All-Solution Processed Single-Layer WOLEDs Using [Pt(salicylidenes)] as Guests in a PFO Matrix

Area of Science:

• Materials Science
• Organic Electronics
• Coordination Chemistry

Background:

• Conjugated polymers like poly[9,9-dioctylfluorenyl-2,7-diyl] (PFO) are crucial for organic light-emitting diodes (OLEDs).
• Platinum(II) complexes are investigated for their phosphorescent properties, essential for efficient light emission in OLEDs.
• Achieving efficient and stable white organic light-emitting diodes (WOLEDs) through solution processing remains a significant challenge.

Purpose of the Study:

• To synthesize and characterize two platinum(II) coordination compounds: platinum(II)[N,N '-bis(salicylidene)-3,4-diaminobenzophenone)] ([Pt(sal-3,4-ben)]) and platinum(II)[N,N '-bis(salicylidene)-o-phenylenediamine] ([Pt(salophen)]).
• To evaluate the performance of these complexes as dopants in PFO for single-layer, all-solution processed WOLEDs.
• To elucidate the structure-property relationships governing the optoelectronic performance of the developed WOLEDs.

Main Methods:

• Synthesis and characterization of Pt(II) coordination compounds.
• Fabrication of single-layer WOLEDs using PFO doped with Pt(II) complexes via solution processing.
• Device performance testing, including external quantum efficiency, current efficiency, luminance, and Commission Internationale de l'Eclairage (CIE 1931) chromaticity.
• Investigation of optoelectronic properties using steady-state and time-resolved photoluminescence.
• Theoretical calculations using relativistic density functional theory (DFT).

Main Results:

• The [Pt(sal-3,4-ben)] complex demonstrated significantly higher external quantum efficiency (15.3%), current efficiency (12.1 cd A⁻¹), and luminance (6224 cd m⁻²) compared to [Pt(salophen)] (2.2%, 2.8 cd A⁻¹, 3103 cd m⁻²).
• Both composites achieved neutral white light emission with CIE 1931 coordinates of (0.33, 0.33) at low doping concentrations (0.1% mol/mol Pt(II):PFO).
• Relativistic DFT calculations attributed the performance differences to Pt(II) phosphorescence and spin-orbit coupling effects, supported by photoluminescence studies and deep-trap space-charge models.

Conclusions:

• The new [Pt(sal-3,4-ben)] complex offers superior performance in solution-processed WOLEDs compared to the established [Pt(salophen)] complex.
• The developed framework provides a good trade-off between device simplicity, ease of synthesis, and performance for WOLED applications.
• These findings present a viable pathway for developing efficient WOLEDs for lighting and signage, leveraging phosphorescent platinum(II) emitters.