Optimizing stability through conformational locking and ring fusion modulation in organic semiconductors

The newly synthesized fused tetrathienophenanthroline (TTP) acceptor molecule, achieved via one-pot superacid catalyzed intramolecular cyclization, offers a promising alternative to the conventional benzodithiophene-4,8-dione (BDD) moieties in high-performance photovoltaic materials. The S, N heteroacene type TTP core exhibits complete planarity and enhanced electron richness compared to the BDD core, paving the way for fine tuning the morphology, optoelectronic properties, and frontier molecular energy levels in donor–acceptor-type materials. Side-chain engineering resulted in a balanced electron-rich nature of the monomer and enhanced solubility/processability of the resulting polymers. These molecular strategies for PTTP1-BDT contribute to improved stability and morphology, crucial for organic electronic device applications. Incorporation of PTTP1-BDT and PBDB-T as donor polymers in organic photovoltaics resulted in a power conversion efficiency (PCE) of ∼3% for PTTP1-BDT and ∼8% for PBDB-T. The compromise in PTTP1-BDT based device efficiency was attributed to lower and unbalanced charge mobility

Indacenodithiazole-Ladder-Type Bridged Di(thiophene)-Difluoro-Benzothiadiazole-Conjugated Copolymers as Ambipolar Organic Field-Effect Transistors

A series of four donor-acceptor conjugated copolymers P1-P4 with linear and branched side chains based on a ladder-type indacenodithiazole (IDTz) moiety containing an electron-deficient thiazole unit are copolymerized with di-2-thienyl-2,1,3-benzothiadiazole (DTBT) and 4,7-di(thien-2-yl)-5,6-difluoro-2,1,3-benzothiadiazole (DTBTff) as building blocks. Their optical, electrochemical, and thermal properties and charge transport behavior in organic field-effect transistors (OFETs) are studied. All copolymers exhibit nearly identical features in solution with good solubility. In the solid state, P1 does not exhibit a significant shift, while P3 shows a 27 nm red shift, thus illustrating the influence of the side chain. In the case of copolymers P1 and P2 having linear side chains, there is a clear effect of fluorination on the film morphology, while it is less pronounced in the case of polymers P3 and P4 having branched side chains. All copolymers P1-P4 have similar highest occupied molecular orbitals regardless of fluorination, while fluorinated polymers P2 and P4 result in an increase in the lowest unoccupied molecular orbital. In addition, density functional theory calculations reveal that the energy levels of IDTz are down-shifted in comparison to its IDT counterpart containing an electron-rich thiophene unit. OFETs based on all copolymers exhibit ambipolar behavior; among the four copolymers, P2 having a linear dodecyl side chain exhibits remarkable transport properties with saturated hole mobility as high as 0.87 cm2 V-1 s-1, while P3 exhibits the highest electron mobility of up to 0.50 cm2 V-1 s-1. Our results set an interesting path to further utilize the electron-deficient thiazole block in semiconducting materials