Fused Bis-Benzothiadiazoles as Electron Acceptors

Fused bis-benzothiadiazoles with different molecular geometries, namely, linear benzoquinone-fused bis­(benzothiadiazole) (Q-BBT) and V-shaped sulfone-fused bis­(benzothiadiazole) (S-BBT), were synthesized. Single crystal analysis of Q-BBT and S-BBT revealed profoundly distinct packing modes, which must be ascribed to the different molecular shapes. Experimental and theoretical studies indicated that both compounds give rise to electron-accepting materials. This work thus also contributes to the diversity of electron acceptors based on bis-benzothiadiazole moieties and highlights the important role of molecular shape for the solid-state packing of organic conjugated materials

Cruciform Electron Acceptors Based on Tetraindeno-Fused Spirofluorene

Two cruciform tetra­indeno­spiro­fluorene-based acceptors embedding carbonyl (<b>Spiro-4O</b>) and dicyano­vinylene (<b>Spiro-8CN</b>) functionalities are synthesized in high yields. Single-crystal X-ray analysis reveals a one-dimensional π–π stacking arrangement for <b>Spiro-4O</b>, while <b>Spiro-8CN</b> adopts a unique two-dimensional isotropic π-interaction. Cyclic voltammetry suggests a high electron affinity of −3.76 eV for <b>Spiro-8CN</b>. Such a packing motif and low LUMO energy for <b>Spiro-8CN</b> are important for bulk electron transport

Keggin-Type PMo₁₁V as a P‑type Dopant for Enhancing the Efficiency and Reproducibility of Perovskite Solar Cells

The conventional perovskite solar cells (PSCs) with 2,2′,7,7′-tetrakis­(<i>N</i>,<i>N</i>-dimethoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) as a hole transporting material commonly suffer from poor stability and reproducibility mainly due to the process of placing the devices in air and illumination for oxidizing the spiro-OMeTAD. Herein, Keggin-type polyoxometalates (POMs)-phosphovanadomolybdate (H₄PMo₁₁V·nH₂O, denoted as PMo₁₁V) is for the first time employed as a p-type dopant for promoting the oxidation of spiro-OMeTAD. Thereby, without illumination and air, the conductivity and hole extraction efficiency of the PMo₁₁V doped spiro-OMeTAD with assistance of lithium bis­(trifluoromethanesulfonyl)­imide (Li-TFSI) and 4-<i>tert</i>-butylpyridine (TBP) can be dramatically enhanced. On the basis of this strategy, the corresponding PSCs exhibit substantially improved photovoltaic performance and good reproducibility. The best performing device yields a power conversion efficiency (PCE) of 14.05%. This work indicates a great potential of polyoxometalates for further applications in solar cells and other optoelectronics devices

Solution-Processable n‑Type Organic Semiconductors Based on Angular-Shaped 2‑(12<i>H</i>‑Dibenzo­fluoren-12-ylidene)malononitrilediimide

The angular-shaped n-type semiconductors 2-(12<i>H</i>-dibenzo­fluoren-12-ylidene)­malono­nitrile­diimide <b>2a</b> and <b>2b</b> were successfully designed, synthesized, and fully characterized by optical absorption and fluorescence, cyclic voltammetry, X-ray crystal structure analysis, XRD, and OFET device performance. The varying alkyl chain lengths of <b>2a</b> and <b>2b</b> caused different molecular orientations with respect to the substrate. Thus, <b>2a</b> presents an electron mobility of 0.01 cm² V^–1 s^–1, whereas <b>2b</b> resulted in poor device performance with a much lower electron mobility of 5 × 10^–4 cm² V^–1 s^–1

Molecular Ordering of Dithieno[2,3‑<i>d</i>;2′,3′‑<i>d</i>]benzo[2,1‑<i>b</i>:3,4‑<i>b</i>′]dithiophenes for Field-Effect Transistors

Four derivatives of dithieno­[2,3-<i>d</i>;2′,3′-<i>d</i>′]­benzo­[1,2-<i>b</i>;3,4-<i>b</i>′]­dithiophene (<b>DT<i>m</i>BDT</b>) have been synthesized to investigate the correlation between molecular structure, thin-film organization, and charge-carrier transport. Phenyl or thiophene end-capped derivatives at alpha positions of the outer thiophenes of <b>DT<i>m</i>BDT</b> present vastly different optoelectronic properties in comparison with bay-position alkyl-chain-substituted <b>DT<i>m</i>BDT</b>, which was additionally confirmed by density functional theory simulations. The film morphology of the derivatives strongly depends on alkyl substituents, aromatic end-caps, and substrate temperature. Field-effect transistors based on <b>DT<i>m</i>BDT</b> derivatives with bay-substituted alkyl chains show the best performance within this studied series with a hole mobility up to 0.75 cm²/V s. Attachment of aromatic end-caps disturbs the ordering, limiting the charge-carrier transport. Higher substrate temperature during deposition of the <b>DT<i>m</i>BDT</b> derivatives with aromatic end-caps results in larger domains and improved the transistor mobilities but not beyond the alkylated <b>DT<i>m</i>BDT</b>