Vacuum-deposited planar heterojunction polymer solar cells

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Poly(3-hexylthiophene) (P3HT) is a key organic semiconductor for photovoltaic applications.
• Vacuum thermal evaporation is a common deposition technique for organic electronic devices.
• Understanding structural changes during P3HT processing is crucial for optimizing device performance.

Purpose of the Study:

• To investigate the structural and chemical modifications of P3HT during vacuum thermal evaporation.
• To correlate these structural changes with the photovoltaic performance of P3HT:C₆₀ solar cells.

Main Methods:

• Vacuum thermal evaporation of P3HT.
• Gel Permeation Chromatography (GPC) to assess molecular weight changes.
• UV-vis absorption spectroscopy, Fourier-Transform Infrared (FTIR) spectroscopy, and Nuclear Magnetic Resonance (NMR) to analyze structural and chemical alterations.
• Fabrication and characterization of bilayer heterojunction solar cells (P3HT:C₆₀).

Main Results:

• Vacuum thermal evaporation significantly reduced P3HT molecular weight.
• A blue-shift in UV-vis absorption spectra indicated a decrease in conjugation length.
• FTIR and NMR confirmed that while conjugation remained largely intact, side chains dissociated from the polymer backbone.
• The processed P3HT layer exhibited altered optical and electronic properties relevant to solar cell function.

Conclusions:

• Vacuum thermal evaporation induces detrimental structural changes in P3HT, including reduced molecular weight and conjugation length.
• These modifications directly impact the performance of P3HT-based photovoltaic devices.
• Further research is needed to mitigate these degradation pathways for improved organic solar cell efficiency.