## 1 Introduction  
Owing to their ability to transduce both electronic and ionic signals, organic electrochemical transistors (OECTs) are ideal candidates for bioelectronics [1, 2], sensors [3, 4], and neuromorphic applications [5, 6, 7, 8]. OECTs are three-terminal devices comprising an organic mixed ionic electronic conductor (OMIEC) [9] as the channel between the source and drain electrode. An electrolyte acts as the ion reservoir between the channel and gate electrode. When the drain-source bias (V\({}_{\text{DS}}\)) is fixed, a changing gate-source voltage (V\({}_{\text{CS}}\)) dictates the flow of the mobile ions between the OMIEC channel and the electrolyte. These ions, in turn, change the doping states and the conductivity (I\({}_{\text{D}}\)) of the OMIEC channel [10]. As a result, OECTs are volumetric devices, which grants them a high transconductance (high amplification), allowing them to operate at relatively low voltages [11]. Various conjugated polymers are suitable as the channel materials of OECTs [12]. One polymer of particular interest that allows precision control over device properties is poly(3,4-ethylenedioxythiophene)tosylate (PEDOT:Tos) [13, 14]. A popular method to deposit PEDOT:Tos is vapor phase polymerization (VPP). Although various variations are possible [15], VPP typically follows the routine of surface preparation by an oxidant, polymerization in vacuum, post-polymerization annealing, and the removal of residuals. Traditionally, the electrolyte used for gating incorporates water with salts (i.e., liquid electrolyte), which can evaporate and contaminate easily and is inconvenient for all-printed applications. Ion gels, a composite material comprising an ionic liquid in a complex polymer matrix [16] (also referred to as solid electrolyte or SE), are printable [17], scalable [18], and photopatternable [19]. The typical figures of merit of OECTs, such as the transconductance, switching ratio, and threshold voltage, are extracted from the transfer curve measurements. It has been shown that OECTs employing an SE have a pronounced hysteresis in the transfer curves [19]. In other words, the device gives two sets of data depending on whether the transfer curve measurement is taken from the ON to the OFF state and vice versa. Previous work has tried to explore the origin of hysteresis from different perspectives where the explanations differ significantly. [PERSON] et al. attributed hysteresis to an incomplete movement of ions [20], which explains the change in hysteresis with changing gate-source voltage scan rates. However, an ionic-movement-based explanation fails to explain a saturating hysteresis (i.e., a hysteresis that sustains even for a sufficiently slow scan rate). [PERSON] et al. argued that hysteresis could be adjusted by controlling the degree of polymer collapse by modifying the concentration of polytetrahydrofuran (PTHF) in the PEDOT:Tos blend [13]. [PERSON] et al. later showed that such a change is instead connected to the trapping of cations by PTHF [14]. However, none of these theories explain the presence of hysteresis in PEDOT:Tos-based OECTs without any PTHF additive. Regardless of the explanations, it is safe to assume that multiple factors might contribute to hysteresis in OECTs. In particular, the influence of defect states on hysteresis remains elusive. Here, we introduce a fully photopatternable PEDOT:Tos OECT employing a solid electrolyte with [EMIJM][EtSO4] as the ionic liquid. Contrary to conventional patterning via parylene peel-off, photolithography coupled with dry etching is cleaner and less complex [21]. We annealed the deposited PEDOT:Tos film for different durations before washing it with ethanol. Upon residual removal from the deposited films and SE deposition, the resulting OECTs showed impressive bias stress stability under prolonged operation. By varying the gate-source voltage (V\({}_{\text{GS}}\)) scan rate, we revealed two distinct regimes of hysteresis distinguishable by their kinetics.