et al. 2013. Efficient charge generation by relaxed charge-transfer states at organic interfaces. Nat. Mater. 13:63–68 [Google Scholar]
20. Vandewal K, Tvingstedt K, Gadisa A, Inganäs O, Manca JV. 20.  2009. On the origin of the open-circuit voltage of polymer–fullerene solar cells. Nat. Mater. 8:904–9 [Google Scholar]
21. Vandewal K, Albrecht S, Hoke ET, Graham KR, Widmer J. 21.  et al. 2014. Efficient charge generation by relaxed charge-transfer states at organic interfaces. Nat. Mater. 13:63–68 [Google Scholar]
22. Bruevich V, Makhmutov TS, Elizarov S, Nechvolodova E, Paraschuk DY. 22.  2007. Raman spectroscopy of intermolecular charge transfer complex between a conjugated polymer and an organic acceptor molecule. J. Chem. Phys. 127:104905 [Google Scholar]
23. Goushi K, Adachi C. 23.  2012. Efficient organic light-emitting diodes through up-conversion from triplet to singlet excited states of exciplexes. Appl. Phys. Lett. 101:023306 [Google Scholar]
24. Liu XK, Chen Z, Zheng CJ, Liu CL, Lee CS. 24.  et al. 2015. Prediction and design of efficient exciplex emitters for high-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes. Adv. Mater. 27:2378–83 [Google Scholar]
25. Zhu XY, Monahan NR, Gong Z, Zhu H, Williams K, Nelson CA. 25.  2015. Charge transfer excitons at van der Waals interfaces. J. Am. Chem. Soc. 137:8313–20 [Google Scholar]
26. Duncan WR, Prezhdo OV. 26.  2007. Theoretical studies of photoinduced electron transfer in dye-sensitized TiO₂.. Annu. Rev. Phys. Chem. 58:143–84 [Google Scholar]
27. Haeldermans I, Vandewal K, Oosterbaan W, Gadisa A, D’Haen J. 27.  et al. 2008. Ground-state charge-transfer complex formation in hybrid poly(3-hexyl thiophene): titanium dioxide solar cells. Appl. Phys. Lett. 93:223302 [Google Scholar]
28. Bansal N, Reynolds LX, MacLachlan A, Lutz T, Ashraf RS. 28.  et al. 2013. Influence of crystallinity and energetics on charge separation in polymer–inorganic nanocomposite films for solar cells. Sci. Rep. 3:1531 [Google Scholar]
29. Piersimoni F, Schlesinger R, Benduhn J, Spoltore D, Reiter S. 29.  et al. 2015. Charge transfer absorption and emission at ZnO/organic interfaces. J. Phys. Chem. Lett. 6:500–4 [Google Scholar]
30. Tvingstedt K, Vandewal K, Zhang F, Inganäs O. 30.  2010. On the dissociation efficiency of charge transfer excitons and Frenkel excitons in organic solar cells: a luminescence quenching study. J. Phys. Chem. C 114:21824–32 [Google Scholar]
31. Würfel P, Würfel U. 31.  2009. Physics of solar cells: from basic principles to advanced concepts Weinheim, Germany: Wiley [Google Scholar]
32. Marcus R. 32.  1989. Relation between charge transfer absorption and fluorescence spectra and the inverted region. J. Phys. Chem. 93:3078–86 [Google Scholar]
33. Gould IR, Noukakis D, Gomez-Jahn L, Young RH, Goodman JL, Farid S. 33.  1993. Radiative and nonradiative electron transfer in contact radical–ion pairs. Chem. Phys. 176:439–56 [Google Scholar]
34. Vandewal K, Tvingstedt K, Gadisa A, Inganäs O, Manca JV. 34.  2010. Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells. Phys. Rev. B 81:125204 [Google Scholar]
35. Street R, Song K, Northrup J, Cowan S. 35.  2011. Photoconductivity measurements of the electronic structure of organic solar cells. Phys. Rev. B 83:165207 [Google Scholar]
36. Burke TM, Sweetnam S, Vandewal K, McGehee MD. 36.  2015. Beyond Langevin recombination: how equilibrium between free carriers and charge transfer states determines the open-circuit voltage of organic solar cells. Adv. Energy Mater. 5111500123 [Google Scholar]
37. Weller A. 37.  1982. Photoinduced electron transfer in solution: exciplex and radical ion pair formation free enthalpies and their solvent dependence. Z. Phys. Chem. 133:93–98 [Google Scholar]
