Polarized Raman Microscopy to Image Microstructure Changes in Silicon Phthalocyanine Thin-Films

Area of Science:

• Materials Science
• Organic Electronics
• Thin-Film Physics

Background:

• Device performance in organic electronics hinges on thin-film properties and charge transport.
• Deposition techniques and post-deposition treatments critically influence these properties.
• Bis(tri-n-propylsilyl oxide) SiPc ((3PS)2-SiPc) is an emerging semiconductor for organic electronic devices.

Purpose of the Study:

• To investigate the impact of deposition method (physical vapor deposition vs. spin-coating) and thermal annealing on the thin-film properties of (3PS)2-SiPc.
• To correlate film microstructure, morphology, and molecular orientation with device performance.
• To understand the process-structure-property relationships in organic semiconductors.

Main Methods:

• Polarized Raman microscopy to determine molecular orientation in thin films.
• X-ray diffraction to analyze microstructure and morphology variations.
• Fabrication and characterization of organic thin-film transistors (OTFTs) to assess charge transport properties.

Main Results:

• Both PVD and spin-coated non-annealed films yielded similar electron mobilities (~10^-2 cm^2 V^-1 s^-1) and threshold voltages (10-20 V).
• PVD films annealed at 175°C formed a new polymorph with altered molecular alignment, leading to reduced device performance.
• Spin-coated films showed no significant structural changes or new polymorph formation upon annealing.

Conclusions:

• PVD films exhibit greater susceptibility to structural and morphological transformations via post-deposition annealing.
• The microstructure of spin-coated films is largely determined during the deposition process itself.
• Tailoring deposition and annealing strategies is crucial for optimizing organic semiconductor performance.