Hot carrier dynamics in HfN and ZrN measured by transient absorption spectroscopy

The hot carrier solar cell is a promising concept for high efficiency photovoltaics. Obtaining the dynamic temperature information for the hot carriers in an absorber is of crucial importance to this concept. In this paper, we present a dynamical hot carrier theory that extracts the carrier temperature and the instantaneous carrier occupation from transient absorption spectra. We have applied this model to two transition metal nitride materials, HfN and ZrN. The analysis showed that for HfN the initial carrier temperature rose to 360 K immediately after a femtosecond pulse excitation and then dropped rapidly to 330 K within 0.13 ps. After this initial process, the carrier temperature still remained relatively elevated at above 320 K for as long as 2 ns. The initial fast process was attributed to the strong carrier-carrier scattering in the material while the slow decay of temperature might be due to unusually weak electron-phonon interactions. A shorter cooling time and overall lower hot carrier temperatures were observed in ZrN. (C) 2016 Published by Elsevier B.V.