38. Foster R. 38.  1969. Organic Charge-Transfer Complexes New York: Academic [Google Scholar]
39. Panda P, Veldman D, Sweelssen J, Bastiaansen JJ, Langeveld-Voss BM, Meskers SC. 39.  2007. Charge transfer absorption for π-conjugated polymers and oligomers mixed with electron acceptors. J. Phys. Chem. B 111:5076–81 [Google Scholar]
40. Konarev DV, Lyubovskaya RN, Natal’ya VD, Yudanova EI, Shulga YM. 40.  et al. 2000. Donor–acceptor complexes of fullerene C60 with organic and organometallic donors. J. Mater. Chem. 10:803–18 [Google Scholar]
41. Vandewal K, Oosterbaan WD, Bertho S, Vrindts V, Gadisa A. 41.  et al. 2009. Varying polymer crystallinity in nanofiber poly(3-alkylthiophene): PCBM solar cells: influence on charge-transfer state energy and open-circuit voltage. Appl. Phys. Lett. 95:123303 [Google Scholar]
42. Ko S, Hoke ET, Pandey L, Hong S, Mondal R. 42.  et al. 2012. Controlled conjugated backbone twisting for an increased open-circuit voltage while having a high short-circuit current in poly(hexylthiophene) derivatives. J. Am. Chem. Soc. 134:5222–32 [Google Scholar]
43. Yang B, Yi Y, Zhang CR, Aziz SG, Coropceanu V, Bredas JL. 43.  2014. Impact of electron delocalization on the nature of the charge-transfer states in model pentacene/C60 interfaces: a density functional theory study. J. Phys. Chem. C 118:27648–56 [Google Scholar]
44. Veldman D, Meskers SC, Janssen RA. 44.  2009. The energy of charge-transfer states in electron donor–acceptor blends: insight into the energy losses in organic solar cells. Adv. Funct. Mater. 19:1939–48 [Google Scholar]
45. Tietze ML, Tress W, Pfützner S, Schünemann C, Burtone L. 45.  et al. 2013. Correlation of open-circuit voltage and energy levels in zinc-phthalocyanine: C60 bulk heterojunction solar cells with varied mixing ratio. Phys. Rev. B 88:085119 [Google Scholar]
46. Bernardo B, Cheyns D, Verreet B, Schaller R, Rand B, Giebink N. 46.  2014. Delocalization and dielectric screening of charge transfer states in organic photovoltaic cells. Nat. Commun. 5:3245 [Google Scholar]
47. Piersimoni F, Chambon S, Vandewal K, Mens R, Boonen T. 47.  et al. 2011. Influence of fullerene ordering on the energy of the charge-transfer state and open-circuit voltage in polymer:fullerene solar cells. J. Phys. Chem. C 115:10873–80 [Google Scholar]
48. Guilbert AA, Schmidt M, Bruno A, Yao J, King S. 48.  et al. 2014. Spectroscopic evaluation of mixing and crystallinity of fullerenes in bulk heterojunctions. Adv. Funct. Mater. 24:6972–80 [Google Scholar]
49. Isaacs EB, Sharifzadeh S, Ma B, Neaton JB. 49.  2011. Relating trends in first-principles electronic structure and open-circuit voltage in organic photovoltaics. J. Phys. Chem. Lett. 2:2531–37 [Google Scholar]
50. Baumeier B, Andrienko D, Rohlfing M. 50.  2012. Frenkel and charge-transfer excitations in donor–acceptor complexes from many-body Green's functions theory. J. Chem. Theory Comput. 8:2790–95 [Google Scholar]
51. Scholz R, Luschtinetz R, Seifert G, Jägeler-Hoheisel T, Körner C. 51.  et al. 2013. Quantifying charge transfer energies at donor–acceptor interfaces in small-molecule solar cells with constrained DFTB and spectroscopic methods. J. Phys. Condens. Matter 25:473201 [Google Scholar]
52. Few S, Frost JM, Kirkpatrick J, Nelson J. 52.  2014. Influence of chemical structure on the charge transfer state spectrum of a polymer:fullerene complex. J. Phys. Chem. C 118:8253–61 [Google Scholar]
53. Few S, Frost JM, Nelson J. 53.  2015. Models of charge pair generation in organic solar cells. Phys. Chem. Chem. Phys. 17:2311–25 [Google Scholar]
54. Vandewal K, Himmelberger S, Salleo A. 54.  2013. Structural factors that affect the performance of organic bulk heterojunction solar cells. Macromolecules 46:6379–87 [Google Scholar]
