A new polyfluorene derivative, poly­[4,4′-(((2-phenyl-9H-fluorene-9,9-diyl)­bis­(hexane-6,1-diyl))­bis­(oxy))­dianiline)] (PFAM) was synthesized via the Suzuki coupling polymerization method in high yields for the rapid and specific recognition of nitroexplosive picric acid (PA) at 22.9 picogram level on solid support using paper strips and at 13.2 ppb level in aqueous solution. The polymer PFAM was well-characterized by means of NMR, UV–vis, fluorescence, time-resolved photoluminescence (TRPL) spectroscopy and cyclic voltammetry. The amplified signal response exclusively for PA was achieved via a strong inner filter effect (IFE), a phenomenon different from the widely reported ground-state charge transfer and/or Förster resonance energy transfer (FRET) based probes for nitroaromatics detection. Pendant amine groups attached on the side chains of PFAM provide enhanced sensitivity and exceptional selectivity via protonation assisted photoinduced electron transfer (PET) even in the presence of most common interfering nitroexplosives, as well as other analytes usually found in natural water. Thus, the PFAM based platform was demonstrated for monitoring traces of PA at very low levels even in competitive environment in solution as well as solid state.

Metal halide perovskite single crystals (MHPSCs) are gaining enormous attention in the energy research community due to their impressive responses both in optical sensing and in photovoltaics. The switching from polycrystalline to monocrystalline morphology, not only allows to maintain the outstanding properties that characterize perovskite materials, but also enhances them. However, the poor control over the thickness and size during growing methods leads to considerable differences between surface and bulk responses. Impedance spectroscopy (IS) has been revealed as a powerful technique to understand the kinetics governing polycrystalline perovskite materials. The ionic migration, trap states, and recombination mechanisms occurring in both bulk and surface of the MHPSCs, need to be analyzed in depth to exploit their full potential. Here, we highlight the importance of IS to further advance our knowledge about monocrystalline perovskite materials, bringing to the table the relevance of other small perturbation techniques to complement the IS.

Picric acid (PA) detection at parts per trillion (ppt) levels is achieved by a conjugated polyelectrolyte (PMI) in 100% aqueous media and on a solid platform using paper strips and chitosan (CS) films. The unprecedented selectivity is accomplished via combination of ground state charge transfer and resonance energy transfer (RET) facilitated by favorable electrostatic interactions.

Chemical passivation of ionic defects in perovskite materials is an effective strategy to reduce charge recombination in perovskite solar cells (PSCs). Although several additives have been used for this purpose, the passivation mechanisms of different functional groups have remained unclear. Herein, the effect of molecules possessing multiple functional anchoring is systematically investigated. Three different multifunctional molecules namely 5‐aminoisophthalic acid (AIA), 5‐hydroxyisophthalic acid (HIA), and chelidamic acid (CA) are strategically chosen. These molecules not only take part in the crystallization process but also passivate the trap states effectively. CA shows superior passivation capacity among all with a better dipolar electron density distribution. The passivated films have considerably improved morphology with fewer pin holes, larger grains, and lower trap states in comparison to the pristine film. CA‐passivated p–i–n structured photovoltaic devices demonstrate the best power conversion efficiency (PCE) of 19.06% with an impressive open circuit voltage (VOC) of 1.097 V, whereas pristine devices show a PCE of 13.60% and VOC of 0.972 V. Moreover, the modified device reveals notable thermal and ambient stability in comparison to the pristine device due to lower defect states and reduced ion migration.

Achieving long-term stability along with high power conversion efficiency (PCE) is the biggest obstacle for the pursuit of organic−inorganic perovskite solar cells (PSCs) toward commercialization. Herein, we demonstrate additive assisted perovskite crystal growth as an effective strategy to improve both power conversion efficiency and thermal stability of methylammonium lead triiodide (MAPbI 3 ) perovskite solar cells. For this, oxalic acid (OA) with two bifacial carboxylic acid groups was employed as an additive into the perovskite precursor solution, which facilitated modulating the crystallization process leading to increase in grain size, reduced grain boundaries and trap states. Subsequently, devices fabricated with the OA additive showed a power conversion efficiency of 17.12%, compared to the control device with 14.06%. Furthermore, enhanced thermal stability was achieved for the OA-modified PSCs compared to that of the pristine device. The device without the OA additive retained 14% of the initial PCE after only 9 h of heat treatment at 100 °C, whereas for the same condition, the OA-modified device retained 90% after 9 h and even 70% after 19 h. These observations suggest that OA-assisted morphological improvement of perovskite can offer an efficient approach to further improve the performance as well as stability of the PSCs.

Lead (Pb)–Tin (Sn) mixed perovskites suffer from large open-circuit voltage (V oc) loss due to the rapid crystallization of perovskite films, creating Sn and Pb vacancies. Such vacancies act as defect sites expediting charge carrier recombination, thus hampering the charge carrier dynamics and optoelectronic properties of the perovskite film. Here, we report the passivation of these defects using a controlled amount of 2-phenylethylazanium iodide (PEAI) in perovskite precursor solution as a dopant to enhance the performance of the 1.25 eV Pb–Sn low-bandgap perovskite solar cell. It was found that the incorporation of PEAI in the perovskite precursor not only improves the perovskite film quality and crystallinity but also lowers the electronic disorder, thereby enhancing the open-circuit voltage up to 0.85 V, corresponding to V oc loss as low as 0.4 V and the power conversion efficiency up to 17.33%. The value of V oc loss obtained with this strategy is among the least obtained for similar band gap Pb–Sn low-bandgap perovskite solar cells. Furthermore, the ambient and dark self-stability of the PEAI-treated devices were also enhanced. This work presents a simple doping strategy to mitigate the V oc loss of Pb–Sn mixed low-bandgap perovskite solar cells.

A novel conjugated cationic polyfluorene (polyelectrolyte) derivative, PFBT, was developed by means of simple and cost-effective oxidative coupling polymerization method. PFBT displayed dual state emission in dimethyl sulfoxide (DMSO) as well as in water, a characteristic phenomenon of polyfluorene homopolymers, and tested for nitroexplosive analytes detection to observe a remarkable fluorescence quenching response for picric acid (PA) in the both solvents. The polymer PFBT demonstrated substantial selectivity and ultrasensitivity toward nitroexplosive PA in both the solvents (DMSO and HO) with exceptional quenching constant values of 2.69 × 10 and 2.18 × 10 M and a ultralow limit of detection of 92.7 nM (21.23 ppb) and 0.19 nM (43.53 ppt) in respective solvents. Furthermore, economical portable test strip devices were prepared for easy and fast on-site PA sensing, which can detect up to 0.22 ag level of PA. PA sensing in vapor phase was also established, that could detect up to 42.6 ppb level of PA vapors. Interestingly, the mechanism of sensing in DMSO solvent was attributed to substantial inner filter effect and photoinduced electron transfer, while in HO the sensing occurs via possible resonance energy transfer and photoinduced electron transfer, which is exceptional and not reported earlier for a single probe.

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