Efeitos optoeletrônicos da incorporação de ftalocianina de Cobalto na camada semicondutora de fototransistores eletroquímicos orgânicos

Abstract

Organic optoelectronics offers a promising route for the development of lightweight, solutionprocessable devices compatible with flexible architectures, targeting applications such as photodetectors, optical sensors, optoelectronic memories, and neuromorphic systems capable of emulating synaptic functions through light stimuli. In this context, this work investigates the incorporation of liquid-crystalline cobalt phthalocyanine (CoPc-LC) into the semiconducting layer of electrolyte-gated organic phototransistors based on the P3HT:PCBM blend. The aim is to evaluate how the incorporation of a liquid crystal modifies the electrical, optical, and functional properties of the active layer, with emphasis on light-to-current transduction and on the possibility of temporarily storing the photoinduced response. For this purpose, devices were fabricated on glass substrates with interdigitated ITO electrodes, using spin coating to deposit the semiconducting layer, an ion gel as the electrolyte, and graphite as the gate electrode. The characterization included output and transfer curves, electrical measurements in the dark and under illumination, absorbance spectra, transient drain-current response under light pulses, retention tests, modulation by light intensity, and protocols inspired by synaptic plasticity. Initially, different CoPc-LC concentrations were compared, and the 50 mg/mL formulation was selected because it presented the best transient photoconductive response. The results show that the incorporation of CoPc-LC increases the on-state current, raises the estimated mobility by approximately 70%, and significantly enhances the transconductance compared with the control device. Under illumination, the CoPc-LC device operates in the µA range and exhibits a current approximately one order of magnitude higher than that of the P3HT:PCBM blend without the additive. In addition, it maintains retention above 70% under white light in the analyzed conditions and shows a response dependent on the intensity and duration of the optical stimulus. The neuromorphic tests indicate behavior compatible with analog response, short-term plasticity, accelerated relearning, and active memory erasure. Therefore, the incorporation of CoPc-LC favors charge transport and intensifies the optoelectronic response of the P3HT:PCBM blend, turning the electrolyte-gated phototransistor into a promising platform for devices capable of detecting, modulating, and retaining light-based information. Thus, the use of liquid crystals emerges as a relevant strategy for the development of organic phototransistors applied to optical sensors, photoactive memories, and low-cost, solution-processable neuromorphic architectures.