New poly(selenophene–thiophene) bearing π-conjugating spacers for polymer field-effect transistors and photovoltaic cells

Abstract

Five new poly(selenophene-thiophene) polymers, including PSe4TV, PSe4TT, PSe4T2T, PSe4TTT, and P2Se4TTT, were synthesized via Stille coupling polymerization and used various π-conjugated spacers of vinylene (V), thiophene (T), bithiophene (2T), and thieno[3,2-b]thiophene (TT). Tuneable structural, optical, and electrochemical properties of polymers were observed because different π-conjugated building blocks in the main polymer chain affected the conformation of the polymer backbone. Details of polymer morphologies were systematically investigated using transmission electron microscopy (TEM), atomic force microscopy (AFM), and grazing incidence X-ray diffraction (GIXD). P2Se4TTT possessed the smallest energy band gap, densest molecular packing structure as well as fibrillar-like nanostructures among the studied polymers because the TT moiety could enhance the coplanarity of the polymer backbone and the inserted biselenophene reduced the hindrance of thiophene side chains. Hence, the highest fieldeffect mobility of this set of polymers was determined to be 0.27 cm 2 V −1 s −1 from a P2Se4TTT-based field-effect transistor device with a high on/off ratio over 10 5 . The power conversion efficiencies (PCEs) of the photovoltaic cells based on polymer/PCBM blends were in the range of 0.43%-1.18% for our synthesized polymers. Among them, the P2Se4TTT-based device could achieve the best PCE of 2.29% using a o-dichlorobenzene-1,8-diiodooctane (98 : 2 v/v) mixture as the processing solvent. The enhancement of active layer uniformity responded to the increment of efficiency. The abovementioned results demonstrated that the newly designed polymers could serve as promising candidates for optoelectronic device applications of polymers. † Electronic supplementary information (ESI) available. See

Biaxially Extended Conjugated Polymers with Thieno[3,2-b]thiophene Building Block for High Performance Field-Effect Transistor Applications

“…The detailed crystallographic parameters of each studied polymer are listed in Table S2 (Supporting Information). The d -spacing of these TT2T-based polymers is similar to the 4T-based polymers in our previous studies (17–25 Å), − and the longer alkyl side chain (dodecyl group) on thiophene side chain slightly enlarges the d -spacing. PTTT2T possesses the smallest d -spacing among the studied polymers, which is probably due to its nonsymmetrical side chain arrangement.…”

“…P2TTT2T and PTVTTT2T, possess a better structural organization and ordered packing properties, as related to their shoulder signals in UV–vis spectra. On the other hand, the side chain torsional angles (θ β ) of the studied polymers are explored in the range of 45°–58°, which is similar to that of 4T-based polymers in our previous studies. − The distortion between thiophene side chain and polymer backbone is mainly attributed to the intramolecular repulsion between sulfur atoms of the side chain thiophene and the main chain spacer rings . Generally, the θ β becomes larger with an increased number of ring spacers.…”

“…Thiophene-based side chains, including single thiophene, bithiophene, , and thienothiophene, have been synthesized onto the conjugated backbone, showing improved charge transfer ability and stable electronic device characteristics. Our group also reported biaxially extended conjugated thiophene-based polymers using bithiophene building block on polymer main chain, − exhibiting a high carrier mobility (up to 0.61 cm 2 V –1 s –1 with dithienthiophene spacer) with a low-lying HOMO level (−5.04 to −5.62 eV).…”

“…Conjugated polymers have attracted extensive scientific interest for flexible electronic and optoelectronic device applications, such as field-effect transistors (FETs), − photovoltaic cells, − and digital data storage devices, − due to the advantages of low cost, light weight, solution processability, and tunable physical properties . Conjugated polymers with biaxially extended conjugated side chains not only facilitated ordered molecular packing but also provided multiple pathways for charge transport, leading to the enhanced field-effect mobility for transistor device. − In addition, such polymers usually possess a good air stability because the side chains can freely rotate, resulting in decreased conjugation length of polymer backbone and low-lying highest occupied molecular orbital (HOMO) level. Thiophene-based side chains, including single thiophene, bithiophene, , and thienothiophene, have been synthesized onto the conjugated backbone, showing improved charge transfer ability and stable electronic device characteristics.…”

Fluorophobic Effect Driven Self‐Organization of Semifluorinated Alkyl Chain Substituted Conjugated Polymer

“…As expected, both films exhibited a large redshift relative to the solution spectra. However, SFA‐P3DT film made from DCB shows a more predominant shoulder peak at 600 nm in comparison to OFT, which is attributed to the enhanced π–π stacking of conjugated polymer . This might imply that SFA‐P3DT in DCB form the self‐organized nanostructure by fluorophobic effect.…”