title: Advanced Characterization and Modelling for Monolithic perovskite/silicon Tandem Solar Cells
Creators: name: Nguyen, Khoa
Publisher: name: The Australian National University
Year: 2025

description: Monolithic perovskite-based tandem solar cells (TSCs) are highly promising candidates for next-generation solar technology. A key challenge with these cells is the interaction between the sub-cells within the monolithic tandem structure, which complicates both characterization and output estimation. Additionally, the stability of perovskite solar cells (PSCs) has been a longstanding issue, especially when compared to silicon solar cells. This thesis focuses on advanced characterization techniques and modelling to explore the impact of degradation on the optoelectronic properties of PSCs, investigate sub-cell interactions in monolithic TSCs, and optimize these structures for outdoor applications. First, a non-destructive technique based on photoluminescence (PL) imaging was developed to extract various optical and electrical parameters of single-junction PSCs. By utilizing hyperspectral cube data, this technique simultaneously extracts optoelectronic parameters and analyses their correlations, making it applicable at various fabrication stages and to post-finished cells. This method enables the evaluation of spatial variations in properties affecting cell performance and the identification of dominant factors during different fabrication stages. Additionally, it facilitates the investigation of correlations between various optoelectronic parameters and their evolution following degradation tests. Next, a fast and non-invasive method was proposed to evaluate the luminescence coupling (LC) effect in monolithic TSCs. This method provides a practical approach to estimating LC efficiency, which is an important input for calculating the energy yield (EY) of a monolithic TSC under varying conditions. It was applied to monolithic perovskite/silicon tunnel oxide passivated contact (TOPCon) and monolithic perovskite/silicon heterojunction TSCs to extract LC effects. The findings demonstrate that the proposed method is effective under standard test conditions (STCs) as well as in outdoor applications. Then, the contribution of each sub-cell to the measured PL spectrum of a monolithic perovskite/silicon TSC was identified using photoluminescence excitation spectroscopy. The PL spectrum of each sub-cell was examined by varying the excitation light wavelength from the near-ultraviolet (UV) region to the near-infrared (NIR) region. We identified a range of excitation wavelengths that induced carrier generation and luminescence in both sub-cells, validated through an isolated single-junction perovskite cell with a structure identical to the top cell in the tandem device. As a result, the optimal maximum and minimum wavelengths needed to obtain a distinct PL spectrum for each sub-cell in monolithic perovskite/silicon TSCs can be determined. Finally, building on the previous results, a comprehensive EY model was developed, accounting for the full range of potential impact factors on the output power of a monolithic tandem device, including the LC effect and the variation in radiative recombination with changes in irradiance - factors that have been omitted in recent models. At each investigated location, we optimized the bandgap of the perovskite top cell at various absorber thicknesses. This data is essential for balancing fabrication costs, device stability, and output power. The results of this study provide valuable guidelines for the development and characterization of monolithic perovskite-based tandem devices.