Koninklijke Bibliotheek, National Library of the Netherlands
IP1604914508288
Effect of different Na supply methods on thin Cu(In,Ga)Se2 solar cells with Al2O3 rear passivation layers
Ledinek, Dorothea
Donzel-Gargand, Olivier
Sköld, Markus
Keller, Jan
Edoff, Marika
text
article
monographic
Solar energy materials and solar cells
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Elektronische Wetenschappelijke Tijdschriften
EWTIJ
10.1016/j.solmat.2018.07.017
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SOLMAT
9544
S0927-0248(18)30379-9
10.1016/j.solmat.2018.07.017
The Authors
Fig. 1
Schematic representation of the different sample types: a) NaF post-deposition treated (post-DT) b) NaF pre-deposition treated (pre-DT), c) barrier, d) baseline. The passivation layer is very thin compared to all other layers and is indicated as a red line on top of the Mo rear contact.
Fig. 1
Fig. 2
Equivalent circuit of a two-diode model for thin film solar cells. The primary diode with a current source in parallel, represents the main junction and the associated currents, i.e. the diode current J
m
and the light current J
lm, the secondary diode with a current source and a shunt in parallel represents an energy barrier at the rear contact and the associated currents: a diode current J
b
, a secondary light current J
lb
and a shunt current J
shb
=G
b
V
b
. The different series resistance components are combined together in a lumped series resistance R
S
.
Fig. 2
Fig. 3
Average open-circuit voltage V
OC
, short-circuit current density J
SC
, fill factor and efficiency for all sample types. The error bars indicate the standard deviation sigma, which is in most cases smaller than the marker and thus not visible. The light intensity was calibrated with a Si solar cell to obtain a photon flux corresponding to 1000 W/m2 at AM 1.5. Post-DT samples were treated with an in-situ post-deposition treatment just after CIGS evaporation. On 15Pre-DT and 7.5Pre-DT a 15 respectively 7.5 nm NaF precursor layer was evaporated on the samples just before the CIGS co-evaporation. On the barrier samples an alkali diffusion barrier was deposited directly onto the glass.
Fig. 3
Fig. 4
Current-voltage (JV) curves (left) in the dark and under illumination and external quantum efficiency (EQE) (right) for selected post-deposition treated (post-DT) samples. Due to measurement artifacts, the data in the region between 900 and 1000 nm has been interpolated.
Fig. 4
Fig. 5
Current-voltage (JV) curves (left) in the dark and under illumination and external quantum efficiency (EQE) (right) for selected samples with a 15 nm NaF precursor layer (15PreDT samples).
Fig. 5
Fig. 6
Current-voltage JV curves (left) in the dark and under illumination and external quantum efficiency EQE (right) for the barrier samples, i.e. the samples with an alkali diffusion barrier deposited directly on the cleaned glass. Due to measurement artifacts, the measurement data in the region between 900 and 1000 nm has been interpolated.
Fig. 6
Fig. 7
Net acceptor concentration N
A
calculated from current-voltage (CV) measurements on 4 cells per sample. The boxes indicate the standard deviation. The sample names are explained in Table 1.
Fig. 7
Fig. 8
Open-circuit voltage-temperature (V
OC
-T) graphs for the temperature dependent current-voltage (JVT) measurements on a) the post-DT0, the post-DT10 sand the barrier0 sample and b) the pre-DT20 and pre-DT50 sample. In graph a) the extrapolations towards 0 K at low (150–180 K) and high temperatures (300–330 K) are illustrated for post-DT samples and the values φ
1
, φ
2
and Δφ are marked on the V
OC
-axis. In graph b) the extrapolation of graphs at low and high temperatures is exemplified for the 7.5pre-DT20 sample. In both cases the green lines mark the extrapolation at low temperatures and magenta lines the extrapolation at high temperatures. The sample names are explained in Table 1.
Fig. 8
Fig. 9
TEM analysis of the samples (A) 7.5pre-DT70 and (B) post-DT50, showing for both the Bright Field image (BF), the red-green-blue (RGB) and the red-blue (R B) reconstructed images (with Red: In – Green: O – Blue: Mo), and the EELS intensity profiles of O, Ga, Cu, In and Mo as integrated over the area symbolized by the white dotted arrows in the RGB maps. In the EELS intensity profile the length of the x-axes corresponds to the length of the arrows in the RGB images and the x-axes’ origin is placed at 0 nm. The aluminum signal correlates with oxygen but cannot be extracted from this data-set due to the used energy range.
Fig. 9
Table 1
Overview of the produced samples. In column three, the first number gives the number of samples produced for every sample type and the numbers in brackets give the number of cells on every sample. The numbers in the fourth column indicates the corresponding number of ALD cycles. The number of ALD cycles replaces xx in the sample name (e.g. ‘post-DT10′ is a post-deposition treated sample passivated with a passivation layer deposited by 10 ALD cycles).
Table 1
Sample type
Sample name
Number of samples (number of cells)
Number of ALD cycles for Al
2
O
3
xx
Post-Deposition
post-DTxx
8 (32, 32, 32, 32, 32, 32, 32, 32)
0, 0, 10, 10, 20, 30, 50, 70
7.5 nm pre-Deposition
7.5pre-DTxx
2 (32, 32)
20, 50
15 nm pre-Deposition
15pre-DTxx
7 (32, 12, 12, 32, 32, 32, 32)
0, 10, 20, 30, 30, 50, 70
Diffusion barrier
barrierxx
3 (32, 32, 32)
0, 10, 20
Baseline
baselinexx
1 (32)
0
Table 2
Parameters φ
1
and φ
2
and their difference Δφ, which were extracted from the open-circuit voltage-temperature (V
OC
-T) graph in Fig. 8 at low temperatures and high temperatures respectively. Δφ is a measure for the bending of the VOC-T curves and a measure for the barrier at the rear contact φ
b
, if φ
1
corresponds to the band gap. Sample names are explained in Table 1.
Table 2
Sample name
ϕ
1
in V
ϕ
2
in V
Δϕ in V
Post-DT0
1.1
0.8
0.3
Post-DT10
1.1
1.0
0.1
7.5Pre-DT20
1.1
0.8
0.3
7.5Pre-DT50
1.1
0.8
0.4
15Pre-DT20
1.1
1.0
0.1
15Pre-DT50
1.1
0.9
0.1
Barrier0
0.7
0.6
0.1
Effect of different Na supply methods on thin Cu(In,Ga)Se2 solar cells with Al2O3 rear passivation layers
Dorothea
Ledinek
⁎
ledinekdorothea@yahoo.de
Olivier
Donzel-Gargand
Skold
Markus
Sköld
Jan
Keller
Marika
Edoff
Uppsala University, The Angström Laboratory, Department of Engineering Sciences, Postal Address: Box 534, 751 21 Uppsala, Sweden
Uppsala University, The Angström Laboratory, Department of Engineering Sciences
Postal Address: Box 534
Uppsala
751 21
Sweden
⁎
Corresponding author.
