Minimizing electro-optical losses of ITO layers for monolithic perovskite silicon tandem solar cells

Monolithic perovskite silicon tandem solar cells promise high efficiency and cost advantage. In such tandem devices a conductive front electrode of high transparency is necessary for lateral transportation of the charges. This study focuses on optimizing the electro-optical properties of DC sputtered ITO films as front electrode in monolithic two-terminal perovskite silicon tandem solar cells. Initially, an ITO thin film is developed by finding a possible optimum doping level that provides both high transparency and low sheet resistance. Moreover, to further decouple the transparency-conductivity trade-off of the ITO bulk properties from the requirements for low-ohmic contact formation, a thin, highly doped ITO interlayer is inserted towards the SnOX interface. The ITO thin film (stack) significantly improved efficiency of the tandem solar cells by improving all solar cell parameters. This optimization led to improved tandem short circuit density with reduced standard deviation from a mean value of 19.3 ± 0.4 mA/cm2 to 19.8 ± 0.2 mA/cm2, increased average fill factor from 68% to 73% and average power conversion efficiency increase from 22% to 25%.