Free-carrier dynamics and band tails in 
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Phuong, Le Quang; Okano, Masaya; Yamashita, G.; Nagai, Masaya; Ashida, Masaaki; Nagaoka, Akinobu; Yoshino, Kenji; Kanemitsu, Yoshihiko

doi:10.1103/physrevb.92.115204

Cited by 20 publications

(19 citation statements)

References 33 publications

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“…By investigating a high-quality, quasi-equilibrium single crystal of CZTSe, we eliminate the effects of grain boundaries and minimize the impact of secondary phases. The strategy of studying single crystals to infer routes to improve polycrystalline thin film PV devices has proven to be remarkably effective for CdTe [33,34], and has recently been employed for CZTSSe as well [35][36][37][38][39][40]. Notably, Kanemitsu et al have investigated carrier dynamics in CZTS [35,36,38] and CZTSSe [37] single crystals.…”

Section: Introductionmentioning

confidence: 99%

Relating Carrier Dynamics and Photovoltaic Device Performance of Single-Crystalline Cu2ZnSnSe4

Lloyd

Hempel

et al. 2019

Phys. Rev. Applied

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Understanding the relationship of photoexcited carrier lifetimes, mobilities, and recombination mechanisms to structural properties and processing of photovoltaic (PV) absorber materials is critical to the design of efficient solar cells. Carrier dynamics in PV absorbers have conventionally been characterized by time-resolved photoluminescence (TRPL), but TRPL may not be suitable or straightforward for all absorbers. Alternative non-contact methods can enable measurement of ultrafast carrier dynamics for a wider range of materials. Here we demonstrate the complementary use of time-resolved terahertz spectroscopy (TRTS) and near-infrared transient reflectance (NIR-TR) spectroscopy along with TRPL to elucidate photoexcited carrier dynamics in a high-quality copper-poor, zinc-rich kesterite Cu2ZnSnSe4 (CZTSe) single crystal. The single-crystalline nature of the sample eliminates complications arising from grain boundaries, secondary phases, and interfaces associated with thin film growth. A single-crystal-based PV device exhibited an efficiency of 6.2% and Voc of 400 mV, consistent with the quasi-Fermi level splitting determined using absolute photoluminescence. NIR-TR showed picosecond-scale cooling and relaxation of carriers into a distribution of band tail states while TRTS revealed a characteristic time scale of 200-260 ps for recombination. Hall effect and TRTS measurements revealed electron and hole mobilities in the range of 50-100 cm 2 /Vs. These dynamics result in a characteristic minority carrier diffusion length of less than 200 nm, leading to incomplete carrier collection, as confirmed by a strongly decreasing external quantum efficiency at long wavelengths. Our approach combining ultrafast spectroscopy and device measurements can lead to more detailed

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Section: Introductionmentioning

confidence: 99%

Relating Carrier Dynamics and Photovoltaic Device Performance of Single-Crystalline Cu2ZnSnSe4

Lloyd

Hempel

et al. 2019

Phys. Rev. Applied

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“…The CZTSSe compound is characterized by a strong self‐doping and high compensation . The interaction between defects, with relevance for the donors, create electrostatic fluctuating potentials along the film (), which determines critically the electronic energy levels structure and the dynamics of the charge carriers in the material . One of the important issues in the physical characterization of an optoelectronic material is the influence of structural properties and growth conditions on the electronic energy levels structure and charge carriers dynamics.…”

Section: Introductionmentioning

confidence: 99%

Optical and structural investigation of Cu₂ZnSnS₄ based solar cells

Teixeira

Salomé

Sousa

et al. 2016

Physica Status Solidi (b)

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The structural and optical properties of two solar cells in which the Cu2ZnSnS4 absorber layer was sulphurized by two different methods (S flux and graphite box), were studied. The grain sizes are dependent on the sulphurization method, the larger ones being obtained for the sulphurization in a S flux. The optical properties were investigated by photoluminescence (PL). A broad and asymmetric band was observed for the sample with the larger grains, whereas for the other one a very broad emission was obtained, mostly influenced by the CdS buffer layer. The dependence on the excitation power revealed the influence of fluctuating potentials created by strong doping and high compensation of the absorber layer. Radiative recombination channels are quite different from the ones typical of semiconductor materials with flat bands. A relationship between the PL intensity from the absorber layer measured at low temperatures, and the final PV performance is established. Thus, we propose that PL can be used as an evaluation experimental technique in order to decide if a certain absorber should be processed into a full solar cell or not.

