Effect of germanium incorporation on the properties of kesterite Cu2ZnSn(S,Se)4 monograins

Oueslati, Souhaib; Grossberg, Michael; Kauk-Kuusik, Marit; Mikli, Valdek; Ernits, K.; Meißner, D.; Krustok, J.

doi:10.1016/j.tsf.2018.11.020

Cited by 14 publications

(19 citation statements)

References 22 publications

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“… 41 A PL study varying excitation power and temperature can identify the radiative recombination mechanisms operating in semiconductors. 42 The PL spectra varying temperatures are shown in Figure 7 b–d. As the temperature decreases, the 40- and 50%-substituted thin films have a dramatic quenching of the main emission peak; meanwhile, one at about 1.4 eV arises.…”

Section: Results and Discussionmentioning

confidence: 99%

Band-Gap Tuning Induced by Germanium Introduction in Solution-Processed Kesterite Thin Films

et al. 2022

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In the last few decades, the attention of scientific community has been driven toward the research on renewable energies. In particular, the photovoltaic (PV) thin-film technology has been widely explored to provide suitable candidates as top cells for tandem architectures, with the purpose of enhancing current PV efficiencies. One of the most studied absorbers, made of earth-abundant elements, is kesterite Cu 2 ZnSnS 4 (CZTS), showing a high absorption coefficient and a band gap around 1.4–1.5 eV. In particular, thanks to the ease of band-gap tuning by partial/total substitution of one or more of its elements, the high-band-gap kesterite derivatives have drawn a lot of attention aiming to find the perfect partner as a top absorber to couple with silicon in tandem solar cells (especially in a four-terminal architecture). In this work, we report the effects of the substitution of tin with different amounts of germanium in CZTS-based solar cells produced with an extremely simple sol–gel process, demonstrating how it is possible to fine-tune the band gap of the absorber and change its chemical–physical properties in this way. The precursor solution was directly drop-cast onto the substrate and spread with the aid of a film applicator, followed by a few minutes of gelation and annealing in an inert atmosphere. The desired crystalline phase was obtained without the aid of external sulfur sources as the precursor solution contained thiourea as well as metal acetates responsible for the in situ coordination and thus the correct networking of the metal centers. The addition of KCl in dopant amounts to the precursor solution allowed the formation of well-grown compact grains and enhanced the material quality. The materials obtained with the optimized procedure were characterized in depth through different techniques, and they showed very good properties in terms of purity, compactness, and grain size. Moreover, solar-cell prototypes were produced and measured, exhibiting poor charge extraction due to heavy back-contact sulfurization as studied in depth and experimentally demonstrated through Kelvin probe force microscopy.

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Section: Results and Discussionmentioning

confidence: 99%

Band-Gap Tuning Induced by Germanium Introduction in Solution-Processed Kesterite Thin Films

et al. 2022

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“…Intriguingly, the Ge based kesterite showed less electrical losses from band tailing/electrostatic potential fluctuations compared to Ge free devices [125,126]. However, the main limiting factors were linked to a high series resistance, leading to imperfect current collection and a high interface recombination [127]. Trying to address these issues, a detailed optimization of the CdS chemical bath deposition has allowed achieving a record efficiency of 7.6% for a CZGSe (E g ∼1.36 eV) absorber [128].…”

Section: Germanium (Ge)mentioning

confidence: 99%

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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“…Sulfide CZTS, in particular, has some features which suggest that it could be a promising tandem partner for Si. Through different solid solutions and cationic substitutions, the bandgap of kesterites can be tuned -for instance, through Ge or Ag incorporation the bandgap of sulfide CZTS can be increased from the nominal 1.5 eV to about 2.1 eV, an ideal range for tandem applications [22,23,24,25,26,27]. Moreover, CZTS and Si are closely lattice-matched, with an a-axis lattice mismatch of less than ± 0.1% [28,29].…”

Section: The Top Cell: Cztsmentioning

confidence: 99%

Monolithic thin-film chalcogenide–silicon tandem solar cells enabled by a diffusion barrier

Hajijafarassar

Martinho

Stulen

et al. 2020

Solar Energy Materials and Solar Cells

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Following the recent success of monolithically integrated Perovskite/Si tandem solar cells, great interest has been raised in searching for alternative wide bandgap top-cell materials with prospects of a fully earthabundant, stable and efficient tandem solar cell. Thin film chalcogenides (TFCs) such as the Cu 2 ZnSnS 4 (CZTS) could be suitable top-cell materials. However, TFCs have the disadvantage that generally at least one high temperature step (> 500 • C) is needed during the synthesis, which could contaminate the Si bottom cell. Here, we systematically investigate the monolithic integration of CZTS on a Si bottom solar cell. A thermally resilient double-sided Tunnel Oxide Passivated Contact (TOPCon) structure is used as bottom cell. A thin (< 25 nm) TiN layer between the top and bottom cells, doubles as diffusion barrier and recombination layer. We show that TiN successfully mitigates in-diffusion of CZTS elements into the c-Si bulk during the high temperature sulfurization process, and find no evidence of electrically active deep Si bulk defects in samples protected by just 10 nm TiN. Post-process minority carrier lifetime in Si exceeded 1.5 ms, i.e., a promising implied open-circuit voltage (i-V oc) of 715 mV after the high temperature sulfurization. Based on these results, we demonstrate a first proof-of-concept two-terminal CZTS/Si tandem device with an efficiency of 1.1% and a V oc of 900 mV. A general implication of this study is that the growth of complex semiconductors on Si using high temperature steps is technically feasible, and can potentially lead to efficient monolithically integrated two-terminal tandem solar cells.

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Effect of germanium incorporation on the properties of kesterite Cu2ZnSn(S,Se)4 monograins

Cited by 14 publications

References 22 publications

Band-Gap Tuning Induced by Germanium Introduction in Solution-Processed Kesterite Thin Films

Band-Gap Tuning Induced by Germanium Introduction in Solution-Processed Kesterite Thin Films

Doping and alloying of kesterites

Monolithic thin-film chalcogenide–silicon tandem solar cells enabled by a diffusion barrier

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