Asymmetrical Squaraines Bearing Fluorine-Substituted Indoline Moieties for High-Performance Solution-Processed Small-Molecule Organic Solar Cells

Structure-activity relationships of aniline-based squaraines for distinguishable staining and bright two-photon fluorescence bioimaging in plant cells

An organelle-selective vision provides insights into the physiological response of plants and crops to environmental stresses in sustainable agriculture ecosystems. Biological applications often require two-photon excited fluorophores with low phototoxicity, high brightness, deep penetration, and tuneable cell entry. We obtained three aniline-based squaraines (SQs) tuned from hydrophobic to hydrophilic characteristics by modifying terminal pendant groups and substituents, and investigated their steady-state absorption and far-red-emitting fluorescence properties. The SQs exhibited two-photon absorption (2PA) ranging from 750 to 870 nm within the first biological spectral window; their structure-property relationships, corresponding to the 2PA cross sections (δ2PA), and structure differences were demonstrated. The maximum δ2PA value was ∼1220 GM at 800 nm for hydrophilic SQ3. Distinct biological staining efficiency and selective SQ bioimaging were evaluated utilizing the onion epidermal cell model. Contrary to the hydrophobic SQ1 results in the onion epidermal cell wall, amphiphilic SQ2 tagged the vacuole and nucleus and SQ3 tagged the vacuole. Distinguishable staining profiles in the roots and leaves were achieved. We believe that this study is the first to demonstrate distinct visualisation efficiency induced by the structure differences of two-photon excited SQs. Our results can help establish the versatile roles of novel near-infrared-emitting SQs in biological applications.

Colorful Squaraines Dyes for Efficient Solution-Processed All Small-Molecule Semitransparent Organic Solar Cells

Semitransparent organic solar cells (ST-OSCs) exhibit highly promising applications to develop integrated photovoltaics and power-generating windows. However, the development of ST-OSCs is significantly lagging behind opaque OSCs, especially for all small-molecule ST-OSCs. Here, four unique squaraines dyes (IDPSQ, SQ-BP, D-BDT-SQ, and AzUSQ) were successfully used as donors in ST-OSCs, whose colors can be tuned from purple to blue, green, and dark green, respectively. While using ultrathin Ag as a transparent electrode, the ST-OSCs fabricated using IDPSQ:PC₇₁BM, SQ-BP:PC₇₁BM, D-BDT-SQ:PC₇₁BM, and AzUSQ:PC₇₁BM yield power conversion efficiencies (PCEs) of 2.96, 4.36, 4.91, and 1.71%, respectively, and their colors are purple, cyan, brown, and light brown, respectively. Compared to their opaque OSCs (PCEs of 3.95, 5.45, 5.84, and 1.91%, respectively), the reduction in the PCEs are as low as 25, 20, 16, and 10%, respectively. Furthermore, each of these ST-OSCs exhibit good average visible transmittance (AVT) of 25-30%, favorable CIE color coordinates, and a color rendering index (CRI) of 71-97%. Finally, by changing the thickness of the Ag electrode, an impressive PCE of 4.9% along with an AVT of 25% and a CRI of 97% can be obtained in D-BDT-SQ:PC₇₁BM-based ST-OSCs, which is the highest PCE among all small-molecule ST-OSCs.

Density Functional Theory Investigations of D-A-D' Structural Molecules as Donor Materials in Organic Solar Cell

Squaraine core based small molecules in bulk heterojunction organic solar cells have received extensive attentions due to their distinguished photochemical properties in far red and infrared domain. In this paper, combining theoretical simulations and experimental syntheses and characterizations, three major factors (fill factor, short circuit and open-cirvuit voltage) have been carried out together to achieve improvement of power conversion efficiencies of solar cells. As model material systems with D-A-D' framework, two asymmetric squaraines (CNSQ and CCSQ-Tol) as donor materials in bulk heterojunction organic solar cell were synthesized and characterized. Intensive density functional theory computations were applied to identify some direct connections between three factors and corresponding molecular structural properties. It then helps us to predict one new molecule of CCSQ'-Ox that matches all the requirements to improve the power conversion efficiency.

π-π stacking induced high current density and improved efficiency in ternary organic solar cells

Ternary blend systems have been used to enhance the short-circuit current density (JSC) and fill factor (FF) of organic solar cells (OSCs). However, it is still a challenge to find suitable third components that concurrently possess complementary light absorption and well-matched energy levels. Here, a small organic molecule, 4,4'-(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(N,N-bis(4-(pyren-1-yl)phenyl)anili-ne) (DFNPy), which contains a triphenylamine core and bulky pyrene rings, was designed and used to construct ternary blend OSCs. DFNPy shows complementary absorption spectra in the 350-450 nm shortwave band, which has seldom been reported in the field of ternary OSCs. Furthermore, the bulky pyrene rings aggregate via π-π stacking to promote charge transfer. As a result, a high power conversion efficiency (PCE) of 10.59% with an enhanced JSC of 19.72 mA cm-2 was realized in PTB7-Th:DFNPy:PC71BM-based ternary OSCs. The addition of DFNPy was found to modulate the film morphology by improving the film phase separation and crystallinity, which can facilitate charge generation and decrease charge recombination, resulting in enhanced mobility. The results demonstrate an effective strategy for improving the photovoltaic performance of OSCs.

Optimized synthesis of π-extended squaraine dyes relevant to organic electronics by direct (hetero)arylation and Sonogashira coupling reactions

This study reports on the synthesis and characterization of four molecular π-extended squaraine compounds relevant to the field of organic electronics.

Unsymmetrical squaraines with new linkage manner for high-performance solution-processed small-molecule organic photovoltaic cells

Two unsymmetrical squaraines were employed as donors for high performance BHJ-OPV devices with J_sc > 13 mA cm⁻² and PCE > 5%.