55. Castet F, D’Avino G, Muccioli L, Cornil J, Beljonne D. 55.  2014. Charge separation energetics at organic heterojunctions: on the role of structural and electrostatic disorder. Phys. Chem. Chem. Phys. 16:20279–90 [Google Scholar]
56. McMahon DP, Cheung DL, Troisi A. 56.  2011. Why holes and electrons separate so well in polymer/fullerene photovoltaic cells. J. Phys. Chem. Lett. 2:2737–41 [Google Scholar]
57. D’Avino G, Mothy S, Muccioli L, Zannoni C, Wang L. 57.  et al. 2013. Energetics of electron–hole separation at P3HT/PCBM heterojunctions. J. Phys. Chem. C 117:12981–90 [Google Scholar]
58. Poelking C, Andrienko D. 58.  2015. Design rules for organic donor–acceptor heterojunctions: pathway for charge splitting and detrapping. J. Am. Chem. Soc. 137:6320–26 [Google Scholar]
59. Graves D, Jankus V, Dias FB, Monkman A. 59.  2014. Photophysical investigation of the thermally activated delayed emission from films of m-MTDATA:PBD exciplex. Adv. Funct. Mater. 24:2343–51 [Google Scholar]
60. Clarke TM, Durrant JR. 60.  2010. Charge photogeneration in organic solar cells. Chem. Rev. 110:6736–67 [Google Scholar]
61. Clarke TM, Ballantyne A, Shoaee S, Soon YW, Duffy W. 61.  et al. 2010. Analysis of charge photogeneration as a key determinant of photocurrent density in polymer:fullerene solar cells. Adv. Mater. 22:5287–91 [Google Scholar]
62. Dimitrov SD, Durrant JR. 62.  2013. Materials design considerations for charge generation in organic solar cells. Chem. Mater. 26:616–30 [Google Scholar]
63. Song Y, Clafton SN, Pensack RD, Kee TW, Scholes GD. 63.  2014. Vibrational coherence probes the mechanism of ultrafast electron transfer in polymer–fullerene blends. Nat. Commun. 5:4933 [Google Scholar]
64. Provencher F, Bérubé N, Parker AW, Greetham GM, Towrie M. 64.  et al. 2014. Direct observation of ultrafast long-range charge separation at polymer–fullerene heterojunctions. Nat. Commun. 5:4288 [Google Scholar]
65. Chen K, Barker AJ, Reish ME, Gordon KC, Hodgkiss JM. 65.  2013. Broadband ultrafast photoluminescence spectroscopy resolves charge photogeneration via delocalized hot excitons in polymer:fullerene photovoltaic blends. J. Am. Chem. Soc. 135:18502–12 [Google Scholar]
66. Falke SM, Rozzi CA, Brida D, Maiuri M, Amato M. 66.  et al. 2014. Coherent ultrafast charge transfer in an organic photovoltaic blend. Science 344:1001–5 [Google Scholar]
67. Coffey DC, Larson BW, Hains AW, Whitaker JB, Kopidakis N. 67.  et al. 2012. An optimal driving force for converting excitons into free carriers in excitonic solar cells. J. Phys. Chem. C 116:8916–23 [Google Scholar]
68. Ward AJ, Ruseckas A, Kareem MM, Ebenhoch B, Serrano LA. 68.  et al. 2015. The impact of driving force on electron transfer rates in photovoltaic donor–acceptor blends. Adv. Mater. 27:2496–500 [Google Scholar]
69. Marcus RA. 69.  1956. On the theory of oxidation–reduction reactions involving electron transfer. I. J. Chem. Phys. 24:966–78 [Google Scholar]
70. Ohkita H, Cook S, Astuti Y, Duffy W, Tierney S. 70.  et al. 2008. Charge carrier formation in polythiophene/fullerene blend films studied by transient absorption spectroscopy. J. Am. Chem. Soc. 130:3030–42 [Google Scholar]
71. Clarke TM, Ballantyne AM, Nelson J, Bradley DD, Durrant JR. 71.  2008. Free energy control of charge photogeneration in polythiophene/fullerene solar cells: the influence of thermal annealing on P3HT/PCBM blends. Adv. Funct. Mater. 18:4029–35 [Google Scholar]
72. Bakulin AA, Rao A, Pavelyev VG, van Loosdrecht PH, Pshenichnikov MS. 72.  et al. 2012. The role of driving energy and delocalized states for charge separation in organic semiconductors. Science 335:1340–44 [Google Scholar]
