In band-like semiconductors, charge carriers form a thermal energydistribution rapidly after optical excitation. In hybrid lead halideperovskites, the cooling of such thermal carrier distributions occurs ontimescales of ~300 fs via carrier-phonon scattering. However, the initialbuild-up of the thermal distribution proved difficult to resolve withpump-probe techniques due to the requirement of high resolution, both in timeand in energy. Here, we use two-dimensional electronic spectroscopy withsub-10fs resolution to directly observe the carrier interactions that lead tothe formation of a thermal carrier distribution. We find that thermalizationoccurs dominantly via carrier-carrier scattering under the investigatedfluences and report the dependence of carrier scattering rates on excess energyand carrier density. We extract characteristic carrier thermalization timesfrom below 10 fs to 85 fs. These values allow for mobilities of up to 500 cm^2V^(-1) s^(-1) at carrier densities lower than 2x10^19 cm^(-3) and limit thetime for carrier extraction in hot carrier solar cells.
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机译：在带状半导体中，电荷载流子在光激发后迅速形成热能分布。在混合卤化钙钛矿中，这种热载流子分布的冷却通过载子-声子散射在约300 fs的时间尺度上发生。然而，由于对时间和能量的高分辨率要求，事实证明，热分布的初始积累难以用泵探针技术解决。在这里，我们使用分辨率低于10fs的二维电子光谱直接观察载流子相互作用，从而形成热载流子分布。我们发现在所研究的影响下，热化主要通过载流子-载流子散射发生，并报告了载流子散射速率对过量能量和载流子密度的依赖性。我们提取了低于10 fs至85 fs的特征载流子热化时间。这些值允许在低于2x10 ^ 19 cm ^（-3）的载流子密度下达到500 cm ^ 2V ^（-1）s ^（-1）的迁移率，并限制了热载流子太阳能电池中载流子提取的时间。
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