Review of carrier thermalization mechanisms in II-VI QDs and their potential application as the absorber in hot carrier solar cells

Abstract

The hot carrier solar cell (HCSC) aims to completely utilize the thermalization energy loss to boost the power conversion efficiency (PCE), where its key components are hot carrier absorber (HCA) sandwiched between two energy selective contacts (ESCs). The HCA is expected to effectively reduce the thermalization rate to few nanoseconds, improving output voltage. Low-dimensional semiconductors like quantum dots (QDs) may satisfy the requirements of HCA through quantum confinement (QC) due to its highest degree of QC. However, the mechanisms underlying the carrier thermalization within these QDs are not yet well understood and there is no consensus for complex material systems such as II-VI QDs. In this review, the effect of key physical parameters of QDs such as core size, shell thickness and interfacial smoothness have been systematically studied by analyzing the mechanisms (i.e. phonon bottleneck effect (PBE), Auger recombination and Auger relaxation) influencing the thermalization rate. The review demonstrates that reducing the core size of QDs can effectively enhance the Auger recombination rate. Meanwhile, most of the research suggests that the presence or thicker shell layers actually inhibit Auger recombination, accelerating the carrier relaxation rate. The relationship between interfacial smoothness and Auger recombination is also not yet well understood. Therefore, the QDs with small core size, thin shell and abrupt interface may satisfy the requirements for an HCA in order to achieve highly efficient HCSCs. This review compares the Auger recombination mechanisms under different conditions and provides an important guideline for HCAs using QDs.