Effective passivation of TiO2/Si by interlayer SiOx controlled by scanning zone annealing for perovskite/Si tandem solar cell

Abstract

A 2-terminal tandem solar cell that utilized organometal halide perovskite as the top cell and crystalline silicon (Si) as the bottom cell has attracted much attention in recent years for its high theoretical energy conversion efficiency. Among many different approaches, high energy conversion efficiency with relatively simple device architecture can be achieved by direct deposition of electron transport material of a perovskite top cell on a Si bottom cell. To maximize the amount of extractable current from this type of solar cell, precise control of surface recombination at the interface between the electron transport layer and Si is a crucial factor. In this study, we proposed the utilization of Scanning Zone Annealing (SZA), a unique heating treatment developed by our research group, to reduce surface recombination by selective treatment of a TiO2/Si interface. This method was proven effective to increase the minority carrier lifetime of a sputtered-TiO2/Si interface from 6.3 μs to 355 μs for p-type float-zone Si, from 7.9 μs to 310 μs for n-type float-zone Si, and from 9.3 μs to 271 μs for p-type Czochralski Si. Furthermore, the origin behind the reduction in surface recombination at a TiO2/Si interface by SZA was proposed based on direct observation of the interface. Here, we found that the thickness of a natively formed SiOx interlayer is crucial to the reduction of the surface recombination at a TiO2/Si interface and is controllable at nanometer scale by adjusting the amount of heat transferred during SZA treatment.