Hydrophilic microporous membranes for selective ion separation and flow-battery energy storage

Membranes with fast and selective ion transport are widely used for water purification and devices for energy conversion and storage including fuel cells, redox flow batteries and electrochemical reactors. However, it remains challenging to design cost-effective, easily processed ion-conductive membranes with well-defined pore architectures. Here, we report a new approach to designing membranes with narrow molecular-sized channels and hydrophilic functionality that enable fast transport of salt ions and high size-exclusion selectivity towards small organic molecules. These membranes, based on polymers of intrinsic microporosity containing Tröger’s base or amidoxime groups, demonstrate that exquisite control over subnanometre pore structure, the introduction of hydrophilic functional groups and thickness control all play important roles in achieving fast ion transport combined with high molecular selectivity. These membranes enable aqueous organic flow batteries with high energy efficiency and high capacity retention, suggesting their utility for a variety of energy-related devices and water purification processes

Benzodithiophene-Based Spacers for Layered and Quasi-Layered Lead Halide Perovskite Solar Cells

Incorporating extended pi-conjugated organic cations in layered lead halide perovskites is a recent trend promising to merge the fields of organic semiconductors and lead halide perovskites. Herein, we integrate benzodithiophene (BDT) into Ruddlesden-Popper (RP) layered and quasi-layered lead iodide thin films (with methylammonium, MA) of the form (BDT)(2)MA(n-1)Pb(n)I(3n+1). The importance of tuning the ligand chemical structure is shown as an alkyl chain length of at least six carbon atoms is required to form a photoactive RP (n=1) phase. With N=20 or 100, as prepared in the precursor solution following the formula (BDT)(2)MA(N-1)Pb(N)I(3N+1), the performance and stability of devices surpassed those with phenylethylammonium (PEA). For N=100, the BDT cation gave a power conversion efficiency of up to 14.7 % vs. 13.7 % with PEA. Transient photocurrent, UV photoelectron spectroscopy, and Fourier transform infrared spectroscopy point to improved charge transport in the device active layer and additional electronic states close to the valence band, suggesting the formation of a Lewis adduct between the BDT and surface iodide vacancies

Bulk Heterojunction Organic Semiconductor Photoanodes: Tuning Energy Levels to Optimize Electron Injection

The use of a bulk heterojunction of organic semiconductors to drive photoelectrochemical water splitting is an emerging trend; however, the optimum energy levels of the donor and acceptor have not been established for photoanode operation with respect to electrolyte pH. Herein, we prepare a set of donor polymers and non-fullerene acceptors with varying energy levels to probe the effect of photogenerated electron injection into a SnO2-based substrate under sacrificial photo-oxidation conditions. Photocurrent density (for sacrificial oxidation) up to 4.1 mA cm???2 was observed at 1.23 V vs reversible hydrogen electrode in optimized photoanodes. Moreover, we establish that a lower-lying donor polymer leads to improved performance due to both improved exciton separation and better charge collection. Similarly, lower-lying acceptors also give photoanodes with higher photocurrent density but with a later photocurrent onset potential and a narrower range of pH for good operation due to the Nernstian behavior of the SnO2, which leads to a smaller driving force for electron injection at high pH

Lead Halide Perovskite Quantum Dots to Enhance the Power Conversion Efficiency of Organic Solar Cells

The facile synthesis, solution-processability, and outstanding optoelectronic properties of emerging colloidal lead halide perovskite quantum dots (LHP QDs) makes them ideal candidates for scalable and inexpensive optoelectronic applications, including photovoltaic (PV) devices. The first demonstration of integrating CsPbI3 QDs into a conventional organic solar cell (OSC) involves embedding the LHP QDs in a donor-acceptor (PTB7-Th:PC71BM) bulk heterojunction. Optimizing the loading amount at 3 wt %, we demonstrate a power conversion efficiency of 10.8 %, which is a 35 % increase over control devices, and is a record amongst hybrid ternary OSCs. Detailed investigation into the mechanisms behind the performance enhancement shows that increased light absorption is not a factor, but that increased exciton separation in the acceptor phase and reduced recombination are responsible

A hybrid bulk-heterojunction photoanode for direct solar-to-chemical conversion

Organic semiconductors (OSs) are emerging candidates as light-harvesting materials in photoelectrochemical (PEC) cells for direct solar-to-chemical conversion. Despite significant recent progress with OS-based photocathodes, the development of efficient and stable OS-based photoanodes remains a challenge. Here, we demonstrate the concept of an in situ formed covalent polymer network (CPN) in a hybrid CPN:SnO2 bulk-heterojunction (BHJ) to increase the photocurrent density (J(ph)) and stability of OS-based photoanodes for PEC splitting of hydroiodic acid (HI). Our results indicate that the CPN:SnO2 BHJ overcomes the limited exciton diffusion length in OSs and provides a J(ph) improvement of more than three orders of magnitude compared to equivalent bilayer heterojunctions. Furthermore, insight into the operation of the hybrid BHJ in direct contact with aqueous electrolyte is gained with electrochemical impedance spectroscopy and PEC measurements under varying pH. With 1 M HI (pH 0) as the electrolyte, an optimized CPN:SnO2 photoanode without catalyst or protection layer delivers a J(ph) of 3.3 mA cm(-2) at the thermodynamic potential of iodide oxidation (+0.54 V vs. the normal hydrogen electrode) and a continuous operation for 27 h (J(ph) loss of 12%), representing a new benchmark for OS photoanodes for solar-to-chemical conversion. Complete HI splitting is further demonstrated in an all-OS photocathode/photoanode PEC cell to produce H-2 and I-3(-) from simulated sunlight without applied bias

Pseudo-halide anion engineering for ??-FAPbI3 perovskite solar cells

Metal halide perovskites of the general formula ABX(3)-where A is a monovalent cation such as caesium, methylammonium or formamidinium; B is divalent lead, tin or germanium; and X is a halide anion-have shown great potential as light harvesters for thin-film photovoltaics(1-5). Among a large number of compositions investigated, the cubic alpha-phase of formamidinium lead triiodide (FAPbI(3)) has emerged as the most promising semiconductor for highly efficient and stable perovskite solar cells(6-9), and maximizing the performance of this material in such devices is of vital importance for the perovskite research community. Here we introduce an anion engineering concept that uses the pseudo-halide anion formate (HCOO-) to suppress anion-vacancy defects that are present at grain boundaries and at the surface of the perovskite films and to augment the crystallinity of the films. The resulting solar cell devices attain a power conversion efficiency of 25.6 per cent (certified 25.2 per cent), have long-term operational stability (450 hours) and show intense electroluminescence with external quantum efficiencies of more than 10 per cent. Our findings provide a direct route to eliminate the most abundant and deleterious lattice defects present in metal halide perovskites, providing a facile access to solution-processable films with improved optoelectronic performance