Enhanced Ballistic Transport of Charge Carriers in Alloyed and K-Passivated Alloyed Perovskite Thin Films

Hybrid organic-inorganic perovskites show remarkable charge transport properties despite their deposition via low-temperature solution phase methods. It has recently been shown that this includes the ballistic transport of charges following photoexcitation, with ballistic transport lengths as large as 150 nm measured in MAPI 3 films, which is almost twice the value reported for GaAs. Here we explore the ballistic transport regime in high-performance triple-cation and K-passivated triple-cation perovskite films, using femtosecond transient absorption microscopy, which allows us to image carrier motion with 10 fs temporal resolution and 10 nm spatial precision. We observe ballistic transport lengths of 160 and 220 nm in triple-cation and K-passivated triple-cation perovskite films, respectively. We propose that the ballistic transport is limited by nanoscale trap clusters at grain boundaries and interfaces, which can be passivated via chemical treatments to enhance the ballistic transport length, which implies that further enhancements are possible as passivation methods are improved.