Hot Carrier Dynamics In Several Semiconductor Materials

Nowadays,how to improve the power conversion efficiency of photovoltaic devices become one of the hottest topics.The hot carriers relax to the edge of band by emitting phonons.However,a lot of heat could be lost which limits the photoelectric conversion in solar cells.If the hot carriers can be cooled down more slowly and extracted before relaxing to the band edge with the generation of electric current,it is possible to double the photoelectric conversion efficiency.In this work,density functional theory?DFT?combining nonadiabatic molecular dynamics have been used to explore the relaxation dynamics of inorganic perovskites SrSnX₃?X=S,Se?and g-C₃N₄/MoS₂,and revealed the hot carrier dynamics properties.The main results are summarized below:?1?We compared the relaxation dynamics in inorganic perovskites SrSnS₃and SrSnSe₃.The results indicate that the hot carriers relaxation dynamics depends on the chalcogenide element in the sysytem.Because of the strong nonadiabatic couplings,both the hot electrons and hot holes have a fast decay time in SrSnS₃ than SrSnSe₃ with the similar excess energy.Also,the hot holes hold a dramatic faster relaxation time than hot electrons for the two systems due to the large density of states and the smaller energy level in the valence band.In general,our findings show that the relaxation time of hot carriers in chalcogenide perovskites SrSnS₃ and SrSnSe₃ is longer than other organic-inorganic perovskites.?2?The heterojunctions of g-C₃N₄/MoS₂ shows the type-?band alignment with direct band gap.The results indicate that the hot carriers relaxation dynamics strongly depends on the NA coupling,band gap and pure-dephasing time.It is found that the hot holes decay faster than hot electrons,because the couplings between the holes states in the valence band are stronger than the electrons states in the conduction band.Moreover,the relaxation process of the hot holes involve interfacial transfer between different layers.Based on these features,the inorganic perovskite SrSnX₃?X=S,Se?and the g-C₃N₄/MoS₂ heterojunction are promising candidates for solar cell applications,and have the potential in optoelectronic applications.