Abstract
The electrical and optoelectronic properties of materials are determined by the chemical potentials of their constituents. The relative density of point defects is thus controlled, allowing to craft microstructure, trap densities and doping levels. Here, we show that the chemical potentials of chalcogenide materials near the edge of their existence region are not only determined during growth but also at room temperature by post-processing. In particular, we study the generation of anion vacancies, which are critical defects in chalcogenide semiconductors and topological insulators. The example of CuInSe2 photovoltaic semiconductor reveals that single phase material crosses the phase boundary and forms surface secondary phases upon oxidation, thereby creating anion vacancies. The arising metastable point defect population explains a common root cause of performance losses. This study shows how selective defect annihilation is attained with tailored chemical treatments that mitigate anion vacancy formation and improve the performance of CuInSe2 solar cells.
Highlights
The electrical and optoelectronic properties of materials are determined by the chemical potentials of their constituents
It is valuable for the control of the physical properties and functionality of chalcogenides in today’s optoelectronic and future spintronic devices based on twodimensional (2D) and three-dimensional (3D) semiconductors[2,3,4] and topological insulators[5]
This condition is compatible with previously reported metastable phase equilibria[8] and affects the surface chemical reactivity of CIS towards air, etchants, post deposition treatments (PDTs) and solar cell finishing processes
Summary
The electrical and optoelectronic properties of materials are determined by the chemical potentials of their constituents. Atoms in a crystalline structure align in a regular lattice, but due to off-stoichiometry, thermal energy, reactions or phase changes, some of the atoms leave their lattice sites or fail to occupy them, generating point defects The density of these defects (such as vacancies, antisites and interstitials) and their charge state (positive, negative and neutral) depend on the (electro)chemical potentials of the constituent atoms and electrons. Understanding the nature of the defects involved, their concentration and mobility during the growth and after subsequent interface reactions is essential for the advancement of many technologies It is valuable for the control of the physical properties and functionality of chalcogenides in today’s optoelectronic and future spintronic devices based on twodimensional (2D) and three-dimensional (3D) semiconductors[2,3,4] and topological insulators[5]. Progress in the performance stability of perovskite-based photovoltaics (PVs) relies on strategies aimed at minimizing the formation, mobility or reactivity of anion vacancies[6]
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