Understanding and control of ultrafast non-equilibrium processes in semiconductors is key to making use of the full photon energy before relaxation, leading to new ways to break efficiency limits for solar energy conversion. In this work, we demonstrate the observation and modulation of slow relaxation in uniformly mixed tin-lead perovskites (MASn_xPb_1-xI₃ and CsSn_xPb_1-xI₃ nanocrystals). Transient absorption measurements reveal that slow cooling mediated by a hot phonon bottleneck effect appears at carrier densities above ~10¹⁸ cm⁻³ for tin-lead alloy nanocrystals, and tin addition is found to give rise to suppressed cooling. Within the alloy nanoparticles, the combination of a newly introduced high-energy band, screened Fröhlich interaction, suppressed Klemens decay and reduced thermal conductivity (acoustic phonon transport) with increased tin content contributes to the slowed relaxation. For inorganic nanocrystals where defect states couple strongly with carriers, sodium doping has been confirmed to benefit in maintaining hot carriers by decoupling them from deep defects, leading to a decreased energy-loss rate during thermalization and an enhanced hot phonon bottleneck effect. The slow cooling we observe uncovers the intrinsic photophysics of perovskite nanocrystals, with implications for photovoltaic applications where suppressed cooling could lead to hot-carrier solar cells.

了解和控制半导体中的超快非平衡过程是利用弛豫前的全部光子能量的关键，从而找到突破太阳能转换效率限制的新方法。在这项工作中，我们展示了均匀混合的锡铅钙钛矿（MASn _x Pb _1-x I ₃和 CsSn _x Pb _1-x I ₃纳米晶体）中缓慢弛豫的观察和调制。瞬态吸收测量表明，对于锡铅合金纳米晶体，热声子瓶颈效应介导的缓慢冷却出现在载流子密度高于~10 ¹⁸  cm ^-3时，并且发现锡的添加会引起抑制冷却。在合金纳米粒子中，新引入的高能带、屏蔽的弗罗利希相互作用、抑制克莱门斯衰变和降低的热导率（声学声子传输）与增加的锡含量的结合有助于减缓弛豫。对于缺陷态与载流子强烈耦合的无机纳米晶体，钠掺杂已被证实有利于通过将热载流子与深层缺陷解耦来维持热载流子，从而降低热化过程中的能量损失率并增强热声子瓶颈效应。我们观察到的缓慢冷却揭示了钙钛矿纳米晶体的固有光物理学，这对抑制冷却可能导致热载流子太阳能电池的光伏应用具有影响。