Contact Engineering Using Manganese, Chromium, and Bathocuproine in Group 14 Phthalocyanine Organic Thin-Film Transistors

Abstract

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: synthesis and resurgent applications

“…Motivated by these results, Lessard et al, investigated the behaviour of fluorophenoxy derivatives of SiPc as n-type transistors. 126,127 It was noticed that the frequency and position of fluorine atoms affected electron mobility and the compounds 3f-3h exhibited some ambipolarity of charge transport (Fig. 8).…”

From chemical curiosity to versatile building blocks: unmasking the hidden potential of main-group phthalocyanines in organic field-effect transistors

“…The same treatment and characterisation methods were also applied to their tin counterparts, namely (F 5 PhO) 2 -SnPc and (2,4,6-F 3 PhO) 2 -SnPc. 34 The results of this study indicate that Mn and Cr interlayers do not strongly affect performance, while BCP can increase the off-current provided the entire organic semiconductor film is covered. These results were attributed to the larger Sn atom, which has a higher propensity for interaction with BCP than SiPc.…”

“…151 In early 2020, Lessard's group extended their research to the synthesis and the OTFT application of complexes with electron-deficient polyfluorinated aryl substituents at the axial positions, including (F 5 Ph) 2 -SnPc and (2,4,6-F 3 Ph) 2 -SnPc. 34 The reaction of Cl 2 -SnPc with fluorophenol in refluxing chlorobenzene resulted in bis(fluorophenoxy) substituted SnPcs in good yields of B80%.…”

“…To enhance device performance and reduce the injection barrier between the organic semiconductor and contacts, Melville et al have introduced either an electron dopant layer (bathocuproine, BCP) or low-work-function metals (Mn/Cr) between the high work-function electrodes (Au, Ag) and the (F 5 PhO) 2 -SiPc semiconductor layer. 34 The device structure is shown in Fig. 16, and the saturation region properties are shown in Fig.…”

“…Regarding molecular electronics, MPcs have gained tremendous traction towards the development of active materials a Department of Chemistry and Biomolecular Sciences, University of Ottawa, in organic photovoltaics (OPVs), [23][24][25][26] light-emitting diodes (OLEDs), [27][28][29][30] and field-effect transistors (OFETs). [31][32][33][34] Given the monumental role of FETs in modern-day devices, the implementation of MPcs as intrinsic organic semiconductors within these devices offers several advantages over their traditional inorganic counterparts. For one, synthetic procedures of MPcs are relatively facile, inexpensive, and ideal for massproduction at an industrial scale.…”