73. Tamura H, Burghardt I. 73.  2013. Ultrafast charge separation in organic photovoltaics enhanced by charge delocalization and vibronically hot exciton dissociation. J. Am. Chem. Soc. 135:16364–67 [Google Scholar]
74. Savoie BM, Rao A, Bakulin AA, Gelinas S, Movaghar B. 74.  et al. 2014. Unequal partnership: asymmetric roles of polymeric donor and fullerene acceptor in generating free charge. J. Am. Chem. Soc. 136:2876–84 [Google Scholar]
75. Gélinas S, Rao A, Kumar A, Smith SL, Chin AW. 75.  et al. 2014. Ultrafast long-range charge separation in organic semiconductor photovoltaic diodes. Science 343:512–16 [Google Scholar]
76. Barker AJ, Chen K, Hodgkiss JM. 76.  2014. Distance distributions of photogenerated charge pairs in organic photovoltaic cells. J. Am. Chem. Soc. 136:12018–26 [Google Scholar]
77. Caruso D, Troisi A. 77.  2012. Long-range exciton dissociation in organic solar cells. PNAS 109:13498–502 [Google Scholar]
78. Howard IA, Mauer R, Meister M, Laquai F. 78.  2010. Effect of morphology on ultrafast free carrier generation in polythiophene:fullerene organic solar cells. J. Am. Chem. Soc. 132:14866–76 [Google Scholar]
79. Jailaubekov AE, Willard AP, Tritsch JR, Chan WL, Sai N. 79.  et al. 2013. Hot charge-transfer excitons set the time limit for charge separation at donor/acceptor interfaces in organic photovoltaics. Nat. Mater. 12:66–73 [Google Scholar]
80. Paraecattil AA, Banerji N. 80.  2014. Charge separation pathways in a highly efficient polymer:fullerene solar cell material. J. Am. Chem. Soc. 136:1472–82 [Google Scholar]
81. Devižis A, De Jonghe-Risse J, Hany R, Nüesch FA, Jenatsch S. 81.  et al. 2015. Dissociation of charge transfer states and carriers separation in bilayer organic solar cells—a time-resolved electroabsorption spectroscopy study. J. Am. Chem. Soc. 1378192–98 [Google Scholar]
82. Burke TM, McGehee MD. 82.  2014. How high local charge carrier mobility and an energy cascade in a three-phase bulk heterojunction enable 90% quantum efficiency. Adv. Mater. 26:1923–28 [Google Scholar]
83. Deibel C, Strobel T, Dyakonov V. 83.  2009. Origin of the efficient polaron-pair dissociation in polymer–fullerene blends. Phys. Rev. Lett. 103:036402 [Google Scholar]
84. Park SH, Roy A, Beaupre S, Cho S, Coates N. 84.  et al. 2009. Bulk heterojunction solar cells with internal quantum efficiency approaching 100%. Nat. Photonics 3:297–302 [Google Scholar]
85. Vandewal K, Ma Z, Bergqvist J, Tang Z, Wang E. 85.  et al. 2012. Quantification of quantum efficiency and energy losses in low bandgap polymer:fullerene solar cells with high open-circuit voltage. Adv. Funct. Mater. 22:3480–90 [Google Scholar]
86. Bartelt JA, Beiley ZM, Hoke ET, Mateker WR, Douglas JD. 86.  et al. 2013. The importance of fullerene percolation in the mixed regions of polymer–fullerene bulk heterojunction solar cells. Adv. Energy Mater. 3:364–74 [Google Scholar]
87. Dimitrov SD, Bakulin AA, Nielsen CB, Schroeder BC, Du J. 87.  et al. 2012. On the energetic dependence of charge separation in low-band-gap polymer/fullerene blends. J. Am. Chem. Soc. 134:18189–92 [Google Scholar]
88. Hahn T, Geiger J, Blase X, Duchemin I, Niedzialek D. 88.  et al. 2015. Does excess energy assist photogeneration in an organic low-bandgap solar cell?. Adv. Funct. Mater. 25:1287–95 [Google Scholar]
89. Parkinson P, Lloyd-Hughes J, Johnston M, Herz L. 89.  2008. Efficient generation of charges via below-gap photoexcitation of polymer–fullerene blend films investigated by terahertz spectroscopy. Phys. Rev. B 78:115321 [Google Scholar]
90. Lee J, Vandewal K, Yost SR, Bahlke ME, Goris L. 90.  et al. 2010. Charge transfer state versus hot exciton dissociation in polymer–fullerene blended solar cells. J. Am. Chem. Soc. 132:11878–80 [Google Scholar]
