Simple A-D2-A Nonfullerene Acceptors for Efficient Binary Bulk Heterojunction Organic Solar Cells

Two new nonfused ring nonfullerene electron acceptors, NFAs, (dicarbazolyl)bis(2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile) (MDCzM-4H) and -(2-(5,6-fluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile) (MDCzM-4F), thus exhibiting an A-D2-A motif, were synthesized and characterized. As thin films, they exhibit the lowest energy absorption signature near 540 nm, extending down to ∼700 nm. This band is due to an intramolecular charge transfer process from the DCz (nonfused dicarbazoyl; DCz) moiety to the malononitrile-based units (M) based on density functional theory calculations (DFT), which are also corroborated by time-dependent DFT (TDDFT) computations. Both NFAs fluoresce in the near-IR region exhibiting a band maximum peaking near 750 nm with biphasic lifetimes in the 75-410 ps time scale. Electrochemical measurements permitted the determination of their HOMO (∼-5.7 eV) and LUMO (∼-4.0 eV) energies. The absorption bands are complementary to those of the commercial copolymer PTB7-Th, which was used to prepare binary blends for photovoltaic cell performance assessments (ITO/PEDOT:PSS/active layer/PFN-Br/Ag). The power conversion efficiencies (PCE) are found to be 10.17% for MDCzM-4H/PTB7-Th (short-circuit current JSC = 15.87 mA cm-2; open-circuit voltage VOC = 1.03 V; fill factor FF = 0.622) and 14.09% for MDCzM-4F/PTB7-Th (JSC = 20.92 mA cm-2; VOC = 0.965 V; FF = 0.698). The use of nonfused ring NFAs achieving such high performances is significant and reveals a path toward simpler NFAs for use in organic photovoltaics.

Machine learning of atomic force microscopy images of organic solar cells

The bulk heterojunction structures of organic photovoltaics (OPVs) have been overlooked in their machine learning (ML) approach despite their presumably significant impact on power conversion efficiency (PCE). In this study, we examined the use of atomic force microscopy (AFM) images to construct an ML model for predicting the PCE of polymer : non-fullerene molecular acceptor OPVs. We manually collected experimentally observed AFM images from the literature, applied data curing and performed image analyses (fast Fourier transform, FFT; gray-level co-occurrence matrix, GLCM; histogram analysis, HA) and ML linear regression. The accuracy of the model did not considerably improve even by including AFM data in addition to the chemical structure fingerprints, material properties and process parameters. However, we found that a specific spatial wavelength of FFT (40-65 nm) significantly affects PCE. The GLCM and HA methods, such as homogeneity, correlation and skewness expand the scope of image analysis and artificial intelligence in materials science research fields.

Cyanomethylation of Substituted Fluorenes and Oxindoles with Alkyl Nitriles

The first example of metal-free cyanomethylenation from alkyl nitriles of sp³ C-H bonds to afford quaternary carbon centers is described. This oxidative protocol is operationally simple and features good functional group compatibility. This method provides a novel approach to highly functionalized fluorene and oxindole derivatives, which are commonly used in material and pharmaceutical areas. Control experiments provide evidence of a radical reaction process.

Fine-tuning the optoelectronic chattels of fluoreno-thiophene centred molecular semiconductors through symmetric and asymmetric push–pull switch

Optoelectronic properties of symmetrical and unsymmetrical fluoreno-thienyl π-semiconductors were studied.

A fluorene-core-based electron acceptor for fullerene-free BHJ organic solar cells—towards power conversion efficiencies over 10%

A small molecule non-fullerene electron acceptor (SMNFEA), bearing a furan π-spacer and dicyano-n-hexyl rhodanine as flanking groups, was designed and synthesized for organic solar cell applications.

Photo-induced characteristic study of the smallest fullerene fragment, 1,6,7,10-tetramethylfluoranthene as an acceptor

In this study, the use of the novel 1,6,7,10-tetramethylfluoranthene as an acceptor in the organic solar cell has been demonstrated.

Butadiene dyes based on 3-(dicyanomethylidene)indan-1-one and 1,3-bis(dicyanomethylidene)indane: synthesis, characterization and solvatochromic behaviour

Novel 1,1-diaryl-substituted butadiene dyes containing 3-(dicyanomethylidene)indan-1-one and 1,3-bis(dicyanomethylidene)indane have been synthetized, and their light absorption and solvatochromic properties evaluated.