Charge traps revisited: from unwanted defects to functional synapses in photosynaptic devices

Charge trap sites have often been considered defects that induce bias stress, reduce stability, and compromise device reliability. In an out-of-the-box perspective, recent work shows that these sites can also act as useful elements that store charge, tune responses, and mimic biological learning. While past research focused on suppressing or eliminating traps, a growing body of studies now takes the opposite view and explores their deliberate use for synaptic functions. This new direction shifts charge traps from unwanted sites to functional components in memory, synaptic, and optoelectronic devices. Studies now demonstrate trap-based weight storage, light-driven plasticity, and hybrid electro-photonic learning. This review summarizes progress in using interface traps for adaptive and multifunctional electronics. We compare device designs that exploit trap dynamics and highlight their impact on neuromorphic and optoelectronic systems. Key challenges include reproducibility, stability, and integration at large scale. This review offers a timely perspective on exploiting charge traps, with an emphasis on their emerging roles in next-generation neuromorphic and optoelectronic technologies.