The SiLEAN project has reached an important result in its efforts to reduce the use of critical raw materials in photovoltaic technologies. A key objective of the project is the replacement of conventional indium-based contact layers in silicon heterojunction (SHJ) solar cells with more sustainable and cost-effective alternatives.
In this latest phase of the work, several indium-free transparent conductive oxides (TCOs) have been investigated, including zinc oxide (ZnO), aluminium-doped zinc oxide (AZO), and tin oxide (SnOx). Initial developments focused on ZnO deposited by plasma-enhanced chemical vapor deposition (PECVD). While this approach enabled integration into SHJ devices, challenges related to deposition rate, electrical resistivity, and stability led researchers to explore alternative materials.
Promising results were achieved with sputtered SnOx layers, which were successfully implemented as contact layers in SHJ solar cells. Fully indium-free devices reached a power conversion efficiency of 22.0%, demonstrating the strong potential of this approach. One of the main challenges identified is a relatively high contact resistivity at the SnOx/amorphous silicon interface, which affects device performance.
This limitation was effectively addressed by introducing a very thin ITO seed layer, resulting in a champion efficiency of 23.4%. Notably, this performance is comparable to conventional ITO-based SHJ solar cells, while reducing indium content by approximately 80%.
Further improvements are expected through ongoing work on advanced contact architectures, including the use of nanocrystalline silicon layers, optimization of processing conditions, and scaling up deposition techniques to industrial wafer sizes.
These results represent a significant step toward high-efficiency, low-resource SHJ solar cells, supporting SiLEAN’s goal of enabling a more sustainable and resilient photovoltaic value chain.
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