The band offsets between crystalline and hydrogenated amorphous silicon (a−Si∶H) are key parameters governing the charge transport in modern silicon heterojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here, we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics runs at an elevated temperature on 30 statistically independent samples. In order to obtain a realistic conduction-band position the electronic structure of the interface is calculated with a hybrid functional. We find a slight asymmetry in the band offsets, where the offset in the valence band (0.29 eV) is larger than in the conduction band (0.17 eV). Our results are in agreement with the latest XPS measurements that report a valence-band offset of 0.3 eV [M. Liebhaber et al., Appl. Phys. Lett. 106, 031601 (2015)].
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This work is supported by the Technology Foundation STW within the framework of the Fundamentals and Applications of Silicon Heterojunctions (FLASH) perspective program (Project Code 12165). We thank SURFsara for the support in using the Lisa Compute Cluster. The work of R. A. G. is part of the research program of the Foundation for Fundamental Research on Matter (FOM). Both SURFsara and FOM are financially supported by the Netherlands Organization for Scientific Research (NWO).
Jarolimek, Karol; Hazrati, E.; de Groot, R. A.; and de Wijs, D. A., "Band Offsets at the Interface Between Crystalline and Amorphous Silicon from First Principles" (2017). Center for Applied Energy Research Faculty Publications. 20.