Acknowledgment

This work was supported by the National Natural Science Foundation of China (Grant No. U1402273), and the Natural Science and Engineering Research Council of Canada.

References

[1] McCarthy M. A., Liu B., Donoghue E. P., Kravchenko I., Kim D. Y., So F., Rinzler A. G.. Science, 2011, 332: 570 CrossRef PubMed ADS Google Scholar http://scholar.google.com/scholar_lookup?author=McCarthy M. A.&author=Liu B.&author=Donoghue E. P.&author=Kravchenko I.&author=Kim D. Y.&author=So F.&author=Rinzler A. G.&publication_year=2011&journal=Science&volume=332&pages=570

[2] Reineke S., Lindner F., Schwartz G., Seidler N., Walzer K., Lüssem B., Leo K.. Nature, 2009, 459: 234 CrossRef PubMed ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Reineke S.&author=Lindner F.&author=Schwartz G.&author=Seidler N.&author=Walzer K.&author=Lüssem B.&author=Leo K.&publication_year=2009&journal=Nature&volume=459&pages=234

[3] Kippelen B., Brédas J. L.. Energ. Environ. Sci., 2009, 2: 251 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Kippelen B.&author=Brédas J. L.&publication_year=2009&journal=Energ. Environ. Sci.&volume=2&pages=251

[4] Zhu X. Y., Yang Q., Muntwiler M.. Acc. Chem. Res., 2009, 42: 1779 CrossRef PubMed Google Scholar http://scholar.google.com/scholar_lookup?author=Zhu X. Y.&author=Yang Q.&author=Muntwiler M.&publication_year=2009&journal=Acc. Chem. Res.&volume=42&pages=1779

[5] Wang J. F., Kawabe Y., Shaheen S. E., Morrell M. M., Jabbour G. E., Lee P. A., Anderson J., Armstrong N. R., Kippelen B., Mash E. A., Peyghambarian N.. Adv. Mater., 1998, 10: 230 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Wang J. F.&author=Kawabe Y.&author=Shaheen S. E.&author=Morrell M. M.&author=Jabbour G. E.&author=Lee P. A.&author=Anderson J.&author=Armstrong N. R.&author=Kippelen B.&author=Mash E. A.&author=Peyghambarian N.&publication_year=1998&journal=Adv. Mater.&volume=10&pages=230

[6] Cocchi M., Virgili D., Giro G., Fattori V., Di Marco P., Kalinowski J., Shirota Y.. Appl. Phys. Lett., 2002, 80: 2401 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Cocchi M.&author=Virgili D.&author=Giro G.&author=Fattori V.&author=Di Marco P.&author=Kalinowski J.&author=Shirota Y.&publication_year=2002&journal=Appl. Phys. Lett.&volume=80&pages=2401

[7] Goushi K., Yoshida K., Sato K., Adachi C.. Nat. Photon., 2012, 6: 253 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Goushi K.&author=Yoshida K.&author=Sato K.&author=Adachi C.&publication_year=2012&journal=Nat. Photon.&volume=6&pages=253

[8] Goushi K., Adachi C.. Appl. Phys. Lett., 2012, 101: 023306 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Goushi K.&author=Adachi C.&publication_year=2012&journal=Appl. Phys. Lett.&volume=101&pages=023306

[9] Liu X. K., Chen Z., Zheng C. J., Liu C. L., Lee C. S., Li F., Ou X. M., Zhang X. H.. Adv. Mater., 2015, 27: 2378 CrossRef PubMed Google Scholar http://scholar.google.com/scholar_lookup?author=Liu X. K.&author=Chen Z.&author=Zheng C. J.&author=Liu C. L.&author=Lee C. S.&author=Li F.&author=Ou X. M.&author=Zhang X. H.&publication_year=2015&journal=Adv. Mater.&volume=27&pages=2378

[10] Chen D., Xie G., Cai X., Liu M., Cao Y., Su S. J.. Adv. Mater., 2016, 28: 239 CrossRef PubMed Google Scholar http://scholar.google.com/scholar_lookup?author=Chen D.&author=Xie G.&author=Cai X.&author=Liu M.&author=Cao Y.&author=Su S. J.&publication_year=2016&journal=Adv. Mater.&volume=28&pages=239

