Papers by Catherine de Castro
Non-fullerene acceptor (NFA)-based ternary bulk heterojunction solar cells (TSC), represent the m... more Non-fullerene acceptor (NFA)-based ternary bulk heterojunction solar cells (TSC), represent the most efficient organic solar cells (OSCs) today due to their broader absorption, but also to quantum efficiencies (QE) often surpassing those of the corresponding binary blends. We study the relation between those QE and the energetics driving charge transfer at the electron donor:electron acceptor (D/A) interfaces in the blends of a donor (PBDB-T-2F) with several pairs of lower bandgap NFAs. Similar to binary blends, the QE increases with the ionization energy offset between donor and acceptor (ΔIE) due to the improved charge transfer efficiency, following an error function that maximizes and plateaus for ΔIE > 0.5 eV. Unexpectedly, photocurrent generation appears to proceed through a single channel, controlled by the difference between the IE of the donor and the weighted-average IE of both NFAs, rather than by individual D:NFA ΔIEs. As a proof of concept, we took a PBDB-T-2F:IEICO b...
Photochemistry
ABSTRACT Fluorescently labeled oligomers and polymers are nowadays of extreme relevance in the ch... more ABSTRACT Fluorescently labeled oligomers and polymers are nowadays of extreme relevance in the characterization of polymer dynamics, protein folding, as molecular rulers, chemosensors, etc. This contribution makes a revision of the photophysical characteristics of probes able to form excited dimers (excimers) in particular of pyrene labeled oligomers or polymers. The presence of different dimer conformations in the ground and excited states, the steric hindrance in particular with relation to the connection of pyrene through positions 1 or 2 leading to the formation of one or two excimers, etc., are discussed. The models used to investigate the kinetics of excimer formation, with the appropriate equations, are described (including the rate constants for a relevant number of published data in different systems). Particular emphasis is put on the properties of these probes in the colloidal domain and as chemosensors.
a Inorganic Chemistry Department, Faculty of Chemistry, University of Santiago de Compostela, 157... more a Inorganic Chemistry Department, Faculty of Chemistry, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain b Department of Chemistry, University of Coimbra, P3004-535 Coimbra, Portugal c BIOSCOPE Group, REQUIMTE/CQFC, Chemistry Department, FCT-UNL, Universidade Nova de Lisboa, 2829-516 Monte de Caparica, Portugal d Ecology Research Group, Department of Geographical and Life Sciences, Canterbury Christ Church University, CT1 1QU Canterbury, UK
Tese de doutoramento em Quimica, no ramo de especializacao em Fotoquimica, apresentada a Faculdad... more Tese de doutoramento em Quimica, no ramo de especializacao em Fotoquimica, apresentada a Faculdade de Ciencias e Tecnologia da Universidade de Coimbra
Journal of Materials Chemistry C
Energy level alignments at the organic donor–acceptor interface cannot be predicted from cyclic v... more Energy level alignments at the organic donor–acceptor interface cannot be predicted from cyclic voltammetry. Onsets for joint density of states and charge generation, reveal cases of energy uphill and – newly observed – downhill charge generation.
Green Chemistry
An approach for screening solvent systems for PSCs to substitute REACH restricted DMF with no los... more An approach for screening solvent systems for PSCs to substitute REACH restricted DMF with no loss in device performance.
Physical Chemistry Chemical Physics
Evaluation of commonly used models to fit the TRPL of perovskites; retrieving meaningful data req... more Evaluation of commonly used models to fit the TRPL of perovskites; retrieving meaningful data requires careful choice of excitation fluence.
