Abstract: Wearable photodetectors have come under the limelight of optoelectronic technologies on account of multiple advantages spanning light weight, easy-portability, excellent bendability, outstanding conformability, etc. Among diverse candidate materials, low-dimensional van der Waals materials (LDvdWMs) have emerged to be preeminent owing to the dangling-bond-free surface, exceptional carrier mobility, nanoscale dimensionality, and excellent light-harvesting capability. However, to date, the majority of flexible LDvdWM photodetectors have been fabricated through exfoliation-, transfer-, or solution-processing methods, which are plagued by limitations such as low production yield, inadequate photosensitivity, and sluggish response rate. Thus far, constructing LDvdWM photodetectors in situ on flexible substrates remains quite challenging due to the irreconcilable contradiction between the weak robustness of flexible polymer substrates against high temperature and the large thermal budget required for crystallization. This study develops scalable preparation of Sb₂Se₃ nanofilm directly on flexible polyimide substrates by exploiting pulsed-laser deposition (PLD), where highly energetic species can be generated to enable overcoming the reaction barrier for crystallization at a relatively low temperature. The corresponding Sb₂Se₃ photodetectors have exhibited high responsivity of 1.15 A/W, exceptional external quantum efficiency of 269%, and impressive specific detectivity reaching 2.4 × 10¹¹ Jones, coupled with swift switching characteristics. Importantly, excellent durability to repeated bending treatments has been confirmed by the consistent photoresponse over 500 convex/concave bending cycles. Furthermore, the device has showcased strong robustness against extrinsic impinging. In the end, by using Sb₂Se₃ photodetectors as sensing components, wide-band imaging beyond human vision and heart rate monitoring have been realized. This study has underscored the high efficacy of PLD for reconciling the long-standing contradiction between the weak robustness of flexible polymer substrates against high temperature and the substantial thermal energy required for crystallization, opening new opportunities towards next-generation wearable optoelectronic industry.

Key words: Pulsed-laser deposition, Antimony selenide, Flexible photodetectors, Wide-band imaging, Heart rate monitoring