Multifunctional polyelectrolyte (or layer-by-layer, LbL) multilayers consisting of a set of nanocompartments separated by impermeable ultrathin barriers, whereby the thickness of the compartments is tuned in the range 1-10 nm, are synthesized. Each compartment contains a different dye, introduced by co-adsorption during multilayer deposition. Different LbL barriers are tested for impermeability towards dye diffusion while simultaneously allowing energy transfer to occur between the compartmentalized dyes. Cross-linked LbL multilayers based on poly(acrylic acid) and poly(allyl amine) are shown to provide the desired impermeability for thicknesses as small as about 2.5 nm. A proof-of-concept system is then realized involving a cascade of two FRET processes, whereby the light energy is collected in a first nanocompartment containing pyranine, sent to a second nanocompartment loaded with fluorescein, before finally being transferred to a third, Nile blue-filled compartment located at the external surface of the film. This demonstrates the possibility to fabricate complex light-harvesting antenna systems by LbL assembly while controlling the architecture of the antenna down to a few nanometers.

Defining low-temperature engineering protocols for efficient planar perovskite solar cell (PSC) preparation is important for fabrication simplification and low-cost production. In the present work, we have defined a low-temperature (123 °C) protocol for the preparation from a solution of SnO layers which are efficient for an application as an electron transporting layer (ETL) in PSCs. Thin, conformal, and transparent layers have been obtained. The related PSCs have shown best devices with a power conversion efficiency of 18.22% and low-hysteresis J- V curves (a hysteresis index of 6.7%). Charge injection has been thoroughly studied by photoluminescence decay measurements. The decay curves followed a biexponential function. The injection of holes into the spiro-OMeTAD layer was found very fast and is a no-limiting step. On the other side, the charge injection into the oxide ETLs depends on its structure and on the oxide. The time constant for the low-temperature SnO layers is close to that of the mesoporous benchmark layers with a fast (surface) and a slow (bulk) component at 11 and 129 ns with relative contributions calculated at 13% and 87%, respectively. The phenomena occurring at a longer time scale have been investigated by impedance spectroscopy. The SnO cell spectra showed no intermediate-frequency inductive loop. The very low frequency part of the spectra was characterized by the beginning of an arc of a circle at the origin of a very large resistance over a large applied potential range. This resistance, along with an intermediate-frequency resistance, has been assigned to a recombination resistance and explains the very large  V achievable with SnO PSCs. The existence of a capacitance at the intermediate frequency with a noticeable low value at about 0.2 mF·cm is linked with the low hysteresis of the devices.

An unprecedented nucleophilic addition of piperidine on an electron acceptor, namely, 2‐(3‐oxo‐2,3‐dihydro‐1H‐cyclopenta[b]naphthalen‐1‐ylidene)malononitrile is reported. This unexpected behavior was observed during the synthesis of push‐pull dyes using the classical Knoevenagel reaction. To overcome this drawback, use of diisopropylethylamine (DIPEA) enabled to produce the expected dyes PP1 and PP2. The optical and electrochemical properties of the different dyes were examined. Theoretical calculations were also carried out to support the experimental results. To evidence the higher electron‐withdrawing ability of this electron acceptor, a comparison was established with two dyes (PP3 and PP4) comprising its shorter analogue.

The wetting properties of spin-coated films of copolymers based on azobenzene and fluorinated units have been investigated. The copolymers, denoted as poly(Azo-co-AcRf6), have been synthesized by free-radical polymerization of different proportions of acrylate monomers bearing either an azobenzene group or a semifluorinated side chain. The UV-visible spectroscopy analysis of the different spin-coating films through a cycle of UV and visible light irradiation indicates the reversible trans-cis isomerization of azobenzene groups. Simultaneously, atomic force microscopy shows that surface roughness does not exceed 1 nm. Advancing and receding contact angles of water and diiodomethane have been measured before and after UV photoirradiation of the different surfaces. In particular, a decrease in the advancing contact angles has been observed upon trans-cis isomerization of azobenzene groups. Switching variations up to 50° have been evidenced without any introduction of surface nanoroughness. Surface free-energy evaluations have been deduced from these measurements, including dispersive and polar components. The results show that, through surface composition and UV photoirradiation, a large range of surface free-energies can be obtained, from 7 to 46 mN·m(-1).

A series of ten push-pull chromophores comprising 1H-cyclopenta[b]naphthalene-1,3(2H)-dione as the electron-withdrawing group have been designed, synthesized, and characterized by UV-visible absorption and fluorescence spectroscopy, cyclic voltammetry and theoretical calculations. The solvatochromic behavior of the different dyes has been examined in 23 solvents and a positive solvatochromism has been found for all dyes using the Kamlet-Taft solvatochromic relationship, demonstrating the polar form to be stabilized in polar solvents. To establish the interest of this polyaromatic electron acceptor only synthesizable in a multistep procedure, a comparison with the analog series based on the benchmark indane-1,3-dione (1H-indene-1,3(2H)-dione) has been done. A significant red-shift of the intramolecular charge transfer band has been found for all dyes, at a comparable electron-donating group. Parallel to the examination of the photophysical properties of the different chromophores, a major improvement of the synthetic procedure giving access to 1H-cyclopenta[b]naphthalene-1,3(2H)-dione has been achieved.