[11] Kirchartz T., Taretto K., Rau U.. J. Phys. Chem. C, 2009, 113: 17958 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Kirchartz T.&author=Taretto K.&author=Rau U.&publication_year=2009&journal=J. Phys. Chem. C&volume=113&pages=17958

[12] Deibel C., Strobel T., Dyakonov V.. Adv. Mater., 2010, 22: 4097 CrossRef PubMed Google Scholar http://scholar.google.com/scholar_lookup?author=Deibel C.&author=Strobel T.&author=Dyakonov V.&publication_year=2010&journal=Adv. Mater.&volume=22&pages=4097

[13] He S. J., White R., Wang D. K., Zhang J., Jiang N., Lu Z. H.. Org. Electron., 2014, 15: 3370 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=He S. J.&author=White R.&author=Wang D. K.&author=Zhang J.&author=Jiang N.&author=Lu Z. H.&publication_year=2014&journal=Org. Electron.&volume=15&pages=3370

[14] Pandey A. K., Nunzi J. M.. Adv. Mater., 2007, 19: 3613 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Pandey A. K.&author=Nunzi J. M.&publication_year=2007&journal=Adv. Mater.&volume=19&pages=3613

[15] He S. J., Wang D. K., Jiang N., Zhang J., Lu Z. H.. Phys. Rev. Appl., 2015, 3: 054011 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=He S. J.&author=Wang D. K.&author=Jiang N.&author=Zhang J.&author=Lu Z. H.&publication_year=2015&journal=Phys. Rev. Appl.&volume=3&pages=054011

[16] He S. J., Lu Z. H.. J. Photon. Energ., 2016, 6: 036001 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=He S. J.&author=Lu Z. H.&publication_year=2016&journal=J. Photon. Energ.&volume=6&pages=036001

[17] Ingram G. L., Nguyen C., Lu Z. H.. Phys. Rev. Appl., 2016, 5: 064002 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Ingram G. L.&author=Nguyen C.&author=Lu Z. H.&publication_year=2016&journal=Phys. Rev. Appl.&volume=5&pages=064002

[18] Ingram G. L., Lu Z. H.. Org. Electron., 2017, 50: 48 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Ingram G. L.&author=Lu Z. H.&publication_year=2017&journal=Org. Electron.&volume=50&pages=48

[19] Niwa A., Kobayashi T., Nagase T., Goushi K., Adachi C., Naito H.. Appl. Phys. Lett., 2014, 104: 213303 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Niwa A.&author=Kobayashi T.&author=Nagase T.&author=Goushi K.&author=Adachi C.&author=Naito H.&publication_year=2014&journal=Appl. Phys. Lett.&volume=104&pages=213303

[20] He S. J., Wang D. K., Jiang N., Tse J. S., Lu Z. H.. Adv. Mater., 2016, 28: 649 CrossRef PubMed Google Scholar http://scholar.google.com/scholar_lookup?author=He S. J.&author=Wang D. K.&author=Jiang N.&author=Tse J. S.&author=Lu Z. H.&publication_year=2016&journal=Adv. Mater.&volume=28&pages=649

[21] A. Weller, Singlet-and Triplet-State Exciplexes (Academic Press Inc., London, 1975), pp. 23-38. Google Scholar http://scholar.google.com/scholar_lookup?title=A. Weller, Singlet-and Triplet-State Exciplexes (Academic Press Inc., London, 1975), pp. 23-38&

[22] Veldman D., Meskers S. C. J., Janssen R. A. J.. Adv. Funct. Mater., 2009, 19: 1939 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Veldman D.&author=Meskers S. C. J.&author=Janssen R. A. J.&publication_year=2009&journal=Adv. Funct. Mater.&volume=19&pages=1939

[23] Burke T. M., Sweetnam S., Vandewal K., McGehee M. D.. Adv. Energ. Mater., 2015, 5: 1500123 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Burke T. M.&author=Sweetnam S.&author=Vandewal K.&author=McGehee M. D.&publication_year=2015&journal=Adv. Energ. Mater.&volume=5&pages=1500123

[24] N. F. Mott, and E. A. Davis, Electronic Processes in Non-Crystalline Materials (Oxford University Press, Oxford, 2012). Google Scholar http://scholar.google.com/scholar_lookup?title=N. F. Mott, and E. A. Davis, Electronic Processes in Non-Crystalline Materials (Oxford University Press, Oxford, 2012)&

