Browsing by Author "Civiletti, Benjamin J."
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Item Effects of defect density, minority carrier lifetime, doping density, and absorber-layer thickness in CIGS and CZTSSe thin-film solar cells(Journal of Photonics for Energy, 2023-06-02) Ahmad, Faiz; Civiletti, Benjamin J.; Monk, Peter B.; Lakhtakia, AkhleshDetailed optoelectronic simulations of thin-film photovoltaic solar cells (PVSCs) with a homogeneous photon-absorber layer made of with CIGS or CZTSSe were carried out to determine the effects of defect density, minority carrier lifetime, doping density, composition (i.e., bandgap energy), and absorber-layer thickness on solar-cell performance. The transfer-matrix method was used to calculate the electron-hole-pair (EHP) generation rate, and a one-dimensional drift-diffusion model was used to determine the EHP recombination rate, open-circuit voltage, short-circuit current density, power-conversion efficiency, and fill factor. Through a comparison of limited experimental data and simulation results, we formulated expressions for the defect density in terms of the composition parameter of either CIGS or CZTSSe. All performance parameters of the thin-films PVSCs were thereby shown to be obtainable from the bulk material-response parameters of the semiconductor, with the influence of surface defects being small enough to be ignored. Furthermore, unrealistic values of the defect density (equivalently, minority carrier lifetime) will deliver unreliable predictions of the solar-cell performance. The derived expressions should guide fellow researchers in simulating the graded-bandgap and quantum-well-based PVSCs.Item The numerical analysis of RCWA and its use in simulating thin-film solar cells(University of Delaware, 2020) Civiletti, Benjamin J.The ability to rapidly compute the electromagnetic field inside a thin-film solar cell given a set of constitutive parameters of the cell is an important tool in the field of solar cell optimization. Many numerical methods exist to model diffraction of electromagnetic waves by periodic gratings. Among these, spectral methods are popular for their computational speed and easy application to many different grating geometries. The main theme of this thesis is to study the convergence properties of a quasi-spectral method called the Rigorous Coupled-Wave Approach (RCWA). To do this, we investigate the relevant scattering problems: scattering of an s- or p-polarized incident plane-wave by an inhomogenous, periodic medium. In each of these two cases, we establish convergence of the RCWA under appropriate assumptions on the consti- tutive parameters of the cell. In many cases we consider, the variational formulation is not coercive so we employ Rellich identities to establish convergence. We present numerical examples to test our prediction of the convergence rate, which suggests that our analytical results could be pessimistic. We also study a new spectral method that combines the RCWA with transformation optics, whereby the domain is first mapped to a simpler one using a coordinate transform. Our preliminary numerical tests demonstrate that this hybrid method could be more stable than the standard RCWA, and might extend to 3D to rapidly solve the full 3D Maxwell system in crossed gratings.