Abstract
In this work, rear-contact passivated Cu(In,Ga)Se2 (CIGS) solar cells were fabricated without any intentional contact openings between the CIGS and Mo layers. The investigated samples were either Na free or one of two Na supply methods was used, i) a NaF precursor on top of the Al2O3 rear passivation layer or ii) an in situ post-deposition treatment with NaF after co-evaporation of the CIGS layer. The thickness of the ALD-Al2O3 passivation layer was also varied in order to find an optimal combination of Na supply and passivation layer thickness. Our results from electrical characterization show remarkably different solar cell behavior for different Na supplies. For up to 1 nm thick Al2O3 layers an electronically good contact could be confirmed independently of Na deposition method and content. When the Al2O3 thickness exceeded 1 nm, the current was blocked on all samples except on the samples with the NaF precursor. On these samples the current was not blocked up to an Al2O3 layer thickness of about 6 nm, the maximum thickness we could achieve without the CIGS peeling off the Al2O3 layer. Transmission electron microscopy reveals a porous passivation layer for the samples with a NaF precursor. An analysis of the dependence of the open circuit voltage on temperature (JVT) indicates that a thicker NaF precursor layer lowers the height of the hole barrier at the rear contact for the passivated cells. This energy barrier is also lower for the passivated sample, compared to an unpassivated sample, when both samples have been post-deposition treated.
Highlights
•
Sufficient current transport through all < 2 nm thick unpatterned Al2O3 rear passivation layers.
•
For thicker Al2O3 layers sufficient current transport only if NaF precursor applied on Al2O3.
•
TEM analysis indicates a porous passivation layer for cells with a NaF precursor.
•
For post-deposition treated cells the Al2O3 layer reduces the hole barrier at the rear contact.
•
For cells with a NaF precursor this barrier is smaller for higher NaF concentrations.
Keywords
Alkali
Back contact
CIGS
Passivation
Thin films
Rear contact
Tunneling
1
Introduction
The record efficiency of Cu(In,Ga)Se2 (CIGS) solar cells has tremendously increased over the last years due to improvements in the bulk quality and the front contact interface [1]. Just as in Si solar cell technology, the thickness of the absorber layer is expected to decrease for commercial CIGS solar cells to save costs and materials. Thus, controlling the recombination and maximizing the light reflection at the CIGS/rear contact interface will be of increasing importance for the solar cell performance.
Inspired by PERC (Passivated Emitter Rear Contact) silicon solar cells, Vermang et al. [2,3] introduced an Al2O3 passivation layer between the CIGS absorber layer and the Mo rear contact. To ensure an electrical contact, different kinds of nano-contacts were developed: conducting Mo-nano-spheres embedded in the passivation layer [4] or nano-openings in the passivation layer [2,3]. Whereas thin (<15 nm) passivation layers mostly increase the open-circuit voltage (V
OC
) by lowering the recombination rate at the rear contact [2], both, thicker Al2O3 layers (30 nm) [3] and Mo nano-spheres [4], also increase the short-circuit current density (J
SC
) by increased reflection at the rear contact and/or by phonons between Mo nano-spheres that enhance absorption. The higher V
OC
has been explained by a field effect [5,6] (electrical passivation) due to negatively charged centers (VAl and/or Oi) in oxygen rich Al2O3 layers [7], which lowers the interface recombination rate at the passivated areas. The electrical passivation effect increases strongly from 5 to 50 nm passivation layer thickness. The interface defect density, however, is found to only be slightly reduced compared to an unpassivated area [7].
The rear contact has been associated with a kink and roll-over in current-voltage (JV) curves of CIGS solar cells measured especially at low temperatures [8–17]. The kink has been explained by a hole extraction barrier [10], whereas the roll-over has been explained by a hole injection barrier [8,10,12]. Some studies identified the valence band off-set between CIGS and MoSe2, that is usually formed between the CIGS and Mo [10,17], as the hole injection barrier. Even a cross-over between the dark and light curve can be explained by a barrier at the rear contact as exemplified for CdTe solar cells [11,18]. However, in the case of CIGS solar cells a conduction band offset between the CIGS and CdS [8] or an acceptor rich layer [10] in the CIGS near the front interface can also explain a kink and cross-over in the JV curve.
The rear contact region is strongly affected by the presence of Na. Whereas the soda-lime glass substrate can act as a source of Na during the CIGS co-evaporation, Na can also be added in a thin NaF precursor layer onto the rear contact before CIGS evaporation (pre-deposition treatment, pre-DT) [19] or by evaporating NaF on top of the CIGS layer during an annealing step after its deposition (post-deposition treatment, post-DT) [9]. While there is a general agreement, that Na application or Na diffusion from the soda-lime glass enhances the electrical properties of the rear contact, the exact mechanism is unclear. For example, a roll-over measured on Na-free devices at room temperature can be reduced by a Na pre-DT [10,19]. Pre-deposited Na [19] or Na from the soda-lime glass [20,21] acts as a catalyst and promotes the formation of MoSe2, which in turn creates an ohmic contact according to references [17,20,21]. In contrast, Yoon et al. [22] doubt that the MoSe2 layer is the origin of the ohmic nature of the rear contact and suggest that Na reduces the barrier at the CIGS/MoSe2 interface as it increases the (effective) doping of the CIGS or the MoSe2 layer. Jarzembowski et. al [23] found that the rear interface recombination rate for samples with an alkali diffusion barrier is lowered by NaF post-DT. They concluded that Na passivates either the MoSe2/CIGS interface or the MoSe2/Mo interface.
In their first work on CIGS rear surface passivation, Vermang et al. [3] observed that the JV curves of solar cells with a 5 nm Al2O3 passivation layer with point contact openings and without adding NaF, exhibited a kink and a roll-over. Insufficient Na from the soda-lime glass was suspected and a NaF precursor layer was successfully applied on the Al2O3 layer before CIGS evaporation. The passivation layer without openings inhibited the electrical contact for the samples without the NaF treatment. This is in agreement with measurements on Al2O3 on Mo with an Hg probe [24]. The sheet resistance as measured with the Hg probe was shown to be negligible for a passivation layer thinner than 3 nm. While direct tunneling dominates for low voltages and thin Al2O3 layers (<3 nm), Fowler-Nordheim tunneling dominates at voltages that are only reached at the rear contact for high forward biases much larger than V
OC
and thicker Al2O3 layers. Vermang et al. [3] did not provide any JV curves for samples without nano-contacts but with NaF pre-deposition.
