A highly efficient tandem solar cell with a perovskite layer placed over a textured silicon heterojunction bottom cell was developed by an international research team. The structure designed by researchers from Saudi Arabia's King Abdullah University of Science and Technology (KAUST), University of Toronto, National Renewable Energy Laboratory and South Dakota State University enabled an independently certified power conversion The researchers with the device that combines industry standard silicon manufacturing with new perovskite technology. Source: Andrea Bachofen-Echt/KAUSTefficiency of 25.7%.

Tandem solar cell architectures offer a path toward higher module efficiencies over single-junction designs due to the ability to split the solar spectrum into multiple bands that can be more efficiently converted by separate devices. Fabricating cells as layers on a substrate can result in photovoltaic devices that surpass the limiting efficiency of single junction silicon cells.

A solution processing technique was used to deposit a layer of perovskite crystals on top of textured silicon. The thickness of the top perovskite layer was adjusted to cover the pyramidal protrusions on the silicon surface. Material deposited at the bottom of these bumps produced an electrical field that separates the electrons generated by the two different layers, increasing the prospects for excited charges to flow into the circuit instead of other cell regions. This process was enhanced with a coating of 1-butanethiol as a self-limiting passivant applied to the perovskite. Negligible performance loss was documented after a 400 hour thermal stability test at 85° C and after 400 hours under maximum power point tracking at 40° C.

An advance in tandem solar cell performance has also been reported by U.S. researchers by including chlorine in the synthesis of stable triple-halide perovskites with a band gap of 1.67 electron volts. Two-terminal tandem silicon solar cells synthesized with this material had a power conversion efficiency of 27%, considerably higher than the 21% achieved by a silicon cell without the perovskite layer.