Institute of Fundamental Technological Research

Development and step-by-step characterizations of a novel cationic thiophene based copolymer (P1buP), including ionic phosphonium salt and dye-tetraphenylporphyrin (TPP) moiety in side chains, with an iconic property of solubility in a wide range of polar solvents is reported. Synthesized by using simple, low-cost, and straightforward procedures, the material is used to fabricate completely halogen-free (i.e., from ethanol) ternary organic solar cells (OSCs), in the presence of an alcohol-soluble ionic 3,4-dialkoxythiophene based homopolymer (P2buP) and a serinol-fullerene derivative (C60-Ser). Indeed, thanks to co-sensitization techniques, where multiple dyes harvest different parts of the solar spectrum, the power conversion efficiency of the best final device dramatically increases up to nearly 5.0%, as the light absorption is usually optimized. Additionally, since the use of a cathode interlayer in OSCs also plays a pivotal role in electron extraction and device stability, a possible application of the ionic TPP material as the interfacial layer is also investigated. Furthermore, to improve and optimize the best performing device, a successful post-metalation with Zn of the porphyrin core is carried out, and a ternary OSC (P1buP:P2buP:C60-Ser = 0.33:0.67:1 w/w) is fabricated, resulting in a photoconversion efficiency (PCE) of ∼6.0%.

Ionic dye-tetraphenylporphyrin, Co-sensitization, Ternary OSCs, Cathode interlayers, Halogen-free deposition

In this study, we introduce a novel family of symmetrical thiophene-based small molecules with a Donor–Acceptor–Donor structure. These compounds feature three different acceptor units: benzo[c][1,2,5]thiadiazole (Bz), thieno[3,4-b]pyrazine (Pz), and thieno[1,2,5]thiadiazole (Tz), coupled with electron donor units based on a carbazole-thiophene derivative. Using Density Functional Theory (DFT), we investigate how the molecular geometry and strength of the central acceptor unit impact the redox and spectroscopic properties. Notably, the incorporation of Pz and Tz moieties induces a significant redshift in the absorption and emission spectra, which extend into the near-infrared (NIR) region, simultaneously reducing their energy gaps (~1.4-1.6 eV). This shift is attributed to the increased coplanarity of the oligomeric inner core, both in the ground (S0) and excited (S1) states, due to the enhanced quinoidal character as supported by bond-length alternation (BLA) analysis. These structural changes promote better π-electron delocalization and facilitate photoinduced charge transfer processes in optoelectronic devices. Notably, we show that Pz- and Tz-containing molecules exhibit NIR electrochromic behavior and present ambivalent character in bulk heterojunction (BHJ) solar cells. Finally, theoretical calculations suggest that these molecules could serve as effective two-photon absorption (2PA) probes, further expanding their potential in optoelectronic applications.

Three new ionic polythiophene derivatives, soluble in polar solvents, are synthesized with good yields using simple, low-cost, and straightforward procedures. They are investigated as interfacial cationic conjugated
polyelectrolyte (CPE) layers for halogen-free bulk heterojunction polymeric solar cells, based on a water-soluble electron-donor polymer
(poly[3-(6-diethanolaminohexyl)thiophene]) and a water-soluble electron-acceptor fullerene derivative (malonodiserinolamide fullerene). The simple insertion of the CPE interlayer between the active layer and the aluminum cathode dramatically increases the power conversion efficiency of the final device up to nearly 5%, resulting from a decrease of the electrode work function, improved electron extraction, and optimization of the morphology of the layers. The obtained results demonstrate that the incorporation of CPE layer is a powerful and convenient methodology for the
development of highly efficient and eco-friendly processable polymeric solar cells.

conjugated polyelectrolyte,electron transport layers,polythiophene

Four new conjugated polymers alternating benzothiadiazole units and thiophene moieties functionalized with ionic phosphonium or sulfonic acid salts in the side chains were synthesized by a postfunctionalization approach of polymeric precursors. The introduction of ionic groups makes the conjugated polymers soluble in water and/or polar solvents, allowing for the fabrication of bulk heterojunction (BHJ) solar cells using environmentally friendly conditions. All polymers were fully characterized by spectroscopic, thermal, electrochemical, X-ray diffraction, scanning electron, and atomic force techniques. BHJ solar cells were obtained from halogen-free solvents (i.e., ethanol and/or anisole) by blending the synthesized ionic push–pull polymers with a serinol-fullerene derivative or an ionic homopolymer acting as electron-acceptor (EA) or electron-donor (ED) counterparts, respectively. The device with the highest optical density and the smoothest surface of the active layer was the best-performing, showing a 4.76% photoconversion efficiency.

donor–acceptor systems, bifunctional materials, phosphonium salts, eco-friendly BHJ solar cells, anisole

Here is reported an expedient synthesis implementing enabling technologies of a family of thiophene-based heptamers alternating electron donor (D) and acceptor (A) units in a D–A′–D–A–D–A′–D sequence. The nature of the peripheral A groups (benzothiadiazole vs. thienopyrrole-dione vs. thiophene-S,S-dioxide) and the strength of the donor units (alkyl vs. thioalkyl substituted thiophene ring) have been varied to finely tune the chemical-physical properties of the D–A oligomers, to affect the packing arrangement in the solid-state as well as to enhance the photovoltaic performances. The optoelectronic properties of all compounds have been studied by means of optical spectroscopy, electrochemistry, and density functional theory calculations. Electrochemical measurements and Kelvin probe force microscopy (KPFM) predicted a bifunctional behaviour for these oligomers, suggesting the possibility of using them as donor materials when blended with PCBM, and as acceptor materials when coupled with P3HT. Investigation of their photovoltaic properties confirmed this unusual characteristic, and it is shown that the performance can be tuned by the different substitution pattern. Furthermore, thanks to their ambivalent character, binary non-fullerene small-molecule organic solar cells with negligible values of HOMO and LUMO offsets were also fabricated, resulting in PCEs ranging between 2.54–3.96%.