Temperature-Dependent Ultrafast Charge Carrier Dynamics in Amorphous and Crystalline Sb₂Se₃ Thin Films

The Earth abundant polycrystalline antimony selenide (Sb₂Se₃) thin film is considered to be a potential photovoltaic material for their appropriate band gap, higher absorption coefficient, and nontoxicity. Interband gap defect states play a major role for efficient solar devices, which depends on the crystallinity of the materials. In the present investigation, we have synthesized an amorphous Sb₂Se₃ thin film by following the thermal evaporation technique and have also converted the film to crystalline after vacuum annealing it at 250 °C. Both amorphous and crystalline thin films were characterized by several analytical techniques, XRD, FE-SEM, optical absorption, XPS, and UPS spectroscopy. The interband gap defect density was found to be much higher in the amorphous thin film as compared to that of the crystalline one. To understand the charge carrier dynamics of the photoexcited Sb₂Se₃ thin film, femtosecond broad-band pump–probe spectroscopy has been employed at cryogenic temperature (5 K) and room temperature (300 K). Carrier trapping and recombination dynamics for both the films were found to be faster at 5 K than at 300 K and were attributed to higher carrier mobility at high temperatures. Understanding carrier dynamics of this photovoltaic materials are immensely useful for designing efficient devices.