A hybrid functional study of native point defects in Cu₂SnS₃: implications for reducing carrier recombination

Abstract

The native point defects in the earth-abundant solar material CuSnS are studied using the hybrid functional. To generate more accurate formation energies of defects, the extended Freysoldt, Neugebauer, and Van de Walle (FNV) method is used for finite-size corrections in the charged supercell calculations. According to the calculated defect energetics, it is found that the usual experimental conditions can lead to abundant deep centers that deteriorate solar cell performance. To reduce the carrier recombination caused by the deep centers, Sn-rich and S-poor conditions should be attempted. The present calculations also give satisfactory explanations for a recent experimental work on the defect levels in CuSnS.

Atomic Layer Deposition of Cu2SnS3 Thin Films: Effects of Composition and Heat Treatment on Phase Transformation

“…21 In a similar analogy, increasing Sn composition can be expected to increase the density of Cu 2 −S−Sn 2 units, while concurrently increasing the population of Sn Cu antisite defects due to the lowering of the formation energy of these defects. 8,38 Similarly, the supply of thermal energy during annealing can enhance atomic motion and induce cation disorder, all of which is readily reflected by changes in Raman spectra. 14,21,39,40 To verify this hypothesis, the CTS films were subjected to further annealing between 350 and 580 °C under 40 Torr H 2 S gas for 30 min.…”

“…In CTS, copper vacancies (V Cu ) have been unanimously identified as the dominant acceptor defects, resulting in p-type characteristics. 37,38,49,50 Hole concentrations are commonly degenerate (>10 19 ) and therefore not favorable for PV applications. Growing CTS films in a sulfur-deficient environment can increase the formation enthalpy of V Cu and decrease hole concentrations.…”

“…The electrical properties of compound semiconductors are determined by a complex interplay between donor and acceptor defects in which the dominant species dictates the final electrical properties. In CTS, copper vacancies (V Cu ) have been unanimously identified as the dominant acceptor defects, resulting in p-type characteristics. ,,, Hole concentrations are commonly degenerate (>10 19 ) and therefore not favorable for PV applications. Growing CTS films in a sulfur-deficient environment can increase the formation enthalpy of V Cu and decrease hole concentrations .…”

Understanding the Intrinsic P-Type Behavior and Phase Stability of Thermoelectric α-Mg3Sb2

“…19 The HSE06 functional mixes 25% of screened Hartree−Fock exchange energy with the screening parameter being 0.2 Å −1 . 20 For the defect calculations, a 3 × 3 × 3 supercell (constructed from the conventional unit cell) was used that consists of 135 atoms when the supercell was defect-free. An energy cutoff of 360 eV was used for plane-wave basis expansion.…”

“…Because the (semi) local functionals such as local density approximation (LDA) and generalized gradient approximation (GGA) usually underestimate the band gap of the semiconductor and cannot correctly predict the energetics of point defects, all the supercell calculations (with and without defects) in the present work were carried out using the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional . The HSE06 functional mixes 25% of screened Hartree–Fock exchange energy with the screening parameter being 0.2 Å –1 . For the defect calculations, a 3 × 3 × 3 supercell (constructed from the conventional unit cell) was used that consists of 135 atoms when the supercell was defect-free.…”