Tail state formation in solar cell materials: First principles analyses of zincblende, chalcopyrite, kesterite, and hybrid perovskite crystals

Nishiwaki, Mitsutoshi; Nagaya, Keisuke; Kato, Masato; Fujimoto, Sanji; Tampo, Hitoshi; Miyadera, Tetsuhiko; Chikamatsu, Masayuki; Shibata, Hajime; Fujiwara, Hiroyuki

doi:10.1103/physrevmaterials.2.085404

Cited by 47 publications

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“…The tail state formation in a-Si:H is caused by the random nature of the amorphous network [34]. Quite large tail absorption in CZTSe and CZTS has been attributed to cation disorder (i.e., Cu/Zn/Sn mixing) [35,36], while the tail state generation is negligible in Cu 2 ZnGeSe 4 (CZGSe) due to the suppression of the cation mixing [36]. been incorporated into the calculation by adopting experimental data, while an unrealistic step function with E U = 0 eV is assumed for the light absorption in the SQ model.…”

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Maximum Efficiencies and Performance-Limiting Factors of Inorganic and Hybrid Perovskite Solar Cells

et al. 2019

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The Shockley and Queisser limit, a well-known efficiency limit for a solar cell, is based on unrealistic physical assumptions and its maximum limit is seriously overestimated.To understand the power loss mechanisms of record-efficiency cells, a more rigorous approach is necessary. Here, we have established a formalism that can accurately predict absolute performance limits of solar cells in conventional thin film form. In particular, a formulation for a strict evaluation of the saturation current in a nonblackbody solar cell has been developed by taking incident angle, light polarization and texture effects into account. Based on the established method, we have estimated the maximum efficiencies of 13 well-studied solar cell materials [GaAs, InP, CdTe, a-HC(NH 2 ) 2 PbI 3 ] in a 1-µm-thick physical limit. Our calculation shows that over 30% efficiencies can be achieved for absorber layers with sharp absorption edges (GaAs, InP, CdTe, CuInGaSe 2 , Cu 2 ZnGeSe 4 ). Nevertheless, many record-efficiency polycrystalline solar cells, including hybrid perovskites, are limited by open-circuit voltage and fill-factor losses. We show that the maximum conversion efficiencies described here present alternative limits that can predict the power generation of real-world solar cells. *fujiwara@gifu-u.ac.jp sc J kT qV J J −  

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Maximum Efficiencies and Performance-Limiting Factors of Inorganic and Hybrid Perovskite Solar Cells

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“…It was reported that fewer antisite defects, such as Cu Zn and Cu Ge (Cu Sn ), and complex defects, such as Cu Zn + Zn Cu , form in CZGSe compared to CZTSe for the bulk material . Moreover, it was reported that fewer mixed crystal phases among primitive‐mixed CuAu (PMMA), stannite, and kesterite crystal structures form in CZGSe compared to CZTSe for the bulk . These reports also indicate that the carrier recombination in CZTGSe bulk is suppressed by an increase in x .…”

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“…Therefore, we consider that the steeper slope in the EQE spectra near the bandgap is due to the reduction of carrier recombination centers in the bulk. In addition, several studies have pointed out that the states of the tail of the absorption spectra are critical issues that must be solved in carrier recombination . Therefore, the origin of the steeper slope in the EQE spectra near the bandgap could be related to the origin of the tail states due to the recombination centers in CZTGSe bulk.…”

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Characterization of Surface and Heterointerface of Cu₂ZnSn_1–xGe_xSe₄ for Solar Cell Applications

Nagai

Kim

Tampo

et al. 2020

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This study analyzes the electronic structure of Cu2ZnSn1–xGexSe4 (CZTGSe) surface and band alignments of CdS and CZTGSe using the Ge/(Sn + Ge) composition ratios of x = 0–1 based on inversed, ultraviolet, and X‐ray photoemission spectroscopy. The conduction band offsets of the CdS/CZTGSe interface linearly decrease with increasing x, which are so‐called spike conduction band connections, whereas the valence band offsets are observed to be independent of x. Moreover, the hole density near the CZTGSe surface increases with an increase in x; this corresponds to the increase in the measured built‐in‐potential with x. However, the open circuit voltage (VOC) saturates to ≈0.5 V for x over 0.2 in spite of the favorable band alignment and larger built‐in‐potential of x at the interface. External‐quantum‐efficiency spectral analysis shows that the carrier recombination in CZTGSe bulk is suppressed with an increase in x, whereas the recombination near the CZTGSe surface is enhanced. The relationship between these recombination centers, electronic structure, and saturation of VOC is discussed.

