Metal-organic frameworks at interfaces in dye-sensitized solar cells

MOF-derived Co2+-doped TiO2 nanoparticles as photoanodes for dye-sensitized solar cells

Facile synthesis and application of nano-sized semiconductor metal oxides for optoelectronic devices have always affected fabrication challenges since it involves multi-step synthesis processes. In this regard, semiconductor oxides derived directly from metal-organic frameworks (MOFs) routes have gained a great deal of scientific interest owing to their high specific surface area, regular and tunable pore structures. Exploring the application potential of these MOF-derived semiconductor oxides systems for clean energy conversion and storage devices is currently a hot topic of research. In this study, titanium-based MIL-125(Ti) MOFs were used as a precursor to synthesize cobalt-doped TiO2-based dye-sensitized solar cells (DSSCs) for the first time. The thermal decomposition of the MOF precursor under an air atmosphere at 400 °C resulted in mesoporous anatase-type TiO2 nanoparticles (NPs) of uniform morphology, large surface area with narrow pore distribution. The Co2+ doping in TiO2 leads to enhanced light absorption in the visible region. When used as photoanode in DSSCs, a good power conversion efficiency (PCE) of 6.86% with good photocurrent density (Jsc) of 13.96 mA cm-2 was obtained with the lowest recombination resistance and the longest electron lifetime, which is better than the performance of the pristine TiO2-based photoanode.

Application of Metal-Organic Frameworks and Covalent Organic Frameworks as (Photo)Active Material in Hybrid Photovoltaic Technologies

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are two innovative classes of porous coordination polymers. MOFs are three-dimensional materials made up of secondary building blocks comprised of metal ions/clusters and organic ligands whereas COFs are 2D or 3D highly porous organic solids made up by light elements (i.e., H, B, C, N, O). Both MOFs and COFs, being highly conjugated scaffolds, are very promising as photoactive materials for applications in photocatalysis and artificial photosynthesis because of their tunable electronic properties, high surface area, remarkable light and thermal stability, easy and relative low-cost synthesis, and structural versatility. These properties make them perfectly suitable for photovoltaic application: throughout this review, we summarize recent advances in the employment of both MOFs and COFs in emerging photovoltaics, namely dye-sensitized solar cells (DSSCs) organic photovoltaic (OPV) and perovskite solar cells (PSCs). MOFs are successfully implemented in DSSCs as photoanodic material or solid-state sensitizers and in PSCs mainly as hole or electron transporting materials. An innovative paradigm, in which the porous conductive polymer acts as standing-alone sensitized photoanode, is exploited too. Conversely, COFs are mostly implemented as photoactive material or as hole transporting material in PSCs.

Current status and future prospects of metal–organic frameworks at the interface of dye-sensitized solar cells

In this Frontier Article recent progresses and challenges at the interface of metal–organic frameworks and dye-sensitized solar cells are highlighted and discussed.

Towards implementing hierarchical porous zeolitic imidazolate frameworks in dye-sensitized solar cells

A one-pot method for encapsulation of dye, which can be applied for dye-sensitized solar cells (DSSCs), and synthesis of hierarchical porous zeolitic imidazolate frameworks (ZIF-8), is reported. The size of the encapsulated dye tunes the mesoporosity and surface area of ZIF-8. The mesopore size, Langmuir surface area and pore volume are 15 nm, 960-1500 m² · g^-1 and 0.36-0.61 cm³ · g^-1, respectively. After encapsulation into ZIF-8, the dyes show longer emission lifetimes (greater than 4-8-fold) as compared to the corresponding non-encapsulated dyes, due to suppression of aggregation, and torsional motions.

