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Organic electrochemical transistors (OECTs) have gained considerable attention due to their potential applications in emerging biosensor platforms. The use of conjugated polyelectrolytes (CPEs) as active materials in OECTs is particularly advantageous owing to their functional, water‐processable, and biocompatible nature, as well as their tunable electronic and ionic transport properties. However, there exists a lack of systematic studies of the structure‐property relationships of these materials with respect to OECT performance. This study shows how by tuning the molecular weight of self‐doped CPE (CPE‐K) it is possible to fabricate OECTs with aµC^*value of 14.7 F cm⁻¹V⁻¹s⁻¹, one order of magnitude higher than previously reported CPE‐based devices. Furthermore, OECTs with a transconductance of 120 mS are demonstrated via device engineering. While CPE‐K batches with different molecular weights show good doping behavior and high volumetric capacitance, as confirmed by spectroelectrochemistry and electrochemical impedance spectroscopy, the medium molecular weight possesses the highest carrier mobility of ≈0.1 cm²V⁻¹s⁻¹leading to the highest transconductance. The enhanced charge transport is due to a favorable charge percolation pathway, as revealed by the combination of X‐ray analysis and conductive atomic force microscope. These insights provide guidelines for further improving the performance of CPE‐based OECTs.

 

Multiple ultrafast spectroscopic techniques and quantum chemical simulations (QCS) were used to investigate the excited state dynamics of BCC-TPTA. This organic chromophore is believed to possess excited state dynamics governed by a thermally activated delayed fluorescence (TADF) mechanism with a reported internal quantum efficiency ( η IQE ) of 84%. In addition, a significant enhancement in its quantum yield ( Φ ) in solution after purging oxygen has been reported. This Φ enhancement has been widely accepted as due to a delayed fluorescence process occurring on the μs time-scale. The spectroscopic measurements were carried out both in solution and blended films, and from fs to μs time-scales. The excited state dynamics of Rhodamine B and Ir(BT) 2 (acac) were also probed for comparison. Investigations in the absence of oxygen were also carried out. Our time-correlated single photon counting (TCSPC) measurements revealed a lack of a long-lived emissive lifetime for BCC-TPTA in any of the media tested. Our ns transient absorption spectroscopy (ns TAS) experiments revealed that BCC-TPTA does not possess triplet transient states that could be linked to a delayed fluorescence process. Instead, the evidence obtained from our spectroscopic tools suggests that BCC-TPTA has the excited state dynamics of a typical fluorescence chromophore and that just comparing the Φ difference before and after purging oxygen from the solution is not an accurate method to claim excited state dynamics governed by a delayed fluorescence mechanism. Consequently, we believe that previous studies, in which the photo-physics of organic chromophores with TADF characteristics are reported, may have overlooked the influence of the host materials on the obtained optical properties in blended films.