The NRC hull form series: an update

This paper describes a systematic series of model experiments that have been carried out on frigate hull forms. Data now available enable trends of performance to be established over a wide range of design parameters.Peer reviewed: NoNRC publication: Ye

Electronic structure of a novel alkylidene fluorene polymer in the pristine state

The electronic structure of a novel conjugated polymer, polyalkylidene fluorene has been studied using a combined experimental-theoretical approach. The densities of states in the valence band region of the new derivative, poly(9-(1'-decylundecylidene)fluorene), were measured by ultraviolet photoelectron spectroscopy and compared with electronic band-structure calculations performed in the valence effective Hamiltonian framework. The results are compared with those of similar studies on the reference polymer poly(9,9-dioctylfluorene). We report the experimentally determined ionization potential for this new material and discuss the role of substitution in altering the electronic properties of the polymer backbone

Core excitations of naphthalene: Vibrational structure versus chemical shifts

High-resolution x-ray photoelectron emission (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectra of naphthalene are analyzed in terms of the initial state chemical shifts and the vibrational fine structure of the excitations. Carbon atoms located at peripheral sites experience only a small chemical shift and exhibit rather similar charge-vibrational coupling, while the atoms in the bridging positions differ substantially. In the XPS spectra, C-H stretching modes provide important contributions to the overall shape of the spectrum. In contrast, the NEXAFS spectrum contains only vibrational progressions from particular C-C stretching modes. The accuracy of ab initio calculations of absolute electronic transition energies is discussed in the context of minute chemical shifts, the vibrational fine structure, and the state multiplicity

Synergistic surface modification of tin-lead perovskite solar cells

Interfaces in thin-film photovoltaics play a pivotal role in determining device efficiency and longevity. Herein, we study the top surface treatment of mixed tin-lead (∼1.26 eV) halide perovskite films for p-i-n solar cells. We are able to promote charge extraction by treating the perovskite surface with piperazine. This compound reacts with the organic cations at the perovskite surface, modifying the surface structure and tuning the interfacial energy level alignment. In addition, the combined treatment with C<sub>60</sub> pyrrolidine tris-acid (CPTA) reduces hysteresis and leads to efficiencies up to 22.7%, with open-circuit voltage values reaching 0.90 V, ∼92% of the radiative limit for the band gap of this material. The modified cells also show superior stability, with unencapsulated cells retaining 96% of their initial efficiency after >2000 hours of storage in N<sub>2</sub> and encapsulated cells retaining 90% efficiency after >450 hours of storage in air. Intriguingly, CPTA preferentially binds to Sn<sup>2+</sup> sites at film surface over Pb<sup>2+</sup> due to the energetically favoured exposure of the former, according to first-principles calculations. This work provides new insights into the surface chemistry of perovskite films in terms of their structural, electronic, and defect characteristics and we use this knowledge to fabricate state-of-the-art solar cells. This article is protected by copyright. All rights reserved