Surface-Supported Metal-Organic Framework Thin-Film-Derived Transparent CoS1.097@N-Doped Carbon Film as an Efficient Counter Electrode for Bifacial Dye-Sensitized Solar Cells

An effective design for counter electrode (CE) catalytic materials with superior catalytic activity, excellent stability, low cost, and a facile fabrication process is urgently needed for industrialization of dye-sensitized solar cells (DSSCs). Herein, we report a facile in situ method to fabricate transparent CoS_1.097 anchored on an N-doped carbon film electrode through sulfurization of a cobalt-metalloporphyrin metal-organic framework thin film on fluorine-doped tin oxide glass. The transparent film as counter electrode in bifacial DSSCs exhibited higher power conversion efficiency (9.11% and 6.64%), respectively, from front and rear irradiation than that of Pt (8.04% and 5.87%). The uniformly dispersed CoS_1.097 nanoparticles on an N-doped carbon film provide a large catalytic active area and facilitate the electron transfer, which leads to the excellent catalytic ability of the CoS_1.097@N-doped carbon film. In addition, the in situ preparation of the uniform film with a nanosheet structure offers high electrical conductivity and unobstructed access for the diffusion of triiodide to available electroactive sites, resulting in excellent device performance with superior long-term stability over 1000 h under natural conditions.

Efficient MOF-Sensitized Solar Cells Featuring Solvothermally Grown [100]-Oriented Pillared Porphyrin Framework-11 Films on ZnO/FTO Surfaces

Owing to their abilities to assemble and organize a large number of redox and photoactive components in highly ordered periodic fashion, crystalline porous metal-organic frameworks (MOFs) have the potential to execute myriad complex functions, including charge transport and light to electrical energy conversion when the required conditions are fulfilled. Herein, we demonstrate an unprecedented spontaneous solvothermal growth of precisely [100]-oriented pillared porphyrin framework-11 (PPF-11) films featuring vertically aligned Zn-tetrakis(4-carboxyphenyl)porphyrin (ZnTCPP) walls and horizontally aligned 2,2'-dimethyl-4,4'-bipyridine beams attached to annealed ZnO-fluorine-doped tin oxide (FTO) surfaces and their remarkable photovoltaic performance in liquid-junction solar cells. The [100]-oriented PPF-11/ZnO-FTO photoanodes displayed excellent photovoltaic response (short-circuit current ( J_SC): 4.65 mA/cm², open-circuit voltage ( V_OC): 470 mV, power conversion efficiency: 0.86%) that easily outperformed all control devices as well as previously reported porphyrin and Ru(bpy)₃²⁺-based visible light-harvesting MOFs with 10-1000 times greater photocurrent density and 2-375 times higher efficiency. The superior photovoltaic behavior of [100]-oriented PPF-11/ZnO films compared to epitaxially grown MOF thin films on insulating self-assembled monolayers and drop-cast PPF films with different orientations can be attributed to several factors, including better charge separation, transport, and injection capabilities of the former. The noncatenated PPF-11 was able to host electron-deficient C₆₀ guests, filling in nearly half of its cavities and engage them in ZnTCPP/C₆₀ charge-transfer interaction. However, the C₆₀-doped PPF-11/ZnO films displayed much weaker photovoltaic response than undoped [100]-oriented PPF-11/ZnO films presumably due to exclusion of I^-/I₃^- electrolyte from the C₆₀-occupied cavities and the inability of isolated C₆₀ guests to support long-range charge movement.

Redox active azo-based metal–organic frameworks as anode materials for lithium-ion batteries

Two redox active azo-based metal–organic frameworks (Cu-MOF 1 and Ni-MOF 2) exhibit high specific capacities, good rate performances and cycling stabilities when directly used as anode materials for lithium-ion batteries (LIBs).

