Cation reactivity inhibits perovskite degradation in efficient and stable solar modules.

Perovskite solar modules (PSMs) show outstanding power conversion efficiencies (PCEs), but long-term operational stability remains problematic. We show that incorporating -dimethylmethyleneiminium chloride into the perovskite precursor solution formed dimethylammonium cation and that previously unobserved methyl tetrahydrotriazinium ([MTTZ]) cation effectively improved perovskite film. The in situ formation of [MTTZ] cation increased the formation energy of iodine vacancies and enhanced the migration energy barrier of iodide and cesium ions, which suppressed nonradiative recombination, thermal decomposition, and phase segregation processes.

Shallow-level defect passivation by 6H perovskite polytype for highly efficient and stable perovskite solar cells.

The power conversion efficiency of perovskite solar cells continues to increase. However, defects in perovskite materials are detrimental to their carrier dynamics and structural stability, ultimately limiting the photovoltaic characteristics and stability of perovskite solar cells. Herein, we report that 6H polytype perovskite effectively engineers defects at the interface with cubic polytype FAPbI, which facilitates radiative recombination and improves the stability of the polycrystalline film.

3D Conjugated Hole Transporting Materials for Efficient and Stable Perovskite Solar Cells and Modules.

The orthogonal structure of the widely used hole transporting material (HTM) 2,2',7,7'-tetrakis(N, N-di-p-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD) imparts isotropic conductivity and excellent film-forming capability. However, inherently weak intra- and inter-molecular π-π interactions result in low intrinsic hole mobility. Herein, a novel HTM, termed FTPE-ST, with a twist conjugated dibenzo(g,p)chrysene core and coplanar 3,4-ethylenedioxythiophene (EDOT) as extended donor units, is designed to enhance π-π interactions, without compromising on solubility.

Dopant-additive synergism enhances perovskite solar modules.

Perovskite solar cells (PSCs) are among the most promising photovoltaic technologies owing to their exceptional optoelectronic properties. However, the lower efficiency, poor stability and reproducibility issues of large-area PSCs compared with laboratory-scale PSCs are notable drawbacks that hinder their commercialization. Here we report a synergistic dopant-additive combination strategy using methylammonium chloride (MACl) as the dopant and a Lewis-basic ionic-liquid additive, 1,3-bis(cyanomethyl)imidazolium chloride ([Bcmim]Cl).

Rapid, Selective Extraction of Silver from Complex Water Matrices with a Metal-Organic Framework/Oligomer Composite Constructed via Supercritical CO.

Every year vast quantities of silver are lost in various waste streams; this, combined with its limited, diminishing supply and rising demand, makes silver recovery of increasing importance. Thus, herein, we report a controllable, green process to produce a host of highly porous metal-organic framework (MOF)/oligomer composites using supercritical carbon dioxide (ScCO ) as a medium. One resulting composite, referred to as MIL-127/Poly-o-phenylenediamine (PoPD), has an excellent Ag adsorption capacity, removal efficiency (>99 %) and provides rapid Ag extraction in as little as 5 min from complex liquid matrices.

Retarding solid-state reactions enable efficient and stable all-inorganic perovskite solar cells and modules.

All-inorganic CsPbI perovskite solar cells (PSCs) with efficiencies exceeding 20% are ideal candidates for application in large-scale tandem solar cells. However, there are still two major obstacles hindering their scale-up: (i) the inhomogeneous solid-state synthesis process and (ii) the inferior stability of the photoactive CsPbI black phase. Here, we have used a thermally stable ionic liquid, (triphenylphosphine)iminium (trifluoromethylsulfonyl)imide ([PPN][TFSI]), to retard the high-temperature solid-state reaction between CsPbI and DMAPbI [dimethylammonium (DMA)], which enables the preparation of high-quality and large-area CsPbI films in the air.

Efficient Computation of Nonadiabatic Coupling Coefficients for Modeling Charge Carrier Recombination in Extended Systems: The Case of Metal-Organic Frameworks.

Modeling excited state charge carrier dynamics and recombination in extended systems, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and other hybrid organic-inorganic materials, by surface-hopping approaches is a challenging task due to the high computational cost. In this work, the steps of the simulations and the bottlenecks for such systems are analyzed. In particular, the bottlenecks related to computation of the nonadiabatic coupling coefficients (NACs) are considered.

