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Na et al. Soft Sci. 2026, 6, 25 Page 15 of 22

density, and local trap distributions can lead to substantial differences in photoresponse, conductance
modulation range, and temporal plasticity [89-91] . To reduce variability, fabrication strategies that ensure
uniformity, morphology, and consistent material properties are required. In addition, adopting chemical
vapor deposition for thin-film deposition techniques may further reduce the variability of zero-power
optoelectronic synapses [92,93] . Establishing such advanced reliability will be crucial for realizing zero-power
optoelectronic synapses that exhibit stable, predictable performance in wearable neuromorphic platforms
operating under dynamic, body-interfaced environments.

Lack of system-level integration
Although individual zero-power optoelectronic synapses have demonstrated promising performance, their
translation into functional large-scale systems remains highly limited. While promising synaptic behaviors
have been demonstrated at the device level, zero-power architectures impose additional constraints at the
system level, particularly in terms of synchronization, crosstalk suppression, and reliable optical
communication without external driving circuitry [36,41,42] . Thus, reproducible computation and reliable signal
transfer across networks are not yet achievable. The absence of circuit-level investigations further impedes
progress toward practical neuromorphic applications, such as hardware-based image recognition or
vector-matrix multiplication, where coordinated and uniform device behavior is essential for accurate
parallel processing.

To bridge the gap, system-level integration must be achieved through concurrent optimization of materials,
device architecture, fabrication strategies, and circuit design. In parallel, scalable manufacturing methods
such as printing, transfer assembly, or hybrid stacking can facilitate realistic integration of soft and
deformable systems. These approaches allow large-area fabrication while preserving material softness and
structural integrity. At the circuit level, implementing passive optical interconnects or wavelength-selective
channels may help minimize crosstalk and reduce power demand during complex data processing. Optical
waveguides allow optical signals to be distributed across synaptic arrays, reducing optical crosstalk and
improving addressability at the system level with low-leakage electrical readout [56,94] . The system-level circuit
should be carefully designed with respect to optical routing and electrical readout to ensure that signal
extraction incurs no electrical overhead from peripheral readout, amplification, or signal circuitry.
Ultimately, achieving uniformity and stability across dense arrays will be key to transforming zero-power
optoelectronic synapses from proof-of-concept devices into fully functional neuromorphic systems for
wearable applications.

Mechanical incompatibility
For practical wearable systems, devices must maintain stable performance under continuous and
multidirectional mechanical deformation while preventing functional failure, physical damage, and user
discomfort to ensure long-term reliability and safety during skin contact. To verify the feasibility of wearable
platforms, mechanical reliability experiments are essential. Beyond simple bending tests, devices must be
evaluated under cyclic tensile and compressive strain experiments to ensure long-term wearable stability.
Moreover, optoelectronic synaptic characterization during deformation is required to directly correlate
mechanical strain with changes in synaptic weight modulation, retention, and variability. The mechanical
reliability is indispensable for validating the practical applicability of zero-power optoelectronic synapses in
wearable neuromorphic platforms. However, most reported zero-power optoelectronic synapses remain
mechanically fragile, relying on rigid or semi-flexible substrates that cannot tolerate realistic
deformation [35-42] . Mechanical degradation phenomena such as cracking, delamination, or the formation of
microdefects further induce irreversible resistance changes, exacerbating functional instability. In addition,
the mechanical mismatch between rigid device components and the soft human body causes discomfort and
limits conformal contact, hindering seamless integration and high-fidelity biosignal monitoring. Although