Convergence of efficiency, stability, and manufacturability in perovskite tandem solar cells

Perovskite-silicon tandem solar cells offer a clear step past the best silicon single junction solar cells in the roadmap of photovoltaics. Having recently reached over 32% efficiency at an R&D scale, they have long-term stability and manufacturability as important things to prove. In this talk, I will discuss Swift Solar' development of perovskite deposition processes that achieve excellent visual and compositional uniformity over standard M6 wafer areas. I will discuss unique challenges to ensuring high yield while fabricating the perovskite thin film device stack on silicon bottom cells, which are rougher than glass surfaces even if planarized silicon is used, and of course have significantly larger roughness in the case of textured surfaces that are typical of commercial silicon solar cells today. To ensure long term stability, I will highlight the photolysis of lead iodide as an important degradation mechanism of the perovskite material under illumination at elevated temperature. Lastly, I will present effects of the chosen contact material in determining mechanical and chemical stability of the contact layer interfaces. With a stable perovskite composition with a tandem-relevant band gap and appropriately chosen contact layer, we demonstrate perovskite solar cells that maintain 97% of their initial performance after over 2000 hours of aging at 70 C under illumination.