| Work Detail |
The Fraunhofer ISE has developed an electro-optimized transparent conductive oxide layer that can reportedly improve the efficiency of perovskite-silicon tandem solar cells. A device built with the film achieved remarkable efficiency and fill factor.
Researchers at the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) and the Fraunhofer Center for Silicon-Photovoltaics (CSP) have fabricated a two-terminal perovskite silicon tandem solar cell based on an electro-optimized transparent conductive oxide layer that serves as a front contact.
“The layer consists of a stack of indium tin oxide (ITO),” Özde Kabakli, corresponding author of the research, explained to pv magazine . “This is a thin interlayer of highly doped ITO between the SnOx tin buffer layer and the moderately doped ITO. With the ITO stack, both high transparency and conductivity can be achieved. The optical adjustments mainly increase the short-circuit current density and the efficiency of the tandems.”
The academics improved the quality of the ITO film by finely adjusting the oxygen flow rate during the sputtering process, which was carried out with a power density of 0.4 W/cm2, a chamber temperature of 50ºC, and argon as sputtering gas. The oxygen deficit of the layer was combined with moderate doping.
They built the cell in tandem with an ITO substrate, SnOx buffer layer, a buckminsterfullerene (C60) electron transport layer, a perovskite layer, an interfacial layer made of PFN polymer, a hole transport layer (HTL) made of polytriarylamine (PTAA), the ITO stack, a p-type silicon layer, another ITO layer, and a silver (Ag) metal contact.
“The silicon-bottom solar cell has a flat front and a random pyramidal texture on the back,” they explained. "The ITO layer is switched between two groups keeping the rest of the stack the same."
Tested under standard lighting conditions, the solar cell achieved a power conversion efficiency of 25.6% and a fill factor of up to 76%. “Improving the electro-optical properties of the optimized ITO layers results in a good combination of moderate sheet strength and low absorbance,” the German team stresses.
The cell technology was presented in the paper Minimizing electro-optical losses of ITO layers for monolithic perovskite silicon tandem solar cells, published in Solar Energy Materials and Solar Cells . Looking ahead, the scientists say they want to apply the proposed multilayer method to fully textured perovskite silicon tandem devices. |
