Chain Coupling and Luminescence in High-Mobility, Low-Disorder Conjugated Polymers.

Area of Science:

• Materials Science
• Polymer Chemistry
• Organic Electronics

Background:

• Multilayer architectures are common in conjugated polymer optoelectronics due to challenges in achieving both efficient luminescence and fast carrier transport within a single material.
• Developing single-layer devices requires polymers that possess both high photoluminescence quantum yield and excellent charge carrier mobility.

Purpose of the Study:

• To investigate the photophysics of a novel class of conjugated polymers with high charge carrier mobility and low energetic disorder.
• To determine if molecular design can enhance photoluminescence quantum yield without compromising carrier mobility in these polymers.

Main Methods:

• Femto- to microsecond timescale exciton dynamics were traced to understand recombination pathways.
• Temperature dependence and electron-phonon coupling were evaluated to identify factors causing internal conversion.
• Side chain substitution was systematically varied to control interchain interactions.

Main Results:

• Non-radiative exciton recombination was primarily attributed to inter-chromophore interactions on adjacent polymer chains.
• Steric reduction of interchain coupling significantly increased the fluorescence quantum yield of low-energy gap polymers.
• A red-NIR-emitting amorphous polymer achieved a record 18% film luminescence quantum efficiency, with mobility surpassing amorphous silicon.

Conclusions:

• Molecular design, specifically reducing interchain coupling via side chain engineering, is effective in enhancing fluorescence quantum yield in conjugated polymers.
• This study presents a viable pathway toward single-layer conjugated polymer optoelectronic devices by simultaneously optimizing luminescence and charge transport properties.