Benzodithiophene Hole‐Transporting Materials for Efficient Tin‐Based Perovskite Solar Cells

Developing efficient interfacial hole transporting materials (HTMs) is crucial for achieving high‐performance Pb‐free Sn‐based halide perovskite solar cells (PSCs). Here, a new series of benzodithiophene (BDT)‐based organic small molecules containing tetra‐ and di‐triphenyl amine donors prepared via a straightforward and scalable synthetic route is reported. The thermal, optical, and electrochemical properties of two BDT‐based molecules are shown to be structurally and energetically suitable to serve as HTMs for Sn‐based PSCs. It is reported here that ethylenediammonium/formamidinium tin iodide solar cells using BDT‐based HTMs deliver a champion power conversion efficiency up to 7.59%, outperforming analogous reference solar cells using traditional and expensive HTMs. Thus, these BDT‐based molecules are promising candidates as HTMs for the fabrication of high‐performance Sn‐based PSCs.     

Intramolecular Locked Dithioalkylbithiophene‐Based Semiconductors for High‐Performance Organic Field‐Effect Transistors

New 3,3′‐dithioalkyl‐2,2′‐bithiophene ( SBT )‐based small molecular and polymeric semiconductors are synthesized by end‐capping or copolymerization with dithienothiophen‐2‐yl units. Single‐crystal, molecular orbital computations, and optical/electrochemical data indicate that the SBT core is completely planar, likely via S(alkyl)?S(thiophene) intramolecular locks. Therefore, compared to semiconductors based on the conventional 3,3′‐dialkyl‐2,2′‐bithiophene, the resulting SBT systems are planar (torsional angle <1°) and highly π‐conjugated. Charge transport is investigated for solution‐sheared films in field‐effect transistors demonstrating that SBT can enable good semiconducting materials with hole mobilities ranging from ≈0.03 to 1.7 cm² V^?1 s^?1. Transport difference within this family is rationalized by film morphology, as accessed by grazing incidence X‐ray diffraction experiments.     

Solution‐Processed High‐Performance Tetrathienothiophene‐Based Small Molecular Blends for Ambipolar Charge Transport

Four soluble dialkylated tetrathienoacene ( TTAR) ‐based small molecular semiconductors featuring the combination of a TTAR central core, π‐conjugated spacers comprising bithiophene ( bT ) or thiophene ( T ), and with/without cyanoacrylate ( CA ) end‐capping moieties are synthesized and characterized. The molecule DbT‐TTAR exhibits a promising hole mobility up to 0.36 cm² V^?1 s^?1 due to the enhanced crystallinity of the microribbon‐like films. Binary blends of the p‐type DbT‐TTAR and the n‐type dicyanomethylene substituted dithienothiophene‐quinoid ( DTTQ‐11 ) are investigated in terms of film morphology, microstructure, and organic field‐effect transistor (OFET) performance. The data indicate that as the DbT‐TTAR content in the blend film increases, the charge transport characteristics vary from unipolar (electron‐only) to ambipolar and then back to unipolar (hole‐only). With a 1:1 weight ratio of DbT‐TTAR DTTQ‐11 in the blend, well‐defined pathways for both charge carriers are achieved and resulted in ambipolar transport with high hole and electron mobilities of 0.83 and 0.37 cm² V^?1 s^?1, respectively. This study provides a viable way for tuning microstructure and charge carrier transport in small molecules and their blends to achieve high‐performance solution‐processable OFETs.     

Solution‐Processable Dithienothiophenoquinoid (DTTQ) Structures for Ambient‐Stable n‐Channel Organic Field Effect Transistors

A series of dialkylated dithienothiophenoquinoids ( DTTQ s), end‐functionalized with dicyanomethylene units and substituted with different alkyl chains, are synthesized and characterized. Facile one‐pot synthesis of the dialkylated DTT core is achieved, which enables the efficient realization of DTTQ s as n‐type active semiconductors for solution‐processable organic field effect transistors (OFETs). The molecular structure of hexyl substituted DTTQ‐6 is determined via single‐crystal X‐ray diffraction, revealing DTTQ is a very planar core. The DTTQ cores form a “zig‐zag” linking layer and the layers stack in a “face‐to‐face” arrangement. The very planar core structure, short core stacking distance (3.30 Å), short intermolecular S? N distance (2.84 Å), and very low lying lowest unoccupied molecular orbital energy level of ?4.2 eV suggest that DTTQ s should be excellent electron transport candidates. The physical and electrochemical properties as well as OFETs performance and thin film morphologies of these new DTTQ s are systematically studied. Using a solution‐shearing method, DTTQ‐11 exhibits n‐channel transport with the highest mobility of up to 0.45 cm² V^?1 s^?1 and a current ON/OFF ratio (I _ON/I _OFF) greater than 10⁵. As such, DTTQ‐11 has the highest electron mobility of any DTT‐based small molecule semiconductors yet discovered combined with excellent ambient stability. Within this family, carrier mobility magnitudes are correlated with the alkyl chain length of the side chain substituents of DTTQ s.