German researchers have studied the role of surface patterning in perovskite-silicon tandem cells and found that several new processes offer the possibility of etching smaller, more uniform textures on the surface of a silicon cell than today’s industry standards. This could facilitate subsequent growth of the perovskite cell on silicon, allowing researchers and manufacturers to target higher performance.
In the manufacture of silicon wafers and cells, the surface of the wafer is usually given a structure of small pyramid shapes, which reduces reflection and captures more light in the cell. This texture is usually achieved by dipping the wafers in liquid chemicals that remove the silicon and leave behind a textured surface.
Some other processes, which typically burn plasma onto the silicon surface, are known to provide better control over the size and uniformity of the pits that make up the structure. However, they are considered by most manufacturers to be too complicated and expensive, with only limited benefits compared to the wet chemical process.
Placing a perovskite solar cell on top, however, brings new demands on the silicon surface. Many of the achievements with tandem cells to date have been made with non-textured silicon, which facilitates perovskite integration, but represents a lost opportunity for silicon cell efficiency. HZB’s team investigated some more complex texturing processes and found that the increased control and smaller surface textures they provide could solve the perovskite integration challenge or even be of interest again in single-junction silicon.
“For tandem cells, a uniform and small-sized Si structure is crucial so that the perovskite surface cell can be wet-processed,” the group explained. “We demonstrated that submicrometer-sized random pyramids by a controlled wet etching process are an interesting approach not only for such tandem solar cells but also for SHJ solar cells.”
In their paper Double-sided nanopatterned surfaces for industrially compatible high-performance silicon heterojunctions and perovskite/silicon tandem solar cells, published in Advances in solar electricity, the group describes experiments with different etching solutions. They found that varying the composition of the solution helped them control the size of the pyramids on the surface, maintaining the desired anti-reflective properties of the etched surface while making it easier to deposit the perovskite layer on top.
“All JV parameters were similar or even slightly better compared to cells with a standard microstructure,” the team said.
Using these new nanotexturing processes, the team demonstrated a 28.9% efficient tandem cell. The researchers said they were confident such a process could be implemented on a large scale.
“We expect that the presented processes will be easily adopted for industrial production, thus contributing to the development of a production process for highly efficient tandem solar cells,” they said.