91. Albrecht S, Vandewal K, Tumbleston JR, Fischer FS, Douglas JD. 91.  et al. 2014. On the efficiency of charge transfer state splitting in polymer:fullerene solar cells. Adv. Mater. 26:2533–39 [Google Scholar]
92. Zusan A, Vandewal K, Allendorf B, Hansen NH, Pflaum J. 92.  et al. 2014. The crucial influence of fullerene phases on photogeneration in organic bulk heterojunction solar cells. Adv. Energy Mater. 4171400922 [Google Scholar]
93. Benson-Smith JJ, Goris L, Vandewal K, Haenen K, Manca JV. 93.  et al. 2007. Formation of a ground-state charge-transfer complex in polyfluorene//[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) blend films and its role in the function of polymer/PCBM solar cells. Adv. Funct. Mater. 17:451–57 [Google Scholar]
94. Faist MA, Kirchartz T, Gong W, Ashraf RS, McCulloch I. 94.  et al. 2011. Competition between the charge transfer state and the singlet states of donor or acceptor limiting the efficiency in polymer:fullerene solar cells. J. Am. Chem. Soc. 134:685–92 [Google Scholar]
95. Ren G, Schlenker CW, Ahmed E, Subramaniyan S, Olthof S. 95.  et al. 2013. Photoinduced hole transfer becomes suppressed with diminished driving force in polymer–fullerene solar cells while electron transfer remains active. Adv. Funct. Mater. 23:1238–49 [Google Scholar]
96. Hoke ET, Vandewal K, Bartelt JA, Mateker WR, Douglas JD. 96.  et al. 2013. Recombination in polymer:fullerene solar cells with open-circuit voltages approaching and exceeding 1.0 V. Adv. Energy Mater. 3:220–30 [Google Scholar]
97. Westenhoff S, Howard IA, Hodgkiss JM, Kirov KR, Bronstein HA. 97.  et al. 2008. Charge recombination in organic photovoltaic devices with high open-circuit voltages. J. Am. Chem. Soc. 130:13653–58 [Google Scholar]
98. Schlenker CW, Chen KS, Yip HL, Li CZ, Bradshaw LR. 98.  et al. 2012. Polymer triplet energy levels need not limit photocurrent collection in organic solar cells. J. Am. Chem. Soc. 134:19661–68 [Google Scholar]
99. Rao A, Chow PC, Gélinas S, Schlenker CW, Li CZ. 99.  et al. 2013. The role of spin in the kinetic control of recombination in organic photovoltaics. Nature 500:435–39 [Google Scholar]
100. Chang W, Congreve DN, Hontz E, Bahlke ME, McMahon DP. 100.  et al. 2015. Spin-dependent charge transfer state design rules in organic photovoltaics. Nat. Commun. 6:6415 [Google Scholar]
101. Ma Z, Sun W, Himmelberger S, Vandewal K, Tang Z. 101.  et al. 2014. Structure–property relationships of oligothiophene–isoindigo polymers for efficient bulk-heterojunction solar cells. Energy Environ. Sci. 7:361–69 [Google Scholar]
102. Bredas JL. 102.  2014. Mind the gap. ! Mater. Horiz. 1:17–19 [Google Scholar]
103. Di Nuzzo D, Wetzelaer GJA, Bouwer RK, Gevaerts VS, Meskers SC. 103.  et al. 2013. Simultaneous open-circuit voltage enhancement and short-circuit current loss in polymer:fullerene solar cells correlated by reduced quantum efficiency for photoinduced electron transfer. Adv. Energy Mater. 3:85–94 [Google Scholar]
104. Baldo M, O’Brien D, Thompson M, Forrest S. 104.  1999. Excitonic singlet–triplet ratio in a semiconducting organic thin film. Phys. Rev. B 60:14422 [Google Scholar]
105. Adachi C, Baldo MA, Thompson ME, Forrest SR. 105.  2001. Nearly 100% internal phosphorescence efficiency in an organic light-emitting device. J. Appl. Phys. 90:5048–51 [Google Scholar]
106. Reineke S, Thomschke M, Lssem B, Leo K. 106.  2013. White organic light-emitting diodes: status and perspective. Rev. Mod. Phys. 85:1245 [Google Scholar]
107. Uoyama H, Goushi K, Shizu K, Nomura H, Adachi C. 107.  2012. Highly efficient organic light-emitting diodes from delayed fluorescence. Nature 492:234–38 [Google Scholar]
