Spoor Frank C M, Grimaldi Gianluca, Delerue Christophe, Evers Wiel H, Crisp Ryan W, Geiregat Pieter, Hens Zeger, Houtepen Arjan J, Siebbeles Laurens D A
Chemical Engineering Department , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands.
IEMN, Départment ISEN , UMR CNRS , 59046 Lille Cedex, France.
ACS Nano. 2018 May 22;12(5):4796-4802. doi: 10.1021/acsnano.8b01530. Epub 2018 Apr 19.
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.
载流子倍增是一个吸收的光子激发两个或更多电子的过程。这对于提高光伏器件的效率有很大的前景。到目前为止，决定载流子倍增起始能量的因素尚未得到令人信服的解释。我们通过实验表明，硫属铅化物量子受限晶体和块状晶体中的载流子倍增起始是由于不对称光学跃迁。在这种跃迁中，超过带隙的大部分光子能量要么给予空穴，要么给予电子。通过对碰撞电离和载流子冷却之间竞争的理论紧束缚计算，证实并解释了这些结果。这些结果在理解载流子倍增方面向前迈出了一大步，并允许筛选载流子倍增起始接近带隙能量两倍的材料。这类材料对于高效光伏器件的开发极具吸引力。
