Highly Efficient Mixed Conduction in N‐type Fused Small Molecule Semiconductors

Abstract

Highly efficient mixed ionic and electronic conduction is critical to developing high‐performance organic electrochemical transistors (OECTs) devices. While currently, the n‐type small molecules mixed conductors design strategy remains extremely lacking. Herein, ethylene glycol (EG) chain substituted electron‐deficient naphthalene bis‐isatin and rhodanine acceptor units with easily accessible steps are rationally fused, affording fused and planar novel semiconductors with weak intramolecular S–O ‘conformation locks', where gNR with EG side chain and hgNR with hybrid alkyl‐EG side chain. The rigid, planar and highly electron‐deficient skeleton enables the resulting small molecule semiconductors to be efficient mixed ionic‐electronic conductors with very high OECT electron mobility up to 0.01 cm2 V−1 s−1. Remarkedly, gNR displays the record value of geometry‐normalized transconductance of 0.4 S cm−1 and μC* of 2.6 F V−1 cm−1 s−1, which can also be compared with the state‐of‐art n‐type semiconducting polymers in OECTs. Moreover, the effect of the alkyl spacer on the n‐type mixed ionic and electronic conduction features of the small molecule materials is investigated. The fused electron‐deficient acceptor‐acceptor (A–A) system with intramolecular conformation lock design strategy in this work provides a new avenue to realize next‐generation high‐performance small molecule mixed ionic and electronic conductors for OECT materials.

Fluorinated Alcohol-Processed N-Type Organic Electrochemical Transistor with High Performance and Enhanced Stability

“…As shown in Figure S9, whether for FAs or CF, progressively increasing the voltage to +0.55 V resulted in the gradual depression of π–π* absorption and the enhancement of polaron absorption. These changes are consistent with the previously reported electrochemical doping studies of gNR . The changes in the intensity of the π–π* absorption features as a function of applied bias are shown in Figure b.…”

“…In contrast, the RMS roughness of the gNR-3FOH film decreased from 11.1 to 8.1 nm, the gNR-6FOH film decreased from 9.1 to 6.5 nm, and the gNR-9FOH film decreased from 71.9 to 69.1 nm. Moreover, similar morphologies to the corresponding FA cast films were observed after doping (Figure S12a), which might explain the significant improvement of the operational stability to some extent . Thus, we attributed the enhanced operational stability to the more stable film microstructure under the FA processing conditions.…”

“…The small-molecule gNR and 4Cl-PDI-4EG were synthesized, as described previously. , All the other chemicals were purchased from Sigma-Aldrich and used as received. The gNR solutions were prepared by keeping the concentration constant at 10 mg/mL in CF, 2,2,2-trifluoroethanol (TFE), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), and perfluoro- tert -butanol (PFTB), respectively.…”

“…The other is the glycolated perylene diimide (PDI) series with a μ C * value of 0.2 F V –1 cm –1 s –1 along with good operational stability . Very recently, our group pushed the μ C * of nonfullerene n-type molecular semiconductors to 2.6 F V –1 cm –1 s –1 for gNR . Thereinto, the gap of the highest μ C * between the current polymeric and molecular semiconductors is still very enormous.…”

“…19 Very recently, our group pushed the μC* of nonfullerene n-type molecular semiconductors to 2.6 F V −1 cm −1 s −1 for gNR. 20 Thereinto, the gap of the highest μC* between the current polymeric and molecular semiconductors is still very enormous. The thin-film microstructure and morphology play important roles in ionic and electronic coupling and subsequently influence the transport properties, device performance, and stability issues in OECTs.…”