Mapping Shunting Paths at the Surface of Cu2ZnSn(S,Se)4 Films via Energy-Filtered Photoemission Microscopy

Cattelan, Mattia; Harniman, Robert L.; Sarua, Andrei; Abbas, Ali; Bowers, Jake W.; Fox, Neil A.; Fermı́n, David J.

doi:10.1016/j.isci.2018.10.004

Cited by 11 publications

(9 citation statements)

References 55 publications

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“…Figure 13(c) also depicts how these trends can affect the CZTS/CdS barrier heights, which have shown a close correlation with recombination activation energies estimated by the temperature dependence of V OC in devices [133]. Interestingly, this approximation to barrier heights enable estimating CZTSSe/CdS conduction band offsets in the range of 0.3 to 0.4 eV [134], which is consistent with values proposed in the literature [135]. However, quantitative analysis of band-offsets remains a highly challenging issue in view of elemental intermixing generated in high-quality junctions as exemplified by the elegant work by Bär et al [136].…”

Section: Germanium (Ge)mentioning

confidence: 57%

Doping and alloying of kesterites

et al. 2019

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Attempts to improve the efficiency of kesterite solar cells by changing the intrinsic stoichiometry have not helped to boost the device efficiency beyond the current record of 12.6%. In this light, the addition of extrinsic elements to the Cu 2 ZnSn(S,Se) 4 matrix in various quantities has emerged as a popular topic aiming to ameliorate electronic properties of the solar cell absorbers. This article reviews extrinsic doping and alloying concepts for kesterite absorbers with the focus on those that do not alter the parent zinc-blende derived kesterite structure. The latest state-of-the-art of possible extrinsic elements is presented in the order of groups of the periodic table. The highest reported solar cell efficiencies for each extrinsic dopant are tabulated at the end. Several dopants like alkali elements and substitutional alloying with Ag, Cd or Ge have been shown to improve the device performance of kesterite solar cells as compared to the nominally undoped references, although it is often difficult to differentiate between pure electronic effects and other possible influences such as changes in the crystallization path, deviations in matrix composition and presence of alkali dopants coming from the substrates. The review is concluded with a suggestion to intensify efforts for identifying intrinsic defects that negatively affect electronic properties of the kesterite absorbers, and, if identified, to test extrinsic strategies that may compensate these defects. Characterization techniques must be developed and widely used to reliably access semiconductor absorber metrics such as the quasi-Fermi level splitting, defect concentration and their energetic position, and carrier lifetime in order to assist in search for effective doping/alloying strategies.

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Section: Germanium (Ge)mentioning

confidence: 57%

Doping and alloying of kesterites

et al. 2019

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“…In a previous study, we examined the valence band spectra of similar work function regions in CZTSSe films, which were consistent with surface confined Sn(II) chalcogenide phases. 32 These low work function regions are not observed in Sb-doped and Na:Sb co-doped films, further suggesting that Sb does play a role in minimizing Sn disorder. As discussed further below, this effect has a clear impact on device performance.…”

Section: Resultsmentioning

confidence: 99%

Mapping the Energetics of Defect States in Cu₂ZnSnS₄ films and the Impact of Sb Doping

Yakushev

Koehler

Cattelan

et al. 2022

ACS Appl. Energy Mater.

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The sub-bandgap levels associated with defect states in Cu 2 ZnSnS 4 (CZTS) thin films are investigated by correlating the temperature dependence of the absorber photoluminescence (PL) with the device admittance spectroscopy. CZTS thin films are prepared by thermolysis of molecular precursors incorporating chloride salts of the cations and thiourea. Na and Sb are introduced as dopants in the precursor layers to assess their impact on Cu/Zn and Sn site disorder, respectively. Systematic analysis of PL spectra as a function of excitation power and temperature show that radiative recombination is dominated by quasi-donor–acceptor pairs (QDAP) with a maximum between 1.03 and 1.18 eV. It is noteworthy that Sb doping leads to a transition from localized to delocalized QDAP. The activation energies obtained associated with QDAP emission closely correlate with the activation energies of the admittance responses in a temperature range between 150 K and room temperature in films with or without added dopants. Admittance data of CZTS films with no added dopants also have a strong contribution from a deeper state associated with Sn disorder. The ensemble of PL and admittance data, in addition to energy-filtered photoemission of electron microscopy (EF-PEEM), shows a detailed picture of the distribution of sub-bandgap states in CZTS and the impact of doping on their energetics and device performance.

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“…In our recent study of localized valence band spectral features of CZTSSe films, supported by DFT calculations, concluded that surfaceconfined Sn 2+ states are responsible for areas of low LEWF. 45 Furthermore, conducting AFM images (Figure S6) reveal local points of high current at the nondoped samples, while significantly less contrast is observed in the doped samples. Photoemission hot-spots are substantially attenuated upon Sb doping (Figure 3b,e), leading to a narrower distribution of LEWF.…”

Section: Acs Energy Lettersmentioning

confidence: 98%

Impact of Sb and Na Doping on the Surface Electronic Landscape of Cu₂ZnSnS₄ Thin Films

et al. 2018

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Open-circuit voltage deficiency is the key limiting factor in Cu2ZnSnS4 (CZTS) thin-film solar cells, which is commonly associated with band tails and deep gap states arising from elemental disorder. The introduction of dopants such as Na and Sb has led to improvement in device performance, yet their effects on the optoelectronic properties of CZTS are yet to be fully elucidated. In this Letter, we unraveled the effect of Sb and Na:Sb co-doping on the surface energy landscape of solution-processed CZTS films employing energy-filtered photoelectron emission microscopy. In the absence of the additives, 150 nm resolution photoemission maps reveal oscillations in the local effective work function as well as areas of low photoemission energy threshold. The introduction of dopants substantially reshapes the photoemission maps, which we rationalize in terms of Cu:Zn and Sn disorder. Finally, we establish unprecedented correlations between the photoemission landscape of thin films and the performance of over 200 devices.

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Mapping Shunting Paths at the Surface of Cu2ZnSn(S,Se)4 Films via Energy-Filtered Photoemission Microscopy

Cited by 11 publications

References 55 publications

Doping and alloying of kesterites

Doping and alloying of kesterites

Mapping the Energetics of Defect States in Cu₂ZnSnS₄ films and the Impact of Sb Doping

Impact of Sb and Na Doping on the Surface Electronic Landscape of Cu₂ZnSnS₄ Thin Films

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Mapping Shunting Paths at the Surface of Cu2ZnSn(S,Se)4 Films via Energy-Filtered Photoemission Microscopy

Cited by 11 publications

References 55 publications

Doping and alloying of kesterites

Doping and alloying of kesterites

Mapping the Energetics of Defect States in Cu2ZnSnS4 films and the Impact of Sb Doping

Impact of Sb and Na Doping on the Surface Electronic Landscape of Cu2ZnSnS4 Thin Films

Contact Info

Product

Resources

About

Mapping the Energetics of Defect States in Cu₂ZnSnS₄ films and the Impact of Sb Doping

Impact of Sb and Na Doping on the Surface Electronic Landscape of Cu₂ZnSnS₄ Thin Films