2T Mechanically Stacked Perovskite/Si tandem Cells Beyond 28%: the Role of 2D Materials in Perovskite Top Cells Coupled with a Commercially Available Bifacial c-Si Heterojunction Cell

Abstract

Perovskite/Silicon tandem technology represents a promising route to achieve 30% power conversion efficiency, by ensuring low levelized costs energy while being competitive with the already commercialized photovoltaic (PV) technologies. Despite the impressive results demonstrated employing a two-terminal (2T) monolithic architecture, the use of record efficiency amorphous/crystalline silicon heterojunction (Si-HJT) cells with micrometer-sized textured front surface, strongly limits the possibility to perform high-temperature and solution processing of the top perovskite cell. To overcome this limitation, we develop a tandem device structure consisting in a mechanically stacked 2T perovskite/silicon tandem solar cell, with the sub-cells independently fabricated, optimized, and subsequently coupled by contacting the back electrode of the mesoscopic perovskite top cell with the texturized and metalized front contact of the silicon bottom cell. The possibility to separately optimize the two sub-cells allows to carefully choose the most promising device structure for both top and bottom cells. Indeed, semi-transparent perovskite top cell performance is boosted through a rational use of bi-dimensional materials (graphene, MXenes and functionalized MoS2) to tune the device interfaces. In addition, a protective buffer layer (PBL) based on MoO3 thin film is used to prevent damages induced by the transparent electrode sputtering deposition over the hole transporting layer. At the same time, a textured amorphous/crystalline silicon heterojunction (c-Si HTJ) cell fabricated with an in-line production process is used as state of art bottom cell. The tandem perovskite/Si tandem device demonstrates remarkable power conversion efficiency of 28%.