Covalent Attachment and Characterization of Perylene Monolayers on Si(111) and TiO₂ for Electron-Selective Carrier Transport

Abstract

We functionalized chemically oxidized Si(111) and TiO2 surfaces with covalently attached rylene molecules and demonstrated further chemical conversion of the attached species. Base-catalyzed activation of perylene tetracarboxylic dianhydride (PTCDA) preceded reaction with phenylaminosilane-terminated surfaces, yielding surface-bound perylene via an imide linkage. Transflection infrared (IR) spectroscopy of the carbonyl vibrational region elucidated the presence of anhydride, imide, and ester species following each reaction stage. The presence of both anhydride and imide IR features following reaction with PTCDA validates successful perylene attachment. Subsequent functionalization of the surface-attached perylenes yielded IR spectra with little or no detectable anhydride features that indicate successful conversion to ester or imide species based on respective reactions with alkyl bromides or aryl amines. X-ray photoelectron spectroscopy quantified fractional coverages of surface-attached perylene species following a post-deposition derivatization with fluorine-containing alkyl bromides and with anilines. Overlayer model interpretation of the photoelectron results determined a perylene surface coverage of ∼15% relative to the surface density of Si(111) atop sites and a ∼10% surface coverage of imide-terminated perylene species. The interpreted coverage data yield an approximate conversion efficiency for the anhydride-to-imide derivatization at surface-attached perylenes of ∼66%. We discuss the present results in terms of possible coverage and packing on oxide-free silicon surfaces and the utilization of covalently attached rylene species as electron-transporting and hole-blocking connecting layers in molecular electronics and tandem-junction photovoltaic designs.

Open-Circuit Photovoltage Exceeding 950 mV with an 840 mV Average at Sb2S3–Thianthrene+/0Junctions Enabled by Thioperylene Anhydride Back Contacts

“… 22 Both regions reveal O 1s and Si 2p structures as previously observed for perylene attachment that utilizes silane linkages to silicon with a thin interfacial chemical oxide layer as well as C 1s features that include desired surface species and adventitious contamination. 22 …”

“…As presented in Figure 1 and described more thoroughly in Section 5 and the Supporting Information section, formation of an amine-terminated surface 2 , a perylene-anhydride-terminated surface 3 , and a diethyl-ester-terminated surface 4 followed efforts as described previously. 22 Treatment of degenerately doped n + -Si(111) with 3-aminopropyltrimethoxysilane yields aminopropyl-terminated surface 2 , from which treatment with PTCDA and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in ethanol and dimethylformamide (DMF) yielded perylene-anhydride-terminated surface 3 . Subsequent reaction of the perylene-anhydride-terminated surface 3 with additional DBU in ethanol and bromoethane yielded the diethyl-ester-terminated surface 4 .…”

“…Previous perylene surface attachment utilized infrared-active carbonyl stretching modes that are unique among anhydride, imide, and ester moieties. 22 Further, the C=O vibration is particularly strong in infrared spectra due to the large dipole change during the carbon–oxygen vibration that enables submonolayer detection of carbonyl-containing surface adsorbates. In contrast to C=O, there is a significantly smaller electronegativity difference between carbon and sulfur, and the resulting C=S oscillation presents observational challenges at monolayer-level surface coverages via traditional IR techniques.…”

“…20 , 21 Separately, we demonstrated the covalent attachment of perylenetetracarboxylic dianhydride, PTCDA, to Si(111) that leverages the anhydride-to-imide conversion on a surface-attached aniline molecule. 22 As part of a broader class of rylene compounds, perylenes are particularly desirable for their electronic tunability, covalent coupling, redox activity, and their low cost due to their use as industrial pigments. 23 − 30 Therefore, rylenes and their derivatives should enable an interconnection layer between inorganic absorbers that is soft, electronically tunable, and chemically matched to each contacting phase.…”

“… 23 − 30 Therefore, rylenes and their derivatives should enable an interconnection layer between inorganic absorbers that is soft, electronically tunable, and chemically matched to each contacting phase. 22 However, such interconnections have not been demonstrated to metal sulfides such as Sb 2 S 3 . We hypothesize that sulfur termination on the organic perylene monolayers may yield such an interconnection between silicon and Sb 2 S 3 .…”