Research progress and application of high efficiency organic solar cells based on benzodithiophene donor materials

In recent decades, the demand for clean and renewable energy has grown increasingly urgent due to the irreversible alteration of the global climate change. As a result, organic solar cells (OSCs) have emerged as a promising alternative to address this issue. In this review, we summarize the recent progress in the molecular design strategies of benzodithiophene (BDT)-based polymer and small molecule donor materials since their birth, focusing on the development of main-chain engineering, side-chain engineering and other unique molecular design paths. Up to now, the state-of-the-art power conversion efficiency (PCE) of binary OSCs prepared by BDT-based donor materials has approached 20%. This work discusses the potential relationship between the molecular changes of donor materials and photoelectric performance in corresponding OSC devices in detail, thereby presenting a rational molecular design guidance for stable and efficient donor materials in future.

An Imide-Based Pentacyclic Building Block for n-Type Organic Semiconductors

A new electron-deficient unit with a fused 5-membered heterocyclic ring was developed by replacing a cyclopenta-1,3-diene from electron-rich donor indacenodithiophene (IDT) with a cyclohepta-4,6-diene-1,3-diimde unit. The imide bridge endows dithienylbenzenebisimide (BBI) with a fixed planar configuration and low energy levels for both the highest occupied molecular orbital (HOMO; -6.24 eV) and the lowest unoccupied molecular orbit (LUMO; -2.57 eV). Organic field-effect transistors (OFETs) based on BBI polymers exhibit electron mobility up to 0.34 cm²  V^-1  s^-1 , which indicates that the BBI is a promising n-type building block for optoelectronics.

Novel Two-Dimensional Conjugated Polymer Containing Fluorinated Bithiophene as Donor and Benzoselenodiazole as Acceptor Units with Vinyl-Terthiophene Pendants for Polymer Photovoltaic Cells

Novel two-dimensional conjugated copolymer, abbreviated as PDTBSeVTT-2TF, containing electron-deficient 4,7-di(thiophen-2-yl)benzo[c][1,2,5]selenodiazole (DTBSe) unit, conjugated vinyl-terthiophene (VTT) side chain and 3,3'-difluoro-2,2'-bithiophene (2TF) was designed and synthesized using microwave-assisted Stille cross-coupling polymerization. UV⁻visible absorption and cyclic voltammetry studies revealed that this copolymer possesses a strong and broad absorption in the range of 300⁻800 nm and a narrow optical bandgap (Eg) of 1.57 eV with low-lying HOMO and LUMO energy levels. Further, the bulk heterojunction polymer solar cells (PSCs) were fabricated using PDTBSeVTT-2TF as donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor with an inverted device structure of ITO/ZnO/PDTBSeVTT-2TF:PC71BM/V₂O₅/Ag. The processing temperature of blend solution for preparing PDTBSeVTT-2TF:PC71BM active layer showed obvious impact on the photovoltaic performance of solar devices. The cell fabricated from the blend solution at 65 °C exhibited enhanced power conversion efficiencies (PCE) of 5.11% with a Jsc of 10.99 mA/cm-2 compared with the one at 50 °C, which had a PCE of 4.69% with a Jsc of 10.10 mA/cm-2. This enhancement is due to the dissolution of PDTBSeVTT-2TF clusters into single molecules and small aggregates, improving the miscibility between the polymer and PC71BM and thus increasing the donor/acceptor interface.

Influences of the backbone randomness on the properties, morphology and performances of the fluorinated benzoselenadiazole–benzothiadiazole based random copolymers

A series of FBT–FBSe ternary random copolymers were synthesized to identify the influences of backbone randomness on the morphology and performances.

The influence of binary processing additives on the performance of polymer solar cells

In this study, we report the investigation of the influence of binary processing additives, 1,8-octanedithiol (ODT) and 1-chloronaphthalene (CN) on the performance of polymer solar cells (PSCs). It was found that the power conversion efficiency (PCE) can be enhanced to 8.55% from the PSCs processed with binary processing additives as compared with ∼6.50% from the PSCs processed with either ODT or CN processing additives. With binary processing additives, the crystallinity of the electron donor polymer, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2 ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]], was elevated, which in turn facilitated charge transport within the bulk heterojunction (BHJ) layer, resulting in a high short-circuit current and large fill factor. By photophysical studies, we further found that the high PCE is majorly attributed to the minimized nongeminate recombination by controlling the kinetic film morphologies of the BHJ composite by binary solvent processing additives.

Synthesis and characterization of conducting polymers containing polypeptide and ferrocene side chains as ethanol biosensors

A novel approach for the fabrication of a biosensor from a conducting polymer bearing polypeptide segments and ferrocene moieties is reported.