In this work, a series of passivated and unpassivated CIGS solar cells was produced. In order to evaluate if thin unpatterned passivation layers can provide a sufficiently strong passivation effect without blocking the current, no point contacts were etched into the passivation layers. Considering the significance of Na outlined above, the Na supply method and the Na concentration were varied in four ways (compare
Fig. 1): i) NaF post-DT, ii) NaF pre-DT, iii) Na supply inhibited by a alkaline diffusion barrier and neither NaF pre-DT nor post-DT and iv) Na supply exclusively from the soda-lime glass substrate (labeled as “baseline”). The passivation layer thickness was varied to optimize it for the different Na supply methods. Current-voltage (JV) measurements at a wide range of temperatures were used to further characterize the rear contact for some combinations of passivation layer thickness and Na supply method.
2
Sample processing and characterization
An overview over the whole matrix of samples produced and sample names can be found in
Table 1 and the different sample types are further illustrated in Fig. 1. Generally, the samples were produced according to our group's baseline process [25]. The cell area was scribed mechanically to an area of 0.5 cm2 and every sample consists of 32 individual cells, except for two samples with 12 cells. In contrast to the baseline process described in reference [25] the co-evaporated CIGS layers were grown with constant evaporation rates, resulting in a flat [Ga]/([Ga]+[In]) ratio throughout the film, i.e. without a built-in electron barrier at the rear of the absorber layer. The Al2O3 diffusion barriers, Al2O3 passivation layers and NaF post- or pre-DT were added to the baseline process in the following way: For samples with a diffusion barrier, 300 cycles Al2O3 were deposited directly on the cleaned glass by atomic layer deposition at 300 °C using H2O and trimethylaluminium (TMA) as precursors and nitrogen as a purge gas. For all passivated samples Al2O3 was deposited on top of the Mo by the same ALD process. The thickness of the Al2O3 layer was determined for 10, 20, 30, 50, 70 and 300 cycles by spectroscopic ellipsometry with a Woollam VASE instrument. The wavelength was swept between 260 and 1700 nm and the angle of incidence was 60, 65 and 70 degrees. A linear regression gave a layer thickness of 0.9 Å per ALD cycle. 7.5 or 15 nm NaF precursor layers (thickness measured by a quartz crystal rate monitor calibrated by measurements with a Dektak 150 stylus profilometer) were evaporated onto the pre-DT samples prior to the CIGS deposition.
To obtain the desired CIGS composition, the Se source was temperature controlled and the other metal sources were controlled by a quadrupole mass spectrometer set to constant evaporation rates. The samples were mounted in a holder heated from behind by IR lamps. The sample holder temperature was raised during the first 100 s from room temperature to 410 °C and stayed there for 1500 s, while the shutter was still closed and the sources were heated up to reach the pre-defined rates. During the first 125 s after the shutter opened, the substrate temperature stayed at 410 °C and during the following 125 s the temperature was linearly raised to 530 °C. Then the temperature was kept constant until the end of the evaporation after 450 more seconds. This last evaporation phase was shortened or prolonged to vary the thickness of the evaporated layer. 450 s gave a nominal CIGS layer thickness of 1.0 µm. The samples that did not undergo a post-DT cooled down to below 60 °C before venting the chamber with nitrogen and proceeding with the deposition of the CdS buffer layer by chemical bath deposition (CBD). For the post-DT absorbers, the samples cooled down to 490 °C. Then, NaF was evaporated onto the CIGS and the temperature was maintained constant for 400 s. Selenium was provided in excess even during the NaF evaporation phase. Subsequently, these samples also cooled down to below 60 °C before venting and CdS deposition.
The average thicknesses, CGI [Cu]/([In]+[Ga]) and the GGI [Ga]/([In]+[Ga]) were determined by XRF measurements that had been calibrated by a standard sample with known composition and mechanical profilometer measurements. In each run, test pieces for XRF measurements were placed on either side of the samples, which were located in the middle of the substrate holder. Therefore the actual composition values for all samples lie within the span of CGI = 0.80–0.92 and GGI = 0.13–0.18. The absorber thickness was determined to 0.95 ± 0.03 µm. The CIGS absorber peeled off from Al2O3 layers deposited by > 70 ALD cycles.
The JV curves were measured in the dark and under illumination by a halogen lamp using a four-point probe setup. The light intensity was calibrated with a Si solar cell to obtain a photon flux corresponding to 1000 W/m2 at AM 1.5. The temperature during the measurements was set to 300 K by a temperature stage cooled by a Peltier element. For the samples with 32 cells the average JV parameters of the eight cells with the highest efficiencies was calculated. For the two samples with 12 cells, the average JV parameters of the three best cells were used. If more than one sample was produced for a cell stack, average JV parameters for the samples and globally averaged JV parameters for the cell stack were calculated. As the sample averages did not differ substantially, only the global averages will be shown. External quantum efficiencies (EQE) were measured on the four best cells per sample under ambient light. The EQE was used to determine an approximate band gap of the absorber, to ensure that differences in V
OC
and J
SC
do not stem from changes in the absorber composition. EQE
2 was plotted against the photon energy E and the curve linearly fitted for the low E part. The intercept of the fitted line with the E-axis gives the approximate band gap energy E
G
. The calculated band gaps for all samples lie between 1.04 and 1.07 eV meaning that differences in the V
OC
larger than 30 meV cannot be explained by differences in the band gap.
Temperature dependent JV measurements were performed in a home-built cryostat on one cell on selected samples. The photon flux from a white light emitting diode (LED) was calibrated at 300 K to result in 100%, 10% and 1% of the J
SC
that was previously measured with the JV set-up at 300 K. The stage temperature varied between 150 and 330 K with temperature steps of 10 K. Additionally, capacitance-voltage (CV) curves were measured for four cells per sample and the net acceptor concentration (N
A
) was calculated from CV curves by applying the depletion approximation [26].
Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS) data acquisition were performed using a Tecnai F30ST (FEI) with a Tridiem post filter (863, Gatan) and was operated at 300 kV accelerating voltage. The subsequent data analysis was done through DigitalMicrograph (GMS 2.32, Gatan). The TEM lamellae were prepared with the help of a Focused Ion Beam (FIB) Strata DB235 (FEI) by the in-situ lift-out technique [27]. To perform the final polishing step the Ga-based ion beam was set to 5 kV and 50 pA for the accelerating voltage and the beam current, respectively.
