Functionalization of boron-doped diamond with a push–pull chromophore via Sonogashira and CuAAC chemistry
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2018-01-01 |
| Journal | RSC Advances |
| Authors | Jorne Raymakers, Hana Krýsová, Anna Artemenko, Jan Čermák, Shannon S. Nicley |
| Institutions | Czech Academy of Sciences, Faculty (United Kingdom) |
| Citations | 18 |
| Analysis | Full AI Review Included |
Technical Analysis: Boron-Doped Diamond Functionalization for High-Performance Photocathodes
Section titled “Technical Analysis: Boron-Doped Diamond Functionalization for High-Performance Photocathodes”6CCVD Ref. Document: 6CCVD-RSC-ADV-2018-33276
Executive Summary
Section titled “Executive Summary”This paper validates Boron-Doped Nanocrystalline Diamond (B:NCD) thin films, grown via MPCVD, as a robust and high-potential photocathode material for tandem Dye-Sensitized Solar Cells (DSSCs). The key findings and technical achievements driving future photovoltaic development include:
- Superior Performance via Sonogashira: Photocurrent densities achieved using Sonogashira cross-coupling (up to 450 nA cm-2 at -0.2 V) were approximately three times higher than those achieved using Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC) (140 nA cm-2).
- Linker Chemistry is Critical: The substantial performance difference, despite similar surface coverage and higher metal contamination from Sonogashira (Pd presence), indicates that the rigid alkyne linker (used in Sonogashira) is preferential to the triazole linker (used in CuAAC) for efficient hole injection into the diamond Valence Band Maximum (VBM).
- Validation of Covalent Grafting: The two-step functionalization process (diazonium grafting followed by secondary coupling) successfully achieved high, uniform coverage of the alkyne-DTP-BT donor-acceptor chromophore, creating a thin, stable photovoltaic layer.
- Low Contamination Potential: Optimization of the CuAAC reaction successfully yielded high sulfur coverage (2.5 at%) with no detectable copper residues via X-ray Photoelectron Spectroscopy (XPS), demonstrating feasibility for metal-free processes.
- Material Suitability Confirmed: B:NCD exhibits excellent optical transparency (300 nm - 1000 nm), protecting the dye from harmful UV light, and possesses high chemical inertness, making it compatible with corrosive electrolyte solutions (e.g., I3-/I-).
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted, detailing the material properties and performance achieved through surface functionalization for p-type DSSC application.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Max Photocurrent Density (Sonogashira) | 450 | nA cm-2 | Bias: -0.2 V, 0.9 Sun illumination (Initial) |
| Max Photocurrent Density (CuAAC) | 140 | nA cm-2 | Bias: -0.2 V, 0.9 Sun illumination (Initial) |
| Maximum Photovoltage | -12 to -14 | mV | Sonogashira coupling, Macroscopic SKP measurement |
| Surface Coverage (Sulfur, Sonogashira) | 2.3 | at% | Corresponds to highest initial photocurrent |
| Surface Coverage (Sulfur, CuAAC) | 2.5 | at% | Highest coverage obtained; performance limited |
| Optical Gap (Eg) of Chromophore (Dye) | 2.30 | eV | Solid-state UV-Vis, Alkyne-DTP-BT dye |
| Dye HOMO Energy Level (Calculated) | -5.59 | eV | Critical for hole injection into diamond VBM |
| Dye LUMO Energy Level (Measured) | -3.29 | eV | Measured via Cyclic Voltammetry (CV) |
| Metal Contamination (Pd Residue) | 0.6 | at% | Sonogashira optimized conditions (detrimental to performance) |
| Metal Contamination (Cu Residue) | Not Detected | at% | CuAAC optimized conditions (via XPS) |
| Hole Diffusion Coefficient (B:NCD) | 2 - 30 | cm2 s-1 | Eight orders of magnitude higher than standard NiO photocathodes |
Key Methodologies
Section titled “Key Methodologies”The functionalization of the H-terminated B:NCD electrodes followed a precise two-step process, tailored for molecular attachment onto the chemically inert diamond surface.
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Diamond Preparation:
- Material: Boron-Doped Nanocrystalline Diamond (B:NCD) thin films.
- Pre-treatment: Hydrogen termination (H-terminated B:NCD).
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Primary Functionalization (Electrochemical Diazonium Grafting):
- Purpose: Introduction of a primary functional handle (Iodophenyl or Azidophenyl) for subsequent cross-coupling.
- Iodophenyl Precursor: in situ diazotization of 4-iodoaniline (5 mM in 0.5 M HCl).
- Azidophenyl Precursor: in situ diazotization of 4-azidoaniline hydrochloride (5 mM in 0.5 M HCl).
