Researchers in the Netherlands have developed a new crystalline solar cell based on poly-SiOx passivating contacts. The efficiency of poly-SiOx technology is 20%, but 4T tandem perovskite-silicon solar cells based on poly-SiOx cell can achieve 28.1 percent efficiency and 2T tandem perovskite-silicon devices can achieve 23.2 percent efficiency.
“Such CSPCs consist of doped poly-Si doped with carbon or oxygen and deposited on very thin SiOx layer, produced by wet chemical process, thermal oxidation, UV/O3 process or low-temperature plasma oxidation,” the researchers said, referring to the new passivating contacts. “The optoelectronic properties of poly-SiOx depends on the oxygen content.”
The scientists built the cell with silicon dioxide (SiO2) layer deposited by plasma enhanced chemical vapor deposition (PECVD). They also used n-type and p-type poly-SiOx passivated contacts, which they deposited on thermal oxide with a two-layer 10-nm-thick internal amorphous silicon (a-Si) layer using a low-pressure chemical vapor deposition (LPCVD) process and a 20-nm-thick layer. hydrogenated α-SiOx layer from the PECVD process.
“Silane (SiH4), carbon dioxide (CO2) and hydrogen (H2) gases are used as sources to deposit these poly-SiOx passivating contacts,” they said, referring to the manufacturing process. “Phosphine (PH3) and diborane (B2B6) gases are used as doping sources for n-type and p-type poly-SiOx passivating contacts, respectively.”
The team also used screen printing to equip the cell with low-temperature Ag-based metal contacts on the front and back. The best solar cell built with this assembly and a p-type wafer achieved a power conversion efficiency of 20.47%, an open-circuit voltage of 95 mV, and a short-circuit current of 36.68 mA/cm.2and a fill factor of 80.33%. On the other hand, hydrogen diffusion in p-type poly-Si. is smaller than n-type, which prevents the accumulation of excess hydrogen around the oxide, which degrades the passivation quality.
When tested together with a previously developed perovskite solar cell with an efficiency of 19.7%, the new cell produced efficiencies of 28.1% and 23.2% in 4T and 2T cells, respectively.
The research team presented their findings on “Crystalline silicon solar cells with thin poly-SiOx carrier-selective passivating contacts for perovskite/c-Si tandem applications”, published recently Advances in solar power. The group includes academics, e.g Eindhoven University of Technology and the Netherlands Organization for Applied Scientific Research (TNO).
TNO is now also developing a four-junction (4T) semi-transparent perovskite-silicon tandem solar cell. It works in collaboration with the Solliance consortium, which includes Delft University of Technology, Eindhoven University of Technology and the Belgian research institute Imec. In September, the device achieved a power conversion efficiency of 30.1%.
A Dutch-German consortium led by TNO is also trying to commercialize 2T perovskite-silicon tandem solar cell technology. FIT4Market, a four-year research project.