Memoirs of the Graduate Schools of Engineering and System Informatics Kobe University, No. 6, pp. 18-24, 2014

Intermediate band electron wave function localization effect on the efficiency limits of InAs/GaAs quantum dot solar cell

Amir Mehdipour, Matsuto Ogawa, and Satofumi Souma

Department of Electrical and Electronic Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan

(Received May 22, 2014; Accepted September 30, 2014; Online published November 21, 2014)

Keywords: Intermediate Band Solar Cell, Quantum Dots, Tight-Binding Method

In the conventional detailed balance theory of quantum dot intermediate band solar cell (QD-IBSC), the electron wave function is assumed to be completely delocalized. Such wavefunctions are known to reduce thermal losses and enhance the photon-harvesting efficiency of an intermediate band. The aim of this study is to investigate the accuracy of the assumption of such “metallic-like IB” in determining the efficiency of IBSC in the presence of one or two IBs. According to our calculations for cubic model QD structures based on the finite element method, the electronic wave functions are strongly concentrated in the QD regions for the realistic QD spacing. The influence of such electron localization effects on the cell efficiency is then carefully examined by introducing the effective electron filling factor along with the detailed balance theory, with particular attention given to the roles played by the number of IBs and sunlight concentration. While the electron localization in IBs is detrimental for cell efficiency, the use of IBs is demonstrated to be still beneficial and improve the efficiency significantly under full sunlight concentration.

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