Optimum bandgap profile analysis of Cu(In,Ga)Se<sub>2</sub> solar cells with various defect densities by SCAPS

Murata, Masashi; Hironiwa, Daisuke; Ashida, Naoki; Chantana, Jakapan; Aoyagi, Kazuhiko; Kataoka, Naoya; Minemoto, Takashi

doi:10.7567/jjap.53.04er14

Cited by 34 publications

(8 citation statements)

References 37 publications

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“…[ 13 ] A double Ga‐gradient profile (Ga‐rich/Ga‐poor/Ga‐rich) is commonly implemented in high‐efficiency CIGSe solar cells. [ 3,12,14 ] The gradient in the conduction band assists in driving electrons (minority carriers in p‐type CIGSe) towards the space charge region (SCR) and the heterojunction with the n‐type CdS layer. [ 15 ] The resulting decrease in electron density near the molybdenum (Mo) back contact has been shown to suppress recombination losses, [ 16–18 ] notably associated with interfacial recombination at the CIGSe/Mo junction, [ 14 ] thereby significantly increasing the device open‐circuit voltage ( V OC ).…”

Section: Introductionmentioning

confidence: 99%

Insights from Transient Absorption Spectroscopy into Electron Dynamics Along the Ga‐Gradient in Cu(In,Ga)Se₂ Solar Cells

Chang

Carron

Ochoa

et al. 2021

Advanced Energy Materials

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CuInSe 2 (CISe) lattice widens the bandgap from 1.04 eV [5,6] up to 1.68 eV [7] in pure CuGaSe 2 , the change affecting the conduction band and leaving the valence band largely unaffected. [8-10] Since 1994, several studies have focused on optimising device efficiency by adjusting the Ga-concentration profile in the CIGSe layer [3,11,12] nowadays reaching record device efficiencies surpassing 23%. [13] A double Ga-gradient profile (Ga-rich/Ga-poor/Ga-rich) is commonly implemented in high-efficiency CIGSe solar cells. [3,12,14] The gradient in the conduction band assists in driving electrons (minority carriers in p-type CIGSe) towards the space charge region (SCR) and the heterojunction with the n-type CdS layer. [15] The resulting decrease in electron density near the molybdenum (Mo) back contact has been shown to suppress recombination losses, [16-18] notably associated with interfacial recombination at the CIGSe/Mo junction, [14] thereby significantly increasing the device open-circuit voltage (V OC). [19-21] Optimisation of the CIGSe film thickness, composition and Ga-gradient profile has largely been carried out by monitoring improvements in device efficiency, with only limited knowledge of the underlying dynamics and diffusion of the minority carriers to the n-contact. In particular, minority carrier mobility and driftdiffusion times in high-efficiency CIGSe solar cells are important parameters to quantify performance losses in state-of-the-art devices. A number of studies report carrier mobility in CISe and CIGSe measured with a variety of techniques as summarised in Table 1. However, the reported mobility values show variations of several orders of magnitude. Furthermore, only a few studies investigated device-relevant Ga-graded CIGSe layers, instead, focusing on simpler, ungraded absorbers with poorer performance. Combining time-resolved photoluminescence (TRPL) spectroscopy and numerical simulations, Weiss et al. extracted minority carrier mobilities between 32 and 45 cm 2 V −1 s −1 in Gafree CISe absorbers, however for back-graded CIGSe (GGI ratio increasing from 0 to 0.28 towards the back) only a lower limit of 8.3 cm 2 V −1 s −1 could be evidenced. [22] Kuciauskas et al. carried out TRPL studies on a typical Ga gradient device and estimated a minority carrier mobility of 55-230 cm 2 V −1 s −1 in the SCR near the CdS/CIGSe interface, [23] but did not address electron transport across the Ga-gradient towards the back contact region. Though transient absorption spectroscopy (TAS) has been utilized in the fields of organic and hybrid organic-inorganic Cu(In,Ga)Se 2 solar cells have markedly increased their efficiency over the last decades currently reaching a record power conversion efficiency of 23.3%. Key aspects to this efficiency progress are the engineered bandgap gradient profile across the absorber depth, along with controlled incorporation of alkali atoms via post-deposition treatments. Whereas the impact of these treatments on the carrier lifetime has been extensively studied in ungraded Cu(In,Ga...

