A DMF-assisted solution process boosts the efficiency in P3HT:PCBM solar cells up to 5.31%

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Achieving ideal phase separation in poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blend films is crucial for efficient organic solar cells.
• Optimizing morphology and charge transport in bulk heterojunction (BHJ) active layers directly impacts device performance.

Purpose of the Study:

• To enhance the phase separation and morphology of P3HT:PCBM blend films using a selective solvent additive.
• To improve vertical phase separation by forming a PCBM-rich layer for better charge transport and hole blocking.
• To optimize film uniformity and interfacial contact through thermal annealing for increased power conversion efficiency (PCE).

Main Methods:

• Addition of dimethylformamide (DMF), a selective solvent for PCBM, to the P3HT:PCBM solution in 1,2-dichlorobenzene.
• Spin-coating a PCBM solution in DMF onto the P3HT:PCBM active layer to create a PCBM-rich top layer.
• Thermal annealing of the fabricated films at 120°C for 10 minutes.

Main Results:

• Addition of 10% DMF improved charge transport and morphology, increasing average PCE from 3.75% to 4.29%.
• The PCBM-rich layer enhanced hole blocking and electron transport, boosting average PCE from 4.29% to 4.83%.
• Thermal annealing resulted in more uniform films with better interfacial contact, further increasing average PCE from 4.83% to 5.17%, with a best PCE of 5.31%.

Conclusions:

• Selective solvent addition (DMF) and controlled vertical phase separation are effective strategies for optimizing P3HT:PCBM solar cells.
• Post-deposition thermal annealing is critical for improving film quality and interfacial properties, leading to significant PCE enhancements.
• The combined approach offers a pathway to achieve higher performance in organic photovoltaic devices.