The two research institutes used silver nanowire lattices as an alternative to indium tin oxide for the cell’s transparent electrodes. They claim this is the first time a metal nanostructure has delivered photonic gain in a solar cell.
Researchers from the Dutch research institute AMOLF and the German Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) have developed a tunnel oxide-passivated contact (TOPCon) solar cell that uses silver nanowire (Ag NW) grids as transparent electrodes.
Due to their optoelectronic and mechanical properties, Ag NW networks are considered a valid alternative to indium tin oxide (ITO) for cell electrodes. “We I strongly believe that the wires will be particularly useful in thin-film-based solar cells, where light collection is more challenging and carrier diffusion lengths are shorter,” says the lead author of the study. Esther Alarcon Llado, narrated pv magazine. “The TOPCon cell was a platform to investigate the transparency of the electricity grid. Due to the long diffusion length of minority carriers from the emitter, this cell type is ideally suited as an electrically active detector.”
The research team grew the Ag NW networks on the solar cell using two scalable and inexpensive techniques: nanoimprint lithography and light-driven electrochemical deposition at room temperature. The latter is already widely used to manufacture back electrodes for solar cells and the former is generally used in the industrial production of large-area photonic devices and displays.
The scientists fabricated the device using double-sided crystalline silicon wafers with a thickness of 300 μm, where the thin oxide layers were grown at 600 C and deposited on both sides via low temperatures. chemical vapor deposition under pressure (LPCVD). They also doped the front and back with phosphorus (P) and boron monofluoroid (BF), respectively, and placed a silver back contact on the back by thermal evaporation.
The researchers assessed the performance of the cell and Ag NW networks by examining their external quantum efficiency (EQE) the ratio between the number of electrons captured by the solar cell and the number of photons that fall on it. It defines how well a solar cell converts photons into electrical current. In traditional solar cells, the maximum EQE is 100%, which corresponds to generating and collecting one electron for every photon absorbed by sunlight.
The analysis found that the EQE of the device is improved by the addition of the silver Ag NW gratings, which the academics said is a result of the increased optical path length due to the diffraction of the gratings themselves. This is the first time that a metal nanostructure provides photonic gain in a solar cell, which is promising for designing the next generation of optically and electrically active layers,” they explained.
“We only compared the cost of the raw materials between the wires and the ITO with comparable performance,” said Alarcon Llado, referring to the production costs of the networks. “We believe the wires can be made in a scalable manner using conformal lithography and electrodeposition, both of which are industrially available.” She also said that the proposed Ag NW gratings can also be used in the bottom cells of perovskite-silicon tandem solar cells, as they can increase the optical path length.
The new production technique was discussed in the study “Improved capture of near-infrared light in Si solar cells with metal nanowire grid front electrodes”, published in Solar energy materials and solar cells.
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