| Work Detail |
A team of scientists from the German Institute for Solar Energy Research Hamelin (ISFH) and the photovoltaic equipment manufacturer Centrotherm has developed a POLO back-junction solar cell using an industrial plasma-enhanced chemical vapor deposition (PECVD) system with a low-frequency plasma source. The device achieved a slightly higher efficiency than a reference device manufactured using more expensive atomic layer deposition (ALD).A group of researchers led by the Institute for Solar Energy Research Hamelin (ISFH) in Germany has fabricated an n+-type polysilicon-on-oxide (POLO) back-junction solar cell with a stack of passivation layers based on aluminum oxide (AlOx) and silicon nitride (SiNy).
“Our study shows for the first time effective industrial cleaning and passivation for the non-diffuse textured front face with excellent passivation quality,” lead author of the research Byungsul Min told pv magazine . Specifically, the AlOx/SiNy passivation layer stack is fabricated using an industrial plasma-enhanced chemical vapor deposition (PECVD) system with a low-frequency (LF) plasma source, which is much more cost-effective than atomic layer deposition (ALD) systems or PECVD systems with a high-frequency (HF) plasma source.”
The novel cell technology was presented in the paper “ 24.2% efficient POLO back junction solar cell with an AlO x / SiN y dielectric stack from an industrial-scale direct plasma-enhanced chemical vapor deposition system ” published in Progress in Photovoltaics . “Our results show a path for the industrialization of novel front-side diffusion-free cell concepts like our POLO back junction solar cell, but is also relevant for a mainstream concept like TOPCon that primarily uses ALD for its AlO x layer.”
The group built a 156.75 mm x 156.75 mm POLO cell using a Czochralski-grown, gallium-doped silicon wafer with a resistivity of 0.73 Ocm. To deposit the AlOx layer, they used an industrial batch LF-PECVD system provided by German photovoltaic equipment manufacturer Centrotherm, whose researchers also collaborated on the research. “We then tailored the recipe by varying the thickness of the silicon oxide (SiO2) layer beneath the AlOx layer between 0 and 2 nm, the thickness of the AlOx layer between 5 and 15 nm thick, and the refractive index of the SiNy layer between 2.05 and 2.4,” the researchers explained.
They also built a reference device based on a Czochralski-grown gallium-doped textured wafer with a resistivity of 0.9 Ocm that was passivated with a 10 nm thick ALD-deposited AlOx layer and a SiN2 layer. “After screen printing the aluminum grid on the front side and the silver grid on the back side, the samples were co-baked in a belt furnace at maximum baking temperatures between 800 ºC and 810 ºC,” they further explained.
Tested under standard lighting conditions, the POLO cell achieved a power conversion efficiency of 24.2%, an open circuit voltage of 725 mV, a short circuit current density of 40.2 mA/cm2 and a fill factor of 83.0%, results confirmed by ISFH CalTeC. The reference device achieved an efficiency of 24.1%, an open circuit voltage of 725 mV, a short circuit density of 39.9 mA/cm2 and a fill factor of 83.2%.
“The integration of this passivation sequence into our existing process flow for POLO BJ solar cells has been successfully demonstrated with POLO BJ solar cells, which show cell efficiencies even higher than those of reference cells manufactured using laboratory-scale processes,” the researchers concluded. |
