Tandem Organic Solar Cells with 21.5% Efficiency.

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Tandem organic solar cells (OSCs) are crucial for improving light harvesting and reducing energy loss.
• Achieving high power conversion efficiency (PCE) in OSCs remains a key research objective.
• Narrow bandgap materials are essential for efficient light absorption in the rear sub-cell of tandem devices.

Purpose of the Study:

• To design and synthesize a novel narrow bandgap acceptor material (BTA-4F) for the rear sub-cell of tandem OSCs.
• To investigate the impact of incorporating a 2-methyl-2H-benzotriazole (BTA) core on the material's optoelectronic properties.
• To evaluate the performance of single-junction and tandem OSCs utilizing the new BTA-4F acceptor.

Main Methods:

• Fabrication of the BTA-4F narrow bandgap acceptor with a BTA central core.
• Systematic characterization of the material's properties, including bandgap and electroluminescence external quantum efficiency.
• Fabrication and performance testing of single-junction and tandem OSC devices under standard (AM 1.5G) and realistic light conditions.

Main Results:

• The BTA-4F acceptor exhibited a narrowed bandgap and enhanced electroluminescence external quantum efficiency due to the BTA core.
• Single-junction OSCs based on BTA-4F showed improved current density and reduced voltage loss.
• BTA-4F-based tandem OSCs achieved a certified power conversion efficiency (PCE) of 21.2% (device PCE 21.5%).

Conclusions:

• Molecular design incorporating electron-donating groups like BTA is effective in narrowing bandgaps and boosting OSC performance.
• The BTA-4F acceptor demonstrates significant potential for enhancing the efficiency of tandem OSCs.
• This study underscores the synergistic effect of molecular engineering and tandem architecture for advancing photovoltaic technology.