Novel Solid-State Solar Cell Based on Hole-Conducting MOF-Sensitizer Demonstrating Power Conversion Efficiency of 2.1

This work reports on designing of first successful MOF-sensitizer based solid-state photovoltaic device, perticularly with a meaningful output power conversion efficiency. In this study, an intrinsically conductive cobalt-based MOFs (Co-DAPV) formed by the coordination between Co (II) ions and a redox active di(3-diaminopropyl)-viologen (i.e., DAPV) ligand is investigated as sensitizer. Hall-effect measurement shows p-type conductivity of the Co-DAPV film with hole mobility of 0.017 cm² V^-1 s^-1, suggesting its potential application as hole transporting sensitizer. Further, the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of Co-DAPV are well-matched to be suitably employed for sensitizing TiO₂. Thus, by layer-by-layer deposition of hole conducting MOF-sensitizer onto mesoporous TiO₂ film, a power conversion efficiency of as high as 2.1% is achieved, which exceeds the highest efficiency values of MOF-sensitized liquid-junction solar cells reported so far.

Efficient photocatalytic and photovoltaic applications with nanocomposites between CdTe QDs and an NTU-9 MOF

CdTe QDs + NTU-9 MOF as a novel photoanode to improve the efficiency of a QD cell by about 1.5%.

An updated roadmap for the integration of metal–organic frameworks with electronic devices and chemical sensors

This review highlights the steps needed to bring the properties of MOFs from the chemical lab to the microelectronics fab.

Surface-supported metal–organic framework thin films: fabrication methods, applications, and challenges

Surface-supported metal–organic framework thin films are receiving increasing attention as a novel form of nanotechnology, which hold great promise for photovoltaics, electronic devices, CO₂ reduction, energy storage, water splitting and membranes.

Efficient photocatalytic degradation of rhodamine 6G with a quantum dot-metal organic framework nanocomposite

The hybrid structures of metal organic frameworks (MOFs) and nanoparticles may offer the realization of effective photocatalytic materials due to combined benefits of the porous and molecular sieving properties of MOF matrix and the functional characteristics of encapsulated nanoparticles. In this study, cadmium telluride (CdTe) quantum dots (QD) are conjugated with a europium-MOF for the synthesis of a novel nanocomposite material with photocatalytic properties. Successful synthesis of a QD/Eu-MOF nanocomposite was characterized with various spectroscopic and microscopic techniques. This QD/Eu-MOF is found to be an effective catalyst to complete the degradation of Rhodamine 6G dye within 50 min.

Prussian blue analogues Mn[Fe(CN)6]0.6667·nH2O cubes as an anode material for lithium-ion batteries

In the present work, Prussian blue analogues, Mn[Fe(CN)6]0.6667·nH2O (Mn-PBA), were synthesized by a simple synthetic route and characterized by XRD, SEM, TEM, FTIR and TGA. When this material was firstly used as an anode for lithium-ion batteries, it exhibited a large capacity, good rate capability and cycling stability with a high Coulombic efficiency. For instance, a reversible capacity of 295.7 mA h g(-1) can be achieved after 100 cycles at 200 mA g(-1).

Rational molecular engineering of cyclopentadithiophene-bridged D-A-π-A sensitizers combining high photovoltaic efficiency with rapid dye adsorption

Dye-sensitized solar cell (DSSC) is considered as a feasible route to the clean and renewable energy conversion technique. The commercial application requires further enhancements on photovoltaic efficiency and simplification on the device fabrication. For avoiding the unpreferable trade-off between photocurrent (JSC) and photovoltage (VOC), here we report the molecular engineering and comprehensive photovoltaic characterization of three cyclopentadithiophene-bridged D-A-π-A motif sensitizers with a change in donor group. We make a careful choice on the donor and conjugation bridge for synergistically increasing JSC and VOC. Comparing with the reference dye WS-2, the photovoltaic efficiency with the single component dye of WS-51 increases by 18%, among one of the rare examples in pure metal-free organic dyes exceeding 10% in combination with traditional iodine redox couples. Moreover, WS-51 exhibits several prominent merits on potentially scale-up industrial application: i) facile synthetic route to target molecule, ii) simple dipping procedure without requirement of co-sensitization, and iii) rapid dye adsorption capability.