TCO and Grid Electrodes for Perovskite-Silicon Tandem Solar Cells: Basic Considerations and Upscaling Aspects

This work addresses general aspects of the front side TCO and grid electrode for application in a Perovskite-Silicon tandem device by optical and electrical modelling. We highlight the need to optimize the front electrode for the tandem case, where in contrast to silicon single junction devices, there is (i) about half the current, which significantly reduces resistive losses in the front electrode, (ii) a lower refractive index of the absorber (most Perovskites at 600 nm:~2.4 vs. Si: ~4.2), (iii) almost no lateral transport in the perovskite top cell, and (iv) a lower thermal device stability (~100-130°C vs. 200°C), which results in less efficient sintering of the Ag pastes and hence higher metal grid resistivity. This study concludes that compared to silicon heterojunction cells (SHJ), the thickness of the front side TCO electrode should be reduced from 75 nm to 20 nm. For the grid electrode, the low-temperature Ag pastes results in higher line resistivities and curing durations. Furthermore, we showcase that for the multi-wire interconnection concept, the number of wires can be significantly reduced from 18 wires to less than 9 depending on the front metallization.