Elucidating the effects of guest-host energy level alignment on charge transport in phosphorescent OLEDs

The correct choice of guest and host molecules in the light-emitting layer is essential for developing high performance phosphorescent organic light emitting devices. However, the effects of the energy level alignment between the guest and the host are yet to be fully elucidated. In this Letter, we use kinetic Monte Carlo simulations to investigate guest-host systems in which the energy gap of the guest and host is fixed, and only the relative energies of the ionization potential/electron affinity are changed to elucidate their effect on charge transport. It was determined that the mobility balance in the blend was sensitive to the energy level alignment, allowing balanced active layer mobility to be achieved despite the hole and electron mobilities being different by around one order of magnitude. It was also found that the mobility of the faster carrier was more sensitive to the energy level alignment than that of the slower carrier due to reduced slower carrier thermalization under deep charge trapping on the guest.

[1]  Paul W. M. Blom,et al.  Efficient and stable single-layer organic light-emitting diodes based on thermally activated delayed fluorescence , 2019, Nature Photonics.

[2]  B. Philippa,et al.  Understanding charge transport in Ir(ppy)3:CBP OLED films. , 2019, The Journal of chemical physics.

[3]  Lei Wang,et al.  Efficient deep red phosphorescent OLEDs using 1,2,4-thiadiazole core-based novel bipolar host with low efficiency roll-off , 2018, Frontiers of Optoelectronics.

[4]  Shi-jian Su,et al.  An ideal universal host for highly efficient full-color, white phosphorescent and TADF OLEDs with a simple and unified structure , 2017 .

[5]  Haoyuan Li,et al.  Kinetic Monte Carlo Modeling of Charge Carriers in Organic Electronic Devices: Suppression of the Self-Interaction Error. , 2017, The journal of physical chemistry letters.

[6]  Tyler B Fleetham,et al.  Phosphorescent Pt(II) and Pd(II) Complexes for Efficient, High‐Color‐Quality, and Stable OLEDs , 2017, Advanced materials.

[7]  T. Voorhis,et al.  Charge Recombination in Phosphorescent Organic Light-Emitting Diode Host–Guest Systems through QM/MM Simulations , 2016 .

[8]  F. So,et al.  Efficiency Roll‐Off in Blue Emitting Phosphorescent Organic Light Emitting Diodes with Carbazole Host Materials , 2016 .

[9]  Junji Kido,et al.  Simultaneous Realization of High EQE of 30%, Low Drive Voltage, and Low Efficiency Roll‐Off at High Brightness in Blue Phosphorescent OLEDs , 2016 .

[10]  Jiuyan Li,et al.  Universal Host Materials for High-Efficiency Phosphorescent and Delayed-Fluorescence OLEDs. , 2015, ACS applied materials & interfaces.

[11]  Liduo Wang,et al.  Tuning of charge balance in bipolar host materials for highly efficient solution-processed phosphorescent devices. , 2011, Organic letters.

[12]  Jingui Qin,et al.  Organic host materials for phosphorescent organic light-emitting diodes. , 2011, Chemical Society reviews.

[13]  K. Char,et al.  Highly Efficient Red Phosphorescent OLEDs based on Non‐Conjugated Silicon‐Cored Spirobifluorene Derivative Doped with Ir‐Complexes , 2009 .

[14]  Ruth Shinar,et al.  Organic light-emitting devices (OLEDs) and OLED-based chemical and biological sensors: an overview , 2008 .

[15]  S. Tokito,et al.  Phosphorescent Organic Light-emitting Devices: Triplet Energy Management , 2008 .

[16]  Jang‐Joo Kim,et al.  Low roll-off of efficiency at high current density in phosphorescent organic light emitting diodes , 2007 .

[17]  Chen‐Han Chien,et al.  Novel host material for highly efficient blue phosphorescent OLEDs , 2007 .

[18]  Bernard Geffroy,et al.  Organic light‐emitting diode (OLED) technology: materials, devices and display technologies , 2006 .

[19]  Mikhail A. Parshin,et al.  Charge carrier mobility in CBP films doped with Ir(ppy)3 , 2006, SPIE Photonics Europe.

[20]  Junji Kido,et al.  Ultra High Efficiency Green Organic Light-Emitting Devices , 2006 .

[21]  M. Michels,et al.  Scaling of current distributions in variable-range hopping transport on two- and three-dimensional lattices , 2005 .

[22]  Stephen R. Forrest,et al.  Ultrahigh energy gap hosts in deep blue organic electrophosphorescent devices , 2004 .

[23]  A. van Dijken,et al.  Carbazole compounds as host materials for triplet emitters in organic light-emitting diodes: tuning the HOMO level without influencing the triplet energy in small molecules. , 2004, Journal of the American Chemical Society.

[24]  S. Forrest,et al.  Nearly 100% internal phosphorescence efficiency in an organic light emitting device , 2001 .

[25]  S. Forrest,et al.  VERY HIGH-EFFICIENCY GREEN ORGANIC LIGHT-EMITTING DEVICES BASED ON ELECTROPHOSPHORESCENCE , 1999 .

[26]  Stephen R. Forrest,et al.  Improved energy transfer in electrophosphorescent devices , 1999 .

[27]  H. Bässler.  Charge Transport in Disordered Organic Photoconductors a Monte Carlo Simulation Study , 1993 .