[25] He S. J., Wang D. K., Jiang N., Lu Z. H.. J. Phys. Chem. C, 2016, 120: 21325 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=He S. J.&author=Wang D. K.&author=Jiang N.&author=Lu Z. H.&publication_year=2016&journal=J. Phys. Chem. C&volume=120&pages=21325

[26] S. M. Sze, and K. K. Ng, Physics of Semiconductor Devices (John Wiley & Sons Inc, Hoboken, 2006). Google Scholar http://scholar.google.com/scholar_lookup?title=S. M. Sze, and K. K. Ng, Physics of Semiconductor Devices (John Wiley & Sons Inc, Hoboken, 2006)&

[27] M. Pope, and C. E. Swenberg, Electronic Processes in Organic Crystals and Polymers (Oxford University Press, New York, 1999). Google Scholar http://scholar.google.com/scholar_lookup?title=M. Pope, and C. E. Swenberg, Electronic Processes in Organic Crystals and Polymers (Oxford University Press, New York, 1999)&

[28] Wang L. W., Califano M., Zunger A., Franceschetti A.. Phys. Rev. Lett., 2003, 91: 056404 CrossRef PubMed ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Wang L. W.&author=Califano M.&author=Zunger A.&author=Franceschetti A.&publication_year=2003&journal=Phys. Rev. Lett.&volume=91&pages=056404

[29] Matsunaga R., Matsuda K., Kanemitsu Y.. Phys. Rev. Lett., 2011, 106: 037404 CrossRef PubMed ADS arXiv Google Scholar http://scholar.google.com/scholar_lookup?author=Matsunaga R.&author=Matsuda K.&author=Kanemitsu Y.&publication_year=2011&journal=Phys. Rev. Lett.&volume=106&pages=037404

[30] Deibel C., Strobel T., Dyakonov V.. Phys. Rev. Lett., 2009, 103: 036402 CrossRef PubMed ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Deibel C.&author=Strobel T.&author=Dyakonov V.&publication_year=2009&journal=Phys. Rev. Lett.&volume=103&pages=036402

[31] Blakesley J. C., Neher D.. Phys. Rev. B, 2011, 84: 075210 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Blakesley J. C.&author=Neher D.&publication_year=2011&journal=Phys. Rev. B&volume=84&pages=075210

[32] Li P., Hong W., Li Y., Ingram G., Lu Z. H.. Adv. Electron. Mater., 2017, 3: 1700115 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Li P.&author=Hong W.&author=Li Y.&author=Ingram G.&author=Lu Z. H.&publication_year=2017&journal=Adv. Electron. Mater.&volume=3&pages=1700115

[33] Park Y. S., Jeong W. I., Kim J. J.. J. Appl. Phys., 2011, 110: 124519 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Park Y. S.&author=Jeong W. I.&author=Kim J. J.&publication_year=2011&journal=J. Appl. Phys.&volume=110&pages=124519

[34] Zhou D. Y., Zamani Siboni H., Wang Q., Liao L. S., Aziz H.. J. Phys. Chem. C, 2014, 118: 24006 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Zhou D. Y.&author=Zamani Siboni H.&author=Wang Q.&author=Liao L. S.&author=Aziz H.&publication_year=2014&journal=J. Phys. Chem. C&volume=118&pages=24006

[35] Shin H., Lee S., Kim K. H., Moon C. K., Yoo S. J., Lee J. H., Kim J. J.. Adv. Mater., 2014, 26: 4730 CrossRef PubMed Google Scholar http://scholar.google.com/scholar_lookup?author=Shin H.&author=Lee S.&author=Kim K. H.&author=Moon C. K.&author=Yoo S. J.&author=Lee J. H.&author=Kim J. J.&publication_year=2014&journal=Adv. Mater.&volume=26&pages=4730

[36] Kim K. H., Moon C. K., Lee J. H., Kim S. Y., Kim J. J.. Adv. Mater., 2014, 26: 3844 CrossRef PubMed Google Scholar http://scholar.google.com/scholar_lookup?author=Kim K. H.&author=Moon C. K.&author=Lee J. H.&author=Kim S. Y.&author=Kim J. J.&publication_year=2014&journal=Adv. Mater.&volume=26&pages=3844