3
Theory - Hole barrier height at the rear contact and JVT measurements
Assuming that a barrier at the rear contact is responsible for the roll-over of JV curves mentioned in the introduction, these curves have been modelled by 1) a secondary (photo)diode in series with the main junction [11,12,16–18,28–30], if the two junctions do not interact, or 2) a phototransistor behavior [13,15], if the two junctions interact (see
Fig. 2). In model 1 and 2, the voltage over the complete solar cell is split into the voltage over the primary photodiode and over the secondary diode, so that the primary diode is forward biased and the secondary diode is reverse biased for voltages higher than V
OC
over the complete solar cell. The secondary diode's saturation current J
0b
is determined by a pre-factor J
00b
and a Boltzmann factor e
−φ
b
/ kT
, with φ
b
being the height of a barrier for holes at the rear contact, i.e. the energy difference between the Fermi level in the CIGS and the valence band at the CIGS-rear contact interface. For sufficiently small φ
b
the reverse biased secondary diode does not limit the current and V
OC
at room temperature. For optically thin solar cells or solar cells with a long minority carrier diffusion length, a secondary photocurrent is additionally generated [31]. If a shunt conductance is added in parallel to the (photo)diode in model 1 [11,29], four current components can flow over the reversely-biased rear contact: the diode's saturation current, a break-down current for reverse biases over the secondary diode higher than its break-down voltage, the secondary photocurrent and the current over the secondary shunt. J
0b
and the photocurrent determine the JV point above V
OC
, where the JV curve becomes current limited, and the slope of the roll-over curve is determined by the value of the shunt conductance. If the shunt conductance at the rear contact equals or is larger than the lumped series resistance of the device, the slope of the roll-over matches the slope of the JV curve between the voltage at the maximum power point and V
OC
and the roll-over disappears regardless of φ
b
[11]. The break-down of a reverse biased secondary diode increases the slope of the JV curves at high voltages drastically. φ
b
may be quantified by JVT measurements, either by extracting J
0b
for model 1 for optically thick solar cells [16,17,30] or from V
OC
-T graphs for model 2 [13] and - as shown in the appendix- even for model 1 for optically thin solar cells. For model 1 the relationship between V
OC
and T is linear for both low and high temperatures, but with different parameters. For low temperatures
V
OC
≈
E
a
q
+
A
m
kT
q
ln
(
J
lm
J
00
m
)
with the activation energy for the dominant recombination process E
a
, the ideality factor for the main diode A
m
, the light current generated at the main junction J
lm
and the temperature dependent pre-factor of the saturation current of the main diode J
00 m
. For the low temperature region this equation becomes
V
OC
≈
E
a
−
φ
b
q
+
kT
q
ln
(
(
J
lm
J
00
m
)
A
m
(
J
00
b
J
lb
−
G
b
∙
V
OCb
)
A
b
)
with the temperature independent pre-factor of the saturation current J
00b
, the ideality factor of the rear contact junction A
b
, the light current generated at the rear contact J
lb
and the current through the shunt at the rear junction J
shb
= G
b
V
OCb
. φ
b
is thus the difference between the extrapolated VOCs at 0 K.
4
Results
4.1
JV and EQE measurement
Fig. 3 summarizes the average photovoltaic parameters extracted from the JV measurements and illustrates the trends for increasing Al2O3 thickness. For the post-DT samples and the barrier samples the passivation layer does not have a beneficial effect on the efficiency and it even has a detrimental effect for those samples with more than 10 ALD cycles. Whereas the J
SC
increased for the post-DT10 and barrier10 samples compared to the corresponding samples without passivation, the V
OC
is reduced for all passivation layer thicknesses. Passivation layers deposited by more than 10 ALD cycles block the current increasingly and the fill factor (FF) deteriorates due to a kink in the JV curve. By contrast, no current blocking occurs when a NaF precursor layer is deposited on top of the Al2O3 layer prior to the CIGS deposition. This is valid for both the 7.5pre-DT and 15pre-DT samples. These results clearly indicate that the rear contact properties of the passivated samples are essentially affected by the Na supply method. We will explore possible mechanisms in the discussion section, but first we present the JV and EQE data in more detail.
The following paragraphs illustrate the results of the JV and EQE measurement of a representative cell for selected constellations. For the post-DT samples (see Fig. 3 and
Fig. 4), the cells with a Al2O3 layer have lower or equal efficiencies compared to the unpassivated samples. Here, a 10 cycle passivation layer leads to a 0.8 mA/cm2 higher J
SC
, but also to a reduced FF and V
OC
as compared to the unpassivated case. The gain in J
SC stems from a higher EQE for medium and long wavelengths. The JV curve of the post-DT20 sample has a kink and all parameters are severely deteriorated. The JV curves of the samples with even thicker passivation layers block the photocurrent even more.
For the 15preDT samples the V
OC
and the FF are roughly independent of the passivation layer thickness (see Fig. 3). The unpassivated sample in
Fig. 5 has a higher EQE between 500 and 750 nm compared to all passivated 15pre-DT samples, resulting in a high J
SC
. For those samples, there is a clear trend towards higher EQEs in the long wave length region for thicker passivation layers. Therefore, the J
SC
of the 15pre-DT10 sample is lowest compared to all other 15pre-DT samples and it increases monotonously with passivation layer thickness, so that the 15pre-DT70 sample delivers even a slightly higher J
SC
than the unpassivated 15preDT0 sample. The efficiency follows the trend of the J
SC
, with a drop from the 15Pre-DT0 to the 15-PreDT10 sample, and an increase in efficiency for thicker passivation layers. However, none of the passivated samples is more efficient than the unpassivated one. Even for the 7.5preDT samples (not presented in a figure) the EQE in the long wavelength region is higher for the 7.5preDT50 sample compared to the 7.5preDT20 sample. When re-measuring the JV curves at 300 K during the JVT measurement sweep, the 7.5Pre-DT50 sample had degraded during 44 days of storage at room temperature and in air. The V
OC
at 300 K was ~50 meV lower than previously measured and the JV curve has a kink and roll-over.
The barrier samples with passivation layer block the current similarly as the post-DT samples (Fig. 3 and
Fig. 6). The major difference from the post-DT samples is an expected lower V
OC
for all samples due to a lack of Na (see for example [32] and references therein). The EQE of the barrier20 sample is lowered independently of the wavelength, which indicated the presence of a barrier for the photocurrent. The photocurrent is also lowered in the corresponding JV curve.
4.2
CV measurements
In order to separate the effects of sodium induced changes in the doping concentration from the passivation effect on the JV and EQE, CV measurements were conducted. The average doping concentration of various samples can be found in
Fig. 7. As expected, the barrier samples have the lowest net acceptor concentration (~ 1015 cm−3). The baseline sample and the 7.5pre-DT samples have similar doping densities (1016 −1017 cm−3). The highest acceptor concentration is measured on the 15preDT and the post-DT samples.