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“…This is supported by the excitation fluence dependence of the CZTS x Se 1-x PL spectra shown in Figure 5. 62,66 In Figure 5a for the CZTSe (x = 0) sample, a new peak becomes dominant at high excitation fluences, which is assigned to the PL from the band edge. The PLE and PL spectra for CZTSe show that the fluctuation of the band edge due to spatial electric fields is small (see Figure 4).…”

Section: Multi-ternarymentioning

confidence: 99%

“…62 In the electrostatic potential fluctuation model, the absorption coefficient α is a function of E g and γ, [62][63][64][65] and the calculation result for α is shown with the red broken curves in Figure 4a. The parameter γ and the Stokes shift are plotted in the lower panel of Figure 4b.…”

Section: Multi-ternarymentioning

confidence: 99%

“…Figure 4a shows the PL and PL excitation (PLE) spectra for four samples with different S contents. 62 The PL spectra can be fitted with a Gaussian function (Figure 4a; black broken curves), and the peak energy and spectral width are shown in the top and center panels in Figure 4b, respectively. We found that the PL peak energy and width increase for a larger S content.…”

Section: Multi-ternarymentioning

confidence: 99%

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Review—Light Emission from Thin Film Solar Cell Materials: An Emerging Infrared and Visible Light Emitter

Kanemitsu

Okano

Phuong

et al. 2017

ECS J. Solid State Sci. Technol.

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In the last decade, there have been extensive studies on fabrication and physics of thin-film solar cell materials and devices. Many high-efficiency solar cell devices have been developed, and the knowledge gained in these studies can be used advantageously to produce bright light-emitting devices. In this review, we summarize recent luminescence spectroscopic studies on new solar-cell materials and discuss their photocarrier dynamics with respect to efficient light emission. © The Author(s) This special issue focuses on fundamental researches and applications for light emitters and phosphors in the infrared and visible spectral region. Here, we would like to introduce novel approaches, applying insights from thin-film solar-cell materials to the development of new light emitting materials. Recent progress in fundamental research on solar cells is remarkable as novel materials such as perovskite thin films, quantum dots, and colloidal nanocrystals being applied to fabrication of solar cells. Huge efforts in this fundamental research area lead to conversion efficiency improvements for many types of solar cells.1 There exist global demands and attention in establishments of affordable, flexible, light-weight and high conversionefficiency devices.The prerequisite as a light absorber for high-efficiency thin-film solar cells, is a direct band-gap semiconductor with large absorption coefficient and band-gap in the near infrared and visible spectral region. 2One of the best indicators of the intrinsic material quality of a semiconductor, which in turn directly determines the carrier loss in a device, is the internal luminescence quantum efficiency. Therefore, highly luminescent semiconductors are excellent light absorber materials for solar cells [3][4][5][6][7][8] and allow for high open-circuit voltages. 2,9 Reversely, excellent solar-cell light absorber materials could be excellent lightemitting materials. In fact, the electroluminescence (EL) measurement is a well-established and widely-used technique for characterizing solar cell devices.10-17 Furthermore, time-resolved photoluminescence (PL) spectroscopy based on modern laser techniques have revealed the charge carrier flow in bulk materials as well as in devices.18-23 PL and EL spectroscopy techniques are not limited to material characterization, but are also able to characterize devices. Taking account of these close relations, utilizing insights and understandings obtained from solar cell research is strategic for developments in novel luminescent materials and devices in the near infrared and visible spectral region.In this short review, we briefly summarize luminescence properties of thin-film solar cell materials that have been recently developed as thin-film light absorbers. By further discussing the photocarrier dynamics, we are able to understand how these materials can be used optimally as light emitters in novel devices. The abundant information from solar cell research can be applied to other devices as well. A deep understanding of the carrier phy...

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Free-carrier dynamics and band tails in Cu2ZnSn(SxSe1−x

Cited by 20 publications

References 33 publications

Relating Carrier Dynamics and Photovoltaic Device Performance of Single-Crystalline Cu2ZnSnSe4

Relating Carrier Dynamics and Photovoltaic Device Performance of Single-Crystalline Cu2ZnSnSe4

Optical and structural investigation of Cu₂ZnSnS₄ based solar cells

Review—Light Emission from Thin Film Solar Cell Materials: An Emerging Infrared and Visible Light Emitter

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Free-carrier dynamics and band tails in Cu2ZnSn(SxSe1−x

Cited by 20 publications

References 33 publications

Relating Carrier Dynamics and Photovoltaic Device Performance of Single-Crystalline Cu2ZnSnSe4

Relating Carrier Dynamics and Photovoltaic Device Performance of Single-Crystalline Cu2ZnSnSe4

Optical and structural investigation of Cu2ZnSnS4 based solar cells

Review—Light Emission from Thin Film Solar Cell Materials: An Emerging Infrared and Visible Light Emitter

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Product

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Optical and structural investigation of Cu₂ZnSnS₄ based solar cells