The performance of semiconductor devices is fundamentally governed by charge-carrier dynamics within the active materials^1,2,3,4,5,6. Although advances have been made towards understanding these dynamics under steady-state conditions, the importance of non-equilibrium phenomena and their effect on device performances remains elusive^7,8. In fact, the ballistic propagation of carriers is generally considered to not contribute to the mechanism of photovoltaics (PVs) and light-emitting diodes, as scattering rapidly disrupts such processes after carrier generation via photon absorption or electric injection⁹. Here we characterize the spatiotemporal dynamics of carriers immediately after photon absorption in methylammonium lead iodide perovskite films using femtosecond transient absorption microscopy (fs-TAM) with a 10 fs temporal resolution and 10 nm spatial precision. We found that non-equilibrium carriers propagate ballistically over 150 nm within 20 fs of photon absorption. Our results suggest that in a typical perovskite PV device operating under standard conditions, a large fraction of carriers can reach the charge collection layers ballistically. The ballistic transport distance appears to be limited by energetic disorder within the materials, probably due to disorder-induced scattering. This provides a direct route towards optimization of the ballistic transport distance via improvements in materials and by minimizing the energetic disorder. Our observations reveal an unexplored regime of carrier transport in perovskites, which could have important consequences for device performance.

半导体器件的性能基本上由活性材料^{1,2,3,4,5,6中的}电荷载流子动力学控制。虽然已经取得了进展，以了解稳态条件下的这些动力学，但非平衡现象的重要性及其对设备性能的影响仍然难以捉摸^7,8。实际上，通常认为载流子的弹道传播对光伏（PV）和发光二极管的机理没有帮助，因为在通过光子吸收或电注入产生载流子后，散射会迅速破坏此类过程⁹。在这里，我们使用10 fs的时间分辨率和10 nm的空间精度的飞秒瞬态吸收显微镜（fs-TAM），在甲基铵碘化钙钛矿钙钛矿薄膜中吸收光子后，立即表征了载流子的时空动力学。我们发现非平衡载流子在20 fs的光子吸收范围内在150 nm上弹道传播。我们的结果表明，在标准条件下运行的典型钙钛矿光伏器件中，大部分载流子可以弹道到达电荷收集层。弹道运输距离似乎受材料内高能紊乱的限制，这可能是由于无序诱发的散射所致。这通过材料的改进和最小化能量的紊乱，为优化弹道运输距离提供了一条直接途径。