4.3
JVT measurements
As mentioned in the introduction, the data from JVT measurements can help to illuminate the physics at the rear contact. First, we examine which model we can use, then we describe the bending of the V
OC
-T curves (
Fig. 8) of different samples qualitatively and finally we quantify the differences in bending with the help of a parameter Δφ, which is also a measure of φ
b
(see the Supplementary information in the Appendix).
For 100% photon flux and regardless of the measurement temperature, none of the JV curves has any roll-over, with exception of the post-DT sample's JV curve which has a slight roll-over at low temperatures. As J
ob
depends exponentially on the temperature (see theory section and appendix), it is negligibly small at low temperatures and G
b
must be large to explain the lack of a roll-over. Apart from the degraded 7.5pre-DT50 sample, no kinks are visible in the JV curves at 100% photon flux. The V
OC
we measured for small light fluxes is always lower than the V
OC
for larger light fluxes at the same temperature – in agreement with the super-position principle [26] and the calculations for model 1 presented in the theory section but in disagreement with the phototransistor model (model 2) as presented in [13] and discussed in the appendix. Therefore model 2 can be excluded and model 1 from the theory section and the appendix will be used.
In Fig. 8 the V
OC
for the samples is plotted over the temperature. Two categories of samples can be discerned concerning the bending of the JV curve: The JV curves of the unpassivated post-DT sample, the barrier sample and the two 15pre-DT samples bend only slightly towards lower V
OC
for decreasing temperatures. Contrary, the JV curves of the post-DT10 and the 7.5pre-DT samples bend strongly towards a much lower V
OC
at decreasing temperatures.
To extract a measure for this difference in the graphs’ curvature, the V
OC
-T graphs were fitted by one linear fit through the four data points at the highest temperatures (300–330 K) and one linear fit through the four data points at the lowest measurement temperatures (150 – 180 K) (see Fig. 8). For both linear fits the V
OC at T = 0 K was extrapolated, giving a value φ
1
for the high temperature fit and φ
2
for the low temperature fit. φ
1,
φ
2
and the difference Δφ are summarized in
Table 2.
Except for the barrier sample, φ
1
lies between 1.07 and 1.14 V for all samples and is somewhat higher than the band gap extracted from EQE measurements of 1.06 eV and thus Δφ is a measure for φ
b
. If the conditions J
0b
> >J
lb
and J
0b
> > G
b
V
OCb,
(compare appendix) were not fulfilled at high temperatures, φ
1
would extrapolate to a lower value than the band gap. φ
1
is neither impacted by the Na supply method nor the existence or the thickness of a passivation layer. For the barrier sample φ
1
is only 0.66 eV. Without a deeper analysis of the temperature dependence of the (main) diode's ideality factor, we can conclude that the recombination for the sample with a diffusion barrier takes place at the front contact interface and differs from the rest of the samples [33]. For this sample Δφ ‡ φ
b
.
The TEM results from the 7.5pre-DT70 and post-DT50 sample are presented
Fig. 9. For the sample 7.5pre-DT70, the presence of the oxide layer can be seen in the Bright Field (BF) image (Fig. 9A) and also in the consecutive RGB and RB reconstructed images (Red=In / Green=O / Blue=Mo). From the RGB image we note discontinuities in the O signal, and from the RB image a smooth transition from Mo to In with no clear gap in between. The line profiles integrated over a weak O area show a low amount of O at the interface, but also no obvious separation between the Cu/In/Ga and the Mo interfaces. We also note an accumulation of Ga correlating with the presence of O. If the line profile is integrated over a non-deteriorated area (i.e. where O signal is manifest), the result is fairly comparable to the profiles shown to the right for the post-DT50 sample. Using EELS maps acquired at higher energy-loss (not shown here) we measured an Al signal correlated with the oxygen location.
For the post-DT50 sample the oxide layer is also visible in the BF and the RGB images in Fig. 9 B. The RB image reveals in this case a clear gap separating the In from the Mo, and the integrated line profiles at the bottom of the same figure show clear signals from O and Ga filling the gap between the Mo back contact and the CIGS absorber layer.
5
Discussion
5.1
JV measurements and TEM
All distorted JV curves measured at 300 K have both a roll-over and a kink (see Fig. 4 and Fig. 6 and the introduction). Generally, a kink in JV curves indicates that hole extraction from the CIGS layer into the rear contact is hindered [10]. A high differential resistance (roll-over) for voltages above V
OC
indicates that hole injection from the contact into the CIGS layer is reduced [8,10,12]. As all samples of the same type have been fabricated during a short period of time with identical process recipes (and in most cases even in the same run batch) and vary only concerning the presence and thickness of the passivation layer, these distortions in the JV curve stem probably only from this variation. Therefore, we conclude that hole injection and hole extraction are impeded by the energy barrier of the Al2O3.
The observation that the current is blocked by Al2O3 layers deposited by more than 20 ALD cycles (~1.8 nm) agrees well with previously measured JV curves for a Mo-Al2O3 stack [24], for CIGS solar cells with an Al2O3 passivation layer at the front contact [34] and CIGS solar cells with a passivation layer at the rear contact without extra Na supply [3]. Vermang et al. [3] measured similarly blocking JV curves on their samples, which were passivated with a < 5 nm thick Al2O3 passivation layer from the same ALD process without contact openings and were produced on soda-lime glass and without extra Na supply. They concluded that their measured JV curves disprove a sufficient contact through the passivation layer and indicate that the passivation layer is intact. For samples with a front contact passivation a thickness of about 1 nm was found to be the maximum thickness that still allows for high tunneling currents and negligible transport losses [34]. The series resistance increased significantly for 1.7 nm thick passivation layers compared to a reference sample. For a 2.2 nm thick passivation layer a kink and roll-over was measured in the light JV curve. In agreement with these references, we conclude that the passivation layer for the post-deposition samples are completely covering after CIGS processing for more than 20 ALD cycles, i.e. 1.8 nm.
The current flow through passivation layers deposited by up to 20 ALD cycles can be either explained by a hole tunneling current through the passivation layer as in [34] or by a hole current directly from the CIGS into the Mo (possibly through MoSe2), if the Al2O3 layer does not completely cover the Mo layer. We will use the data from the JVT measurements to get further insight into this question.
As the JV curves of pre-DT samples are not visibly distorted by the Al2O3 layer for at least up to 70 ALD cycles (see Fig. 5), the hypothesis that intentionally patterned Al2O3 passivation layers conduct current only via the nano-point contacts needs to be reconsidered. Especially, Al2O3 passivation layers, that were deposited by the same ALD process to similar thicknesses, intentionally patterned either by nano-particles [2,3] or electron-beam lithography [4] and had a NaF precursor applied onto them before the CIGS evaporation, probably do not conduct current only through the intentional contacts. On the other hand, post-DT solar cells with 27 nm thick Al2O3 passivation layers that were patterned by electron-beam lithography with a similar pitch and contact area have been shown to be sufficiently conductive [31].
