The transition to renewable energy sources is essential to mitigate the impacts of climate change, with solar energy playing a pivotal role in this shift. Photovoltaic (PV) technology. However, the traditional single-junction cells are reaching their theoretical efficiency, which currently stands at 29.43%. Through the use of tandem solar cells, this efficiency limit can be surpassed. The tandem cell is being researched further to increase the power conversion efficiency (PCE). However, the conventional two-terminal (2T) and four-terminal (4T) tandem configurations face challenges related to current matching and optical losses, respectively.
This project addresses these challenges by focusing on the development and optimization of a three-terminal (3T) perovskite/silicon tandem module. The research aims to enhance the energy yield of 3T module under real-world conditions by developing a comprehensive 3T model within the Photovoltaic Material and Devices (PVMD) Toolbox, bridging the gap between cell-level and module-level optimization, which has been underexplored in existing studies.
The first step involved the development of the 3T model, which incorporates independent connections for each sub-cell and utilizes an interdigitated back contact (IBC) on the bottom cell as the third terminal. The 3T model is developed and simulated in MATLAB to be validated, showing close alignment of IV curves compared to the existing literature. The 3T model is then used to simulate a 72-cell module to be validated with a widely used electrical simulator called LTspice. The validation of the developed MATLAB 3T model against LTSpice simulations demonstrated a close match, with an RMSE result of 0.02% errors, confirming the model's accuracy in predicting the IV curves and energy yield for various operating conditions.
The second phase of the research involved detailed comparisons between the performances of 2T and 3T modules, each consisting of 72 cells, under both standard test conditions (STC) and real-world conditions in Delft as a sample. The simulations revealed that the 3T module provides less annual energy yield than 2T. However, the 3T module performs better than 2T at handling spectral irradiance variations and current mismatch situations under real-world conditions. At a certain hour, 3T outperforms 2T by yielding 220.75 W compared to 219.1 W. The loss analysis confirms that the 3T module produces less mismatch loss under real conditions than the 2T module. The simulations at four different locations also show that 3T has a certain number of times when 3T yields more energy than 2T. This shows the potential of 3T to outperform 2T by optimizing the perovskite bandgap energy and thickness.
The optimization of the 3T module focused on adjusting the perovskite layer's bandgap energy and thickness. The optimal bandgap energy is identified as 1.64 eV, and the ideal thickness is 600 nm for 2T, yielding 588.79 kWh. On the other hand, 3T has optimal perovskite bandgap energy and thickness of 1.82 eV and 600 nm, respectively, yielding lower energy of 583.24 kWh. Then, the modules are expanded into 144-cell modules, which results in 3T consistently yielding around 0.4% to 0.8% more energy at its optimum perovskite bandgap energy and thickness at 4 location samples compared to the 2T. For example, at Delft, the 3T yields more annual energy of 1172 kWh than 2T of 1167 kWh. This is due to the reduced end loss produced by 3T at a larger number of cells in the module. These results show that the 3T outperforms 2T at its respective optimum perovskite bandgap energy and thickness at every location sample and at a larger number of cell modules. Although the current 3T technology with IBC is still expensive, it is expected to become competitively priced in the future. These findings highlight the importance of ongoing optimization and development of 3T modules to fully unlock their potential in various environmental conditions.