Calculation of point defect concentration in Cu2ZnSnS4: Insights into the high-temperature equilibrium and quenching

Abstract

Herein we study the native point defect equilibrium in Cu2ZnSnS4 (CZTS) by applying a statistical thermodynamic model. The stable chemical-potential space (SCPS) of CZTS at elevated temperature was estimated directly, on the basis of deviations from stoichiometry calculated for the different combinations of chemical potential of the components. We show that the SCPS is narrow due to high concentration of ( − − + ) complex which is dominant over other complexes and isolated defects. The CZTS was found to have p-type conductivity for both stoichiometric and Cu-poor/Zn-rich composition. It is established that the reason for this is that the majority of donor-like + antisites are involved in the formation of ( − − + ) complex making − dominant and providing p-type conductivity even for Cupoor/Zn-rich composition. However, our calculation reveals that the hole concentration is almost insensitive to the variation of the chemical composition within the composition region of the single-phase CZTS due to nearly constant concentration of dominant charged defects. The calculations for the full equilibrium and quenching indicate that hole concentration is strongly dependent on the annealing temperature and decreases substantially after the drastic cooling. This means that precise control of annealing temperature and post-annealing cooling rate are critical for the tuning of electrical properties of CZTS.

A Deep Dive into Cu2ZnSnS4(CZTS) Solar Cells: A Review of Exploring Roadblocks, Breakthroughs, and Shaping the Future

“…The intrinsic CZTS is always p-type due to the large population of Cu Zn and V Cu acceptor defects. [75,76] However, due to the relatively deep acceptor level, a higher concentration of Cu Zn defects is considered detrimental to device performance. [75,77] Preparing CZTS films under Cu-poor and Zn-rich environments can promote more ideal V Cu generation.…”

Crystal chemistry investigations on photovoltaic chalcogenides

“…I would suggest that you insert one or two sentences about Cu/Zn disorder in kesterites before you start with "our goal". The CZTSSe materials have been thoroughly investigated through theoretical calculations specifically to determine the nature of defects (and their concentration) which could explain their semiconducting properties 29,30 . These studies demonstrated that at the thermodynamic equilibrium for the stoichiometric Cu2ZnSnS4 composition, many defects in high concentration may exist in this material.…”

Defects properties and vacancy diffusion in Cu2MgSnS4

“…Comparing CZTS to the Cu(In/Ga)S 2 (CIGS) absorber material, CZTS often suffers from a high open-circuit voltage (V OC ) deficit [7−9] larger than 0.6 eV, low external quantum efficiency (EQE) in the long wavelength region, low carrier lifetime, and thus fill factor [10] . These observations are commonly attributed to the abundance of point defects and defect complexes [11,12] , band edge or electrostatic potential fluctuation induced by defect compensation [13] , interface defects [14,15] , unfavorable band alignment [16,17] and secondary phases due to composition inhomogeneity, and back contact decomposition [15,18] . Defect abundance in CZTS originates from the intrinsically low formation energy of point defects in thermodynamic limit [8,19] .…”