[37] Kim K. H., Lee S., Moon C. K., Kim S. Y., Park Y. S., Lee J. H., Woo Lee J., Huh J., You Y., Kim J. J.. Nat. Commun., 2014, 5: 4769 CrossRef PubMed ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Kim K. H.&author=Lee S.&author=Moon C. K.&author=Kim S. Y.&author=Park Y. S.&author=Lee J. H.&author=Woo Lee J.&author=Huh J.&author=You Y.&author=Kim J. J.&publication_year=2014&journal=Nat. Commun.&volume=5&pages=4769

[38] Liu X. K., Chen Z., Zheng C. J., Chen M., Liu W., Zhang X. H., Lee C. S.. Adv. Mater., 2015, 27: 2025 CrossRef PubMed Google Scholar http://scholar.google.com/scholar_lookup?author=Liu X. K.&author=Chen Z.&author=Zheng C. J.&author=Chen M.&author=Liu W.&author=Zhang X. H.&author=Lee C. S.&publication_year=2015&journal=Adv. Mater.&volume=27&pages=2025

[39] Kim K. H., Yoo S. J., Kim J. J.. Chem. Mater., 2016, 28: 1936 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Kim K. H.&author=Yoo S. J.&author=Kim J. J.&publication_year=2016&journal=Chem. Mater.&volume=28&pages=1936

[40] Nakanotani H., Furukawa T., Morimoto K., Adachi C.. Sci. Adv., 2016, 2: e1501470 CrossRef PubMed ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Nakanotani H.&author=Furukawa T.&author=Morimoto K.&author=Adachi C.&publication_year=2016&journal=Sci. Adv.&volume=2&pages=e1501470

[41] Campbell I. H., Crone B. K.. Appl. Phys. Lett., 2012, 101: 023301 CrossRef ADS Google Scholar http://scholar.google.com/scholar_lookup?author=Campbell I. H.&author=Crone B. K.&publication_year=2012&journal=Appl. Phys. Lett.&volume=101&pages=023301

[42] Sampat S., Mohite A. D., Crone B., Tretiak S., Malko A. V., Taylor A. J., Yarotski D. A.. J. Phys. Chem. C, 2015, 119: 1286 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Sampat S.&author=Mohite A. D.&author=Crone B.&author=Tretiak S.&author=Malko A. V.&author=Taylor A. J.&author=Yarotski D. A.&publication_year=2015&journal=J. Phys. Chem. C&volume=119&pages=1286

[43] Kumar A., Pace G., Bakulin A. A., Fang J., Ho P. K. H., Huck W. T. S., Friend R. H., Greenham N. C.. Energ. Environ. Sci., 2013, 6: 1589 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Kumar A.&author=Pace G.&author=Bakulin A. A.&author=Fang J.&author=Ho P. K. H.&author=Huck W. T. S.&author=Friend R. H.&author=Greenham N. C.&publication_year=2013&journal=Energ. Environ. Sci.&volume=6&pages=1589

[44] Nie W., Gupta G., Crone B. K., Liu F., Smith D. L., Ruden P. P., Kuo C. Y., Tsai H., Wang H. L., Li H., Tretiak S., Mohite A. D.. Adv. Sci., 2015, 2: 1500024 CrossRef PubMed Google Scholar http://scholar.google.com/scholar_lookup?author=Nie W.&author=Gupta G.&author=Crone B. K.&author=Liu F.&author=Smith D. L.&author=Ruden P. P.&author=Kuo C. Y.&author=Tsai H.&author=Wang H. L.&author=Li H.&author=Tretiak S.&author=Mohite A. D.&publication_year=2015&journal=Adv. Sci.&volume=2&pages=1500024

[45] Kleemann H., Schumann S., J?rges U., Ellinger F., Leo K., Lüssem B.. Org. Electron., 2012, 13: 1114 CrossRef Google Scholar http://scholar.google.com/scholar_lookup?author=Kleemann H.&author=Schumann S.&author=J?rges U.&author=Ellinger F.&author=Leo K.&author=Lüssem B.&publication_year=2012&journal=Org. Electron.&volume=13&pages=1114