Research Projects

This project aims to constructively exploit the transient photodoping effect of n-type organic semiconductors to develop prototype artificial photosynaptic devices. Photosynaptic devices, which use light to mimic synaptic behaviour, offer a transformative approach for neuromorphic computing and artificial perception. Unlike conventional electronics, organic semiconductors provide a highly tunable platform for these devices due to their adaptable chemical structures and hybrid electronic–ionic transport properties. A key mechanism is transient photodoping, where light induces reversible changes in charge carrier density, enabling behaviours such as learning and forgetting, similar to biological synapses. This proposal explores the integration of photo-redox chemistry, molecular design, and optoelectronic functionality to develop organic neuromorphic devices-specifically focusing on robust n-type semiconductors like naphthalenediimides (NDIs) known for reversible photodoping. The goal is not just performance enhancement but a redefinition of function-creating adaptive, multifunctional systems. Two central research questions guide the work: (a) How can real-time, controlled doping modulate charge carriers to enable neuromorphic behaviour? (b)What governs the transition between transient and steady-state doping, and how does it affect material properties? By studying doping kinetics, reversibility, and photophysical properties, the project aims to establish doping as a design strategy, not merely a tuning parameter. The outcome is expected to be a foundational framework for bioinspired, light-responsive organic materials capable of dynamic synaptic function. Photoinduced electron transfer as the mode of dynamic photodoping in n-type semiconductor films to achieve ultra-fast, sensitive, long-term term and short-term plasticity to envisage flexible artificial photosynaptic devices is the key objective of the proposal. Considering the ultrafast electron transfer rate (order of 10-12 seconds), a fast response time can be envisaged. Due to the electron affinity and the stability of the reduced forms of the host matrix, STP and LTP can be materialised. Following the absorption profiles of the molecular semiconductors/dopants, an acceptable wavelength-selective plasticity can also be achieved. With the stated objective, this proposal leverages transient photodoping-induced enhancements in electrical conductance as a core strategy for developing high-performance photosynaptic devices. To ensure ambient and operational stability, the project will focus on the design of tailored n-channel semiconductors and optimised OFET device architectures. The lowest unoccupied molecular orbital energy level for the host n-type active layer should be -4.0 - -4.2 eV. This approach aims to yield solution-processable, flexible photosynaptic devices that operate under ambient conditions with ultra-low power consumption (less than 20 fJ per write operation). The envisioned prototype device (as illustrated in Scheme 3) will target the following key performance parameters: • Low operational voltage (less than 1.5 V in two-terminal geometry) or low threshold voltage (less than 4 V for OFETs), • Functional features including short-term plasticity, long-term plasticity, spike-timing-dependent plasticity (STDP), and wavelength-selective plasticity • ON/OFF current ratio greater than 10³ at 0.5 V • Fast response time (in the range of 40-100 ns), energy consumption 10–50 fJ, with less than 20 nJ optical power per synaptic event. • Spike retention of nearly 2 hours, and • Endurance exceeding 103 cycles. A proof-of-concept device with an active area of 2 × 2 mm² will be fabricated to demonstrate the above benchmark functionalities.