Dopant-Free Hole Transport Materials Afford Efficient and Stable Inorganic Perovskite Solar Cells and Modules.

The emerging CsPbI perovskites are highly efficient and thermally stable materials for wide-band gap perovskite solar cells (PSCs), but the doped hole transport materials (HTMs) accelerate the undesirable phase transition of CsPbI in ambient. Herein, a dopant-free D-π-A type HTM named CI-TTIN-2F has been developed which overcomes this problem. The suitable optoelectronic properties and energy-level alignment endow CI-TTIN-2F with excellent charge collection properties.

Effect of Ligand Functionalization on the Rate of Charge Carrier Recombination in Metal-Organic Frameworks: A Case Study of MIL-125.

Ligand functionalization is a powerful approach for modifying the electronic structure of metal-organic frameworks when targeting the optimal electronic properties for photocatalysis and photovoltaics. However, its effect on the charge carrier lifetimes and recombination pathways remains unexplored. In this work, first-principles simulations, including nonadiabatic molecular dynamics, are performed for the representative TiO-based metal-organic framework systems MIL-125-X to unravel the impact of ligand functionalization on the nonradiative electron-hole recombination process, decoherence rates, and phonon modes giving the largest contribution to the nonradiative decay.

Preparation of Highly Porous Metal-Organic Framework Beads for Metal Extraction from Liquid Streams.

Metal-organic frameworks (MOFs) offer great promise in a variety of gas- and liquid-phase separations. However, the excellent performance on the lab scale hardly translates into pilot- or industrial-scale applications due to the microcrystalline nature of MOFs. Therefore, the structuring of MOFs into pellets or beads is a highly solicited and timely requirement.

α-CsPbI Bilayers via One-Step Deposition for Efficient and Stable All-Inorganic Perovskite Solar Cells.

The emerging inorganic CsPbI perovskites are promising wide-bandgap materials for application in tandem solar cells, but they tend to transit from a black α phase to a yellow δ phase in ambient conditions. Herein, a gradient grain-sized (GGS) CsPbI bilayer is developed to stabilize the α phase via a single-step film deposition process. The spontaneously upward migration of (adamantan-1-yl)methanammonium (ADMA) based on the hot-casting technique causes self-assembly of the hierarchical morphology for the perovskite layers.

Band Alignment as the Method for Modifying Electronic Structure of Metal-Organic Frameworks.

Electronic-level ordering in metal-organic frameworks (MOFs) is a route to modulate their electronic properties such as optical absorption, band alignment, work function, charge separation, charge carrier lifetimes, and ground- or excited-state conductivity. A systematic application of this approach requires the knowledge on how a MOF chemical composition affects its electronic structure. In this work, the fundamental principles for selecting MOF components to achieve targeted level alignment are considered.

Carrier Lifetimes and Recombination Pathways in Metal-Organic Frameworks.

Understanding the excited-state charge carrier relaxation in metal-organic frameworks (MOFs) and revealing ways to alternate its rate are of primary importance for the development of novel hybrid photoactive materials with sufficiently long carrier lifetimes; in particular, shedding light on the main recombination pathways in this class of compounds is needed. Therefore, in this work the radiative and phonon-assisted nonradiative electron-hole recombination is investigated theoretically for a model MOF system, and the nonradiative pathway is demonstrated to be dominant even for a pristine defect-free material. Theoretically predicted electron-hole lifetimes are in line with the available experimental data, suggesting that the adopted methodology is suitable for prediction of carrier lifetimes and helpful for the interpretation of experimental data.

Metal Substitution as the Method of Modifying Electronic Structure of Metal-Organic Frameworks.

Targeted modification of electronic structure is an important step in the optimization of metal-organic frameworks (MOFs) for photovoltaic, sensing, and photocatalytic applications. The key parameters to be controlled include the band gap, the absolute energy position of band edges, the excited state charge separation, and degree of hybridization between metal and ligand sites. Partial metal replacement, or metal doping, within secondary building units is a promising, yet relatively unexplored route to modulate these properties in MOFs.