Lattice Dynamics of Cu 2 ZnSn(S x ,Se 1- x ) 4 Kesterite Thin-Film Solar Cells Studied by Nuclear Inelastic Scattering

• Published in: Journal of physical chemistry. C 2024-10, Vol.128 (41), p.17483-17491
• Main Authors: Edla, Raju, Nowak, David, Hauschild, Dirk, Sergueev, Ilya, Pareek, Devendra, Gütay, Levent, Heske, Clemens, Weinhardt, Lothar, Stankov, Svetoslav
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.4c03689

Phonons play a crucial role in thermalization and non-radiative recombination losses in semiconductors, impacting the power conversion efficiency of solar cells. To shed light on the lattice dynamics in Cu ZnSn(S ,Se ) (CZTSSe) thin-film solar cells and validate the extensive number of theoretical studies, we determine the Sn-partial phonon density of states (Sn-PDOS) by nuclear inelastic X-ray scattering. CZTSSe-based devices, one with near-stoichiometric and two with off-stoichiometric compositions, are investigated, and the results are correlated with the corresponding power conversion efficiencies (PCEs) of 3.2, 7.6, and 10.6%, respectively. Compared to the near-stoichiometric cell, the main Sn-PDOS peak of the off-stoichiometric cells broadens and slightly shifts to higher energy; this effect is correlated with the type and concentration of the characteristic defects in the studied samples. Furthermore, the Sn-PDOS of the 10.6% device is also obtained under (maximum power point) and open-circuit conditions. A comparison of the Sn-PDOS before and after the measurements suggests structural changes, likely due to the formation of metastable defects. In agreement with the theoretical studies, the Sn-PDOS of the CZTSSe absorber shows additional peaks compared to CZTSe attributed to coupling of Sn to the vibrations of Se and S atoms. This work paves the way for a further understanding of the lattice dynamics and subsequent enhancement of the PCEs of thin-film solar cells as well as other applied materials and devices containing elements that are Mössbauer-active and hence suitable for nuclear inelastic scattering.