Perovskite technology remains one of the fastest growing areas of solar cell research. Germanys HZB and Switzerlands EPF have further advanced the field, by developing a process for perovskite-HJT tandem cells.
To achieve this, the team had to develop a method for depositing an intermediate layer between the HJT silicon cell and the perovskite. Titanium dioxide is often used for this, however it needs to be sintering at 500C, which damages the amophous silicon layer. The HZB-EPF team replaced titanium dioxide with tin dioxide, which can be deposited at low temperature. The perovskite layer can then be applied using a spin-coating process.
Perovskite layers could considerably increase the efficiency level [of crystalline silicon PV cells], said HZBs Bernd Resch, who heads the HZB Institute for Silicon Photovoltaics. To achieve this, the fabrication techniques only need to be supplemented with a few more production steps. For that reason, our work is also extremely interesting for industry.
The perovskite-HJT cells produced by the HZB-EPF team has an open-circuit voltage of 1.78 volts. This represents an increase on the 1.65 volt cell produced by a combined MIT-Stanford group earlier this year.
The research team is additionally looking at the role light trapping texturing of the silicon wafer can play in further boosting the tandem cells efficiency.
This perovskite-silicon tandem cell is presently still being fabricated on a polished silicon wafer, said HZBs Lars Korte. By texturing this wafer with light-trapping features, such as random pyramids, the efficiency might be increased further to 25 or even 30%.
While the research is certainly promising, HZBs Resch acknowledges that the stability of the perovskite semiconductor remains a major challenge in the commercialization of the technology.
The research was published in the journal Energy and Environmental Science.