Chemical passivation of the under coordinated Pb2+ defects in inverted planar perovskite solar cells via β-diketone Lewis base additives

Hybrid organic-inorganic perovskite solar cells (PSCs) are promising new generations of solar cells, which is low in cost with high power conversion efficiency (PCE). However, PSCs suffer from structural defects generated from the under coordinated ions at the surface, which limits their photovoltaic performances. Herein we report, two β-diketone Lewis base additives 2,4-pentanedione and 3-methyl-2,4-nonanedione within the chlorobenzene anti-solvent to passivate the surface defects generated from the under coordinated Pb²⁺ ions in CH₃NH₃PbI₃ perovskite films. The incorporation of the two β-diketone passivators could successfully enhance the open-circuit voltage of the PSCs by 52 mV and 17 mV for 3-methyl-2,4-nonanedione and 2,4-pentanedione, respectively, with improved PCE by 45% for 3-methyl-2,4-nonanedione compared to the pristine PSC. This enhancement in the photovoltaic performance of the PSCs can be attributed to passivation of the defects through the interaction between two carbonyl groups of the β-diketone Lewis base additives and the under coordinated Pb²⁺ defects in the perovskite film, which improved the PSCs PCE and stability.

New Pure Organic and Peroxide-Free Redox Initiating Systems for Polymerization in Mild Conditions

Redox initiating systems (RISs) are highly worthwhile for polymerization in mild conditions (at room temperature—RT) without external thermal or light activation. With high performance redox initiating systems RIS, the free radical polymerization FRP can even be carried out under air and without inhibitors/stabilizers removal from the monomers/resins. However, efficient RISs are still based on peroxides or metal complexes. In this work, a pure organic and peroxide-free RIS is presented based on the interaction of a well-selected triarylamine derivative (T4epa) with iodonium salt used as reducing and oxidizing agents, respectively. The redox polymerization (Redox FRP) was followed through pyrometry and thermal imaging experiments. Remarkably, a full control of the work time as well as a high reactivity is observed for mild conditions.

Peroxide-free redox initiating systems for polymerization in mild conditions

Redox free radical polymerization (RFRP) is considered as a cost-effective technique for the production of polymers in a very short time scale and without any energy consumption.

Recent Advances on Copper Complexes as Visible Light Photoinitiators and (Photo) Redox Initiators of Polymerization

Metal complexes are used in numerous chemical and photochemical processes in organic chemistry. Metal complexes have not been excluded from the interest of polymerists to convert liquid resins into solid materials. If iridium complexes have demonstrated their remarkable photochemical reactivity in polymerization, their high costs and their attested toxicities have rapidly discarded these complexes for further developments. Conversely, copper complexes are a blooming field of research in (photo) polymerization due to their low cost, easy syntheses, long-living excited state lifetimes, and their remarkable chemical and photochemical stabilities. Copper complexes can also be synthesized in solution and by mechanochemistry, paving the way towards the synthesis of photoinitiators by Green synthetic approaches. In this review, an overview of the different copper complexes reported to date is presented. Copper complexes are versatile candidates for polymerization, as these complexes are now widely used not only in photopolymerization, but also in redox and photoassisted redox polymerization processes.

High Performance Redox Initiating Systems Based on the Interaction of Silane with Metal Complexes: A Unique Platform for the Preparation of Composites

Currently, Redox Initiating Systems (RISs) of Free Radical Polymerization (FRP) are mainly based on the interaction of aromatic amines with peroxides (e.g., dibenzoyl peroxide (BPO)) that can be both toxic and unstable. In the present work, we aim to replace these hazardous substances in new RIS that can be peroxide-free and amine-free. Our redox two components (2K) initiating system is based on diphenylsilane (DPS) as reducing agent combined with different metal complexes (Mn(acac)₂, Cu(AAEMA)₂ or Fe(acac)₃) as oxidizing agents. For the new proposed RIS, an excellent reactivity is found for the polymerization of benchmark methacrylate monomers under mild conditions (redox polymerization done under air and at room temperature); remarkably, it is also possible to finely control the gel time. Different techniques (optical pyrometry, Real-Time FTIR spectroscopy, Cyclic Voltammetry and Electron Spin Resonance (ESR)) were used to follow the polymerization processes but also to shed some light on the new redox chemical mechanisms.

Recent Advances on Visible Light Metal-Based Photocatalysts for Polymerization under Low Light Intensity

In recent years, polymerization processes activated by light have attracted a great deal of interest due to the wide range of applications in which this polymerization technique is involved. Parallel to the traditional industrial applications ranging from inks, adhesives, and coatings, the development of high-tech applications such as nanotechnology and 3D-printing have given a revival of interest to this polymerization technique known for decades. To initiate a photochemical polymerization, the key element is the molecule capable to interact with light, i.e., the photoinitiator and more generally the photoinitiating system, as a combination of several components is often required to create the reactive species responsible for the polymerization process. With the aim of reducing the photoinitiator content while optimizing the polymerization yield and/or the polymerization speed, photocatalytic systems have been developed, enabling the photosensitizer to be regenerated during the polymerization process. In this review, an overview of the photocatalytic systems developed for polymerizations carried out under a low light intensity and visible light is provided. Over the years, a wide range of organometallic photocatalysts has been proposed, addressing both the polymerization efficiency and/or the toxicity, as well as environmental issues.

Charge-Transfer Complexes as New Inhibitors/Photoinitiators for On-Demand Amine/Peroxide Redox Polymerization

Redox free-radical polymerizations have widespread applications but still clearly suffer from poor time control of the reaction. Currently, the workability (delay of the gel time) in redox polymerization after mixing is possible thanks to two main types of inhibitors (radical scavengers): phenols and nitroxides. Out of this trend, we propose in this work an alternative strategy for time delaying of the redox polymerization, which is based on charge-transfer complexes (CTCs). Thanks to iodonium salt complexation, the amine (here 4-N,N-trimethylaniline) is proposed to be stored in a CTC equilibrium and is slowly released over a period of time (as a result of the consumption of free amines by peroxides). This alternative strategy allowed us to double the gel time (e.g., from 60 to 120 s) while maintaining a high polymerization efficiency (performance comparable to reference nitroxides). More interestingly, the CTCs involved in this retarding strategy are photoresponsive under visible LED@405 nm and can be used on demand as photoinitiators, allowing (i) spectacular increases in polymerization efficiencies (from 50 °C without light to 120 °C under mild irradiation conditions); (ii) drastic reduction of the oxygen-inhibited layer (already 45% C=C conversion at a 2 μm distance from the top surface) compared to the nonirradiated sample (thick inhibited layer of more than 45 μm); and (iii) external control of the redox polymerization gel time due to the possible light activation.

Stable copper acetylacetonate-based oxidizing agents in redox (NIR photoactivated) polymerization: an opportunity for the one pot grafting from approach and an example on a 3D printed object

Stable Cu(ii) ox. agent for redox (graft) polymerization.