First-Principles Calculations
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 within the framework of density functional theory (DFT) play an increasingly important role in advanced solar energy research. By leveraging fundamental quantum-mechanical principles, DFT enables atomic-scale simulations of functional materials, providing unprecedented insight into complex systems. At the Solar Cell Technology Division, these calculations are currently employed for several key purposes, as described below.
Contact: Kostiantyn V. Sopiha
Simulation of Structural Signatures
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:
- 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:
- 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
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:
- 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
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:
- 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.