Luminescent 2D single crystals of thiophene-phenylene co-oligomers for field-effect devices

• Published in: Materials chemistry frontiers 2022-10, Vol.6 (21), p.3279-3295
• Main Authors: Fedorenko, Roman S, Kuevda, Alexey V, Trukhanov, Vasiliy A, Sosorev, Andrey Yu, Bakirov, Artem V, Dorokhov, Artem I, Surin, Nicolay M, Borshchev, Oleg V, Ponomarenko, Sergey A, Paraschuk, Dmitry Yu
• Format: Article
• Language: English
• Subjects: Carrier mobility; Charge transport; Conjugation; Crystal structure; Current carriers; Field effect transistors; Monolayers; Oligomers; Optical properties; Optoelectronics; Photoluminescence; Semiconductor devices; Single crystals; Transistors; Transport properties; Two dimensional materials
• ISSN: 2052-1537; 2052-1537
• DOI: 10.1039/d2qm00768a

Two-dimensional (2D) organic semiconductor macroscopic single crystals have recently demonstrated their excellent charge-transport properties competing with their 3D counterparts. However, the combination of efficient charge transport and prominent luminescent properties in an organic 2D material is still a challenge. Here, we report on 2D emissive semiconductor single crystals based on four and five-ring thiophene-phenylene co-oligomers with didecyl terminal substituents-DD-PTTP and DD-PTPTP, where P and T stand for phenylene and thiophene, respectively-and investigate how the insertion of a P-ring in the PTTP conjugated core impacts the molecular and various solid-state properties of the material. DD-PTTP and DD-PTPTP were synthesized and characterized, and then macroscopic 2D single crystals of both oligomers in the form of monolayer and few-layer films were grown from solution and studied by optical interference, photoluminescence (PL), and atomic-force microscopies. Polarization-sensitive PL microscopy revealed the orientation of the conjugated cores in 2D crystals relative to their facets and indicated that the molecules are H-aggregated. 2D organic field-effect transistors (OFETs) based on both oligomers showed good stability, and their performance nicely followed the Shockley model with a charge-carrier mobility of up to 0.2 cm 2 V −1 s −1 , which is among the best values for various materials based on linearly conjugated oligomers. The highest charge-carrier mobility was demonstrated for the monolayer devices indicating high molecular order in the monolayer single crystals. 2D organic light-emitting transistors (OLETs) with DD-PTTP and DD-PTPTP active layers were demonstrated, and the DD-PTPTP-based 2D OFETs and OLETs showed higher performance. The latter was assigned to the stronger intermolecular interactions in DD-PTPTP stemming from its longer conjugation length despite the almost equal optical gaps of DD-PTTP and DD-PTPTP. The results obtained show that macroscopic 2D single crystals of thiophene-phenylene co-oligomers are a promising platform for 2D organic optoelectronics. Photo/electroluminescent and semiconductor properties of macroscopic 2D single crystals are presented, and the impact of phenylene insertion is investigated.