Characterization of Cu(In,Ga)Se2 (CIGS) films with varying gallium ratios

Peace, Bernadette; Claypoole, Jesse; Sun, Neville; Dwyer, Daniel J.; Eisaman, Matthew D.; Haldar, Pradeep; Efstathiadis, Harry

doi:10.1016/j.jallcom.2015.09.006

Cited by 31 publications

(14 citation statements)

References 7 publications

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“…Molybdenum‐coated soda lime glass substrates were used. In the literature, similar studies have mainly been performed on Cu(In,Ga)Se 2 evaporated with a 3‐stage process …”

Section: Resultsmentioning

confidence: 99%

“…In the literature, similar studies have mainly been performed on Cu(In,Ga)Se 2 evaporated with a 3-stage process. [21][22][23][24] It can be observed in the SEM images that the grain size is reduced with increased GGI. This general observation is often reported in the literature.…”

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confidence: 97%

“…This general observation is often reported in the literature. The grain size reduction has been found to be influenced by a number of factors, such as film thickness, 22 substrate temperature, 21 and Se flux. 4 The single-step CuGaSe 2 absorber (Figure 1d) is unintentionally thinner than the other absorber layers.…”

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confidence: 99%

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Record 1.0 V open‐circuit voltage in wide band gap chalcopyrite solar cells

Larsson

Nilsson

Keller

et al. 2017

Progress in Photovoltaics

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Tandem solar cell structures require a high-performance wide band gap absorber as top cell. A possible candidate is CuGaSe 2 , with a fundamental band gap of 1.7 eV. However, a significant open-circuit voltage deficit is often reported for wide band gap chalcopyrite solar cells like CuGaSe 2 . In this paper, we show that the open-circuit voltage can be drastically improved in wide band gap p-Cu(In,Ga)Se 2 and p-CuGaSe 2 devices by improving the conduction band alignment to the n-type buffer layer. This is accomplished by using Zn 1−x Sn x O y , grown by atomic layer deposition, as a buffer layer. In this case, the conduction band level can be adapted to an almost perfect fit to the wide band gap Cu(In,Ga) It has been proven difficult to maintain a good device quality when the gallium content is increased. The main problem is that the opencircuit voltage (V oc ) does generally not scale with the band gap energy as predicted, and it tends to saturate for absorber band gap energies above roughly 1.3 eV. 7,8 This lack of performance in high gallium CIGS devices has been the subject of numerous studies. 7-11The dominating recombination paths, in CuGaSe 2 devices, have been assigned to tunneling enhanced recombination either in the space-charge region or at the interface. 12,13 A possible explanation is trap states formed by cation anti-site (In Cu /Ga Cu ) or anion vacancy (V Se ) defects that become deeper positioned within the band gap when the gallium content increases, and thereby form more effective recombination centers. 11 Furthermore, the difference between the Fermi level and the valence band energy at the absorber surface seems to remain constant around 0.8 eV, independently of gallium content. 13 Consequently, the Fermi level position at the absorber/buffer interface is closer to the middle of the band gap at high gallium contents, and no beneficial type inversion can be expected. Thus, the influence of recombination close to or at the interface appears to become more prominent when the CIGS band gap is widened. The bulk recombination rate is also expected to increase with a large number of these defects, but it has not In the first section of this study, the growth and material characterization of nongraded CIGS absorbers with varying gallium contents (0.3 ≤ GGI ≤ 1) deposited in a single-stage co-evaporation process are described. These absorbers are applied in the second section, where we use the temperature dependence of ALD grown ZTO buffer layers to show that the V oc deficit in wide band gap CIGS can be reduced by improving the absorber/buffer conduction band alignment.In the last section, we further investigate the effect of an improved band alignment by using CuGaSe 2 absorbers of higher material quality, evaporated in a 3-stage type process. 21-24It can be observed in the SEM images that the grain size is reduced with increased GGI. This general observation is often reported in the literature. The grain size reduction has been found to be influenced by a number of factors, such as film t...

