Metal phthalocyanines (MPcs) are versatile conjugated macrocycles that have attracted a great deal of interest as active components in modern organic electronic devices. In particular, the charge transport properties of MPcs, their chemical stability, and their synthetic versatility make them ideal candidate materials for use in organic thin-film transistors (OTFTs). This article reviews recent progress in both the material design and device engineering of MPc-based OTFTs, including the introduction of solubilizing groups on the MPcs and the surface modification of substrates to induce favorable MPc self-assembly. Finally, a discussion on emerging niche applications based on MPc OTFTs will be explored, in addition to a perspective and outlook on these promising materials in OTFTs. The scope of this review is focused primarily on the advances made in the field of MPc-based OTFTs since 2008.

The first example of Silicon phthalocyanines (SiPcs) in organic thin-film transistors (OTFTs). This study outlines the need for careful selection of processing conditions for optimized performance.

Silicon and tin­(IV) phthalocyanines, which have been demonstrated as simple-to-synthesize materials for n-type organic thin-film transistors (OTFTs), have relatively shallow lowest unoccupied molecular orbital (LUMO) levels that create a Schottky barrier with the gold source–drain contacts typically used in device fabrication. To reduce the contact resistance (R C) associated with this barrier and improve the OTFT performance, we fabricated bottom-gate top-contact (BGTC) devices using low-work-function metals (Mn/Cr) and an electron dopant material (bathocuproine, BCP) as contact interlayers. We characterized two tin phthalocyanines (SnPcs), tin bis­(pentafluorophenoxy)­phthalocyanine (F10-SnPc) and tin bis­(2,4,6-trifluorophenoxy)­phthalocyanine (246F-SnPc), as organic semiconductors (OSCs) and compared them to their silicon phthalocyanine (SiPc) analogues. We found that using Mn and Cr interlayers with SiPc OTFTs reduces R C to as low as 11.8 kΩ cm and reduces the threshold voltage (V T) to as low as 7.8 V while improving linear region characteristics compared to devices using silver or gold electrodes only. BCP interlayers appear to reduce V T in all SiPc and SnPc devices and increase the off-state conductivity of SnPc devices if covering the entire OSC. Overall, this work demonstrates the potential for metal interlayers and solid-state organic interlayers for improving electron transport in low-cost, n-type OTFTs using group 14 phthalocyanines.

Silicon phthalocyanines (SiPcs) are a class of conjugated, planar molecule that have recently been investigated for use in organic photovoltaics (OPVs), organic light‐emitting diodes (OLEDs), and organic thin‐film transistors (OTFTs) due to their variable structure and ease of synthesis. Bottom‐gate, bottom‐contact OTFTs with four SiPc derivatives used as the semiconducting layers are prepared using physical vapor deposition. Devices using bis(pentafluorophenoxy) silicon phthalocyanine (F10‐SiPc) deposited on 140 °C substrates demonstrate electron field‐effect mobilities (μ) of up to 0.54 cm2 V−1 s−1, among the best currently reported for N‐type phthalocyanine‐based transistors. All materials show dramatic changes in charge transport when characterized under vacuum (P < 0.1 Pa) compared to in air at atmospheric pressure, typically switching from electron majority charge carriers to holes, with the change dependent on material structure and energetics. F10‐SiPc is close to balanced ambipolar in air, with μ around 5 × 10−3 cm2 V−1 s−1 for both holes and electrons. These results demonstrate SiPcs' potential as N‐type semiconductors in OTFTs as well as their adjustable charge transport as affected by operation environment.

Silicon phthalocyanines (SiPcs) have shown great potential as n-type or ambipolar organic semiconductors in organic thin-film transistors (OTFTs) and organic photovoltaics. Although properly designed SiPcs rival current state-of-the-art n-type organic semiconducting materials, relatively few structure–property relationships have been established to determine the impact of axial substituents on OTFT performance, hindering the intelligent design of the next generation of SiPcs. To address this omission, we have developed structure–property relationships for vapor-deposited SiPcs with phenoxy axial substituents. In addition to thorough electrical characterization of bottom-gate top-contact OTFTs, we extensively investigated SiPc thin films using X-ray diffraction, atomic force microscopy (AFM), grazing-incidence wide-angle X-ray scattering (GIWAXS), and density functional theory (DFT) modeling. OTFT performance, including relative electron mobility (μe) of materials, was in general agreement with values obtained through DFT modeling including reorganization energy. Another significant trend observed from device performance was that increasing the electron-withdrawing character of the axial pendant groups led to a reduction in threshold voltage (V T) from 47.9 to 21.1 V. This was corroborated by DFT modeling, which predicted that V T decreases with the square of the dipole induced at the interface between the SiPc pendant and substrate. Discrepancies between modeling predictions and experimental results can be explained through analysis of thin-film morphology and orientation by AFM and GIWAXS. Our results demonstrate that a combination of DFT modeling to select prospective candidate materials, combined with appropriate processing conditions to deposit molecules with a favorable thin-film morphology in an “edge-on” orientation relative to the substrate, yields high-performance n-type SiPc-based OTFTs.