Efficient low bandgap polymer solar cell with ordered heterojunction defined by nanoimprint lithography

Area of Science:

• Materials Science
• Organic Electronics
• Nanotechnology

Background:

• Low bandgap conjugated polymers are crucial for efficient organic solar cells.
• Achieving well-ordered bulk heterojunctions is key to maximizing charge separation and transport.
• Fabrication techniques that control nanostructure morphology are needed to enhance device performance.

Purpose of the Study:

• To demonstrate the feasibility of nanoimprint lithography (NIL) for fabricating efficient low bandgap polymer solar cells.
• To investigate the impact of PCPDTBT nanostructure geometry on solar cell performance.
• To explore NIL's effect on the structural ordering of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b’]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT).

Main Methods:

• Fabrication of high-quality PCPDTBT nanogratings using nanoimprint lithography (NIL).
• Fabrication of PCPDTBT/C70 solar cells with varying nanograting feature sizes.
• Characterization of nanostructure geometry and its correlation with solar cell performance metrics.

Main Results:

• NIL successfully created ordered PCPDTBT nanogratings, a first for this material.
• Power conversion efficiency (PCE) increased with nanograting height and PCPDTBT/C70 junction area, while decreasing nanograting width.
• NIL enhanced PCPDTBT chain interaction and structural ordering, leading to a PCE of 5.5% in optimized devices.

Conclusions:

• Nanoimprint lithography is a viable technique for producing efficient low bandgap polymer solar cells with controlled morphology.
• Optimizing nanostructure geometry via NIL significantly improves the performance of PCPDTBT/C70 solar cells.
• The enhanced structural ordering induced by NIL contributes to achieving high power conversion efficiencies.