Charge transport in quantum dot sensitized solar cells: A mathematical model

Abstract

In this paper, charge transport in quantum dot (QD) thin films is modeled by considering trap-state assisted tunneling among the QD thin films. Multiple parameters associated with traps like density, position, and capture/emission rates which can significantly affect tunneling, have been considered in the model. The model is further extended to the quantum dot sensitized solar cells (QDSSC), and the effects of tunneling rate variation in accordance with the trap-states at the QD-QD interfaces and/or in the shell of QDs is analyzed. In the proposed model, multiple silicon QD layers as active material are considered, which are sandwiched between ZnO as electron transport layer (ETL) and a MoO3 as hole transport layer (HTL). The model couples drift–diffusion framework for charge transport in ETL and HTL, and a system of rate equations for carrier dynamics among the QDs and their interfaces with ETL and HTL. Our analysis shows that the variations in trap-state concentration significantly affect the charge extraction and recombination scenario in the active layer of QDSSC, consequently producing a direct impact on device characteristics.