Enhanced Vertical Concentration Gradient in Rubbed P3HT:PCBM Graded Bilayer Solar Cells

Area of Science:

• Materials Science
• Renewable Energy
• Organic Electronics

Background:

• Graded bilayer solar cells offer comparable efficiency to bulk heterojunctions in Poly(3-hexylthiophene) (P3HT) - [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) systems.
• Controlling vertical concentration gradients in these cells using simple methods has been a challenge.

Purpose of the Study:

• To demonstrate a simple technique for controlling the vertical concentration gradient in P3HT:PCBM solar cells.
• To investigate the morphological changes induced by this technique and their impact on device performance.

Main Methods:

• Employing a rubbing technique on the P3HT layer before PCBM deposition.
• Utilizing energy-dispersive X-ray spectroscopy (EDX) element mapping to analyze vertical morphology.
• Investigating molecular orientation changes in P3HT crystallites.

Main Results:

• Rubbing the P3HT layer induces significant morphological changes, creating an ideal vertical donor-acceptor concentration gradient.
• P3HT crystallites reorient from edge-on to face-on configurations, improving vertical charge transport.
• These morphological improvements result in high-performance solar cells.

Conclusions:

• Simple mechanical rubbing is an effective method for controlling vertical morphology in graded bilayer solar cells.
• The optimized morphology leads to record efficiencies for spin-coated graded bilayer devices.
• This technique offers a pathway to enhanced performance in organic solar cells.