Optimization of drop-casting parameters for fabrication of n-type accumulation mode organic electrochemical transistors (OECTs) using gNDI-Br2

Abstract

Organic electrochemical transistors (OECTs) have received significant attention because of their unique operating mechanisms and diverse applications. We have reported the synthesis of an n-type naphthalene diimide (NDI)-based small-molecule OMIEC, gNDI-Br₂, which could be employed as the channel material for OECTs, and their fabrication parameters still need to be further examined. Here, we have explored the performance optimization of drop-cast gNDI-Br₂ OECTs by investigating various processing parameters that affect their functionality, including the solution concentration, number of drop-cast layers, and annealing temperature. Upon investigating different concentrations of the gNDI-Br₂ solution, we concluded that higher concentrations (>50 mg mL⁻¹) resulted in more than two-fold improved OECT transconductance (g_m = 813.7 ± 124.2 µS for 100 mg mL⁻¹). By increasing the number of drop-cast gNDI-Br₂ layers, OECTs showed consistent maximum drain current (I_D,max) and an improvement in transconductance (g_m). Increasing the solution concentration and number of layers results in more densely packed gNDI-Br₂ molecules within the channel area, allowing enhanced electron transport and device performance. By increasing the thin film annealing temperature to 120 °C, a significant enhancement in device performance was achieved, with a more than five times increase in the normalized g_m (5.73 ± 0.87 mS cm⁻¹), which is likely due to enhanced molecular rearrangement at a higher processing temperature. Hence, this study provides valuable insights into the optimization of gNDI-Br₂ OECT performance through parameter exploration. Future work will focus on refining the fabrication techniques and material selection to further enhance device stability and functionality.