(a) Schematic diagram and (b) flat-band energy-level diagram of a NIR QLED based on Si QDs with a PFN interlayer. (c) Power efficiency versus voltage for NIR QLEDs based on Si QDs with P3HT, P3HT/PFN, and poly-TPD. (d) Decay of the EL stimulated by a 4 V electrical spike. The inset shows the electrical spike and the corresponding optical power of the EL. (e) PPF induced by two successive electrical spikes. (f) Optical power of a synaptic device stimulated by two to thirty 4 V electrical spikes. Reproduced with permission from Ref. [71]. Copyright 2019, Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature.