Crystalline silicon solar cell with front and rear polysilicon passivated contacts as bottom cell for hybrid tandems

In this paper we analyze and model perovskite/c-Si tandem cells with front and rear polySi passivated contacts on the bottom cell. A high-efficiency tandem approach will benefit from the high V_oc potential of a c-Si bottom cell with front and rear polySi passivated contacts while the combination with a high band gap, semi-transparent, perovskite top cell will largely diminish the UV-Vis parasitic absorption in a polySi front side layer on the c-Si cell. On the other hand since the J_sc is strongly reduced in a tandem bottom cell, free carrier absorption, to which both front and rear polySi layers contribute, will become a relatively more important loss mechanism. We investigate the trade-off between the optical gains and resistive losses from reducing the polySi thickness for cell configurations without transparent conductive oxide (TCO) and also consider the potential of the combination with TCOs. From our optical simulations we conclude that optical losses in the polySi layers of 100 nm and below are limited when applied on the bottom cell. Taking into account resistive losses in the polySi layers of varying thickness the optimal thickness is found to be 50 nm. In combination with the high V_oc values resulting from the application of polySi passivating contacts this offers a promising route to establish a bottom cell with high efficiency. The combination of very thin polySi with highly transparent TCOs is likely to further improve bottom cell performance.