Monolithic Perovskite/Silicon Tandem Solar Cells Enabled by Multifunctional TiO_x Interconnects

Perovskite-on-silicon tandem solar cells have emerged as a leading technology enabling high power conversion efficiencies (PCE) over 30%. Despite current progress, the intrinsic multilayer device design presents vast challenges in complexity, which can be a drawback in future mass production. Multifunctional nanolayer materials that simplify large-scale production are therefore highly desirable. Herein, a TiO_x layer (∼3-5 nm) grown by atomic layer deposition (ALD) enables a series interconnection of a perovskite n-i-p top cell with a silicon wafer directly. The TiO_x layer serves as an all-in-one interconnect, fulfilling the functions of silicon surface passivation, hole extraction from silicon, and recombination junction at the top/bottom cell interface. As a result, a proof-of-concept 22.4%-efficient tandem device is demonstrated. Furthermore, an improved PCE of 26.5% is achieved by capping the TiO_x with a thin ALD-TiN_y layer (∼4 nm). This represents a performance as high as the reference tandem device (PCE = 25.5%) that uses amorphous silicon passivating selective contacts and an indium-tin-oxide interlayer. Such a TiO_x multifunctional nanolayer can reduce the number of deposition tools and eliminate the need of an indium-based interconnection. It offers a potential for low-cost, scalable, and sustainable tandem solar cell manufacturing.