Abstract
Carrier Multiplication (CM) is a Coulomb-driven non-radiative recombination mechanism which leads to the generation of multiple electron-hole pairs after absorption of a single high-energy photon. Recently a new CM process, termed space separated quantum cutting, was introduced to explain a set of new experiments conducted in dense arrays of silicon nanocrystals. The occurrence of this effect was hypothesized to generate the formation of Auger unaffected multiexciton configurations constituted by single electron-hole pairs distributed on different interacting naocrystals. In this work we discuss ab-initio results obtained by our group in the study of CM effects in systems of strongly interacting silicon nanocrystals. By solving a set of rate equations, we simulate the time evolution of the number of electron-hole pairs generated in dense arrays of silicon nanocrystals after absorption of high energy photons, by describing the circumstances under which CM dynamics can lead to the generation of Auger unaffected multiexciton configurations.
Highlights
Nano-structured third generation solar cell devices are promising systems to increase the percentage of electrical energy generated by photovoltaic (PV) modules
By solving a set of rate equations, we simulate the time evolution of the number of electron-hole pairs generated in dense arrays of silicon nanocrystals after absorption of high energy photons, by describing the circumstances under which Carrier Multiplication (CM) dynamics can lead to the generation of Auger unaffected multiexciton configurations
When a relative energy scale is adopted, that is when the CM is reported as a function of the ratio between the initial carrier excess energy and Eg, CM is proven to be more efficient in small NCs
Summary
Nano-structured third generation solar cell devices are promising systems to increase the percentage of electrical energy generated by photovoltaic (PV) modules. In single junction solar cells, the maximum theoretical thermodynamic conversion efficiency is defined by the Shockley-Queisser limit [1], that is about the 30%. Similarities between PL signals recorded in Er3+ doped Si-NCs and in Si-NCs organized in dense arrays were interpreted by hypothesizing the occurrence of a new quantum-cutting CM effect, termed space separated quantum cutting (SSQC). When this effect occurs, a high energy excited carrier decay toward the band edge (conduction band (CB) edge for electrons, valence band (VB) edge for holes) by transferring its excess energy to a nearby NC where an extra e-h pair is generated. Abinitio techniques based on the Density Functional Theory (DFT) have been already applied by our group to calculate
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