Chloride-Based Additive Engineering for Efficient and Stable Wide-Bandgap Perovskite Solar Cells.

Metal halide perovskite based tandem solar cells are promising to achieve power conversion efficiency beyond the theoretical limit of their single-junction counterparts. However, overcoming the significant open-circuit voltage deficit present in wide-bandgap perovskite solar cells remains a major hurdle for realizing efficient and stable perovskite tandem cells. Here, a holistic approach to overcoming challenges in 1.8 eV perovskite solar cells is reported by engineering the perovskite crystallization pathway by means of chloride additives. In conjunction with employing a self-assembled monolayer as the hole-transport layer, an open-circuit voltage of 1.25 V and a power conversion efficiency of 17.0% are achieved. The key role of methylammonium chloride addition is elucidated in facilitating the growth of a chloride-rich intermediate phase that directs crystallization of the desired cubic perovskite phase and induces more effective halide homogenization. The as-formed 1.8 eV perovskite demonstrates suppressed halide segregation and improved optoelectronic properties.

Multiscale modeling of the cellular uptake of C6 peptide-siRNA complexes.

In gene therapy utilising short interfering RNA (siRNA), delivery of the siRNA therapeutics to the target site is a major obstacle, due to low cellular uptake. Efficient delivery systems such as cell penetrating peptides (CPPs) are in the forefront for the development of efficient, safe, non-viral gene delivery. The C6 peptide series are a class of synthetic CPPs, developed specifically for the delivery of siRNA. This series of peptides are derivatives of the original C6 peptide, modified to increase cellular uptake and efficiency. In this study, multiscaled computational simulations of these peptides were performed in aqueous media, interrogating the relationship between the structure and behaviour. All atom molecular dynamic (MD) simulation results show that all CPPs show stable α-helical amphipathic secondary structures. Furthermore, docking calculations indicate that the C6 peptides can fit into the major groove of the siRNA double-helix, and once filled, could bind randomly along the minor grooves and to other, previously bound peptides. Coarse grained MD simulations were also used to generate free energy profiles for the dimerization of peptides, and binding of the peptide to siRNA. Simulation results confirm that all peptides favour binding to siRNA, they however, also favour dimerization. This affinity for aggregation may trigger the formation of larger complexes with siRNA and enhance the cellular uptake. These results indicate the capacity of C6 peptides as efficient delivery vehicles. As expected the amino acid sequence plays a crucial role in the helicity, peptide self-assembly, interaction of peptide with cell membrane and formation of stable siRNA-CPP complex.

Evaluation of the AMOEBA force field for simulating metal halide perovskites in the solid state and in solution.

In this work, we compare the existing nonpolarizable force fields developed to study the solid or solution phases of hybrid organic-inorganic halide perovskites with the AMOEBA polarizable force field. The aim is to test whether more computationally expensive polarizable force fields like AMOEBA offer better transferability between solution and solid phases, with the ultimate goal being the study of crystal nucleation, growth, and other interfacial phenomena involving these ionic compounds. In the context of hybrid perovskites, AMOEBA force field parameters already exist for several elements in solution, and we decided to leave them unchanged and to only parameterize the missing ones (Pb2+ and CH3NH3 + ions) in order to maximize transferability and avoid overfitting to the specific examples studied here. Overall, we find that AMOEBA yields accurate hydration free energies (within 5%) for typical ionic species while showing the correct ordering of stability for the different crystal polymorphs of CsPbI3 and CH3NH3PbI3. Although the existing parameters do not accurately reproduce all transition temperatures and lattice parameters, AMOEBA offers better transferability between solution and solid states than existing nonpolarizable force fields.

Trends in the Binding of Cell Penetrating Peptides to siRNA: A Molecular Docking Study.

The use of gene therapeutics, including short interfering RNA (siRNA), is limited by the lack of efficient delivery systems. An appealing approach to deliver gene therapeutics involves noncovalent complexation with cell penetrating peptides (CPPs) which are able to penetrate the cell membranes of mammals. Although a number of CPPs have been discovered, our understanding of their complexation and translocation of siRNA is as yet insufficient. Here, we report on computational studies comparing the binding affinities of CPPs with siRNA, considering a variety of CPPs. Specifically, seventeen CPPs from three different categories, cationic, amphipathic, and hydrophobic CPPs, were studied. Molecular mechanics were used to minimize structures, while molecular docking calculations were used to predict the orientation and favorability of sequentially binding multiple peptides to siRNA. Binding scores from docking calculations were highest for amphipathic peptides over cationic and hydrophobic peptides. Results indicate that initial complexation of peptides will likely occur along the major groove of the siRNA, driven by electrostatic interactions. Subsequent binding of CPPs is likely to occur in the minor groove and later on bind randomly, to siRNA or previously bound CPPs, through hydrophobic interactions. However, hydrophobic CPPs do not show this binding pattern. Ultimately binding yields a positively charged nanoparticle capable of noninvasive cellular import of therapeutic molecules.