Novel Spiro-Core Dopant-Free Hole Transporting Material for Planar Inverted Perovskite Solar Cells

Hole-transporting materials (HTMs) have demonstrated their crucial role in promoting charge extraction, interface recombination, and device stability in perovskite solar cells (PSCs). Herein, we present the synthesis of a novel dopant-free spiro-type fluorine core-based HTM with four ethoxytriisopropylsilane groups (Syl-SC) for inverted planar perovskite solar cells (iPSCs). The thickness of the Syl-SC influences the performance of iPSCs. The best-performing iPSC is achieved with a 0.8 mg/mL Syl-SC solution (ca. 15 nm thick) and exhibits a power conversion efficiency (PCE) of 15.77%, with J_sc = 20.00 mA/cm², V_oc = 1.006 V, and FF = 80.10%. As compared to devices based on PEDOT:PSS, the iPSCs based on Syl-SC exhibit a higher V_oc, leading to a higher PCE. Additionally, it has been found that Syl-SC can more effectively suppress charge interfacial recombination in comparison to PEDOT:PSS, which results in an improvement in fill factor. Therefore, Syl-SC, a facilely processed and efficient hole-transporting material, presents a promising cost-effective alternative for inverted perovskite solar cells.

Twisted One-Dimensional Charge Transfer and Related Y-Shaped Chromophores with a 4H-Pyranylidene Donor: Synthesis and Optical Properties

Three series of push–pull derivatives bearing 4H-pyranylidene as electron donor group and a variety of acceptors were designed. On one hand, one-dimensional chromophores with a thiophene ring (series 1H) or 5-dimethylaminothiophene moiety (series 1N) as an auxiliary donor, non-coplanar with the π-conjugated system, were synthesized. On the other hand, related two-dimensional (2D) Y-shaped chromophores (series 2) were also prepared to compare how the diverse architectures affect the electrochemical, linear, and second-order nonlinear optical (NLO) properties. The presence of the 5-dimethylaminothiophene moiety in the exocyclic C=C bond of the pyranylidene unit gives rise to oxidation potentials rarely low, and the protonation (with an excess of trifluoroacetic acid) of its derivatives results in the apparition of a new blue-shifted band in the UV–visible spectra. The analysis of the properties of derivatives with and without the additional thiophene ring shows that this auxiliary donor leads to a higher NLO response, accompanied by an enhanced transparency. Y-shaped chromophores of series 2 present a blue-shifted absorption, higher molar extinction coefficients, and higher E_ox values compared to their linear twisted counterparts. As concerns NLO properties, 2D Y-shaped architecture gives rise to somewhat lower μβ values (except for thiobarbiturate derivatives).

(Super)gelators derived from push–pull chromophores: synthesis, gelling properties and second harmonic generation

New organogelators including push–pull chromophores are described and show that second harmonic generation active materials can be prepared without sophisticated processes.

Promoting Spontaneous Second Harmonic Generation through Organogelation

An organogelator based on the Disperse Red nonlinear optical chromophore was synthesized according to a simple and efficient three-step procedure. The supramolecular gel organization leads to xerogels which display a spontaneous second harmonic generation (SHG) response without any need for preprocessing, and this SHG activity appears to be stable over several months. These findings, based on an intrinsic structural approach, are supported by favorable intermolecular supramolecular interactions, which promote a locally non-centrosymmetric NLO-active organization. This is in sharp contrast with most materials designed for SHG purposes, which generally require the use of expensive or heavy-to-handle external techniques for managing the dipoles' alignment.

Polarization, second-order nonlinear optical properties and electrochromism in 4H-pyranylidene chromophores with a quinoid/aromatic thiophene ring bridge

The second-order NLO responses and spectroelectrochemical properties of donor–π–acceptor systems featuring a quinoid/aromatic thiophene unit have been studied.

