What Should be Considered While Designing Hole-Transporting Material for Perovskite Solar Cells? A Special Attention to Thiophene-Based Hole-Transporting Materials

The molecular design and conformations of hole-transporting materials (HTM) have unravelled a strategy to enhance the performance of environmentally sustainable perovskite solar cells (PSC). Several attempts have been made and several are underway for improving the efficiency of PSCs by designing an efficient HTM, which is crucial to preventing corrosion, facilitating effective hole transportation, and preventing charge recombination. There is a need for a potential alternative to the current market-dominating HTM due to its high cost of production, dopant requirements, moisture sensitivity, and low stability. Among several proposed HTMs, molecules derived from thiophene exhibit unique behaviour, such as the interaction with under-coordinated Pb2+, thereby facilitating the passivation of surface defects in the perovskite layer. In addition, coupling a suitable side chain imparts a hydrophobic character, eventually leading to the development of a moisture-sensitive and highly stable PSC. Furthermore, thiophene-backboned polymers with ionic pendants have been employed as an interfacial layer between PSC layers, with the backbone facilitating efficient charge transfer. This perspective article comprehensively presents the design strategy, characterization, and function of HTMs associated with thiophene-derived molecules. Hence, it is observed that thiophene-formulated HTMs have an enhanced passivation effect, good performance in an open-circuit environment, longevity, humidity resistance, thermostability, good hole extraction, and mobility in a dopant-free condition. For a better understanding, the article provides a comparative description of the activity and function of thiophene-based small molecules and polymers and their effect on device performance.

Atroposelective Kinetic Resolution of 8H-Indeno[1,2-c]thiophen-8-ols via Pd-Catalyzed C-C Bond Cleavage Reaction

The present work demonstrates a palladium-catalyzed kinetic resolution/ring-opening reaction of 8H-indeno[1,2-c]thiophen-8-ols. The reaction proceeds in a highly regioselective manner, and both optically active thiophene-phenyl atropisomers and stereogenic 8H-indeno[1,2-c]thiophen-8-ols were obtained with high enantiomeric excesses. The synthetic applications of the obtained thiophenyl atropisomers were briefly investigated.

ipso-Arylative Ring-Opening Polymerization as a Route to Electron-Deficient Conjugated Polymers

ipso-Arylative ring-opening polymerization of 2-bromo-8-aryl-8H-indeno[2,1-b]thiophen-8-ol monomers proceeds to M_n up to 9 kg mol^-1 with conversion of the monomer diarylcarbinol groups to pendent conjugated aroylphenyl side chains (2-benzoylphenyl or 2-(4-hexylbenzoyl)phenyl), which influence the optical and electronic properties of the resulting polythiophenes. Poly(3-(2-(4-hexylbenzoyl)phenyl)thiophene) was found to have lower frontier orbital energy levels (HOMO/LUMO=-5.9/-4.0 eV) than poly(3-hexylthiophene) owing to the electron-withdrawing ability of the aryl ketone side chains. The electron mobility (ca. 2×10^-3  cm²  V^-1  s^-1 ) for poly(3-(2-(4-hexylbenzoyl)phenyl)thiophene) was found to be significantly higher than the hole mobility (ca. 8×10^-6  cm²  V^-1  s^-1 ), which suggests such polymers are candidates for n-type organic semiconductors. Density functional theory calculations suggest that backbone distortion resulting from side-chain steric interactions could be a key factor influencing charge mobilities.