Self-Powered PhotodetectorsBased on Cu₂SnS₃/TiO₂ Nanorod Heterojunctions

Solution-processed photodetectors have attracted significant research interest due to their multimodal functionalities, ease of fabrication, and compatibility with various substrates. However, these devices often face challenges such as limited performance and slow response times. This study reports the development of a zero-bias photodetector employing a p–n junction heterostructure that combines environmentally benign copper tin sulfide (Cu₂SnS₃, CTS) with low-temperature-processed TiO₂ nanorods. CTS, a nontoxic and earth-abundant chalcogenide, was deposited onto hydrothermally synthesized TiO₂ nanorods via chemical bath deposition, resulting in a robust and efficient CTS/TiO₂ heterostructure. XRD analysis revealed the rutile phase of TiO₂ and the mixed tetragonal-wurtzite phases of Cu₂SnS₃. The heterojunction demonstrated broad spectral absorption across the UV–visible range, with TiO₂ (3.1 eV) absorbing primarily UV light and Cu₂SnS₃ (1.75 eV) effectively covering the visible spectrum. <i>I</i>–<i>V</i> characteristics depicted a nonlinear relationship, indicating the presence of a built-in potential at the p–n junction, which enhances photocurrent generation under illumination. Notably, the detector operates efficiently at 0 V, highlighting its self-powered capability. Temporal response analysis revealed rapid rise and fall times (∼40 ms), emphasizing the potential of this solution-processed heterostructure for fast and reliable photodetection. The detector exhibited excellent performance metrics, including a low dark current (477 nA), high photocurrent (15.7 μA), high ON/OFF ratio (33), and high responsivity (50 mA/W). The nanorod heterostructure architecture offers conformable junction between Cu₂SnS₃ and TiO₂ and thereby offers an efficient pathway for photocarrier collection. The demonstrated CTS-TiO₂ nanorod detector is promising for the development of sustainable photodetectors for various potential applications, viz., environmental monitoring, medical diagnostics, and portable electronics.