Fig. 1. (Color online) (a) Schematic diagram of the PdTe₂ multilayer/thin Si heterostructure-based flexible photodetector. (b) Cross-sectional SEM images (top panel) thin Si films with different thicknesses. The bottom panel shows photographs of thin Si films under bending conditions. (c) Absorption spectra of thin Si films with different thicknesses. (d) SEM images, (e) height profile, (f) XRD pattern, and (g) XPS spectra of as-prepared PdTe₂ multilayer. Inset in (e) displays an AFM image of the PdTe₂ multilayer. (h) Raman spectra of as-prepared PdTe₂ multilayer on a SiO₂/Si substrate and PdTe₂ multilayer transferred onto a thin Si film.

Fig. 2. (Color online) (a) I−V curves, (b) transient photoresponse at zero bias and (c) responsivity versus light wavelength of PdTe₂ multilayer/thin Si heterostructure with diverse Si thicknesses. (d) I−V curves of PdTe₂ multilayer/thin Si heterostructure with different PdTe₂ thicknesses.

Fig. 3. (Color online) (a) Dark I−V curve of the PdTe₂ multilayer/thin Si heterostructure in linear and logarithmic coordinates. (b) The comparison of the I−V curves in darkness and upon 730 nm light irradiation. (c) Transient photoresponse upon periodically switched 730 nm light irradiation. Transient photoresponse (d) after over 650 cycles of working and (e) before and after storage for 3 months in air conditions. (f) Energy band diagram of the heterostructure upon light irradiation at 0 V.

Fig. 4. (Color online) (a) I−V characteristics and (b) transient photoresponse of the heterostructure photodetector under 730 nm light irradiation with diverse intensities. (c) Photocurrent at 0 V versus intensity of incident light. The dark current level and deviation current from linearity determine the LDR of the light detector. (d) Dependence of responsivity and EQE on wavelength of incident light.

Fig. 5. (Color online) (a) Transient photoresponse upon 730 nm light irradiation with various modulated frequencies. (b) Relative balance (V_max − V_min)/V_maxversus incident light frequency, showing a 3 dB frequency at about 994 Hz. (c) An individual cycle transient photoresponse.

Fig. 6. (Color online) (a) I−V curves and (b) dark current and photocurrent of the heterostructure-based flexible light detector under different bending radii of curvature. (c) I−V curves and (d) photocurrent and dark current of the heterostructure-based flexible light detector before and after 100 and 200 cycles of bending tests.

Fig. 7. (Color online) (a) Schematic diagram and (b) experimental setup of the HR detection system. LED and PD represent light emitting diode and photodetector, respectively. Normalized transient photoresponse of the heterostructure (c) at normal and (d) after exercise conditions (upon 730 nm light illumination). Insets in (c) and (d) are photographs of a commercial Mi smart bracelet, showing HR measurement results at normal and after exercise statuses, respectively.