Fundamental Carrier Lifetime Exceeding 1 µs in Cs<inf>2</inf>AgBiBr<inf>6</inf> Double Perovskite

Abstract

There is current interest in finding non-toxic alternatives to lead-halide perovskites for optoelectronic applications. Silver-bismuth double perovskites have recently gained attention, but evaluating their carrier lifetime and recombination mechanisms from photoluminescence measurements is challenging due to their indirect bandgap. In this work, we use transient absorption spectroscopy to directly track the photocarrier population in Cs2AgBiBr6 by measuring the ground state bleach dynamics. We resolve a small initial drop in the ground state bleach on a picosecond timescale, after which the remaining photocarriers decay mono-exponentially with a lifetime of 1.4 μs. The majority of the early-time decay is attributed to hot-carrier thermalization from the direct transition to the indirect bandgap, and the 1.4 μs lifetime represents the recombination of most photocarriers. From this lifetime, we calculate a steady-state excess carrier density of 2.2 × 10^16 cm-3 under 1 sun, which is an order of magnitude larger than that for methylammonium lead iodide, suggesting that charge transport and extraction can be efficient in Cs2AgBiBr6 solar cells.