Advanced Functional Materials
Perovskite solar cells have attracted a great deal of attention thanks to their high efficiency, ... more Perovskite solar cells have attracted a great deal of attention thanks to their high efficiency, ease of manufacturing, and potential low cost. However, the stability of these devices is considered their main drawback and needs to be addressed. Mesoporous carbon perovskite solar cells (m-CPSC), consisting of three mesoporous layers (TiO 2 /ZrO 2 /C) infiltrated with CH 3 NH 3 PbI 3 (MAPI) perovskite, have presented excellent lifetimes of more than 10 000 h when the additive NH 2 (CH 2) 4 CO 2 HI (5-aminovaleric acid iodide; 5-AVAI) is used to modify the perovskite structure. Yet, the role of 5-AVAI in enhancing the stability has yet to be determined. Here, superoxide-mediated degradation of MAPI m-CPSC with and without the 5-AVAI additive is studied using the fluorescence probe dihydroethidium for superoxide detection. In situ X-ray diffractometry shows that amino valeric acid methylammonium lead iodide (AVA-MAPI) perovskite infiltrated in mesoporous layers presents higher stability in an ambient environment under illumination, evidenced by a slower decrease of the MAPI/PbI 2 peak ratio. Superoxide yield measurements demonstrate that AVA-MAPI generates more superoxide than regular MAPI when deposited on glass but generates significantly less when infiltrated in mesoporous layers. It is believed that superoxide formation in m-CPSC is dependent on a combination of competitive factors including oxygen diffusion, sample morphology, grain size, and defect concentration.
Materials Letters
Shining a light on the photoluminescence behaviour of methylammonium lead iodide perovskite: Inve... more Shining a light on the photoluminescence behaviour of methylammonium lead iodide perovskite: Investigating the competing photobrightening and photodarkening processes. Materials Letters
Journal of Molecular Liquids
Abstract A comprehensive investigation of the multiequilibria of 6,7‑dihydroxycoumarin (4‑methyle... more Abstract A comprehensive investigation of the multiequilibria of 6,7‑dihydroxycoumarin (4‑methylesculetin, 67dH4MC) and of the monomethoxylated, 7‑hydroxy‑6‑methoxycoumarin or Scopoletin (7H6MetC), and the dimethoxylated, 6,7‑dimethoxy‑4‑methylcoumarin (67dMet4MC) in the singlet and triplet states has been undertaken in organic solvents and in aqueous solution. In the singlet state (S1), the obtained ground and excited state acidity constants (pKa and pKa*) of 7H6MetC (pKa = 7.4 and pKa*~ 0.95) are different to the 67dH4MC with pKa1,2 (and pK*a1,2) approximately identical in the ground and excited state: 7.1 (7.7) and 12.2 (12.1). The fluorescence quantum yields and decay times were obtained in dioxane: water mixtures and found, in the case of 67dMet4MC, to increase with the solvent polarity thus showing the presence of nearby n,π* and π,π* states. In the case of the hydroxylated 67dH4MC and 7H6MetC multiequilibria involving the excited neutral (N*), anionic (A*), dianionic (A2−*) and tautomeric (T*) - in the case of 67dH4MC - forms were observed. The phosphorescence emission (and lifetimes) obtained in acidic, neutral and alkaline media, allowed to obtain the spectral features of the different T1 species present. The data indicate that for 67dMet4MC only a neutral emissive triplet exists (N*T1) whereas in the case of 7H6MetC and 67dH4MC in an alkaline matrix (ether:ethanol:NH3) the anionic triplet (A*T1) exists and is identical for both compounds in agreement with the similar pKa1,2 values for the S1 state of the di-hydroxy 67dH4MC. Kinetic schemes coupling the ground, singlet and triplet states are proposed.
