The effect of degradation on the lifetime energy yield of crystalline-silicon/perovskite tandems

Abstract

Throughout the development of crystalline-silicon/perovskite tandem solar cells, the degradation rate of the perovskite top cells has become a limiting parameter. Currently, perovskite faces stability issues, mainly caused by corrosion and the light-soaking effect. This work investigates the degradation rate of the perovskite top cell, where a model is created to determine the parameters from the single diode model that change the IV-curve of a solar cell and lifetime energy yield simulations were performed to find the maximum tolerable degradation rate of perovskite in a tandem module to obtain a higher energy yield compared to a single-junction module Using experimental data from the King Abdullah University of Science and Technology (KAUST), where the external parameters from the measurements were provided, the changes over time in the ideality factor, saturation current, shunt resistance, and series resistance were estimated, using a numerical model. Linear trend lines through the fitting parameters over time were used and lifetime energy yield simulations were performed. For these simulations, a crystalline-silicon/perovskite tandem cell with an efficiency of 31.1% was compared to to a single-junction cell with an efficiency of 23.9%, where the single-junction cell’s optics are the same as the tandem cell’s bottom cell. To perform lifetime energy yield simulations, the PVMD toolbox is used.
Simulating the lifetime energy yield over 10 years, a perovskite degradation rate of 27.5%/year was found using the electrical parameters under STC, where the power output decreased from 4.95W to 0.24W per cell. Comparing 2T and 4T configurations, where the cell optics were kept the same, degradation rates of 21.2%/year and 9.5%/year were found for 2T and 4T, respectively. Looking at different geographical locations, degradation rates of 19%, 20%, 20.6% and 21.2% per year were found for Delft, Lagos, Lisbon and Shanghai, respectively. These differences were caused by current mismatch between the top and bottom cell, where the highest mismatch of 0.55 mA/cm2 was found in Shanghai.
To determine the maximum tolerable degradation rate of the perovskite top cell resulting in a higher lifetime energy yield for a tandem module compared to a single-junction module over 25 years, various degradation rates were analyzed. The perovskite degradation rate must be lower than 1.5%/year and 3.1%/year for 2T and 4T configurations, respectively, assuming no degradation in the silicon single-junction cell and the tandem cell’s bottom cell.