The substantial difference in rear contact conductivity for different Na supply methods raises the question about how these methods modify the rear contact region. We propose two hypotheses on how the NaF precursor alters the conductivity through the Al2O3 layer: 1) It opens up holes in the Al2O3 and a MoSe2 layer is formed between the Mo and CIGS layer, so that the current transport occurs from the CIGS to the Mo via the MoSe2 layer. 2) It changes the Al2O3 chemically and thus its electrical properties.
In [35] X-ray photospectrocoscopy (XPS) was used to confirm hypothesis 1. MoSe2 is formed in the holes of a locally non-covering passivation layer, whereas no MoSe2 is formed on a closed passivation layer. Thus, dedecting MoSe2 would indicate that the passivation layer is not closed. XPS could however not confirm the existence of MoSe2 on samples with a NaF precursor layer on a Mo-coated glass substrate with an Al2O3 layer, which were annealed in a Se atmosphere and vacuum as a reference. This result neither excludes nor confirms hypothesis 1. A possibility to verify hypothesis 2 is to prove the existence of other Al-compounds than Al2O3 at the rear contact. However, when comparing annealed glass-Mo-Al2O3 stacks with and without a NaF precursor on top, the existence of an additional chemical shift in the Al signal for the samples with NaF could not be verified. Especially, AlF3 signals could not be distinguished from the Al signals. This result neither confirms nor contradicts hypothesis 2.
From the TEM analysis, we confirm a conformal Al2O3 layer growth but we also identified a fair amount of Ga incorporated into this oxide layer, apparently as GaO. When the NaF was introduced as a precursor layer, the passivation layer deteriorates leading to direct contact between the CIGS absorber layer and the Mo back contact, as reflected by the line profiles in Fig. 9. In such locations we consistently observe a more gradual drop in Mo signal intensity that can indicate the underlying formation of MoSe2. The use of a NaF-PDT preventing the direct contact between the NaF and the Al2O3 seems to preserve the oxide layer integrity, but does not prevent the formation of GaO. Therefore, and despite the substantial 6.3 nm Al2O3 layer, a direct contact between the CIGS and the Mo seems to occur for the 7.5pre-DT70 sample, but not for the post-DT50 one.
5.2
EQE measurements
In Figs. 4 and 5, EQE at long wavelengths increases for thicker Al2O3 layers. Four effects can be responsible for these differences: doping effects, differences in minority carrier diffusion length, optical effects or passivation effects. For photons with long wavelengths free electrons are created closer to the rear contact. Thus, the collection probability for these free electrons is sensitive to the recombination at the rear contact and a short diffusion length. If the acceptor concentration is low, the space charge region reaches further back into the CIGS layer and the influence of the rear contact recombination and short diffusion length on the collection probability is counteracted by the electrical field in the space charge region. This mechanism explains the difference between the very high EQEs for long wavelengths for the samples with a diffusion barrier, which have lower acceptor concentrations according to the CV measurements, and the low EQEs for long wavelengths 15pre-DT samples, which have a higher acceptor concentration. Therefore, the EQEs should be only compared for samples with similar apparent doping from Fig. 7.
Optical effects leading to differences in the EQE may stem from a higher reflectance at passivated rear contacts [4,31] compared to the unpassivated ones. In that case higher reflection at the rear contact enhances especially the absorption of photons with long wavelengths, as photons with short wavelengths have a high absorption coefficient and are mostly already absorbed before they reach the rear contact. But despite that the rear reflectance increases with increasing Al2O3 thickness, earlier SCAPS and optical simulations [4,31] and electrical modelling [31] comparing unpassivated reference samples with samples coated with a 300 cycle Al2O3 layer (4 times the thickness used in this study) show that the higher EQE for passivated samples can only partially (< 10%) be explained by the higher reflection at the passivated contact. Thus, within a sample type (compare Fig. 1 and Table 1) differences in the EQE stem most probably from a passivation effects leading to reduced back contact recombination.
5.3
JVT measurements
For the post-DT samples, a 10 cycle passivation layer lowers Δφ by 0.2 eV compared to the (unpassivated) post-DT0 sample. If we assume that the Al2O3 layer is completely covering for post-DT samples, the hole current needs to tunnel through the Al2O3 layer and pass the rear interface region of the CIGS absorber where the electrical field effect stemming from the negative charges in the passivation layer [7] reduces the band bending and thus φ
b
. As long as the passivation layer is so thin, that the holes can tunnel through it, the energy off-set at the passivation layer is not visible in the JVT measurements, but the reduced band bending due to the negative oxide charge in the Al2O3 is. On the other hand, if sufficiently large conducting holes existed in the passivation layer, the hole current would not be affected by the electrical field. We can thus conclude that the passivation layer on post-DT samples probably completely covers the rear contact and that the current probably tunnels through the layer.
If we assume that there are holes in the Al2O3 layer for the pre-DT samples (hypothesis1), the measured Δφ is an estimate of φ
b
at the CIGS-MoSe2 interface. If the holes were large enough, the band bending at the CIGS-MoSe2 interface would not be affected by the field effect and φ
b
would not depend on the thickness of a passivation layer. Indeed, our results do not show any correlation between Δφ and the passivation layer thickness. Contact resistance, φ
b
and the likelihood for a roll-over in a temperature range between 100 and 300 K decreases for higher Na concentrations at CIGS-MoSe2 interfaces according to the literature [19,22]. Δφ is indeed 0.2 eV lower for the 15preDT20 and the 15preDT50 sample compared to the 7.5PreDT20 (and 0.3 eV lower compared to the 7.5PreDT50 sample, which had however - as mentioned in the results section –degraded). In summary, our results do not contradict hypothesis 1.
The current blocking for the post-DT samples with more than 2 nm thick Al2O3 layers, indicate that the direct tunneling of holes can be excluded for these Al2O3 layers and that the energy barrier associated with the Al2O3 layer is too large to be overcome. According to hypothesis 2 then, Na or F doping lowers this barrier. For example, it has been shown that oxygen vacancies VO in AlOx can form a defect band close to the band gap, which acts as a “conduction band” [36]. Doping can also introduce traps that increase the likelihood for Frenkel-Poole emission, which is a conduction-limited and trap-assisted carrier transport mechanism [37]. However, the JVT measurements probe the largest energy barrier in the valence band at the rear contact, and cannot per-se distinguish the energy barrier associated with the Al2O3 layer from the one associated with the band bending in the CIGS. If Na or F doping reduces the former below the latter, the latter will be detected and changes in barrier height will be changes in band bending. Yoon et al. [22] proposed that Na directly reduces the barrier height at the CIGS-MoSe2 interface by increasing the carrier concentration in the CIGS or MoSe2, and not indirectly by enhancing the formation of MoSe2. Even this effect can explain our results. Thus, the JVT measurement, cannot distinguish between the two hypotheses, conduction through holes in the passivation layer or conduction due to a change of the electrical properties of the passivation layer.
