Ionic Ir(III) complex-interfacial layer for efficient carrier collection via induced electric dipole

Area of Science:

• Materials Science
• Photovoltaics
• Organic Electronics

Background:

• Polymer solar cells (PSCs) achieve high power conversion efficiency (PCE) >19% via non-fullerene acceptors.
• Interfacial layers (ILs) are crucial for optimizing charge extraction in PSCs.
• Developing advanced ILs is key to further improving PSC performance and stability.

Purpose of the Study:

• To introduce novel ionic iridium(III) (Ir(III)) complexes as interfacial layers in PSCs.
• To investigate the role of alkali metal cations (Li+, Na+, K+) in Ir(III) complexes for enhancing charge collection.
• To evaluate the impact of these ILs on PSC power conversion efficiency (PCE) and operational stability.

Main Methods:

• Synthesis of ionic Ir(III) complexes with varying alkali metal cations.
• Fabrication of PSCs utilizing these Ir(III) complexes as interfacial layers.
• Characterization of device performance using techniques including PCE measurements and electrochemical impedance spectroscopy.
• Assessment of device stability under UV light and AM 1.5 G irradiation.

Main Results:

• Ionic Ir(III) complexes, particularly Ir-K+, improved PCE from 14.0% to 15.6% in PM6:Y6-based PSCs.
• The complexes enhance internal electric fields, improving charge collection efficiency.
• PSCs with Ir(III) ILs exhibited significantly improved stability, retaining ~60% PCE after UV exposure compared to ~20% for control devices.

Conclusions:

• Ionic Ir(III) complexes effectively function as interfacial layers, boosting PSC performance.
• The induced internal electric field and enhanced charge collection contribute to higher PCE.
• The inherent UV absorption and photo-durability of Ir(III) complexes significantly improve PSC operational stability.