ACS Applied Nano Materials
Low dimensional semiconductor quantum dots (<10 nm) have received great attention for potential u... more Low dimensional semiconductor quantum dots (<10 nm) have received great attention for potential use in biomedical applications (diagnosis and therapy) for which larger nanoparticles (>10 nm) are not suitable. Here, we demonstrate a green, biogenic synthesis route for making CdS quantum dots (QDs) with 2-5 nm particle size using tea leaf extract (Camellia sinensis) as a toxic-free particle stabilizing agent. We have explored the biological activity of these CdS QDs in different applications, namely; a) antibacterial activity b) bioimaging and c) apoptosis of lung cancer cells. The antibacterial activity of the CdS QDs has been studied against different types of bacteria growth, showing that CdS QDs effectively inhibit the bacterial growth and exhibit cytotoxicity towards A549 cancer cells when compared to a control (no QD treatment). We have compared this cytotoxicity effect on A549 cancer cells with a standard drug, cisplatin, showing comparable results. Additionally, these CdS QDs produce high contrast fluorescence images of A549 cancer cells indicating a strong interaction with the cancer cell. To further understand the role of CdS QDs in bioimaging and cytotoxicity effect in A549 cells, fluorescence emission and flow cytometry analysis were carried out. The fluorescence emission of CdS QDs were recorded with λexc= 410 nm, showing concentration dependence fluorescence emission centered at 670 nm. From the flow cytometry analysis, it is confirmed that the CdS QDs are arresting the A549 cell growth at the S phase of cell cycle, inhibiting further growth of lung cancer cell. The multifunctional advantages of Camellia sinensis extract mediated green CdS QDs will be of widespread interest in implementing in-vivo based bioimaging and therapeutic cancer treatment applications.
Chemical Communications
We demonstrate improved performance and colour control of tri-bromide perovskite through co-sensi... more We demonstrate improved performance and colour control of tri-bromide perovskite through co-sensitisation with organic dyes.
ACS applied materials & interfaces, Jan 12, 2017
The photochemistry and stability of fullerene films is found to be strongly dependent upon film n... more The photochemistry and stability of fullerene films is found to be strongly dependent upon film nanomorphology. In particular, PC61BM blend films, dispersed with polystyrene, are found to be more susceptible to photobleaching in air than the more aggregated neat films. This enhanced photobleaching correlated with increased oxygen quenching of PC61BM triplet states, and the appearance of a carbonyl FTIR absorption band indicative of fullerene oxidation. sug-gesting PC61BM photo-oxidation is primarily due to triplet-mediated singlet oxygen generation. PC61BM films were observed to undergo photo-oxidation in air for even modest (≤ 40 mins) irradiation times, degrading electron mobility substantially, indicative of electron trap formation. This conclusion is supported by observation of red shifts in photo- and electro-luminescence with photo-oxidation, shown to be in agreement with time-dependent density functional theory calculations of defect generation. These results provide importan...
Dyes and Pigments, 2016
Abstract Two new pyrene chemosensors (bipyrenyl ligands L 1 and L 2 ) have been synthesized, full... more Abstract Two new pyrene chemosensors (bipyrenyl ligands L 1 and L 2 ) have been synthesized, fully characterized and their sensing ability towards metal cations (Cu 2+ , Ag + , Pb 2+ , Zn 2+ , Cd 2+ and Hg 2+ ) has been investigated by absorption and fluorescence (steady-state and time-resolved) techniques in solution. The absorption spectra of the two free ligands displays a single band (attributed to the monomer absorption) whereas the emission spectra show two bands, which were attributed to the emission of the monomer and dimer. For L 1 , time-resolved fluorescence measurements indicate the presence of a single component that becomes double exponential when the metal ion (in the investigated case, Pb 2+ ) is added. From both steady-state and time-resolved data it is concluded that this dimer likely involves the interaction of two pyrene units, but the absence of a rising component in the fluorescence decays discards the possibility of the presence of a dynamic excimer. Upon addition of a metal ion, this band changes in shape mirroring the fact that a new complex, involving the metal ion and the ligand, is formed. From the overall spectroscopic and photophysical data rationalized by Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) it was concluded that both L 1 and L 2 ligands are able to discriminate Ag + and Pb 2+ from all the other metal ions, with L 2 displaying a higher sensing ability (as seen from HCA/PCA analysis) towards Pb 2+ . This global approach, joining spectral and photophysical data with multivariate analysis, has shown to constitute a powerful tool for revealing important patterns in this type of system.
Science progress, 2017
To celebrate the centenary of Science Progress we offer a short survey of the progress made over ... more To celebrate the centenary of Science Progress we offer a short survey of the progress made over the past one hundred years in the research and application of photoinduced charge transfer. After a brief historical overview and introduction to photoinduced charge transfer, we discuss developments in the theory and practice of photography, photovoltaics, photocatalysis, fluorescent probes and chemosensing.
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Papers by Catherine de Castro