Promising quaternary chalcogenides as high-band-gap semiconductors for tandem photoelectrochemical water splitting devices: A computational screening approach

Abstract

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Assessing the defect tolerance of kesterite-inspired solar absorbers

“…The exciton binding energy of CSTS is estimated as 62 meV using our calculated static dielectric constant of 6.1 and previously calculated average effective masses (0.22m 0 for electrons and 0.82m 0 for holes). 12,51 Assuming the same temperature dependence of the band gap as in CBTS, the BT peak lies B24 meV below the estimated low-temperature band gap of CSTS, in good agreement with the tail state depth estimated by the blue shift of the TI peak (B30 meV). PL transitions involving defects that are shallower than the band tails would merge with tail emission, so the existence of shallow defects with ionization energy o30 meV cannot be confirmed nor excluded.…”

“…Formation energies and band gaps of competing crystal structures are also available for various kesterite-inspired materials as a single consistent data set. 12,71 Two clearly distinct types of experimental band tail data can be found. The first is a measure of the abruptness of optical absorption around the absorption onset, which can be derived either by optical measurements or by external quantum efficiency (EQE) measurements.…”

“…We find that the FX peak of CBTS red-shifts by 43 meV between 79 K and 300 K, in good agreement with the known temperature coefficient of the CBTS band gap. 19 We estimate the exciton binding energy of CBTS as C65 meV from the hydrogen model using our calculated dielectric constant of 6.1 and average electron-and hole effective masses of 0.22m 0 and 0.92m 0 , respectively 12,51 (m 0 is the electron rest mass). A blue shift of 65 meV would be quite substantial, yet it is not observed in Fig.…”

“…2(a) and C is Haynes' constant, which depends on the defect type and can be determined from the ratio of the effective masses of CBTS. 57,58 Assuming the same effective masses that we used for the estimation of E b , 12,51 three possibilities exist. If the exciton was bound to an ionized impurity, the ionization energy of the latter would be B27 meV as CB 1 for both donors and acceptors.…”

“…9 A possible strategy to mitigate the efficiency losses due to non-radiative recombination and band tailing is to perform isoelectronic element substitutions on the Cu 2 ZnSn(S,Se) 4 template in the hope to obtain a more defect-tolerant material than the original. 1,[10][11][12] A popular approach has been to partially substitute certain cations with small amounts of other cations (e.g. Sn with Ge and Cu with Li).…”