We present a numerical study of the effect of in-plane uniaxial strain on the photoconductivity of graphene, where special attention is paid to the dependences of the photoconductivity on the direction of the strain, the strength of the strain, and the polarization direction in linearly polarized light irradiated perpendicularly to graphene. Our calculations showed that the anisotropic feature of the photoconductivity predicted for unstrained graphene is strongly modulated by applying strain. In particular, it was found that the estimation of anisotropy factors, defined by the ratio between the diagonal conductivities along the strain direction for two different light polarizations P ¼ 0 and =2 relative to the strain axis, enables us to not only determine the strain ratio but also obtain information about the crystal orientation along which the strain is applied.

We propose a simplified theoretical model to analyze the absorption coefficients in quantum dot intermediate band solar cell (QD-IBSC) structure. Our theoretical model, based on the multiband tight-binding Hamiltonian including the conduction, valence, and the intermediate band, can capture some essential features in the actual QD-IBSC such as the absorption path dependence of the absorption strength and the line shape of the absorption spectrum in spite of its simplicity. The main feature of this model is its ability to be applied to any QD-IBSC system regardless of the geometrical parameters (QDs shapes and spacing) or the base materials by changing the relevant coupling parameters. The proposed simplified should be of useful for the semi-quantitative understanding and modeling of QD-IBSC.

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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.