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Abstract: The chemical structure of non-fullerene acceptors (NFAs) affects their light-harvesting capabilities, energy levels and molecular orders, all of which play a crucial role in determining the efficiency of organic solar cells (OSCs). In this work, we have systematically investigated a series of ladder-type NFAs having different carbon-oxygen-bridged electron-donating cores, and revealed the effects of core structures and film casting conditions on molecular ordering and performance of OSCs. We found that NFAs containing the thieno [3,2-b]thiophene centered, 6 or 8 fused rings (i.e. COi6DFIC, COi8DFIC) exhibit narrower optical band gaps than NFAs containing the benzene centered, 5 or 7 fused rings (i.e. COi5DFIC, COi7DFIC). NFAs containing less fused rings in the carbon-oxygen-bridged core (i.e. COi5DFIC and COi6DFIC) exhibit edge-on molecular orientation in the blends with face-on oriented PTB7-Th donor, and result in low device efficiency. Although NFAs containing more fused rings (i.e. COi7DFIC and COi8DFIC) possess a pronounced flat-on lamellar crystalline structure in the pure state, the crystallization can be reduced when blending with PTB7-Th and under hot-substrate casting, while the lamella in COi8DFIC can be effectively suppressed to form face-on H- and J-type aggregates, leading to enhanced efficiency.

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Abstract: Ageing mechanisms in Li‐ion batteries are dependent on the operational temperature but the detailed mechanisms on what processes that takes place at what temperature is still lacking. The electrochemical performance and capacity fading of the common cell chemistry LiNi1/3Mn1/3Co1/3O2 (NMC)/Li4Ti5O12 (LTO) pouch cells is studied at the temperatures: −10 °C, 30 °C and 55 °C. The full cells are cycled with the moderate upper cut‐off potential: 4.3 V vs. Li+/Li. The electrode interfaces are characterized post‐mortem using photoelectron spectroscopy techniques (SOXPES, HAXPES, XANES). Stable cycling at 30 °C is explained by electrolyte reduction forming a stabilizing interphase, thereby preventing further degradation. This initial reaction, between LTO and the electrolyte, seems to be beneficial for the NMC‐LTO full cell. At 55 °C, continuous electrolyte reduction and capacity fading is observed. It leads to formation of a thicker surface layer of organic‐species on the LTO surface than at 30 °C, contributing to an increased voltage hysteresis. At −10 °C, large cell‐resistances are observed, caused by poor electrolyte conductivity in combination with a relatively thicker and LixPFy‐rich surface layer on LTO, which all limit the capacity. ‘Slippage’ with a reduced voltage window showing the loss of active Li+ was observed using XRD.

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Abstract: Hybrid organic–inorganic halide perovskites are promising materials for thin-film solar cells. However, the toxicity and instability of best-in-class lead–halide perovskite materials make them nonideal. To combat these issues, we replaced lead with bismuth and explored the sensitivity of these new lead-free materials to the valency and bonding of their cationic organic groups. Specifically, we synthesized and characterized the materials properties and photophysical properties of hexane-1,6-diammonium bismuth pentaiodide ((HDA2+)BiI5) and compared them to an analogue containing a more volatile organic group with half the number of carbon and nitrogen atoms in the form of n-propylammonium ((PA+)xBiI3+x, where 1 < x < 3). The full crystallographic structures of (HDA2+)BiI5 and (PA+)xBiI3+x were resolved by single-crystal X-ray diffraction. (HDA2+)BiI5 was shown to be pure-phase and have a one-dimensional structure, whereas (PA+)xBiI3+x was shown to be a mix of one-dimensional and zero-dimensional phases. Structures of the materials were confirmed by synchrotron X-ray diffraction of powders. Both (HDA2+)BiI5 and (PA+)xBiI3+x exhibit steady-state photoluminescence at room temperature. Density functional theory calculations of (HDA2+)BiI5 predict electronic absorption features and a ∼2 eV bandgap that are consistent with those observed experimentally. Structure–property relationships of the materials were examined, and moisture tolerance and film quality were found to be superior for dication-containing (HDA2+)BiI5 in relation to monocation-containing (PA+)xBiI3+x. We hypothesize that these trends are in part due to a molecular bridging effect enabled by the presence of the dicationic hexanediammonium groups in (HDA2+)BiI5. Solar cells fabricated using (HDA2+)BiI5 as the photoactive layer exhibited photovoltaic action while those containing (PA+)xBiI3+x did not, suggesting that organic dicationic groups are beneficial to light-absorber morphology and ultimately solar-cell performance.

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Abstract: Multiple electrochemical processes are involved at the catalyst/electrolyte interface during the oxygen evolution reaction (OER). With the purpose of elucidating the complexity of surface dynamics upon OER, we systematically studied two Ni-based crystalline oxides (LaNiO3-δ and La2Li0.5Ni0.5O4) and compared them with the state-of-the-art Ni-Fe (oxy)hydroxide amorphous catalyst. Electrochemical measurements such as rotating ring disk electrode (RRDE) and electrochemical quartz microbalance microscopy (EQCM), coupled with a series of physical characterizations including transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) are conducted to unravel the exact pH effect on both the OER activity and the catalyst stability. We demonstrate that for Ni-based crystalline catalysts the rate for surface degradation depends on the pH and is greater than the rate for surface reconstruction. This behavior is unlike for amorphous Ni oxyhydroxide catalyst which is found more stable and pH independent.

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Abstract: Understanding the structural transformations that materials undergo during the insertion and deinsertion of Li-ions is crucial for designing high performance intercalation hosts as these deformations can lead to significant capacity fade over time. Here we present a study of the metallic defect perovskite ReO3, with the goal of determining whether these distortions are driven by polaronic charge transport (i.e. the electrons and ions moving through the lattice in a coupled way) due to the semiconducting nature of most oxide hosts. Employing a range of techniques including galvanostatic/potentiometric electrochemical probes, operando X-ray diffraction, X-ray photoelectron spectroscopy, and density functional theory calculations we nd that the cubic structure of ReO3 experiences multiple phase changes involving the correlated twisting of rigid octahedral subunits during the insertion of two equivalents of Li-ions. This extensive rearrangement of the structure results in exceptionally poor long-term cyclability due to large strains that result within the structure, all in spite of the fact that the phase retains its metallic character for all values of Li content from ReO3 to Li2ReO3. These results suggest that phase transformations during alkali ion intercalation are the result of local strains in the lattice and not exclusively due to polaron migration.