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Elimination of charge carrier trapping in diluted semiconductors

Abstract

In 1962, Mark and Helfrich demonstrated that the current in a semiconductor containing traps is reduced by N/Ntr, with N the amount of transport sites, Nt the amount of traps and r a number that depends on the trap energy distribution. For r > 1, the possibility opens that trapping effects can be nearly eliminated when N and Nt are simultaneously reduced. Solution-processed conjugated polymers are an excellent model system to test this hypothesis, because they can be easily diluted by blending them with a high-bandgap semiconductor. We demonstrate that in conjugated polymer blends with 10% active semiconductor and 90% high-bandgap host, the typical strong electron trapping can be effectively eliminated. As a result we were able to fabricate polymer light-emitting diodes with balanced electron and hole transport and reduced non-radiative trap-assisted recombination, leading to a doubling of their efficiency at nearly ten times lower material costs.

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Figure 1: Hole transport in MEH-PPV:PVK blends.
Figure 2: Simulated hole mobility parameters.
Figure 3: Hole and electron transport in MEH-PPV:PVK blends.
Figure 4: Electron trap density as a function of MEH-PPV fraction in the blends with PVK (squares) and PFO (circles).
Figure 5: Voc versus light intensity for MEH-PPV:PFO blend-based PLEDs.
Figure 6: Transport and performance of pristine and blend PLEDs.

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Acknowledgements

The authors acknowledge J. Harkema for technical support, B. Noheda and J. M. Varghese for assistance with AFM, and C. Schaefer for his contribution to the calculations of the phase diagrams. D.A. is supported by the Dutch Polymer Institute (DPI), Project No. 733.

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Contributions

P.W.M.B. proposed and supervised the project. D.A. and A.K. carried out experiments. D.A., G.A.H.W. and N.I.C. analysed the transport data. J.J.M. analysed the phase separation. K.K. carried out and interpreted the CLSM measurements. I.L. carried out and interpreted the TEM measurements. D.A. and P.W.M.B. wrote the manuscript.

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Correspondence to P. W. M. Blom.

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The authors declare no competing financial interests.

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Abbaszadeh, D., Kunz, A., Wetzelaer, G. et al. Elimination of charge carrier trapping in diluted semiconductors. Nature Mater 15, 628–633 (2016). https://doi.org/10.1038/nmat4626

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