A Binary Cathode Interlayer Coupling Dipole Regulation and Molecular Orientation Enables 20.1%-Efficient Organic...

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Organic solar cell (OSC) performance is limited by inefficient electron extraction at the cathode interface.
• Suboptimal energy alignment and disordered molecular packing in cathode interlayers hinder charge transport.

Purpose of the Study:

• To develop a binary cathode interlayer that synergistically couples interfacial dipole engineering and molecular orientation ordering.
• To optimize energy-level alignment and enhance vertical charge transport for improved OSC performance.

Main Methods:

• Fabrication of a binary cathode interlayer using an n-type small molecule (NDI-Ph) and an electron-transporting polymer (PNDIT-F3N-Br).
• Characterization of interfacial properties, including work function, molecular packing, charge extraction, and carrier lifetime.
• Fabrication and testing of single-junction OSCs with PM6:BTP-eC9 and PM6:L8-BO active layers.

Main Results:

• The binary interlayer lowered the cathode work function to 3.23 eV and promoted face-on π-π stacking.
• Accelerated electron extraction (0.27 µs) and prolonged carrier lifetime (3.38 µs) were observed.
• OSCs with PM6:BTP-eC9 achieved a power conversion efficiency (PCE) of 20.1%, and with PM6:L8-BO achieved 19.5% PCE.

Conclusions:

• Synergistic dipole-ordering coupling in binary cathode interlayers is a fundamental design principle for high-performance OSCs.
• The developed binary interlayer universally enhances performance across different state-of-the-art active layers.
• This approach offers a pathway to overcome interfacial limitations and achieve higher PCEs in organic photovoltaics.