Carrier multiplication is a process in which one absorbed photon excites two or more electrons. This is of great promise to increase the efficiency of photovoltaic devices. Until now, the factors that determine the onset energy of carrier multiplication have not been convincingly explained. We show experimentally that the onset of carrier multiplication in lead chalcogenide quantum confined and bulk crystals is due to asymmetric optical transitions. In such transitions most of the photon energy in excess of the band gap is given to either the hole or the electron. The results are confirmed and explained by theoretical tight-binding calculations of the competition between impact ionization and carrier cooling. These results are a large step forward in understanding carrier multiplication and allow for a screening of materials with an onset of carrier multiplication close to twice the band gap energy. Such materials are of great interest for development of highly efficient photovoltaic devices.

中文翻译：

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不对称的光学跃迁决定了硫族元素铅量子受限和块状晶体中载流子增殖的开始。

载流子增殖是一个过程，其中一个吸收的光子激发两个或多个电子。这对于提高光伏装置的效率具有巨大的希望。到目前为止，还没有令人信服地解释了决定载波倍增能量的因素。我们从实验上表明，硫族元素铅量子约束和块状晶体中载流子增殖的开始是由于不对称的光学跃迁。在这样的跃迁中，超过带隙的大部分光子能量被提供给空穴或电子。结果通过碰撞电离与载体冷却之间竞争的理论紧密结合计算得到证实和解释。这些结果是在理解载流子倍增方面向前迈出的一大步，并允许以接近两倍于带隙能量的载流子倍增的开始筛选材料。这样的材料对于开发高效的光伏器件具有极大的兴趣。