A small molecular electron acceptor based on asymmetric hexacyclic core of thieno[1,2-b]indaceno[5,6-b']thienothiophene for efficient fullerene-free polymer solar cells

Recent synthetic approaches towards thienothiophenes: a potential template for biologically active compounds

Heterocyclic compounds are attractive candidates because of their vast applications in natural and physical sciences. Thienothiophene (TT) is an annulated ring of two thiophene rings with a stable and electron-rich structure. Thienothiophenes (TTs) fully represent the planar system, which can drastically alter or improve the fundamental properties of organic, π-conjugated materials when included into a molecular architecture. These molecules possessed many applications including, pharmaceutical as well as optoelectronic properties. Different isomeric forms of thienothiophene showed various applications such as antiviral, antitumor, antiglaucoma, antimicrobial, and as semiconductors, solar cells, organic field effect transistors, electroluminiscents etc. A number of methodologies were adopted to synthesize thienothiophene derivatives. In this review, we have addressed different synthetic strategies of various isomeric forms of thienothiophene that have been reported during last seven years, i.e., 2016-2022.

Asymmetric Non-Fullerene Small Molecule Acceptor with Unidirectional Non-Fused π-Bridge and Extended Terminal Group for High-Efficiency Organic Solar Cells

We designed and synthesized an asymmetric non-fullerene small molecule acceptor (NF-SMA) IDT-TNIC with an A–D–π–A structure, based on an indacenodithiophene (IDT) central core, with a unidirectional non-fused alkylthio-thiophene (T) π-bridge, and 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene)malononitrile (NIC) extended terminal groups. IDT-TNIC molecules still maintain a good coplanar structure, which benefits from the non-covalent conformational locks (NCL) between O···S and S···S. The asymmetric structure increases the molecular dipole moment, and the extended terminal group broadens the absorption of the material, resulting in an excellent photovoltaic performance of IDT-TNIC. The photovoltaic device, based on PBDB-T:IDT-TNIC, exhibits an energetic PCE of 11.32% with a high V_oc of 0.87 V, high J_sc of 19.85 mA cm⁻², and a low energy loss of 0.57 eV. More importantly, IDT-TNICs with asymmetric structures show a superior property compared to symmetric IDT-Ns. The results demonstrate that it is an effectual strategy to enhance the properties of asymmetric A–D–π–A-based NF-SMAs with non-fused NCL π-bridges and extended terminal groups.

Structural symmetry-breaking of perylene diimide acceptor at N-position for enhanced photovoltaic performance

The vinylene-bridged helical perylene diimide dimer (PDI2) and derivatives have received considerable attention for application in nonfullerene organic solar cells (OSCs). Benefit from the large natural dipole moment and the...

Recent Progress in the Design of Fused-Ring Non-Fullerene Acceptors-Relations between Molecular Structure and Optical, Electronic, and Photovoltaic Properties

Organic solar cells are on the dawn of the next era. The change of focus toward non-fullerene acceptors has introduced an enormous amount of organic n-type materials and has drastically increased the power conversion efficiencies of organic photovoltaics, now exceeding 18%, a value that was believed to be unreachable some years ago. In this Review, we summarize the recent progress in the design of ladder-type fused-ring non-fullerene acceptors in the years 2018-2020. We thereby concentrate on single layer heterojunction solar cells and omit tandem architectures as well as ternary solar cells. By analyzing more than 700 structures, we highlight the basic design principles and their influence on the optical and electrical structure of the acceptor molecules and review their photovoltaic performance obtained so far. This Review should give an extensive overview of the plenitude of acceptor motifs but will also help to understand which structures and strategies are beneficial for designing materials for highly efficient non-fullerene organic solar cells.

Over 15.7% Efficiency of Ternary Organic Solar Cells by Employing Two Compatible Acceptors with Similar LUMO Levels

Efficient organic solar cells (OSCs) are fabricated using polymer PM6 as donor, and IPTBO-4Cl and MF1 as acceptors. The power conversion efficiency (PCE) of IPTBO-4Cl based and MF1 based binary OSCs individually arrive to 14.94% and 12.07%, exhibiting markedly different short circuit current density (J_SC ) of 23.18 mA cm^-2 versus 17.01 mA cm^-2 , fill factor (FF) of 72.17% versus 78.18% and similar open circuit voltage (V_OC ) of 0.893 V versus 0.908 V. The two acceptors, IPTBO-4Cl and MF1, have similar lowest unoccupied molecular orbital levels, which is beneficial for efficient electron transport in the ternary active layer. The PCE of optimized ternary OSCs arrives to 15.74% by incorporating 30 wt% MF1 in acceptors, resulting from the simultaneously increased J_SC of 23.20 mA cm^-2 , V_OC of 0.897 V, and FF of 75.64% in comparison with IPTBO-4Cl based binary OSCs. The gradually increased FFs of ternary OSCs indicate the well-optimized phase separation and molecular arrangement with MF1 as morphology regulator. This work may provide a new viewpoint for selecting an appropriate third component to achieve efficient ternary OSCs from materials and photovoltaic parameters of two binary OSCs.

Planar Benzofuran Inside-Fused Perylenediimide Dimers for High VOC Fullerene-Free Organic Solar Cells

Bulk heterojunction organic solar cells based on perylenediimide (PDI) derivatives as electron acceptors have afforded high power conversion efficiency (PCE) but still lagged behind fullerene-based analogues. Design of novel molecular structures by adjusting the PDI ring and/or connection mode remains the breakthrough point to improve the photovoltaic performance. After introducing benzofuran at the inside bay positions and being linked with a single bond and a fluorene unit, mandatory planar PDI dimers were achieved and named FDI₂ and F-FDI₂. Both acceptors show high-lying LUMO energy levels and realize high V_OC beyond 1.0 V when using the classic polymer of PBDB-T as an electron donor. However, FDI₂ and F-FDI₂ gave totally different photovoltaic performance with PCEs of 0.15 and 6.33%, respectively. The central fluorene linkage increased the miscibility of materials and ensured a much higher short-circuit current because of the formation of suitable phase separation. Our results demonstrated that utilizing the mandatory planar skeleton of PDI dimers is a simple and effective strategy to achieve high-performance nonfullerene electron acceptors, and the modulation of central conjugated units is also vital.