Abstract
Doped hydrogenated nanocrystalline (nc-Si:H) and silicon oxide (nc-SiOx:H) materials grown by plasma-enhanced chemical vapor deposition have favourable optoelectronic properties originated from their two-phase structure. This unique combination of qualities, initially, led to the development of thin-film Si solar cells allowing the fabrication of multijunction devices by tailoring the material bandgap. Furthermore, nanocrystalline silicon films can offer a better carrier transport and field-effect passivation than amorphous Si layers could do, and this can improve the carrier selectivity in silicon heterojunction (SHJ) solar cells. The reduced parasitic absorption, due to the lower absorption coefficient of nc-SiOx:H films in the relevant spectral range, leads to potential gain in short circuit current. In this work, we report on development and applications of hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) from material to device level. We address the potential benefits and the challenges for a successful integration in SHJ solar cells. Finally, we prove that nc-SiOx:H demonstrated clear advantages for maximizing the infrared response of c-Si bottom cells in combination with perovskite top cells.
Highlights
Hydrogenated nanocrystalline silicon [1] thin films consists of a two-phase material of Si crystallites embedded in an hydrogenated amorphous silicon (a-Si:H) matrix
Layer stacks were deposited on glass substrates and consisted of a 6-nm thick (i)a-Si:H film coated with a 25-nm thick nanocrystalline layer to enable the investigation of the effect of substrate nature on FC
Besides cell efficiency of 22.5%, we demonstrated that nanocrystalline silicon oxide material fulfil production requirements such as high throughput (60 s plasma-enhanced chemical vapor deposition (PECVD) process time) and excellent cell homogeneity both in laboratory-scale [28] and in industry application [71]
Summary
Hydrogenated nanocrystalline silicon (nc-Si:H) [1] thin films consists of a two-phase material of Si crystallites embedded in an hydrogenated amorphous silicon (a-Si:H) matrix. In the early 1990s, Sanyo developed a new technology that combined crystalline silicon wafer-based absorbers with the materials and processing known from thin-film silicon technology to acting as passivated p- and n-contacts [16], thereby forming a-Si:H/c-Si silicon heterojunction (SHJ) solar cells. This device concept owns an exceptionally high open-circuit voltage up to 750 mV [17], achieved due to the excellent passivation of the c-Si surfaces by only a few nanometres thin intrinsic a-Si:H. We discuss the interplay between optical and electrical properties on solar cells parameters and strategies to overcome these issues
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