Optoelectronic device geometries for maximizing photocurrent and flexibility

Flexible silicon micromembranes have gained considerable interest as leadless optoelectronic tissue-stimulation devices. To make these microscale silicon films both flexible and stretchable, they are patterned into serpentine, horseshoe, and spiral shapes, among others. However, all these strategies present a trade-off between flexibility and the device's overall surface area. Although this is not a major concern for traditional flexible electronics, an optoelectronic device's performance depends on its overall surface area. Here, we explore geometric strategies to optimize the photoelectrochemical performance of thin silicon membranes without compromising their flexibility and stretchability. Computational modeling and mechanical testing demonstrated that island elements increasing the device area can be connected "out-of-line" without increasing stiffness. Additionally, spiral-shaped interconnects increased both the area and flexibility of the device by increasing the number of spiral cycles. Characterization of the photogenerated current distribution above the devices confirms a higher photocurrent yield for high-fill-factor geometries. Lastly, employing the membrane designs for optoelectronic modulation of an isolated rat heart demonstrated that higher membrane fill factors reduced the optical power pacing threshold.