Optoelectronic Synaptic Devices Based On Poly(3-hexylthiophene) And Silicon Nanocrystals

Neuromorphic(brain-like)computing has great potential to solve the von Neumann bottleneck due to its self-adaptive learning,high-parallel computing and lowpower consumption.The realization of neuromorphic computing depends on the development of synaptic devices that mimic biological synapses.Synaptic devices are initially electronic ones,which face great challenges in the optimization of bandwidth,connectivity and density.It has been recently shown that the incorporation of light to make optoelectronic synaptic devices brings new opportunities for the development of synaptic devices.On one hand,light enables high bandwidth,low crosstalk,low energy consumption and no delay.On the other hand,optoelectronic devices can be used to simulate special neurobehavioral functions such as vision.As the basis of optoelectronic integrated neural networks,optoelectronic synaptic devices are expected to greatly contribute to the development of high-performance and low-power neuromorphic computing.In this work,we use one of the most typical organic semiconductors Poly(3-hexylthiophene)(P3HT)to prepare a transistor-type optoelectronic synaptic device at first.This device can mimic a series of important synaptic characteristics due to photogating effect generated by light pulse stimulation.Meanwhile,synaptic functionalities can also be achieved by electrical spikes from the back-gate electrode.The synergistic effect of light stimulation and electrical stimulation can also be used to realize the dynamic logic function.Since boron-doped silicon nanocrystals have considerable light absorption in a wide spectral range from ultraviolet(UV)to nearinfrared(NIR),introducing them into synaptic devices can often give the device photoresponse in the broad UV-to-NIR spectral range.Considering this,we designed and prepared organic-inorganic hybrid optoelectronic synaptic devices based on P3HT/B-doped silicon nanocrystals.The hybrid structure bring the synaptic device a wider-range absorption and faster light response,showing better comprehensive performance.Therefore,this work has enriched the material systems that can be applied to artificial optoelectronic synaptic devices,and can be expected to provide a new technical route for the development of high-performance computing and other fields in the future.The main research content is as follows:(1)We prepared transistor-type optoelectronic synaptic device based on P3 HT and characterized the surface morphology,light absorption and other basic characteristics of the materials through various experimental equipment such as optical microscope(OM),atomic force microscope(AFM).Then,electrical pulses and light pulses with different durations,interval times,number of stimulations and frequencies of stimulations were applied to a single device to stimulate basic synaptic plasticity,such as excitatory post-synaptic current(EPSC),paired-pulse facilitation(PPF),and longterm plasticity(LTP),and its mechanism was discussed.As the device shows differences in the retention of optical signal information and electrical signal information,we conducted a photoelectric coupling study to achieve the dynamic logic function under the combined light and electrical stimulation.(2)Boron-doped silicon nanocrystals with good light absorption in a wide spectral range from UV,visible to NIR were prepared by non-thermal plasma method,and combined with channel materials P3 HT to prepare the optoelectronic synaptic devices.First,X-ray diffraction(XRD)and high-resolution transmission electron microscopy(TEM)were used to characterize the crystal size and crystal characteristics.The UVvisible-NIR absorption spectra was employed to demonstrate the light absorption characteristics of the film before and after hybridization,and scanning electron microscopy(SEM)was used to characterize the structure of the device.Besides,the basic synaptic plasticity under 532 nm light pulse of the optoelectronic synaptic device based on P3HT/B-doped silicon nanocrystals was successfully simulated and compared with the light response of pure P3 HT synaptic devices to discuss the working principle of the devices.Finally,the device was tested under the light pulse stimulation of 375 nm and 1342 nm,and its different response to 532 nm and 375 nm light pulses was used to simulate superlinear and sublinear behavior.