Efficiency Roll-Off in Light-Emitting Electrochemical Cells

Area of Science:

• Materials Science
• Electrochemistry
• Optoelectronics

Background:

• Light-emitting electrochemical cells (LECs) offer cost-effective fabrication via ambient-air printing.
• In situ p-n junction formation in LECs complicates efficiency analysis.
• Understanding efficiency roll-off is crucial for designing brighter, more efficient emissive technologies.

Purpose of the Study:

• To develop a method for separating and quantifying major loss factors in LECs.
• To investigate the impact of current on p-n junction position and outcoupling efficiency.
• To elucidate the role of singlet-polaron quenching (SPQ) in LEC efficiency roll-off.

Main Methods:

• Quantification of LEC loss factors, including outcoupling efficiency and exciton quenching.
• Measurement of the emissive p-n junction shift with increasing current.
• Analysis of singlet-polaron quenching (SPQ) dependence on current density and polaron concentration.

Main Results:

• The emissive p-n junction position shifts significantly with increasing current, affecting outcoupling efficiency.
• High electrochemical doping in LECs leads to significant SPQ even at low current densities.
• SPQ increases super-linearly with current, dominating singlet-singlet quenching and contributing substantially to efficiency roll-off.

Conclusions:

• A novel method allows for the deciphering of efficiency roll-off in LECs.
• SPQ is a major contributor to efficiency roll-off in printed LECs at relevant current densities.
• This work facilitates the rational design of efficient, all-printed LEC devices for high-luminance applications.