Theoretical analysis of the influence of defect parameters on photovoltaic performances of composition graded InGaN solar cells

In this paper, we have used simulations to evaluate the impact of the distribution of electrically active defects on the photovoltaic performances of InGaN-based solar cell. The simulations were carried out using Silvaco's ATLAS software. We have modeled a P-GaN/Grad-InGaN/i-In0.53Ga0.47N/Grad-InGaN/N-ZnO where Grad-InGaN corresponds to an InGaN layer with a graded composition. This layer is inserted to eliminate the band discontinuities at the interface between InGaN and the GaN and ZnO layers. The defects were modeled through the introduction of band tails and a Gaussian distribution of defects in i-InGaN material. We have evaluated the influence of band tail widths as well as the parameters of the Gaussian distribution (i.e. defect density, mean position and standard deviation) on the short-circuit current, the open-circuit voltage and the fill-factor (efficiency) of the solar cell. These results have allowed us to identify key structural parameters useful for the optimization of InGaN solar cells, as well as to give realistic estimates of the performances of such cells.

► We have modeled a p–i–n InGaN-based solar cell with gradual bandgap layers.
► InGaN defects have been modeled by two band tails and one localized energy level.
► Energetic position and band tail widths have a low effect on device efficiency.
► The localized defect FWHM has a significant impact on performance.
► The efficiency drops radically when the defect density is higher than the P-doping.