A brief introduction to the RSC’s portfolio of journals covering the breadth of energy, materials, nanoscience and catalysis, and our initiatives to share and highlight research with the community.

Third generation solar cells have the potential to provide a viable source of renewable energy to help decarbonize our economy and power wearable devices. With their exceptional performance in diffused light under indoor conditions, dye-sensitized solar cells (DSCs) remain competitive for powering the next digital revolution forming the internet of things.[1] When integrated with an energy storage system such as an electric double layer capacitor (EDLC), DSCs can offer reliable uninterrupted energy output as a photocapacitor. However, conventional DSCs use liquid electrolyte as the redox mediator, which limits the suitability of the technology for scale up and commercialization.  Joining the quest for stable, reproducible solid-state hole transport materials (HTM), we are exploring nanostructured metal-organic frameworks (MOFs).  These emerging materials possess the highly ordered structure of inorganic materials combined with the chemically tailorable properties and low cost of organics, and have outperformed their precursors in a wide range of applications.[2]

In my talk, I will introduce copper benzenetetrathiol (CuBTT) system with highly efficient redox conductivity as a solid state HTM. We demonstrate that creation of highly interconnected networks of these polymeric nanowires improves the conductivity and when epitaxially assembled, these nanowire architectures infiltrate and form better contact with the dye molecules. We also show that modulator assisted bottom-up synthesis gives stacked 2D layers penetrated by 1D cylindrical channels for ion conduction.  This can act as a suitable interface when the DSC is coupled with an EDLC in a photocapacitor architecture. This work establishes MOF nanosheets as efficient interface materials for solar capture and storage devices.

The optimization of various mechanisms is essential to reach the efficiency limit in solar cells, as highlighted by Shockley and Queisser[1]. One critical aspect involves enhancing the transparent conductive oxide (TCO) positioned at the front of the device. The TCO plays a crucial role in extracting photogenerated carriers and acts as a window for the Sun's light. Additionally, introducing periodic micro- and nanostructures on TCO surfaces has the potential to increase transmittance and surface area, leading to improved efficiency[2–5]. In this research, direct laser interference patterning (DLIP) was employed to modify thin films of fluorine-doped tin oxide (FTO) and indium tin oxide (ITO), which were subsequently utilized as TCOs for perovskite solar cells.

Results reveal dot-like periodic sub-microstructures with an approximate 700 nm spatial period, increasing incident light spread and total transmittance. These structured films improved perovskite solar cell performance, demonstrating the positive impact of the generated patterning in the light-trapping capabilities. Additionally, the increase in effective surface area might lead to a more efficient charge transfer in the interface between FTO/ITO and SnO₂.

Doping or alloying strategies are heavily employed in the design of new catalysts for photoelectrochemical, photochemical and electrochemical conversion reactions with enhanced solar energy harvesting efficiencies and/or desired surface chemistry. In the electrochemical reduction of CO₂ for example, efforts are focused on the development of electrocatalysts with high activity and selectivity towards C₂₊ products ideally breaking the scaling relations currently observed for metal surfaces.[1] In photoelectrochemical and photocatalytic devices research has focused on developing catalysts with light harvesting in the visible, strong surface electric fields and long charge carrier lifetimes.[2,3] In both, electro- and photocatalytic systems, perovskite oxides have been employed heavily, offering a more versatile defect chemistry platform.

Here, I will showcase some of our studies on oxide perovskite materials employed in photo- and electrocatalysis discussing links between defect chemistry and catalytic performance. One example will be the visible light absorber (La,Sr)(Rh,Ti)O3 employed in the Z-scheme photocatalyst sheet device from Profs. Wang and Domen which led to a record 1% solar-to-hydrogen efficiency.[4,5] Taking inspiration from this material, we have been investigating the performance of other dopants and compositions in photo- and electrocatalytic conversion of CO₂ leading us to look very closely into the material surface compositions and the ways of reporting of catalytic activity.

