High-Performance Multi-Walled Carbon Nanotubes-Organic Passivated Si Solar Cells Enabled by Spatially Selective Harvesting of High-Quality Sponges

Carbon nanotubes/Si (CNTs/Si) solar cells have emerged as promising photovoltaic devices due to their high performance and relatively simple fabrication processes. Multi-walled CNTs (MWCNTs) in solar cells exhibit better cost-effectiveness owing to the broader processing tolerance of MWCNTs synthesis. However, their efficiency previously reached only 12.49%, which has often been attributed to the higher defect density and inferior quality of MWCNTs compared with single-walled CNTs. In this study, by selecting high-quality pristine MWCNTs synthesized via floating catalyst chemical vapor deposition, we achieved a champion efficiency of 22.74% for MWCNTs:Nafion/Si solar cells. This breakthrough stems from the finding that while both the inner and outer parts of MWCNTs sponge can be uniformly dispersed when mixed with Nafion, the inner MWCNTs ink exhibits better stability than the outer MWCNTs ink due to amorphous carbon and copper impurities in the outer MWCNTs. The synergy between Nafion and the inner MWCNTs results in a high-work-function MWCNTs:Nafion film and a defect-passivated Si surface, leading to favorable band alignment, excellent carrier-selective transport properties, and consequently high device performance. This work challenges the conventional view that the higher defect density in MWCNTs inherently limits device performance and provides new insights for developing low-cost, high-efficiency carbon-based/Si solar cells.