Metal halide perovskites are emerging as an intriguing class of solution-based semiconductors with significant potential for optoelectronic devices; thus, better understanding of carrier dynamics and stability of the material is critical to the development of solar cell physics. In this study we investigate the triple halide perovskite (FA,Cs)Pb(I,Br,Cl)₃, which is known to be amongst the most stable metal halide perovskite systems available. This stability allows a comprehensive study of the hot carrier dynamics to be assessed under steady-state conditions at high fluence and various temperatures in a device structure. 

    A systematic set of measurements including simultaneous power-dependent (PDPL) and temperature-dependent photoluminescence (TDPL), and current-voltage (J-V) measurements were performed to probe the hot carriers and electron-phonon coupling in operational solar cells. These measurements support the presence of hot carriers in the device in advance of any negative effects due to halide segregation or decomposition. Indeed, the competition between hot carrier dynamics and photo induced halide segregation are shown to be strongly dependent upon temperature. At 100 K, clear evidence of hot carriers was observed via increasing carrier temperatures in the high energy tail of the PL coupled with ballistic transport in J-V measurements. At room temperature, however, the blue shift in the PL and high energy broadening characteristic of hot carrier generation at higher laser excitation are shown to compete with a gradual redshift in the PL peak energy as photo induced halide segregation begins to occur at higher lattice temperature.

    The presence and properties of hot carrier dynamics is also presented in in the ultrafast regime using transient absorption spectroscopy. Here, the dynamics of hot carriers were assessed in a device with upper and lower ITO electrodes to enable photoexcitation in the perovskite absorber in the region of both the upper and lower electron-transporting and hole transporting interfaces of the device, respectively. These devices were assessed at operational conditions and the hot carrier thermalization assessed at the maximum power and under short circuit current and open circuit voltage conditions.  Two distinct cooling (decay) times are observed when exciting at the two interfaces. The first decay which is a fast process, has a timescale of 25 ps. This is followed by a much slower decay that extends to hundreds of ps.[2] These data are discussed with respect to non-equivalent carrier extraction, the relative, photoexcited carrier absorption and density, and the role these play in facilitating a phonon bottleneck in these systems.