Portable applications powered by solar energy face challenges with both sunlight's intermittency and illumination variability from outdoor to indoor transitions necessitating the development of efficient energy storage systems to ensure consistent power availability. In this context, photosupercapacitor could represent a viable solution toward an efficient energy supply. In this presentation, after introducing the concept of photosupercapacitor I will report on the realization of  flefible hybrid photosupercapacitor based on the combination of an ultra-flexible carbon screen printed interdigitated supercapacitor on paper and a flexible perovskite solar module (PSM) on PET.
This all-flexible device functions as a self-powering unit for both energy conversion and storage. Impressively, the supercapacitor showcases remarkable stability and a coulombic efficiency of 100%. Through a hybrid bifurcated structure designed to enhance their applicability, the supercapacitors were connected in series. They were neatly layered on a paper substrate with the solar module strategically placed on top.
The device quickly reached saturated voltage value with exposure to various light intensities such as 1 sun, 1000 lx, 500 lx and 200 lx and displayed a self-discharge beaviour which lasted more than two minutes. With peak overall and storage
efficiencies determined to be 2.8% and 23% respectively. The integrated hybrid photosupercapacitor exhibited an extensive potential window of 3.8 V making it an prominent choice for real time application in electronic systems.

Solution processability of high-quality metal halide perovskites (MHPs) with a wide range of compositions has enabled the unprecedented evolution of perovskite solar cells (PSCs) and perovskite light-emitting devices (PLEDs), which has fascinated researchers from academia and industry. Due to the ionicity and antibonding nature of valence and conduction band states, highly luminescent crystalline structures ranging from nanocrystals to thin films are produced in the case of metal halide perovskites using solution-based strategies. The vulnerability of the lattice of metal halide perovskites towards distortions is increased due to their ionic nature when exposed to bias and illumination both in materials and devices, which further amplifies ionic motions under operational conditions. Although the development in terms of efficiencies and stability has been phenomenal, the mixed conduction of electrons and ions has proven to be an "Achilles heel" for perovskite devices thus far. Mixed conduction behaviour allows migration and accumulation of ions in PSCs and PLEDs, which induce detrimental chemical and structural changes both in the bulk of MHP layer and at the interfaces under external stimuli. Interestingly, the nature of chemical bonding in other solution-processable molecular and quantum dot semiconductors has also provided us with adequate insights regarding their performance and stability issues, especially in a device configuration.

In my presentation, I will discuss some intriguing examples illustrating the significance of chemical bonding both in the active perovskite layer and charge conductors in a solar cell configuration.

The Internet of Things (IoT) underpins our future smart world where various electronic devices will be integrated with, and controlled by, wireless communication.[1] Many of these devices will be standalone or portable, creating an urgent demand for off-grid power sources. Solar photovoltaic (PV) cells are viable alternatives to batteries as perpetual power sources for IoT devices. However, crystalline silicon (c-Si) PV cells (which currently account for 95% of the global PV market) are not designed to work with diffuse, artificial indoor light-emitting diode (LED) lighting and perform poorly under these conditions.[2]

Luminescent waveguide-encoded lattices (LWELs) are a new class of photonic material that have recently been proposed to compensate for the limitations of c-Si PV cells for indoor PV.[3,4] LWELs consist of a thin (ca. 1 mm) luminescent polymer film encoded with a patterned array of discrete waveguides. The waveguide array is formed through the self-trapping of incident beams of light within a photopolymerisable matrix. This leads to the permanent inscription of polychromatic cylindrical waveguide channels within the polymer matrix, which impart LWELs with an exceptionally wide field-of-view (80% enhancement shown previously[5]). The LWEL is retrofitted to the top surface of a PV cell to enhance light collection.

While the optical and materials properties of non-emissive WELs are reasonably well-understood [5,6], the inclusion of a luminophore can complicate the self-trapping processes that led formation of the waveguide channels. In this talk, the relationship between the photopolymerization kinetics, materials composition and optical properties of LWELs will be discussed, with a view to understanding the design rules that underpin efficient performance upon integration with PV cells.

