Correlating Morphology, Molecular Orientation, and Transistor Performance of Bis(pentafluorophenoxy)silicon Phthalocyanine Using Scanning Transmission X-ray Microscopy

Abstract

Understanding the effect of processing conditions on thin-film morphology is required to develop high-performance organic thin-film electronics such as organic thin-film transistors. Thin films of bis-(pentafluorophenoxy) silicon phthalocyanine (F 10 -SiPc) were evaporated onto surfaces treated with or without octyltrichlorosilane while being held at different substrate temperatures from room temperature to 150 °C. Scanning transmission X-ray microscopy (STXM), performed at various orientations of the linearly polarized monochromatic X-rays, was used to investigate the resulting film morphology. By monitoring the intensity of the π CC * transition from the fluorinated substituent as a function of the polarization angle, we were able to determine the local molecular orientation. Processing the compositional maps enabled the development of structure−property relationships between processing conditions through plane domain sizes and grain boundaries. Atomic force microscopy, which only characterizes the thin-film surface, corroborated the STXM morphology results. This study highlights the potential of STXM to enable a comprehensive characterization across the entire thickness of silicon phthalocyanine thin films and simultaneously prove molecular orientational maps in addition to the morphological features of the domains of the film, not just the surface.

Not Just Surface Energy: The Role of Bis(pentafluorophenoxy) Silicon Phthalocyanine Axial Functionalization and Molecular Orientation on Organic Thin-Film Transistor Performance

“…Our group has demonstrated that Ag electrodes with an Mn interlayer are a cost-effective and high-performance alternative to Au electrodes owed to the lower work function of Mn, enabling better electron injection into the LUMO of F 10 -SiPc , which according to inverse photoemission spectroscopy (IPES) is around 4 eV . Substrates were held at 100 °C during the deposition of F 10 -SiPc since this temperature has been demonstrated to yield improved thin-film texture and OTFTs with a higher average μ e than those fabricated on substrates held at room temperature . The results are highlighted in Table , where the OTS surface yields transistors with the highest μ e and the lowest V T , whereas the fluorinated FPTS has the lowest μ e and the second highest V T .…”

“…27 Substrates were held at 100 °C during the deposition of F 10 -SiPc since this temperature has been demonstrated to yield improved thinfilm texture and OTFTs with a higher average μ e than those fabricated on substrates held at room temperature. 31 The results are highlighted in Table 1, where the OTS surface yields transistors with the highest μ e and the lowest V T , whereas the fluorinated FPTS has the lowest μ e and the second highest V T . Interestingly, the trend for relative μ e differs from our previous results for the nonfluorinated bis(benzoate) silicon phthalocyanine (PhCOO-SiPc) where evaporation on ODTS yielded a slightly higher average μ e and reduced V T compared to OTS.…”

“…evaporated on OTS yielded large, anisotropic features consistent with observations from our previous works. 25,31 F 10 -SiPc evaporated on ODTS yielded a topography with large, anisotropic grains similar to OTS, but with different packing, yielding larger oriented features and larger feature boundaries. Films evaporated on FPTS and PhTS both yielded small, similarly sized isotropic features, while films evaporated on p-6P yielded small, slightly anisotropic grains across the substrate.…”

A smart and visible way to switch the aromaticity of silicon(iv) phthalocyanines

“…Silicon( iv ) Pcs (SiPcs) are very popular dyes due to their versatility, and they have been applied in medicinal chemistry, organic photovoltaic solar cells, organic light emitting diodes, organic thin film transistors, and photocatalysis. 4,23–30 Interestingly, in this work, we unexpectedly found that the aromaticity of an SiPc ring could be readily regulated by alkalis and acids through a reversible nucleophilic addition reaction of the Pc skeleton with alkalis, resulting in a reversible allochroism phenomenon. The blue SiPc solutions immediately turned purple in the presence of alkalis, such as NaOH, NaOCH 3 , or Na 2 S, and they immediately turned back to blue upon the addition of acids, including HCl, trifluoroacetic acid (TFA), and acetic acid.…”

Low-Cost Silicon Phthalocyanine as a Non-Fullerene Acceptor for Flexible Large Area Organic Photovoltaics

“…Phthalocyanines are common dye molecules which have been utilized as a semiconducting material in organic light emitting diodes, , organic thin film transistors − and organic photovoltaics. − Phthalocyanines (Pcs) are already synthesized on the ton scale annually and found in everyday textiles, paints, colorants, and inks . Silicon phthalocyanine ((R) 2 -SiPc) are emerging as an exciting class of phthalocyanines due to their ability to enable n-type operation in electronics and their axial groups provide a handle to tune the physical and thermodynamic properties such as miscibility, solubility, nucleation, and solid-state arrangement. − In terms of synthetic complexity (SC), SiPcs have been reported with an SC index of 12, almost five times lower than those of high-performing NFAs such as Y6 (SC of 59) and ITIC (SC of 67) . Traditionally, (R) 2 -SiPcs have been utilized as ternary additives in donor–acceptor OPVs, providing more than 20% increase in photocurrent due to the extended solar absorption ,− Recently, (R) 2 -SiPc derivatives have also been used as NFAs with different donor polymers P3HT, PTB7, and PBDB-T and achieved high power conversion efficiencies (>4%). , These promising results demonstrate a great potential for low cost OPVs through the use of materials that have low synthetic complexity.…”