Memory, parallel processing and efficient interconnectivity are key requirements in neuromorphic computing. To emulate the highly distributed nature of biological neural networks, neuromorphic computing utilizes billions of nodes(neurons) and tunable weighted connections(synapses) to perform data-centric tasks such as classification and projection. However, the efficiency of electrical connections relying on physical wires is severely limited by its interconnectivity issues. In contrast, optoelectronically connected systems make use of the fan-out or diffuse nature of light to transmit spikes to multiple receivers in a parallel fashion. While an optoelectronic connection involves both transmitter and receiver nodes, recent optoelectronic approaches only utilize photosensitive memory devices known as the photomemristors to encode the temporal characteristics of the input spikes at the receiver nodes. Light-emitting devices with temporal memory as the transmitter nodes are yet to be explored.

Here, we fabricated a tandem memory LED device comprising of organic and perovskite emitters. Firstly, the memory LED device exhibits temporal memory behaviour with a dynamic gain of 400%. With repeated electrical stimulation, the luminosity of the device increases over time and shown to be highly frequency-dependent. Secondly, the device has dual-color emissions with distinct memory characteristics.  Initially, the red organic emitter is first activated due to the small recombination zone spatially located at the organic emitter layer. However, with repeated electrical pulsing, ionic drift in the halide perovskite layer results in the widening of the recombination zone, enabling the green perovskite layer to emit. We first studied the widening of the recombination zone; both the electroluminescence and photoluminescence spectra of the bilayer stack are compared. Interestingly, the photoluminescence spectra did not exhibit any emission from the red organic emitter. This highly suggests that the color change is not due to reabsorption but a spatial shift in recombination zone. Finally, we showcase two use cases in optoelectronic neuromorphic computing. An array of tandem memory LEDs was experimentally utilized as a neuromorphic pre-processor to enhance contrast of noisy digits by 3.81x and maintain the recognition accuracy (from -30% to only -1.46% drop). Additionally, we also demonstrated experimentally the inhibition of return mechanism by emulating heterogeneous synaptic connections in a Winner-takes-all circuit. The inhibition of return mechanism is a pivotal functionality in regulating visual attention via thorough scanning of visual field for multiple salient cues. Through these demonstrations, we highlight the essence of utilizing the dual-color tandem memory LED as the dynamic node for optoelectronic neuromorphic pre-processing.