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Section: Introductionmentioning

confidence: 99%

Insights from Transient Absorption Spectroscopy into Electron Dynamics Along the Ga‐Gradient in Cu(In,Ga)Se₂ Solar Cells

Chang

Carron

Ochoa

et al. 2021

Advanced Energy Materials

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“…Because the thicknesses of CIGS thin films are comparable, we can exclude film thickness-dependent short-circuit current densities [33]. On the other hand, the Ga/(In+Ga) depth profile results in a comparable graded bandgap profile [40], which determines the power conversion efficiency. In an earlier report [11], we demonstrated that the Ga/(In+Ga) depth profile is more graded with increasing NaF thickness, indicating the influence of Na concentration on the optoelectronic parameters, defect densities, and power conversion efficiencies of CIGS thin films.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast pump-probe reflectance spectroscopy: Why sodium makes Cu(In,Ga)Se2 solar cells better

Eid

Usman

Gereige

et al. 2015

Solar Energy Materials and Solar Cells

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(O.F.M.) 2 | P a g e TOC graphicCIGS thin-film samples were investigated for the first time using femtosecond pump-probe differential reflection spectroscopy with broadband capabilities and 120-fs temporal resolution.The pump-and-probe beams were focused on ~1.6 m-thick CIGS films. The reflected probe light from the samples was collected and focused on the broadband infrared detector (D) for recording the carrier dynamics of CIGS in real time.3 | P a g e ABSTRACT Although Cu(In,Ga)Se 2 (CIGS) solar cells have the highest efficiency of any thin-film solar cell, especially when sodium is incorporated, the fundamental device properties of ultrafast carrier transport and recombination in such cells remain not fully understood. Here, we explore the dynamics of charge carriers in CIGS absorber layers with varying concentrations of Na by femtosecond (fs) broadband pump-probe reflectance spectroscopy with 120-fs time resolution.By analyzing the time-resolved transient spectra in a different time domain, we show that a small amount of Na integrated by NaF deposition on top of sputtered Cu(In,Ga) prior to selenization forms CIGS, which induces slower recombination of the excited carriers. Here, we provide direct evidence for the elongation of carrier lifetimes by incorporating Na into CIGS. KEYWORDSCIGS solar cells, ultrafast photophysics, pump-probe reflectance spectroscopy, carrier recombination, dielectric function model 4 | P a g e

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“…In addition, the absorption coefficient α can be determined by [18] α ¼ A α ðhν À E g Þ 1 2 (11) Table 1 lists the fundamental characteristics of AZO, I-ZnO, CdS, and CiS based on some previous studies. [19][20][21]…”

Section: Growth Of Culnse 2 Film With Direct Inkjet Printingmentioning

confidence: 99%

Numerical Study of CiS Solar Cell with CuInSe₂‐Undoped Layer

Allam

Boudaoud

Soufi

et al. 2022

Physica Status Solidi (a)

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Herein, a CuInSe2 thin film solar cell with an intrinsic thin layer (HIT) is modeled and simulated using SCAPS. The HIT is deposited between a thin CdS window layer of reduced thickness of 20 nm to minimize cadmium toxicity and an absorbing layer of variable thickness. The aim is to study the influence of the thickness of absorber and HIT layer, level doping and defect densities of CuInSe2 layer, and high work function (between 5 and 5.6 eV) effect on performance parameters of the solar cell. In general, a significant increase in efficiency is observed. The HIT and the absorber thicknesses are optimized to be 0.3 and 0.5 μm, respectively. A conversion efficiency of 24.2%, a V oc of 0.78 V, J sc of 45.4 mA cm−2, and an FF of 68.3% are obtained for the proposed AZO/ZnO/CdS/CuInSe2/Mo/glass. These simulation results encourage using intrinsic thin layers in CIS solar cell structure.

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Optimum bandgap profile analysis of Cu(In,Ga)Se₂ solar cells with various defect densities by SCAPS

Cited by 34 publications

References 37 publications

Insights from Transient Absorption Spectroscopy into Electron Dynamics Along the Ga‐Gradient in Cu(In,Ga)Se₂ Solar Cells

Insights from Transient Absorption Spectroscopy into Electron Dynamics Along the Ga‐Gradient in Cu(In,Ga)Se₂ Solar Cells

Ultrafast pump-probe reflectance spectroscopy: Why sodium makes Cu(In,Ga)Se2 solar cells better

Numerical Study of CiS Solar Cell with CuInSe₂‐Undoped Layer

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Optimum bandgap profile analysis of Cu(In,Ga)Se2 solar cells with various defect densities by SCAPS

Cited by 34 publications

References 37 publications

Insights from Transient Absorption Spectroscopy into Electron Dynamics Along the Ga‐Gradient in Cu(In,Ga)Se2 Solar Cells

Insights from Transient Absorption Spectroscopy into Electron Dynamics Along the Ga‐Gradient in Cu(In,Ga)Se2 Solar Cells

Ultrafast pump-probe reflectance spectroscopy: Why sodium makes Cu(In,Ga)Se2 solar cells better

Numerical Study of CiS Solar Cell with CuInSe2‐Undoped Layer

Contact Info

Product

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Optimum bandgap profile analysis of Cu(In,Ga)Se₂ solar cells with various defect densities by SCAPS

Insights from Transient Absorption Spectroscopy into Electron Dynamics Along the Ga‐Gradient in Cu(In,Ga)Se₂ Solar Cells

Insights from Transient Absorption Spectroscopy into Electron Dynamics Along the Ga‐Gradient in Cu(In,Ga)Se₂ Solar Cells

Numerical Study of CiS Solar Cell with CuInSe₂‐Undoped Layer