6
Conclusion
For NaF post-DT samples and samples with an alkaline diffusion barrier between the glass and the Mo film, a good contact between the CIGS and the Mo layer – probably a tunneling contact - can be established for very thin Al2O3 passivation layers of about1 nm. Although these thin layers increase the J
SC
, they do not increase the solar cell efficiency either due to a lower FF and/or due to a lower V
OC
. The 1 nm thick passivation layer decreases the energy barrier for holes at the rear contact compared to the unpassivated case, probably as a negative oxide charge reduces the band bending in the CIGS. For even thicker Al2O3 layers, the current is blocked and therefore the efficiency is not enhanced for any passivation layer thickness. In contrast, for samples with NaF pre-deposition treatment and up to about 6.3 nm (70 cycles) thick Al2O3 layers, the NaF precursor increases the conductivity through the passivation layer so that the current is not blocked. Although the efficiency of these passivated solar cells does not exceed the efficiency of the unpassivated reference, an increase in the EQE in long wave region for thicker Al2O3 layers probably indicates a passivation effect. The TEM analysis of a sample that was pre-deposition treated with NaF reveals a passivation layer degradation leading to a direct contact between the CIGS absorber layer and the Mo back contact and maybe a subsequent formation of MoSe2. For pre-deposition treated samples, an analysis of the dependence of the open circuit voltage on temperature indicates that a thicker NaF precursor layer lowers the height of the hole barrier at the rear contact. In conclusion, using thin Al2O3 layers and a NaF pre-deposition treatment may be a cost-effective way of creating nano-openings in a rear-contact passivation layer without the need of patterning the passivation layer for contacting in an extra fabrication step.
Acknowledgements
The authors thank Carl Hägglund for determining the thickness of the Al2O3 layers by ellipsometry measurements.
Funding sources
This work was supported by the Swedish Science Council via grant 43523-1 and StandUp for Energy as well as the EU-funded project ARCIGS-M.
Conflict of interest
The authors declare that there is no conflict of interest regarding the publication of this article.
Appendix A
Supplementary material
The method of extracting the hole barrier height at the rear contact from JVT measurements is explained and derived in the online version at doi:10.1016/j.solmat.2018.07.017. Even assumptions and limitations of the method are outlined there.
Appendix A
Supplementary material
Supplementary material
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The Authors
Effect of different Na supply methods on thin Cu(In,Ga)Se2 solar cells with Al2O3 rear passivation layers
Dorothea
Ledinek
⁎
ledinekdorothea@yahoo.de
Olivier
Donzel-Gargand
Skold
Markus
Sköld
Jan
Keller
Marika
Edoff
Uppsala University, The Angström Laboratory, Department of Engineering Sciences, Postal Address: Box 534, 751 21 Uppsala, Sweden
Uppsala University, The Angström Laboratory, Department of Engineering Sciences
Postal Address: Box 534
Uppsala
751 21
Sweden
⁎
Corresponding author.
Abstract
In this work, rear-contact passivated Cu(In,Ga)Se2 (CIGS) solar cells were fabricated without any intentional contact openings between the CIGS and Mo layers. The investigated samples were either Na free or one of two Na supply methods was used, i) a NaF precursor on top of the Al2O3 rear passivation layer or ii) an in situ post-deposition treatment with NaF after co-evaporation of the CIGS layer. The thickness of the ALD-Al2O3 passivation layer was also varied in order to find an optimal combination of Na supply and passivation layer thickness. Our results from electrical characterization show remarkably different solar cell behavior for different Na supplies. For up to 1 nm thick Al2O3 layers an electronically good contact could be confirmed independently of Na deposition method and content. When the Al2O3 thickness exceeded 1 nm, the current was blocked on all samples except on the samples with the NaF precursor. On these samples the current was not blocked up to an Al2O3 layer thickness of about 6 nm, the maximum thickness we could achieve without the CIGS peeling off the Al2O3 layer. Transmission electron microscopy reveals a porous passivation layer for the samples with a NaF precursor. An analysis of the dependence of the open circuit voltage on temperature (JVT) indicates that a thicker NaF precursor layer lowers the height of the hole barrier at the rear contact for the passivated cells. This energy barrier is also lower for the passivated sample, compared to an unpassivated sample, when both samples have been post-deposition treated.
Highlights
•
Sufficient current transport through all < 2 nm thick unpatterned Al2O3 rear passivation layers.
•
For thicker Al2O3 layers sufficient current transport only if NaF precursor applied on Al2O3.
•
TEM analysis indicates a porous passivation layer for cells with a NaF precursor.
•
For post-deposition treated cells the Al2O3 layer reduces the hole barrier at the rear contact.
•
For cells with a NaF precursor this barrier is smaller for higher NaF concentrations.
