Visible light (532 nm) passed over a representative photodetector induces a photoresponse that can be captured as current–voltage (I–V) characteristics for different illumination intensities (Fig. 2d). The photocurrent (Iph) increases with intensity and with bias voltage, in a manner that is symmetric around 0 V. The linear behavior and symmetric I–V characteristics are consistent with approximately ohmic contacts between the graphene and MoS2 (Supplementary Fig. 7). The maximum ratio of Iph in illuminated and dark states reaches ~427 at an intensity of 103 W m−2 (Supplementary Fig. 8). The photoresponsivity, calculated as Rph=Iph/Pin, where Iph is the photocurrent and Pin is the incident laser power, is 38 A W−1 at an intensity of 0.3 W m−2, and decreases with increasing intensity (Fig. 2e). These observations are qualitatively and quantitatively comparable to the Rph values previously reported in MoS2-based photodetector devices27–32. Time-resolved measurements at different bias voltages (Fig. 2f) indicate that the device responds to the “on” and “off” switching of the laser beam, and its corresponding temporal Iph is quite uniform (1.49, 0.84, and 0.28 µA corresponding to bias voltages of 1, 3 and 5 V, respectively, at 1000 W m−2 power density) through multiple cycles at each bias voltage27–32. The estimated rise (τrise) and decay (τdecay) times of the Iph are 290 ± 130 ms and 420 ± 210 ms, respectively,27,28,31. The time-resolved photoresponses are lower than those of similar devices fabricated on SiO2 substrates (Supplementary Fig. 9), possibly due to the larger number of surface traps at the MoS2/SU-8 interface than at the MoS2/SiO2 interface30,38. The detection mechanism is based on photoresistive behavior, with a response time that is slower than that of devices such as photodiodes or phototransistors30,32. The photodetectors responded 20 times faster when encapsulated with the sandwich structure: Al2O3/MoS2/Al2O3. The high-k dielectric Al2O3 layer significantly reduces interface trap charges and results in a clean, conformal and low roughness interface that also efficiently suppresses Coulombic impurities (Supplementary Fig. 10)39,40. For all cases, the 3D structures (the octagonal prism, octagonal prismoid, and hemisphere) can be reversibly stretched and deformed from 2D to 3D states; the corresponding stability behaviors, as in Fig. 2g, are consistent with robust operation under the high strain levels and cycling. Further, the 3D photodetectors are environmentally stable (Supplementary Fig. 11) and can be formed in high density layouts (up to 10,000 on a single hemispherical surface) across arrays of separate 3D devices that can all be assembled in a single step. The mechanical flexibility of the supporting substrate and the intrinsic deformability of the 3D structures allow such systems to be bent, stretched and twisted in a reversible, non-destructive fashion (Supplementary Figs. 12−14 and Movie 2). These features in stability, manufacturability, and deformability suggest potential for use in practical applications with unique modes of operation.