Periodic Reporting for period 1 - SLICE (Surface Lifetime Investigation for Characterization and Enhancement of passivating contacts in c-Si solar cells)
Período documentado: 2021-04-01 hasta 2023-03-31
One key action to mitigate the adverse impacts of climate change is transitioning to sustainable energy production, notably through photovoltaic (PV) power generation. PV technologies based on crystalline silicon (c-Si) currently represent ∼95% of the global market and will thus be the main driving force toward the expected growth of worldwide PV installations to the multi-terawatt scale. Lately, further increase of the conversion efficiency of industrial mainstream c-Si solar cells has relied on the integration of passivating contacts based on a highly-doped polycrystalline silicon (poly-Si) layer on top of a thin silicon oxide (SiOx) buffer layer (so-called “poly-Si contacts”).
The overall objective of SLICE was to elucidate the interrelation between the functional properties of poly-Si contacts (especially surface passivation) and their fabrication process in order to guide the developments of better surface passivation and ultimately c-Si solar cells with higher efficiency. Throughout the project, we developed novel methodologies that enabled the identification of the first order limitation to reaching poly-Si contacts featuring both high surface passivation and good electrical properties. Based on this key finding, we optimized the fabrication process to eventually demonstrate poly-Si contacts providing higher and better thermally stable surface passivation.
The overall objective of SLICE was to elucidate the interrelation between the functional properties of poly-Si contacts (especially surface passivation) and their fabrication process in order to guide the developments of better surface passivation and ultimately c-Si solar cells with higher efficiency. Throughout the project, we developed novel methodologies that enabled the identification of the first order limitation to reaching poly-Si contacts featuring both high surface passivation and good electrical properties. Based on this key finding, we optimized the fabrication process to eventually demonstrate poly-Si contacts providing higher and better thermally stable surface passivation.
The first part of the project consisted in breaking-down the different contributions to the surface passivation to identify the limiting one based on novel characterization methodologies and set-ups developed for the project. Doing so, we identified that the main limitation to reaching a regime in which the poly-Si contact provides both high surface passivation and good electrical properties was the degradation of the thin SiOx buffer layer at high thermal budget. This key finding led the developments of buffer layers demonstrating better thermal stability in the second part of the project. This was achieved through an alternative process to grow the thin SiOx layer at the poly-Si/c-Si interface. This process enabled to reduce the recombination current density at the interface up to 60% compared to the reference process. Moreover, it improved the thermal stability of the thin SiOx up to 930°C (against 860°C for reference SiOx). This alternative process for growing the thin SiOx is currently being integrated in our baseline process for fabrication of high-efficiency c-Si solar cells. So far, the novel methodologies and results achieved throughout the project were disseminated through two scientific publications in peer-reviewed journals and five oral presentations at international PV conferences.
The results produced from SLICE generated state-of-the-art knowledge in terms of understanding interfacial passivation of poly-Si contacts. Such understanding was obtained through novel methodologies that enabled identifying the limiting factors to higher surface passivation within limited experimental and modelling studies. Through this understanding, we could identify technological strategies to enhance the surface passivation of p-type poly-Si contacts notably using an alternative process to grow the thin SiOx layer as well as alternative materials. This knowledge will drive the development of silicon solar cells with higher efficiencies compatible with mass production. This will help reducing the cost of solar electricity for consumers and thus support the expected terawatt deployment of silicon solar cells for a significant increase in the capacity of installed solar PV. In the long term, this will lead to reduced CO2 emissions and expanded electrification of the energy economy. The outcomes of SLICE are thus supporting 2 of the 5 missions identified by Horizons Europe, including “Adaptation to Climate Change” and “Climate -Neutral Cities”.