Assessing the defect tolerance of kesterite-inspired solar absorbers

Crovetto, Andrea; Kim, Sung-Hyun; Fischer, Moritz; Stenger, Nicolas; Walsh, Aron; Chorkendorff, Ib; Vesborg, Peter Christian Kjærgaard

doi:10.1039/d0ee02177f

Cited by 33 publications

(51 citation statements)

References 79 publications

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“…The error bar is rather large for two main reasons: (i) broadening of the excitonic absorption feature at room temperature, causing some degree of correlation between fitting parameters; (ii) the large apparent sub-band gap absorption, which has to be deconvolved from the absorption onset before fitting the spectra with the Elliott function. Taking the static dielectric constant and the directionaveraged electron-and hole effective masses from other computational works, 12,13,36 the hydrogen model predicts exciton binding energies of 65 meV for CBTS and 62 meV for CSTS, in fair agreement with the measured values. The existence of appreciable excitonic absorption at room temperature in CBTS and CSTS is a unique feature of these compounds with respect to CZTS or most other kesterite-inspired materials, and it resembles the absorption features of some halide perovskites instead.…”

Section: B Spectroscopic Ellipsometrysupporting

confidence: 67%

“…We argue that exciton recombination is the most likely origin of room-temperature PL for two reasons: (i) the op- tical absorption onset of CBTS and CSTS has a significant excitonic contribution even at room temperature, as discussed in the previous section; (ii) the position of the main PL peak as a function of temperature is not consistent with a transition from exciton recombination to band-to-band recombination with increasing temperature, as discussed in Ref. 36. Micro-PL maps over 14 × 14 µm regions (Fig.…”

Section: Photoluminescence Spectroscopymentioning

confidence: 80%

“…37,38 It can be explained by the lower dielectric constant, wider band gap, and higher hole effective masses in CBTS and CSTS with respect to CZTS. 12,13,36 The spectral onset of the photocurrent, based on external quantum efficiency (EQE) measurements of CBTS and CSTS solar cells, is plotted in Fig. 4 together with the optically-detemined absorption coefficients.…”

Section: B Spectroscopic Ellipsometrymentioning

confidence: 99%

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Experimental and first-principles spectroscopy of Cu$_2$SrSnS$_4$ and Cu$_2$BaSnS$_4$ photoabsorbers

Crovetto¹,

Xing²,

Fischer³

et al. 2020

Preprint

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The Cu 2 BaSnS 4 (CBTS) and Cu 2 SrSnS 4 (CSTS) semiconductors have been recently proposed as potential wide band gap photovoltaic absorbers. Although several measurements indicate that they are less affected by band tailing than their parent compound Cu 2 ZnSnS 4 , their photovoltaic efficiencies are still low. To identify possible issues, we characterize CBTS and CSTS in parallel by a variety of spectroscopic methods complemented by first-principles calculations. Two main problems are identified in both materials. The first is the existence of deep defect transitions in low-temperature photoluminescence, pointing to a high density of bulk recombination centers. The second is a low electron affinity, which emphasizes the need for an alternative heterojunction partner and electron contact. We also find a tendency for downward band bending at the surface of both materials. In CBTS, this effect is sufficiently large to cause carrier type inversion, which may enhance carrier separation and mitigate interface recombination. Optical absorption at room temperature is exciton-enhanced in both CBTS and CSTS. Deconvolution of excitonic effects yields band gaps that are about 100 meV higher than previous estimates based on Tauc plots. Although the two investigated materials are remarkably similar in an idealized, defect-free picture, the present work points to CBTS as a more promising absorber than CSTS for tandem photovoltaics.

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Section: B Spectroscopic Ellipsometrysupporting

confidence: 67%

Section: Photoluminescence Spectroscopymentioning

confidence: 80%

Section: B Spectroscopic Ellipsometrymentioning

confidence: 99%

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Experimental and first-principles spectroscopy of Cu$_2$SrSnS$_4$ and Cu$_2$BaSnS$_4$ photoabsorbers

Crovetto¹,

Xing²,

Fischer³

et al. 2020

Preprint

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“…Over the recent years, attempts have been made to circumvent these actual limitations using alloying and doping of kesterite materials with other elements. 3,[18][19][20][21][22][23] Both theoretical and experimental approaches have been used. A wide range of cationic substitutions have been investigated: Cu by Ag, 24,25 Zn by Cd, 24,[26][27][28] Sn by Ge, [28][29][30][31][32] S by Se 4 and doping of both Cu 2 -ZnSnS 4 and Cu 2 ZnSnSe 4 by Na, Li, Ga 33 and Ge 18,[34][35][36] or even using more exotic elements as in ref.…”

Section: Introductionmentioning

confidence: 99%

Relevance of Ge incorporation to control the physical behaviour of point defects in kesterite

et al. 2022

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“…Over the recent years, attempts have been made to circumvent these actual limitations using alloying and doping of kesterite materials with other elements [17,18,19,3,20,21]. Both theoretical and experimental approaches have been used.…”

Section: Introductionmentioning

confidence: 99%

Relevance of Ge incorporation to control the physical behaviour of point defects in kesterite

Ratz,

Nguyen,

Brammertz

et al. 2021

Preprint

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To reduce the prominent VOC -deficit that limits kesterite-based solar cells efficiencies, Ge has been proposed over the recent years with encouraging results, as the reduction of the non-radiative recombination rate is considered as a way to improve the well-known Sn-kesterite world record efficiency. To gain further insight into this mechanism, we investigate the physical behaviour of intrinsic point defects both upon Ge doping and alloying of Cu2ZnSnS4 kesterite. Using a first-principles approach, we confirm the p-type conductivity of both Cu2ZnSnS4 and Cu2ZnGeS4, attributed to the low formation energies of the VCu and CuZn acceptor defects within the whole stable phase diagram range. Via doping of the Sn-kesterite matrix, we report the lowest formation energy for the substitutional defect GeSn. We also confirm the detrimental role of the substitutional defects XZn (X=Sn,Ge) acting as recombination centres within the Sn-based, the Ge-doped and the Ge-based kesterite. Finally, we highlight the reduction of the lattice distortion upon Ge incorporation resulting in a reduction of the carrier capture cross section and consequently a decrease of the non-radiative recombination rate within the bulk material.

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Assessing the defect tolerance of kesterite-inspired solar absorbers

Abstract: Various thin-film I2-II-IV-VI4 photovoltaic absorbers derived from kesterite Cu2ZnSn(S,Se)4 have been synthesized, characterized, and theoretically investigated in the past few years. The availability of this homogeneous materials dataset is an...

Cited by 33 publications

References 79 publications

Experimental and first-principles spectroscopy of Cu$_2$SrSnS$_4$ and Cu$_2$BaSnS$_4$ photoabsorbers

Experimental and first-principles spectroscopy of Cu$_2$SrSnS$_4$ and Cu$_2$BaSnS$_4$ photoabsorbers

Relevance of Ge incorporation to control the physical behaviour of point defects in kesterite

Relevance of Ge incorporation to control the physical behaviour of point defects in kesterite

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