System-level operation requires electrical interconnects to external data acquisition equipment, with designs capable of accommodating the 3D transformation and associated buckling processes. Figure 2a shows a 2D precursor that satisfies these requirements, along with the corresponding 3D structure that results after releasing the pre-strain (46%) (Supplementary Movie 1). These traces (as well as interconnects in the active regions of the device) exploit bi-layer graphene sandwiched between two SU-8 layers. As with main part of the system, selective bonding regions result from patterned UV ozone exposure. These traces evolve into their own 3D shapes, in parallel with the central hemisphere. The maximum strain (2.17%) appears in the regions of smallest bending radius, designated as 1 (circled, Fig. 2a). Supplementary Fig. 4 presents the strain distribution for two designated points 1 and 2 located on the interconnects. The maximum strains, as estimated in simulations, are again far below the intrinsic elastic limit of graphene (~6%)33–35. The areal proportion of the regions that undergo significant strain (>2%) is less than 0.2% (Supplementary Fig. 5). Figure 2b presents an SEM image of the resulting 3D system. The hemispherical structure supports three MoS2 photodetectors on each arm, for a total of 48 devices in the entire array, all interconnected with a network of bi-layer graphene traces (Fig. 2c shows a magnified view of SEM (left) and simulated (right) parts of the structure). The resistance of the graphene in the regions of lowest bending radius (where the strain is maximized at 2.17%) is ~20.7 kΩ vs. ~18.3 kΩ in the flat geometry (Supplementary Fig. 6). Such slight variations in resistance have a negligible effect on the overall operation, as they are much lower than the resistance of the photoactive material MoS2 (~1 MΩ).Fig. 2Interconnect design and photoinduced response of MoS2 photodetectors on a 3D hemispherical structure. a FEA of the 3D hemisphere structures before and after compressive buckling, showing the distributions of maximum principal strains in the MoS2 photodetectors and 3D interconnects. b Colorized SEM image of MoS2 photodetectors consisting of MoS2 (green), graphene (light gray), and SU-8 (gray) on the hemisphere with 3D interconnects. c Magnified view of the SEM image in b and corresponding FEA results for the strain distribution. Inset: schematic illustration of the unit device enclosed by the red box in the main image. d I–V characteristics of the 3D photodetector at different bias voltages (laser-beam wavelength = 532 nm, power density = 1000 W m−2). e Photoresponsivity of the MoS2 photodetector at a bias voltage of 3 V for different laser power densities. (Standard deviation of 48 sampling distribution recorded from 48 devices.) f Time-resolved photoresponses of the devices under laser illumination at different power densities. g Variation in photocurrent during repeated buckling processes for the octagonal prism (top), octagonal prismoid (middle), and hemispherical structure (bottom)