Novel ethyladamantyl solubilization side groups were found to induce π–π interactions between the conjugated cores through adamantyl–adamantyl stacking in soluble diketopyrrolopyrrole (DPP) derivatives. The closeness of the DPP cores amplifies charge transfer in the material, as far as the π–π interaction is a dominant charge-hopping pathway. As a result, tenfold enhancement of hole mobilities exceeding those obtained for insoluble derivatives was reached. Moreover, due to high crystallinity and co-planarity of the conjugated cores, electron transfer was preserved with a mobility of 0.2 cm² V⁻¹ s⁻¹ for dithiophene-DPP. At the same time, the material remained soluble, which is a significant advantage for purification and processing. This approach can be universally applied for many types of semiconducting organic materials containing the imide motif, where solubilization is achieved by side-group substitution.

Human cell cultures provide a potentially powerful means for pharmacological and toxicological research. A microplate with a multielectrode array of 96 organic electrochemical transistors (OECTs) based on the semiconductive polymer poly(3,4-ethylenedioxythio-phene):poly(styrene sulfonic acid) PEDOT:PSS was developed and fabricated by the screen printing method. It consists of a microplate of a 12 × 8 chimney–well array with transistors on the bottom. The OECT is circular with a channel of 1.5 mm² in the centre surrounded by the circular gate electrode. The device is designed for electrogenic cell monitoring. Simulations with the electrolyte revealed good electrical characteristics and indicated the setup information of the experimental conditions. A transconductance of g = 1.4 mS was achieved in the wide range of gate voltages V_gs = ±0.4 V when the drain potential V_ds = −0.735 V was set and the long term relaxation was compensated for. The time constant 0.15 s limited by the channel-electrolyte charge electrical double layer (EDL) capacitance was measured. The device was tested on a 3T3 fibroblast cell culture and the sudden environmental changes were recorded. The living cells can be observed on the channel of the OECT and during electrical stimulation by gate voltage, as well as during the source current response.

Organic electrochemical transistors (OECTs) with variable electrode resistance and channel conductivity were studied. The effect of parasitic serial resistance on OECT function, especially transconductance, was evaluated. It was shown that due to the non-optimized serial resistance, the transistors can have a transconductance lower by tens of percent compared to the theoretical intrinsic transconductance. We show here that by simply reducing the contacts’ resistance it is possible to prepare a planar OECT with a high transconductance of 108 mS, which is close to the intrinsic transconductance 121 mS. These values represent some of the highest ones reported so far, despite the fact that the PEDOT:PSS used here have a lower conductivity.