Monolithic 3-terminal perovskite/silicon HBT-based tandem compatible with both-side contact silicon cells: a theoretical study

Abstract

The heterostructure bipolar transistor solar cell architecture offers an attractive route to realize monolithic 3-terminal perovskite/silicon tandem solar cells compatible with both-side contact Si photovoltaic technologies. Essentially, the HBT implements two counter series diodes with the common third terminal realized at the interface between the two diodes through an interdigitated contact. Concrete design solutions require optimizing the HBT multilayer stack for maximum power conversion efficiency of the intrinsic cell and designing appropriate layouts for the current collecting grid of the middle terminal. In this work, we develop a modeling framework that combines electro-optical simulations of the intrinsic tandem stack with circuit-level simulations to quantify the impact of shadow and resistive losses associated with the metal contacts on the scalability of the cell size. We present a design of a HBT with homojunction silicon bottom cell that can surpass 40% efficiency with a perovskite bandgap of 1.55 eV, i.e. much higher than the limit efficiency of a series connected tandem with the same material system. Then, we explore the implications of the middle contact in terms of interdependence between the subcells and parasitic losses, by considering a top interdigitated layout and cell architectures with both homojunction and heterojunction silicon cells. We show that in most configurations proper grid design can enable the scaling up of these devices to large areas, and that the scalability can be markedly improved, especially for the case of Si heterojunction bottom cells, by developing a layout with overlapped grids.