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“…Recently, Zamulko et al [19] re-examined first principle theory at different levels in order to improve the description of the electronic structure and optical properties of CZTSSe. Nishiwaki et al [20] performed density functional calculation to study absorption band tail of the kesterites. In particular, a theoretical estimate for the tail energy of ∼30 meV for both CZTS and CZTSe was obtained.…”

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The electrical and optical properties of kesterites

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Kesterite Cu 2 ZnSn(S x Se 1-x ) 4 (CZTSSe) semiconductor materials have been extensively studied over the past decade, however despite significant efforts, the open circuit voltage remains below 60% of the theoretical maximum. Understanding the optical and electrical properties is critical to explaining and solving the voltage deficit. This review aims to summarize the present knowledge of optical and electrical properties of kesterites and specifically focuses on experimental data of intrinsic defects, charge carrier density and transport, and minority carrier lifetime and related rate-limiting recombination mechanisms. It concludes with suggestions for further investigation of the electrical and optical properties of kesterite materials. of the (001) cationic planes are randomly occupied by Cu and Zn atoms [6,7]. While theoretical calculations by Chen et al [8] find the lowest formation energy for the kesterite crystal structure, cation disorder is present in CZTSSe due to the low energy difference between the stannite-and kesterite-related structures. It has been suggested that the Cu-Zn disorder in Cu 2 ZnSnS 4 (CZTS) follows a second order phase transition with a critical temperature of ∼260°C for CZTS, which was first observed and introduced to describe the modifications in the Raman spectra of CZTS annealed at different temperatures [9]. A similar phenomenon has also been found in Cu 2 ZnSnSe 4 (CZTSe), with a critical temperature of 200°C [10], where the measured increase in band gap is explained by thermally induced ordering of Cu and Zn cations. While the remarkable effect of the orderdisorder transition on the band gap and vibrational spectra is explained by Vineyard's theory [11], the disorder parameter itself is not experimentally determined in the probed samples. A recent direct comparison between resonant x-ray diffraction and photoluminescence (PL) data in CZTSe has confirmed a relationship between the Cu-Zn disorder and the band gap modification [12]. A change in the order parameter from 0 to 0.7 leads to a OPEN ACCESS RECEIVED significant increase in the band gap on the order of ∼0.11 eV and ∼0.20 eV for CZTSe and CZTS, respectively [10,13].The absorption coefficient for CZTS and CZTSe is about ∼2-3 × 10 4 cm −1 at 1.6 eV and at 1.1 eV, respectively, as determined by the normal reflectance and transmittance [2, 13] spectroscopic ellipsometry (SE) [14-16] and external quantum efficiency [17] methods. In the recent review by Choi et al [18] the main theoretical and experimental results on the energy band structure and SE data were discussed and summarized. Recently, Zamulko et al [19] re-examined first principle theory at different levels in order to improve the description of the electronic structure and optical properties of CZTSSe. Nishiwaki et al [20] performed density functional calculation to study absorption band tail of the kesterites. In particular, a theoretical estimate for the tail energy of ∼30 meV for both CZTS and CZTSe was obtained. It was suggested that quite large Urbach energi...

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Tail state formation in solar cell materials: First principles analyses of zincblende, chalcopyrite, kesterite, and hybrid perovskite crystals

Cited by 47 publications

References 50 publications

Maximum Efficiencies and Performance-Limiting Factors of Inorganic and Hybrid Perovskite Solar Cells

Maximum Efficiencies and Performance-Limiting Factors of Inorganic and Hybrid Perovskite Solar Cells

Characterization of Surface and Heterointerface of Cu₂ZnSn_1–xGe_xSe₄ for Solar Cell Applications

The electrical and optical properties of kesterites

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Tail state formation in solar cell materials: First principles analyses of zincblende, chalcopyrite, kesterite, and hybrid perovskite crystals

Cited by 47 publications

References 50 publications

Maximum Efficiencies and Performance-Limiting Factors of Inorganic and Hybrid Perovskite Solar Cells

Maximum Efficiencies and Performance-Limiting Factors of Inorganic and Hybrid Perovskite Solar Cells

Characterization of Surface and Heterointerface of Cu2ZnSn1–xGexSe4 for Solar Cell Applications

The electrical and optical properties of kesterites

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Characterization of Surface and Heterointerface of Cu₂ZnSn_1–xGe_xSe₄ for Solar Cell Applications