Thermal transport in Cu2ZnSnS4 thin films

Abstract

The stability of kesterite Cu2ZnSnS4 (CZTS) under a range of compositions leads to the formation of a number of stable defects that appear to be necessary for high efficiency photovoltaic applications. In this work, the impact of the presence of these defects on the thermal conductivity of CZTS thin films has been explored. Thermal conductivities of CZTS thin films, prepared by pulsed laser deposition with differing compositions, were measured from 80 K to room temperature using the 3ω-method. The temperature dependence of the thermal conductivity indicates that the phonon mean free path is limited by strain field induced point defect scattering from sulfur vacancies in sulfur deficient thin films. The sulfurization of these films in a 10% N2 + H2S ambient at 500 °C increased the sulfur content of the films, reducing the concentration of sulfur vacancies, and produced a negligible change in grain size with an unexpected factor of 5 increase in phonon boundary scattering. This, along with anisotropies in the x-ray diffraction peak profiles of the sulfurized films, suggests that the phonon mean free path in sulfurized films is limited by the presence of cation exchange induced stacking faults. The resulting room temperature thermal conductivities for sulfurized and sulfur deficient thin films were found to be 4.0 W/m K and 0.9 W/m K, respectively.

Static and dynamic components of Debye–Waller coefficients in the novel cubic polymorph of low-temperature disordered Cu2ZnSnS4

“…Several other reports of wurtzite-type CZTS can be found, all reporting the use of DDT in the synthesis (Li et al, 2014;Mainz et al, 2014;Singh et al, 2013Singh et al, , 2012Zhou et al, 2015;Lu et al, 2011) and/or nanometredimensions (Azanza Ricardo et al, 2015;Syafiq et al, 2019). By cross-comparing results from different works, we noted a general higher abundance of wurtzite CZTS for grains with nanometre dimensions [<30 nm average dimensions (Li et al, 2014;Mainz et al, 2014;Singh et al, 2013Singh et al, , 2012Lu et al, 2011;Zhou et al, 2015;Azanza Ricardo et al, 2015)], while, for increasing domain size, the hexagonal phase seems to reduce to stacking faults (Kattan et al, 2015;Thompson et al, 2016;Engberg et al, 2020;Li et al, 2014;Syafiq et al, 2019) up to the point that neither (hexagonal arrangements nor faults) can be observed.…”

Tuning Electrical, Optical, and Thermal Properties through Cation Disorder in Cu2ZnSnS4

“…The range for CZTS is defined by our measurements on d-CZTS (white stars, with error bars) and by previously published measurements on CZTS (white squares). All data besides d-CZTS are from the literature: (KBr) 1– x (KCN) x , PbTi x Zr 1– x O 3 (PZT), entropy-stabilized oxides (ESO), (KCl) 1– x (KBr) x , ordered and disordered FePt, and Si x Ge x . ,,,, The previously published CZTS data include the following: sintered powder (κ = 4.7 Wm –1 K –1 ); sintered nanocrystals (κ = 2.95 Wm –1 K –1 ); thin films, fully and incompletely sulfurized (κ = 4 and 0.9 Wm –1 K –1 , respectively) . The d-CZTS samples include low-gap samples grown at room- T and then annealed at temperature up to 450 °C and high-gap samples with growth temperature between room- T and 450 °C.…”

“…A sharply defined shoulder on a particular diffraction peak (HKL) can indicate the presence of stacking faults with surface-normal direction {HKL}. ,, For CZTS, {112} is the close-packed direction (corresponding to {111} in high-temperature cubic unit cell), and the shoulder can be well-modeled as the result of a high concentration of stacking faults with {112} surface-normal. Here we show that our data are well-described by a model of CZTS with a high incidence of stacking faults along {112}.…”

“…33,37,39,40,44 The previously-published CZTS data include: sintered powder ( = 4.7 Wm -1 K -1 ); 42 sintered nanocrystals ( = 2.95 Wm -1 K -1 ); 43 thin films, fully and incompletely sulfurized ( = 4 and 0.9 Wm -1 K -1 , respectively). 45 The d-CZTS samples include low-gap samples grown at room-T and then annealed at temperature up to 450 °C, and high-gap samples with growth temperature between room-T and 450 °C.…”

“…33,37,39,40,44 The previously published CZTS data include the following: sintered powder (κ = 4.7 Wm −1 K −1 ); 42 sintered nanocrystals (κ = 2.95 Wm −1 K −1 ); 43 thin films, fully and incompletely sulfurized (κ = 4 and 0.9 Wm −1 K −1 , respectively). 45 The d-CZTS samples include low-gap samples grown at room-T and then annealed at temperature up to 450 °C and high-gap samples with growth temperature between room-T and 450 °C. relatively high modulation frequency of the pump pulses, the thermal penetration depth during our TDTR measurements is much less than the CZTS film thicknesses, and thus we are insensitive to the thermal properties of the substrate in our TDTR analyses.…”