A Highly Crystalline Fused-Ring n-Type Small Molecule for Non-Fullerene Acceptor Based Organic Solar Cells and Field-Effect Transistors

N-type organic small molecules (SMs) are attracting attention in the organic electronics field, due to their easy purification procedures with high yield. However, only a few reports show SMs that perform well in both organic field-effect transistors (OFETs) and organic solar cells (OSCs). Here, the synthesis and characterization of an n-type small molecule with an indacenodithieno[3,2-b]thiophene (IDTT) core unit and linear alkylated side chain (C₁₆) (IDTTIC) are reported. Compared to the state-of-the-art n-type molecule IDTIC, IDTTIC exhibits smaller optical bandgap and higher absorption coefficient, which is due to the enhanced intramolecular effect. After mixing with the polymer donor PBDB-T, IDTIC-based solar cells deliver a power conversion efficiency of only 5.67%. In stark contrast, the OSC performance of IDTTIC improves significantly to 11.2%. It is found that the superior photovoltaic properties of PBDB-T:IDTTIC blends are mainly due to reduced trap-assisted recombination and enhanced molecular packing coherence length and higher domain purity when compared to IDTIC. Moreover, a significantly higher electron mobility of 0.50 cm² V⁻¹ s⁻¹ for IDTTIC in OFET devices than for IDTIC (0.15 cm² V⁻¹ s⁻¹) is obtained. These superior performances in OSCs and OFETs demonstrate that SMs with extended π-conjugation of the backbone possess a great potential for application in organic electronic devices.