Maximizing Efficiency—A Numerical Modeling of 2-Terminal Perovskite/Silicon Tandem Devices as to Different Bottom Cell Structures

2-terminal perovskite/silicon (Si) tandem solar cells have made significant progress in terms of efficiency and are considered suitable candidates for the next generation of photovoltaic devices. To date, most studies on 2-terminal perovskite/Si tandems have primarily focused on the development of the top cell, including tuning the perovskite bandgap, passivating interface defects, and improving film deposition methods on textured Si surfaces. Additionally, significant efforts have been dedicated to optimizing the interlayer types and properties. Existing optimizations of the silicon bottom cell have often been limited to specific structures previously reported to exhibit high efficiency or have explored new configurations such as “Inverted TOPCon” and “PERC+TOPCon” combination structure [1-2].<br/>However, to achieve broader and higher efficiency possibilities, it is crucial to optimize each bottom Si solar cell structure independently. In tandem design, the spectrum transferred to the bottom cell significantly varies depending on the bandgap and structure of the top perovskite cell. It has been confirmed that the generation profile of the bottom cell differs based on the transmitted spectrum, particularly showing a more uniform generation profile when receiving filtered light compared to the standard AM1.5G spectrum. This variation influences the selection of the optimal structure for the bottom cell. Therefore, the electrical and optical requirements for bottom cells vary and must be reconsidered to meet these specific needs.<br/>In this study, optical and electrical optimization modeling was conducted using SunSolve and Quokka2 programs to verify the characteristics and maximum efficiency of the 2-terminal perovskite/Si tandem cell considering the Si bottom cell structure. Optical optimization and current matching were performed by adjusting the thickness of each layer using the n-i-p and p-i-n tandem structures, reported to exhibit high efficiency. We considered two types of bottom cell structure: homojunction (PERC, TOPCon) and heterojunction (HIT). Additionally, the bottom cell structure was fixed as an opening local front-contact structure within the passivation layer for the homojunction to maintain a commercially dominant single-cell structure and good electrical connectivity to the transparent conductive oxide (TCO) interlayer. Moreover, to optimize the electrical characteristics, the bulk characteristics, substrate type, and junction location were changed to perform modeling, and the maximum efficiency possible for each structure was determined. Consequently, we proposed an improvement method and structure capable of achieving maximum possible efficiency of more than 30% as a tandem device for each bottom cell structure.