Fully Indium-Free Monolithic Two-Terminal Perovskite/Perovskite/Silicon Triple-Junction Solar Cells: Replacing All Four TCO Electrodes.

Employing indium-based transparent conductive oxides (TCO) such as indium tin oxide (ITO) in silicon solar cells is already a hurdle due to the scarcity of indium for the photovoltaic community. This is even more challenging in perovskite/silicon multijunction solar cells where TCO layers are necessary for multiple applications beyond transparency and lateral carrier transport. Development of perovskite/perovskite/silicon triple-junction solar cells is a relatively new research focus. It is important to consider this criticality of the raw materials used during the design and development phase. In this work, we successfully replaced all four ITO layers used in our perovskite/perovskite/silicon triple-junction solar cell with an indium-free material. We mainly used zinc-doped tin oxide (ZTO), while for the silicon bottom cell's front and rear contacts an interfacial layer of aluminum-doped zinc oxide (AZO) was used to ensure low contact resistance/efficient vertical transport to the silicon thin films. To replace the ITO top TCO of the perovskite top cell, a ZTO material with lower ZnO fraction was used to achieve a lower sheet resistance/more efficient lateral transport. With this, we present the first fully indium-free silicon-based triple-junction solar cell with no efficiency penalty.