Boosting Hole Mobility: Indenofluorene-Arylamine Copolymers and Their Impact on Solution-Processed OLED Performance

Area of Science:

• Materials Science
• Organic Electronics
• Polymer Chemistry

Background:

• Solution-processed organic light-emitting diodes (s-OLEDs) require efficient and stable hole transport layers (HTLs).
• Developing thermally cross-linkable materials can improve solvent resistance and device stability in s-OLEDs.
• Existing HTLs often face limitations in charge mobility and efficiency, hindering s-OLED performance.

Purpose of the Study:

• To design and synthesize novel thermally cross-linkable hole transport copolymers for s-OLED applications.
• To investigate the relationship between molecular design, charge transport properties, and device performance.
• To evaluate the potential of these copolymers as high-performance HTLs in green phosphorescent s-OLEDs.

Main Methods:

• Synthesis of three novel indenofluorene-based copolymers (PIF-TPD, PIF-F2PCz, PIF-TPAPCz) incorporating benzocyclobutene (BCB) and styrene-based cross-linking units.
• Characterization of copolymer properties including thermal stability, solvent resistance, charge carrier mobility, and triplet energy levels.
• Fabrication and testing of green phosphorescent s-OLEDs utilizing the synthesized copolymers as HTLs.

Main Results:

• The synthesized copolymers exhibited high solvent resistance at a low cross-linking temperature (150 °C).
• Outstanding hole charge carrier mobility of 1.61 × 10^-2 cm^2 V^-1 s^-1 was achieved, attributed to planar indenofluorene units and favorable orientation of hole transport moieties.
• s-OLEDs incorporating these copolymers as HTLs demonstrated a maximum external quantum efficiency of 15.3% and a maximum current efficiency of 53.9 cd A^-1 with minimal efficiency roll-off.

Conclusions:

• The newly designed thermally cross-linkable hole transport copolymers show significant promise for advancing s-OLED technology.
• These materials offer a viable alternative to vacuum-deposited layers, enabling high-performance and potentially lower-cost OLED fabrication.
• The strategic molecular design allows for tunable properties, paving the way for future development of efficient organic electronic devices for displays and lighting.