108. Zhang Q, Li B, Huang S, Nomura H, Tanaka H, Adachi C. 108.  2014. Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence. Nat. Photonics 8:326–32 [Google Scholar]
109. Goushi K, Yoshida K, Sato K, Adachi C. 109.  2012. Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion. Nat. Photonics 6:253–58 [Google Scholar]
110. Li J, Nomura H, Miyazaki H, Adachi C. 110.  2014. Highly efficient exciplex organic light-emitting diodes incorporating a heptazine derivative as an electron acceptor. Chem. Commun. 50:6174–76 [Google Scholar]
111. Greenham NC, Friend RH, Bradley DD. 111.  1994. Angular dependence of the emission from a conjugated polymer light-emitting diode: implications for efficiency calculations. Adv. Mater. 6:491–94 [Google Scholar]
112. Kim H, Kim JY, Park SH, Lee K, Jin Y. 112.  et al. 2005. Electroluminescence in polymer–fullerene photovoltaic cells. Appl. Phys. Lett. 86:183502 [Google Scholar]
113. Vandewal K, Tvingstedt K, Gadisa A, Inganäs O, Manca JV. 113.  2009. On the origin of the open-circuit voltage of polymer–fullerene solar cells. Nat. Mater. 8:904–9 [Google Scholar]
114. Vandewal K, Tvingstedt K, Inganäs O. 114.  2011. Charge transfer states in organic donor–acceptor solar cells. Semicond. Semimet. 85:261–95 [Google Scholar]
115. Würfel U, Neher D, Spies A, Albrecht S. 115.  2015. Impact of charge transport on current-voltage characteristics and power-conversion efficiency of organic solar cells. Nat. Commun. 6:6951 [Google Scholar]
116. Hörmann U, Kraus J, Gruber M, Schuhmair C, Linderl T. 116.  et al. 2013. Quantification of energy losses in organic solar cells from temperature-dependent device characteristics. Phys. Rev. B 88:235307 [Google Scholar]
117. Vandewal K, Tvingstedt K, Manca JV, Inganäs O. 117.  2010. Charge-transfer states and upper limit of the open-circuit voltage in polymer:fullerene organic solar cells. IEEE J. Sel. Top. Quantum Electron. 16:1676–84 [Google Scholar]
118. Graham KR, Erwin P, Nordlund D, Vandewal K, Li R. 118.  et al. 2013. Re-evaluating the role of sterics and electronic coupling in determining the open-circuit voltage of organic solar cells. Adv. Mater. 25:6076–82 [Google Scholar]
119. Sulas DB, Yao K, Intemann JJ, Williams ST, Li CZ. 119.  et al. 2015. Open-circuit voltage losses in selenium-substituted organic photovoltaic devices from increased density of charge-transfer states. Chem. Mater. 19:6583–91 [Google Scholar]
120. Wang E, Bergqvist J, Vandewal K, Ma Z, Hou L. 120.  et al. 2013. Conformational disorder enhances solubility and photovoltaic performance of a thiophene–quinoxaline copolymer. Adv. Energy Mater. 3:806–14 [Google Scholar]
121. Vandewal K, Widmer J, Heumueller T, Brabec CJ, McGehee MD. 121.  et al. 2014. Increased open-circuit voltage of organic solar cells by reduced donor–acceptor interface area. Adv. Mater. 26:3839–43 [Google Scholar]
122. Perez MD, Borek C, Forrest SR, Thompson ME. 122.  2009. Molecular and morphological influences on the open circuit voltages of organic photovoltaic devices. J. Am. Chem. Soc. 131:9281–86 [Google Scholar]
123. Schlenker CW, Thompson ME. 123.  2011. The molecular nature of photovoltage losses in organic solar cells. Chem. Commun. 47:3702–16 [Google Scholar]
124. Hormann U, Lorch C, Hinderhofer A, Gerlach A, Gruber M. 124.  et al. 2014. V_oc from a morphology point of view: the influence of molecular orientation on the open circuit voltage of organic planar heterojunction solar cells. J. Phys. Chem. C 118:26462–70 [Google Scholar]
125. Bartynski AN, Gruber M, Das S, Rangan S, Mollinger S. 125.  et al. 2015. Symmetry-breaking charge transfer in a zinc chlorodipyrrin acceptor for high open circuit voltage organic photovoltaics. J. Am. Chem. Soc. 137:5397–405 [Google Scholar]