First-principles calculation
Simulation of structural signatures of compounds, calculation of electronic properties, analysis of stability and phase transformations and for mapping point defect chemistry in functional semiconductors.
First principles calculations in the framework of density functional theory (DFT) are playing an increasingly important role in advanced research in photovoltaic technology.
In the toolkit of advanced solar cell technology research, an increasingly significant role is played by the first-principles calculations within the Density Functional Theory (DFT) framework. Building on the most basic quantum-mechanical principles, DFT allows to simulation of materials at the atomic scale and thereby
resolves the behavior of complex systems with an unprecedented level of detail.
This information is indispensable for both applied technological and fundamental understanding of solar energy materials. At present, DFT calculations at the solar cell technology division are utilized for the areas presented here.
Kontakt: Kostiantyn V. Sopiha
Simulation of structural signatures of compounds
X-ray/neutron diffraction patterns, Raman scattering, and optical absorption spectra. These simulation results serve as a handy reference for experimental measurements to identify all components formed at different stages and conditions of solar cell processing. For example, these functionalities are used in our investigation of J. K. Larsen et al., “Experimental and theoretical study of stable and metastable phases in sputtered CuInS2”, Adv. Sci., 2022, 9(23), 2200848.
Calculation of electronic properties
Band structures, densities of states, and band offsets at heterogeneous interfaces in solar cell stacks. These properties assist the discovery of novel solar
absorbers and buffer layer materials for the most efficient photogeneration and collection of charge carriers.
A good example here is our recent study on: Keller et al., “Wide-gap (Ag,Cu)(In,Ga)Se2 solar cells with different buffer materials – a path to a better heterojunction”, Prog. Photovolt.: Res. Appl., 2020, 28, 237–250.
Analysis of stability and phase transformations in multicomponent systems
Judging by the formation, stable (and therefore feasible) novel photovoltaic materials can be identified, and the device degradation due to phase decompositions during fabrication, operation, and/or storage preemptively eliminated. Phase equilibria deduced from the first-principles calculations also
indicate new routes and optimum conditions for solar cell deposition. For example, thermodynamic stability analysis has helped us to identify:
- V. Sopiha et al., “Thermodynamic stability, phase separation and Ag grading in (Ag,Cu)(In,Ga)Se2 solar absorbers”, J. Mater. Chem. A, 2020, 8(17), 8740-8751.
- V. Sopiha et al., “Off-stoichiometry in I-III-VI2 chalcopyrite absorbers: a comparative analysis of structures and stabilities”, Faraday Discuss., 2022, 239, 357-374.
Unraveling point defect chemistry of functional semiconductors
Point defects can be intrinsic (vacancies, substitutional, and interstitial defects) and extrinsic (dopants and impurities). These species often interplay and compensate in complex and sophisticated ways, totally changing the optoelectronic and transport properties of semiconductors. First-principles calculations are useful
to determine the concentration and impact of each defect species, as well as the tendencies for defect binding and compensation, helping to obtain desired material characteristics. Recent examples of our point defect studies are
- Aboulfadl et al., “Alkali dispersion in (Ag,Cu)(In,Ga)Se2 thin film solar cells – insight from theory and experiment”, ACS Appl. Mater. Interfaces, 2021, 13(6), 7188-7199.
- Grini et al., “Strong interplay between sodium and oxygen in kesterite absorbers: complex formation, incorporation, and tailoring depth distributions”, Adv. Energy Mater., 2019, 1900740.