Simulation of optimum band-gap grading profile of Cu₂ZnSn(S,Se)₄solar cells with different optical and defect properties

Abstract

The effect of the band-gap profile on the performance of Cu 2 ZnSn(S x ,Se 1%x ) 4 (CZTSSe) solar cells was investigated using a solar cell capacitance simulator (SCAPS) device simulation program. The band gap of CZTSSe is tunable from 1.0 to 1.5 eV by changing the S/(S + Se) ratio. Currently, the evolution of the electron affinity (χ) of CZTSSe at various band gaps has not been clarified yet, although two models with different χ values at various band gaps of CZTSSe have been proposed. We simulated solar cell performance using these two models and the differential rates of efficiency were compared between them. As a result, we were able to design the optimum band-gap profile using both models. Meanwhile, the characteristics of a solar cell with various optical absorption coefficients and defect densities of the CZTSSe absorber were simulated. The superiority of the graded band-gap profile was demonstrated by comparing the cell performances with and without a grading profile structure.

Towards highly efficient thin-film solar cells with a graded-bandgap CZTSSe layer

“…is the intrinsic energy. Both N c (z) and N v (z) are functions of z because they depend on the bandgap but we took them to be independent of z, following Hironiwa et al [32], because bandgap-dependent values are unavailable for CZTSSe. The 1D drift-diffusion model comprises the three differential equations [43, Sec.…”

“…An empirical model recently suggested that a linearly graded 1150-nm-thick absorber layer can deliver 16.9% efficiency. Several simulations performed with SCAPS software [37] have predicted efficiencies between 12.4% and 19.7% with absorber layers between 1000 and 3500-nm thickness and the bandgap grading being linear [31], piecewise linear [32], parabolic [31,34], or exponential [31,33]. However, the SCAPS software is optically elementary in that it relies on the Beer-Lambert law [38] rather than on the correct solution of an optical boundary-value problem; a rigorous optoelectronic model is needed to examine bandgap grading for CZTSSe solar cells.…”

Kesterite Solar Cells: Insights into Current Strategies and Challenges

“…The optimal front band grading is a suitably steep grading within the depletion region, which is generally less than 300 nm for CZTSSe. [ 144 ] However, the diffusion length of sulfur is usually too large if the sulfur source is introduced in the entire annealing process. [ 151 ] On the other hand, the diffusion depth can be controlled by introducing the sulfur source after a high temperature annealing process.…”

Band gap engineering of organo metal lead halide perovskite photovoltaic absorber

“…2. To simulate this planer perovskite solar cell (FTO/TiO 2 /MAPbI 3 /Spiro-OMeTAD/Au), the drift-diffusion model is derived from Poisson's equation and continuity equations for electrons and holes that are commonly used to describe the electrical behavior of semiconductor devices (Hironiwa et al 2014). Material parameters required for simulation of device are summarized in Liu and Kelly 2014;Burschka et al 2013;Como and Acevedo 2010;Snaith and Gratzel 2007;Laban and Etgar 2013).…”