Work function characterization of hydrogenated nanocrystalline silicon for interface optimization in SHJ solar cells

Silicon heterojunction (SHJ) solar cells are among the most efficient crystalline silicon-based photovoltaic technologies, combining a crystalline silicon absorber with thin hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) layers that act as carrier-selective contacts. While a-Si:H has traditionally been used, doped nc-Si:H has recently emerged as a promising alternative, offering higher conductivity and improved optical properties. Optimizing the electronic properties of SHJ structures is therefore crucial, with particular focus on interfacial properties that govern charge transport and contact selectivity. Among these, the work function plays a key role, as it directly influences band alignment and overall device performance. This thesis investigates the work function of highly doped hydrogenated nanocrystalline silicon (nc-Si:H), used as a rear emitter in SHJ devices and as the bottom cell in tandem configurations. The nc-Si:H layers were deposited on hydrogenated amorphous silicon (a-Si:H) using Plasma-Enhanced Chemical Vapor Deposition (PECVD) and characterized through a combination of techniques: Scanning Kelvin Probe (SKP), Ultraviolet Photoelectron Spectroscopy (UPS), and X-ray Photoelectron Spectroscopy (XPS). These measurements were conducted under different environmental conditions to assess technique agreement and surface sensitivity. To further understand the influence of contamination and native oxides, surface treatments such as hydrofluoric acid and ozone were applied. The results highlight differences between measurement techniques and the influence of surface treatments on reproducibility. These findings underscore the importance of accurate and reliable work function characterization for optimizing interfacial engineering in high-efficiency SHJ and tandem solar cells.