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“…Molybdenum‐coated soda lime glass substrates were used. In the literature, similar studies have mainly been performed on Cu(In,Ga)Se 2 evaporated with a 3‐stage process …”

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 97%

See 1 more Smart Citation

Record 1.0 V open‐circuit voltage in wide band gap chalcopyrite solar cells

Larsson

Nilsson

Keller

et al. 2017

Progress in Photovoltaics

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“…We have recently considered theoretically some issues of such cells all of; bandgap grading both in conduction and valence bands [9], modeling of the recombination and generation mechanisms [10,11], Auger process [12]. Beside of such studies, the electrical properties of these devices can be presented in the form of equivalent circuits [13], where the electrical parameters can be obtained by admittance spectroscopy and electrical measurements.…”

Section: Introductionmentioning

confidence: 99%

Electrical Characterization of CIGS Thin Film Solar Cells by Two and Four-Wires Probe Technique

Mosavi¹,

Beszedes²,

Felde³

et al. 2019

Preprint

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The characterization of thin-film solar cells is of huge importance for obtaining high opencircuit voltage and low recombination rates from the interfaces or within the bulk of the main materials. Among the many electrical characterization techniques, the two-and fourwire probe using the Cascade instrument is of interest since the resistance of the wires, and the electrical contacts can be excluded by the additional two wires in 4-wire probe configuration. In this paper, both two and four-point probes configuration are employed to characterize the CIGS chalcogenide thin-film solar cells. The two-wire probe has been used to measure the current-voltage characteristics of the cell which results in a huge internal resistance. Therefore, the four-wire connection are also used to eliminate the lead resistance to enhance the characterization's accuracy. The load resistance in the two-wire probe diminishes the photogenerated current density at smaller voltage ranges. In contrast, the proposed four-wire probe collects more current at higher voltages due to enhanced carrier collection efficiency from contact electrodes. The current conduction mechanism is also identified at every voltage region represented by the value of the ideality factor of that voltage region. It is observed that a longer time given to the charge collection results in increased current density at a higher voltage. According to the results and device characteristics, a novel double-diode model is suggested to extract the saturation current density, shunt and series resistances and the ideality factor of the cells. These cells are shown to be efficient in terms of low recombination at the interfaces and with lower series resistance as the quality of the materials is in its most possible conductive form. The measured internal resistance and saturation current density and ideality factor of the two measurement configuration are measured and compared.

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“…This capability is employed in high-performance solar cell designs to produce internal field gradients for improved carrier collection and thus higher conversion efficiencies. [1][2][3][4] Conversely, the very nature of such compositional flexibility-especially in a phase-rich alloy system like CIGS, where low-cost deposition methods with relatively poor composition and uniformity control (compared to single-crystal epitaxial methods) are effectively obligatory-creates the potential for the formation of a wide range of detrimental solid solutions, ordered compounds and defect structures, metallic phases and domains, and so forth. 5 The extraction of bandgap information with nanoscale resolution, and subsequent correlation with compositional nonuniformities and defect structures, has proven challenging.…”

Section: Introductionmentioning

confidence: 99%

Bandgap profiling in CIGS solar cells via valence electron energy-loss spectroscopy

Deitz

Karki

Marsillac

et al. 2018

Journal of Applied Physics

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A robust, reproducible method for the extraction of relative bandgap trends from scanning transmission electron microscopy (STEM) based electron energy-loss spectroscopy (EELS) is described. The effectiveness of the approach is demonstrated by profiling the bandgap through a CuIn 1-x Ga x Se 2 solar cell that possesses intentional Ga/(In þ Ga) composition variation. The EELSdetermined bandgap profile is compared to the nominal profile calculated from compositional data collected via STEM-based energy dispersive X-ray spectroscopy. The EELS based profile is found to closely track the calculated bandgap trends, with only a small, fixed offset difference. This method, which is particularly advantageous for relatively narrow bandgap materials and/or STEM systems with modest resolution capabilities (i.e., >100 meV), compromises absolute accuracy to provide a straightforward route for the correlation of local electronic structure trends with nanoscale chemical and physical structure/microstructure within semiconductor materials and devices.

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Characterization of Cu(In,Ga)Se2 (CIGS) films with varying gallium ratios

Cited by 31 publications

References 7 publications

Record 1.0 V open‐circuit voltage in wide band gap chalcopyrite solar cells

Record 1.0 V open‐circuit voltage in wide band gap chalcopyrite solar cells

Electrical Characterization of CIGS Thin Film Solar Cells by Two and Four-Wires Probe Technique

Bandgap profiling in CIGS solar cells via valence electron energy-loss spectroscopy

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