Engineering of organic and hybrid phototransistor for effective near-infrared light detection and neuromorphic application

Light-sensing components and devices are used in various fields, from nanomedicine and biomedicine to environmental and agrifood monitoring. Organic phototransistors offer advantages such as flexibility, light weight, low-cost fabrication, tunable properties, and low power consumption. In particular, multilayer phototransistors can be designed to optimize spectral sensitivity, response time, and gain, making them competitive for fast detection applications. However, in materials fabricated through solution processes, the optimization of optoelectronic performance is often limited by processing challenges to prevent degradation of underlying layers and by the lack of simple screening methods to correlate material or process modifications with device performance. In the framework of the interplay between the assessment of new strategies in the design of phototransistor configurations and architectures and the implementation of innovative photoactive materials compatible with solution processing, my PhD internship identified multiple research topics to develop. Firstly, a hybrid multilayer phototransistor based on an unconventional tri-channel architecture was realized and optimized aiming at obtaining a high- sensitive device. Then, an approach for assessing the photo-gain of solution-processed donor:acceptor bulk heterojunctions when used as photoactive layer in OPTs was proposed: a qualitative correlation between the space-charge-limited currents in simplified diode devices and the photosensitivity of the corresponding OPT devices was identified and demonstrated. Following the smart design and the simplified methodology of characterization of the OPT devices, an innovative molecular electron-acceptor component (namely, a persistent neutral radical) was introduced for the first time in photoactive bulk heterojunction of multilayer solution-processed OPTs for improving optoelectronic performance. Finally, by exploiting the peculiar property of these radical molecules to retain electrons for a long time, it was possible to demonstrate the use of this device for an appealing application such as neuromorphic optoelectronics.