The efficiency of antimony selenide (Sb2Se3) solar cells has been improved from <2% to >10% within only 7 years, but fundamental properties at the heterojunction interface such as the charge carrier transfer and the trap state localizing process has not been studied yet. Here, the carrier competing dynamics in Sb2Se3-based heterojunction has been systematically investigated. We find the competition between the band-edge electron transfer and the trapping process in CdS/Sb2Se3 will result in less-efficient charge separation and hence low open circuit voltage in photovoltaic devices. In contrast, the hot electron extraction at the SnO2/Sb2Se3 interface is nearly an order of magnitude faster than the trapping process, which can effectively escape the trapping carrier loss and potentially lead to higher open-circuit voltages. Our results reveal the hidden role of the buffer interface in the ultrafast charge extraction and provide a potential strategy to improve the performance of Sb2Se3-based solar cells.

The Dirac fermion, a high-mobility electron in the Dirac cone of monolayer graphene, has significant potential for use in the terahertz probing technique. For undoped graphene, ultrafast terahertz conductivity relaxation is mostly driven by electron–acoustic phonon supercollision coupling. The decay time of this coupling can be increased to tens or hundreds of picoseconds by decreasing the temperature. However, for chemical vapor deposition (CVD)-grown graphene, which exhibits negative photoinduced terahertz conductivity, there is currently no consensus on the dominant aspects of the terahertz conductivity relaxation process on time scales of less than 10 ps. In this study, the competition between electron–acoustic and optical–acoustic phonon coupling processes during the cooling of CVD graphene was systematically investigated. We experimentally verified that the ultrafast disorder-assisted optical–acoustic phonon interaction plays a key role in ultrafast terahertz conductivity relaxation. Furthermore, the ultrafast cooling process was found to be robust under different pump wavelengths and external temperatures, and it could be modulated by substrate doping. These findings are expected to contribute to a possible cooling channel in CVD graphene and to increase hot electron extraction efficiency for the design of graphene-based photoconversion devices.