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Received Jun 9, 2017; Accepted Nov 23, 2017
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1. Introduction
Quantum dots (QDs) are being widely investigated since several years as a promising material for advanced concepts such as multiple junction [1], intermediate band [2, 3], and hot carrier [4] solar cells. The basic building block of such devices is typically made by an almost standard diode structure embedding a region with QDs. Electronic effects and charge transfer mechanisms in the QDs and between the QD localized states and the continuum states of the host semiconductor present quantum mechanical features, while a large part of the device is made by bulk regions working in the semiclassical transport regime. Thus, device level simulation models of QD solar cells inherently require multiscale approaches which shall be able to combine the micro- and macroscale description at an affordable computational cost [5].
In the hierarchy of multiscale models for the simulation of QD solar cells (QDSCs), one of the simplest approaches is provided by spatially resolved rate equation-based models, which couple microscopic calculated quantities such as the QD electronic structure, optical properties, and scattering rates to macroscopic equations for transport in the extended states. Several of the QD model parameters can also be extracted from routinary experimental data, making such approach suitable for both design and interpretation purposes. Modelling approaches able to reproduce the behavior of realistic devices and analyze the interplay of the involved physical mechanisms allow gaining insight into experimental results and provide useful feedback to the technology development. In this respect, while detailed balance theory of QDSCs has received a lot of attention and is useful to indicate the long-term target efficiency [6–8], less effort has been devoted to models based on semiconductor transport equations [9–13] and to the implications of QD carrier dynamics on the photovoltaic performances [14]. On the other hand, previous work by some of the present authors has shown that introducing a proper description of interband and intersubband QD dynamics is a crucial asset to address some of the most critical issues encountered in QDSCs, such as poor carrier collection efficiency and...