Tremendous advances have been made in photovoltaics (PV) in recent years, including in the development of emerging technologies such as perovskite PV, organic PV and dye-sensitised solar cells (DSSCs). These technologies can be applied to areas where silicon PV is not well suited, including power for consumer electronics, electromobility, building-integrated PV with attractive appearance, flexible, light-weight and semi-transparent PV, indoor energy scavenging and more. In some of these applications areas, simplicity and low-cost for the devices can become as important as efficiency to achieve practical systems. DSSCs offer a promising choice for applications requiring low-cost indoor power generation for powering the emerging internet-of-things. However, they currently include complex and costly sensitizers which require long synthesis procedures, alongside electrolytes that can be detrimental to stability and/or ease of fabrication. The presentation will focus on our recent work on DSSCs aiming to simplify the dye [1, 2] and the electrolyte components [3, 4] towards more-readily fabricated and readily-scaled technology.

Electron collection in dye-sensitized solar cells (DSCs) is determined by a delicate equilibrium between electronic transport within the mesoporous oxide layers and recombination losses. While state-of-the-art DSC devices have shown quantitative collection under standard 1-sun conditions, the nonlinear nature of the trapping/detrapping dynamics in the oxide layer in relation to the overall electron density may result in suboptimal performance under the lower illumination levels commonly encountered in indoor settings. In this study, we thoroughly examine the key factors influencing electron collection with respect to light intensity using impedance spectroscopy and numerical analysis

The development of renewable energy sources is a global challenge, as we seek new routes to address increasing CO₂ levels, climate change and energy security. Many solutions have been suggested, including hydrogen generation.  Photocatalytic water splitting using photosensitisers (PS) together with catalytic centres (Cat) (artificial photosynthesis) have been extensively studied by us and others.^[1-4] The ultimate goal is to incorporate these assemblies into dye-sensitised photoelectrochemical cells.  We have developed a range of intramolecular assemblies (inorganic and organic systems) containing various bridges such as terpyridine, triazole, or imines linking the PS to the catalytic centre to enhance hydrogen generation. We have also modified these systems and used them for CO₂ reduction. We have performed in depth time-resolved studies to probe the excited states of the complexes to investigate the nature of the electron transfer processes, and carried out spectroelectrochemistry to aid in design of superior photocatalysts for both reduction processes.  Our studies indicate that many parameters must be considered when designing such assemblies.

In nature, solar energy is captured and stored in chemical bonds by activating small molecules such as CO₂ and H₂O. This requires catalysts capable of carrying out CO₂ reduction and water oxidation catalysis. In this presentation, molecular catalysts and mechanisms related to these two processes will be discussed. CO₂ reduction to C₁ products has received considerable attention as part of many efforts to try to address the devastating effects of climate change. Among various C₁ reduction products, liquid fuels such as formic acid and methanol are particularly important to achieve carbon-neutral cycles. But the underlying chemistry to generate liquid fuels from CO₂ efficiently and selectively has yet to be developed, particularly in the case of methanol. Cascade strategies using a combination of catalysts that can carry out some of the required multistep reactions are being pursued because achieving this goal with a single catalyst is difficult. One of these strategies involves CO₂ reduction to CO by one catalyst and further reduction of CO to a liquid fuel by another catalyst or a combination of catalysts.  In this presentation, a strategy for the generation of methanol efficiently and selectively from CO is discussed, with a transition metal-organic hydride combination. Using NMR, IR and mass spectrometry, together with labeling studies, chemical synthesis of authentic samples of intermediates and theoretical calculations, selective and efficient conversion of CO to methanol is demonstrated. The key to the high selectivity is the use of organic hydride donors that are inactive towards direct CO₂ reduction and hydrogen generation. These organic hydride donors are inexpensive and renewable and are a promising platform for solar fuels generation from CO₂. In the water oxidation front, a new mechanism for water oxidation catalysis with molecular catalysts will be presented. In this mechanism, the transition metal participates in the redox chemistry but not in the thermally activated processes, which take place on the ligands. In the oxygen evolution step, the ligands are returned to their original state and, as a result, these catalysts are very robust because they follow a “self-healing” mechanism. In addition, because the mechanism is ligand-based, no open coordination site is required and this enables the development of highly active molecular catalysts for water oxidation with first-row transition metals.