- Protocol: Cyclic voltammetry performed between +500 mV and -600 mV (Iodophenyl) or +300 mV and -800 mV (Azidophenyl) vs. Ag/AgCl reference electrode.
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Secondary Functionalization (Sonogashira Cross-Coupling):
- Target: Covalent attachment of the alkyne-DTP-BT chromophore to the iodophenyl layer.
- Catalyst System: Pd(PPh3)2Cl2 (5 mol% minimum) as catalyst; CuI (10 mol% minimum) as co-catalyst.
- Solvents/Base: Dry THF and Triethylamine (TEA) (2:1 ratio) or Diisopropylamine (DIPA).
- Result: Highest performance (450 nA cm-2), confirmed presence of Pd (up to 0.6 at%).
-
Secondary Functionalization (CuAAC Click Chemistry):
- Target: Covalent attachment of the alkyne-DTP-BT chromophore to the azidophenyl layer via a triazole linker.
- Catalyst System: CuBr (100 mol%) with PMDETA (200 mol%) or THPTA stabilizing ligands.
- Conditions: Performed in glovebox under Ar atmosphere at 55 °C for 16 h (using dry THF/DMF solvents).
- Result: Highest coverage (2.5 at% S), but lowest performance (140 nA cm-2), minimal metal contamination (Cu not detected).
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD provides the specialized MPCVD diamond materials necessary to replicate, optimize, and scale the high-performance photocathodes detailed in this research. Our capabilities directly address the material specifications required for next-generation diamond-based hybrid photovoltaics.
Applicable Materials & Substrates
Section titled “Applicable Materials & Substrates”The research confirms the efficacy of Boron-Doped Nanocrystalline Diamond (B:NCD) for photoelectrochemical applications due to its transparency, stability, and high hole mobility.
- Optimal Material Match: Polycrystalline Boron-Doped Diamond (PCD/BDD). 6CCVD offers custom-grown, heavily B-doped films that match the electrical requirements of the B:NCD used in this study, ensuring high hole conductivity (p-type semiconductor behavior).
- High-Purity Alternative: For researchers seeking even greater structural control or optical homogeneity, 6CCVD provides Single Crystal Boron-Doped Diamond (SCD/BDD) substrates and films. While typically more conductive, SCD allows for fundamental studies requiring ultra-low defect densities.
- Custom Dopant Control: We offer precise control over boron incorporation during the MPCVD growth phase, allowing engineers to fine-tune the conductivity and VBM position for optimal energy level alignment relative to novel organic chromophores.
Customization Potential for Scale and Integration
Section titled “Customization Potential for Scale and Integration”Scaling DSSC technology requires reliable, large-area substrates and integrated electrode components—core strengths of 6CCVD.
| Requirement Addressed in Paper | 6CCVD Customization Capability | Value Proposition |
|---|---|---|
| Substrate Size & Thickness | Custom plates/wafers up to 125 mm (PCD). Thickness control for PCD/SCD from 0.1 µm up to 500 µm. | Facilitates transition from lab prototypes (thin films) to production-scale, inch-size devices. |
| Surface Finish & Morphology | Polishing services achieving Ra < 5 nm for inch-size PCD wafers. | Critical for achieving the highly uniform surface coverage necessary for consistent functionalization (as demonstrated by KPFM analysis). |
| Metal Residue Management | Custom Internal Metalization Services (Au, Pt, Ti, Cu, W, Pd). | Eliminates external contamination risk. Researchers requiring integrated contacts can use 6CCVD’s services to deposit highly pure contact metals directly onto the diamond, bypassing the risk of surface fouling encountered with external catalyst residues (like the Pd contamination noted in the Sonogashira study). |
| H-Termination | Standardized, high-quality H-termination processes following MPCVD growth. | Ensures a chemically active and consistent surface necessary for the initial electrochemical diazonium grafting step. |
Engineering Support & Application Extension
Section titled “Engineering Support & Application Extension”This research opens significant avenues in efficient energy conversion and photoelectrochemistry.
6CCVD’s in-house PhD engineering team can assist with material selection, interface chemistry, and performance optimization for similar Diamond-Based Hybrid Photovoltaic and Photoelectrochemical projects. We offer consultation to help researchers select the optimal MPCVD recipe, surface termination (H, O, or tailored groups), and polishing specification to maximize charge transfer efficiency and stability in aggressive environments.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Functionalization of boron-doped diamond with a push-pull chromophore <italic>via</italic> Sonogashira cross-coupling affords better photovoltaic performances as compared to functionalization <italic>via</italic> CuAAC.