The tandem configuration consisting of two or more solar cells is practically the only approach to overcome the Shockley-Queisser limit, as evidenced by the III-V multijunction solar cells. From theoretical calculation, it has been found that the combination of a top cell with a large bandgap energy (e.g. 1.5~1.7 eV) and a bottom cell with a low bandgap energy (e.g. 1.0~1.1 eV) can lead to a conversion efficiency higher than 30%. Given that the bandgap energy of most commercial single junction solar cells is around 1.1 eV, the perovskite solar cells with a bandgap energy around 1.6 eV must be a very promising candidate for the top cell of tandem solar cells.
In this presentation, I will discuss the essential requirements for preparing highly performing perovskite top cells of perovskite-based tandem solar cells. Firstly, the strategies for improving the performance of the p-i-n type planar perovskite solar cell, mostly focusing on the interfacial charge transfer, will be introduced. After a series of interfacial engineering procedures to the charge extraction layers, a conversion efficiency as high as 19% could be achieved. Secondly, strategies for fabricating transparent perovskite solar cells with a TCO top electrode layer will be discussed. Finally, some of the recent results on the highly efficient (> 23%) tandem solar cells incorporating the transparent perovskite top cell will be introduced.