Currently, the key issues in the solar cell market are reducing price and improving efficiency of the device. The crystalline silicon solar cell, which account for more than 90% of the total solar cell market, are already limited in terms of the high efficiency, reaching the theoretical limit. Also, in case of Al-BSF p-type silicon solar cells, it has an excellent price of 0.2$/Wp. There is a tandem solar cell as a way to improve the limited cell efficiency of a standard silicon cells to a more high efficiency. By joining the top cell with high bandgap and the bottom cell with low bandgap, the high efficiency can be achieved. In particular, perovskite solar cell, which has reached the highest efficiency of 22.1% in recent year, is an ideal material for tandemization with silicon solar cells because it is easy to control the bandgap by adjusting the chemical composition of perovskite. According to reported simulation data, the highest theoretical efficiency of perovskite/silicon tandem solar cell is expected to be over 30%.
Thanks to these advantages, many structures of perovskite/silicon tandem solar cells have been actively studied. Some results for 2-terminal, 4-terminal tandem solar cells already have been reported. However, the current matching and junction techniques of the upper and lower devices have not yet been optimized. For monolithic tandem solar cell fabricating the perovskite on top of the silicon bottom cell, the current matching and tunneling junction are crucial points. On the other hand, mechanically 4-terminal tandem solar cells can be made without the current matching.
In this study, we report a mechanically 2-terminal perovskite/silicon tandem solar cells. The low-cost Al-BSF p-type silicon solar cell with TCO was used for better light absorption. In case of the top devices, a transparent perovskite solar cell was used minimized the light loss. Through the mechanical junction of the upper and lower solar cell, the current flowed well to the interface, and high Voc, which is over 1.5V, was obtained. It is expected that the independent optimization of the upper and lower cells contributes to enhancement of the cell efficiency and it has a good place in the future tandem solar cell market.