Aromatic/proaromatic donors in 2-dicyanomethylenethiazole merocyanines: from neutral to strongly zwitterionic nonlinear optical chromophores

Push-pull compounds, in which a proaromatic electron donor is conjugated to a 2-dicyanomethylenethiazole acceptor, have been prepared, and their properties compared to those of model compounds featuring an aromatic donor. A combined experimental (X-ray diffraction, (1) H NMR, IR, Raman, UV/Vis, nonlinear optical (NLO) measurements) and theoretical study reveals that structural and solvent effects determine the ground-state polarisation of these merocyanines: whereas 4H-pyran-4-ylidene- and 4-pyridylidene-containing compounds are zwitterionic and 1,3-dithiol-2-ylidene derivatives are close to the cyanine limit, anilino-derived merocyanines are essentially neutral. This very large range of intramolecular charge transfer (ICT) gives rise to efficient second-order NLO chromophores with μβ values ranging from strongly negative to strongly positive. In particular, pyranylidene derivatives are unusual in that they show an increase in the degree of ICT on lengthening the π-spacer, a feature that lies behind the very large negative μβ values they display. The linking of the formally quinoidal 2-dicyanomethylenethiazole moiety to proaromatic donors seems a promising approach towards the optimisation of zwitterionic NLO chromophores.

Linear and V-shaped nonlinear optical chromophores with multiple 4H-pyran-4-ylidene moieties

A simple synthesis of dipolar one- and two-dimensional chromophores bearing two or three 4H-pyran-4-ylidene moieties is reported. Whereas the pyranylidene fragments acting as donors are proaromatic, the spacer one is not. In the linear derivatives, chain elongation gives rise to a sharp increase in the second order nonlinear optical responses, but some V-shaped derivatives display first hyperpolarizabilities (beta) lower than those of their linear analogues. This uncommon feature lends experimental support to previous theoretical studies on the relative contribution and sign of the beta-tensor components.

4H-Pyran-4-ylidenes: strong proaromatic donors for organic nonlinear optical chromophores

Merocyanines where a polyenic spacer separates a 4H-pyran-4-ylidene moiety and different strong organic acceptors have been synthesized. According to NMR studies and X-ray diffraction data, these compounds have weakly alternated structures and remarkably zwitterionic ground states, with a partial aromatic character that is compared to those of other pyran derivatives. The proaromaticity of the 4H-pyran-4-ylidene donor lies behind the cyanine-like behavior and low (positive or negative) second-order optical nonlinearities of the shorter derivatives. On the other hand, lengthening the pi-spacer gives rise to rapidly increasing mubeta(1907) values up to 17,400 x 10(-48) esu.

Synthesis, Structure, and Optical Properties of 1,4-Dithiafulvene-Based Nonlinear Optic-phores

Polyenic nonlinear optic (NLO)-phores with a proaromatic 1,4-dithiafulvene electron donor and the little explored 1,1,3-tricyano-2-phenylpropene acceptor have been synthesized. Their configurational and conformational features, ground state polarization, and linear and nonlinear optical properties have been determined experimentally and theoretically, and the results are compared to those of tetrathiafulvalene-related derivatives. The newly prepared compounds show close to optimal bond length alternation values for maximizing the first molecular hyperpolarizability, and one of them displays the highest mu beta0 value ever reported for a dithiafulvene-based NLO-phore. The first example of a dithiafulvenylmethylene transfer reaction is also reported.

Vibrational fingerprint of the structural tuning in push-pull organic chromophores with quinoid or proaromatic spacers

The Raman spectra of a series of push-pull molecules containing probenzenoid or quinoid spacers which are substituted with 1,3-dithiol-2-ylidene as donor and dicyano-methylene or barbituric acid as acceptors have been analyzed. The experimental spectra have been assigned and interpreted according to density functional theory calculations. Correlations between the Raman spectra of the isolated spacers and of the substituted molecules have been done. Raman bands in the 1620-1560 cm-1 interval provide vibrational markers of the quinoid<-->aromatic structural evolution. This finding is supported by a careful inspection of geometrical parameters, namely, bond length alteration data and particular bond distances. As a result, the peak positions and relative intensities of these Raman features can be used to evaluate the benzenoid character of the spacer as a function of the donor/acceptor substitution pattern. This paper shows that Raman spectroscopy is a powerful spectroscopic tool for the analysis of the conjugational properties (i.e., intramolecular donor-->acceptor charge transfer) of new organic materials.