Keywords
Alkali
Back contact
CIGS
Passivation
Thin films
Rear contact
Tunneling
KBJ00000000013892
2020-11-05T18:42:19
S300.6
S300
S0927-0248(18)30379-9
10.1016/j.solmat.2018.07.017
SOLMAT
0927-0248
9544
FLA
NON-CRC
UNLIMITED
NONE
2018-08-08T10:36:18Z
09270248/v187sC/S0927024818303799/main.xml
120973
MAIN
JA 5.5.0 ARTICLE
FULL-TEXT
09270248/v187sC/S0927024818303799/main.assets/gr1.jpg
70171
IMAGE-DOWNSAMPLED
09270248/v187sC/S0927024818303799/main.assets/gr2.jpg
14258
IMAGE-DOWNSAMPLED
09270248/v187sC/S0927024818303799/main.assets/gr3.jpg
72253
IMAGE-DOWNSAMPLED
09270248/v187sC/S0927024818303799/main.assets/gr4.jpg
38259
IMAGE-DOWNSAMPLED
09270248/v187sC/S0927024818303799/main.assets/gr5.jpg
34270
IMAGE-DOWNSAMPLED
09270248/v187sC/S0927024818303799/main.assets/gr6.jpg
34570
IMAGE-DOWNSAMPLED
09270248/v187sC/S0927024818303799/main.assets/gr7.jpg
13788
IMAGE-DOWNSAMPLED
09270248/v187sC/S0927024818303799/main.assets/gr8.jpg
39163
IMAGE-DOWNSAMPLED
09270248/v187sC/S0927024818303799/main.assets/gr9.jpg
165822
IMAGE-DOWNSAMPLED
09270248/v187sC/S0927024818303799/main.assets/gr1.sml
6677
IMAGE-THUMBNAIL
09270248/v187sC/S0927024818303799/main.assets/gr2.sml
7418
IMAGE-THUMBNAIL
09270248/v187sC/S0927024818303799/main.assets/gr3.sml
7867
IMAGE-THUMBNAIL
09270248/v187sC/S0927024818303799/main.assets/gr4.sml
5667
IMAGE-THUMBNAIL
09270248/v187sC/S0927024818303799/main.assets/gr5.sml
5232
IMAGE-THUMBNAIL
09270248/v187sC/S0927024818303799/main.assets/gr6.sml
4696
IMAGE-THUMBNAIL
09270248/v187sC/S0927024818303799/main.assets/gr7.sml
5847
IMAGE-THUMBNAIL
09270248/v187sC/S0927024818303799/main.assets/gr8.sml
5970
IMAGE-THUMBNAIL
09270248/v187sC/S0927024818303799/main.assets/gr9.sml
15201
IMAGE-THUMBNAIL
09270248/v187sC/S0927024818303799/main.assets/mmc1.docx
21605
APPLICATION
09270248/v187sC/S0927024818303799/main.pdf
2133771
MAIN
1.7 6.5
DISTILLED OPTIMIZED BOOKMARKED
09270248/v187sC/S0927024818303799/main.raw
55369
S0927-0248(18)X0012-9
SOLMAT
0927-0248
187
C
20181201
1
282
S0927-0248(18)30379-9
10.1016/j.solmat.2018.07.017
160
169
main.pdf
PDF
1.7
local
1604914508032
collectiebehoudsniveau 1
2020-11-09T09:53:15.990+01:00
local
1604914508544
0
SHA-512
944bbbed89ce8e1de6728c76cb6128a34d0dbf9d6dd1ce7bfcd8e3bcdb3308dfa97a2a9dd21e297f6e1dd872a4a4356cc3f2710e97a6d63a1cdfcc1cf26fcfcf
java.security.MessageDigest
2133771
Adobe Acrobat Document
1.7
DIAS
62
DIAS tentative identification
main.pdf
local
1604914508545
0
SHA-512
98d3208a014f62dd12713a0d50e05228f77943f5afe538303753fbbccb34da1826ff5a973d210dba07ef9909f6e544f3c6f0b60f1583a11f8a339c55d0ac76cc
java.security.MessageDigest
55369
not checked
main.raw
local
1604914508546
0
SHA-512
26bacaef2acea570f5a6d7f4334cd6bb9e65db420389b4cada0c3b6e8ce383ff746eb4885fed40dd6ff8fe1f0a7a3efdc52e5a31acfe26314a5da7be6a0b0340
java.security.MessageDigest
120973
not checked
main.xml
local
1604914508547
0
SHA-512
e710e0cbe10f4da4627a05203089eaa70a6b0f530173982ccc8d4e6e1e3d0e88d8613419a0e2f711ee653d9978c6a7787692e7030be73dfb5cf39ad67939123a
java.security.MessageDigest
2961
not checked
si0001.gif
local
1604914508548
0
SHA-512
be2b3425b8ca0c7df658853736ca411bb6cd187bdc7f6f442ac77ae0cd3b89cdbe355dadcf717efffdcaf21f472c323717216f4da7ac185a3de573e04d623e45
java.security.MessageDigest
5548
not checked
si0002.gif
local
1604914508549
0
SHA-512
a80d83bea33d238f2685b3931f95453467636e5b8a516e333d387fe03cb57f1549a444b4c62392f09def467b2f74c5596deea750ffab337131a07491bab734dc
java.security.MessageDigest
70171
not checked
gr1.jpg
local
1604914508550
0
SHA-512
28c5fbb12ddd88798384ad2a78e4658fabf3f88456a99de840e425f2bd5186de7a9ae49339e3a33f13271d2f903b12651e6ab637c8d2b3a15b99a23a349f5ce6
java.security.MessageDigest
6677
not checked
gr1.sml
local
1604914508551
0
SHA-512
36d7f2be1370deb0077530317f335160d748648baea6f97445d2a1782b02ea7fdeb8ea8bda2f6d8e5ca3d1431c53a0e72e0378597efc8eb5fafca60a3aa664a0
java.security.MessageDigest
14258
not checked
gr2.jpg
local
1604914508552
0
SHA-512
bcc39fb8239b308a895b157a98e9ede5bd3d3d1a6e84145d18c9352450876e487baeb7ec5f71b8d6b297e791a1bd42ab05c11da1ba931f575633b1836de18865
java.security.MessageDigest
7418
not checked
gr2.sml
local
1604914508553
0
SHA-512
1c449d4ecec8fb3b4220390f6f14eec1d43b9b68bf4b4d74aeb105b924f1ec9ad874d21664dc0d31e79a30a9bc4b725ae492aaa37d4423b88d6f370d4013da70
java.security.MessageDigest
72253
not checked
gr3.jpg
local
1604914508554
0
SHA-512
b5b9d08b11850bf4cd122d989a352ee5fc0eb2b64ab72f9a81e53fd3d53af0f9787d21fc8121ef4ea342539325aee7a4ba52d8311f78289852913156c2d8a4f9
java.security.MessageDigest
7867
not checked
gr3.sml
local
1604914508555
0
SHA-512
c69a7456ba8f0e490c6fc53569da6c1b8ab2f8b58913d5beff432159896a899c12d2c2d2481cd3552ada7bc5b1ec9bb01d7990905f8f23598a3979faeaef5e4c
java.security.MessageDigest
38259
not checked
gr4.jpg
local
1604914508556
0
SHA-512
e1ba8578817af457c2eebadc19c714279648cff2ec46a86545eb0ab744841483a12f36156d26a80a94624b0e37b4a516159ece0a5ecdab991d9d955f165304f5
java.security.MessageDigest
5667
not checked
gr4.sml
local
1604914508557
0
SHA-512
0664dd1276140d2d8e994c47a5505b035adf54da0363fc2b911f299c0f94dbe676b76a9b91d5161694f9bfd2b74b56a00bd647757efcaf20f79494fd4dda6302
java.security.MessageDigest
34270
not checked
gr5.jpg
local
1604914508558
0
SHA-512
a1a9c60a339df8e922832f1168387b7cd522f7e2eaccf33f10aad1b39eb5de25fdf1470df8103bc521ab1adf08ab16a1b5762b5e1a39ce84edd38d041ba33afc
java.security.MessageDigest
5232
not checked
gr5.sml
local
1604914508559
0
SHA-512
81ee2cf672e972ba5ce09ae48b2589de3485be07c8a4a42591b4824ab38b2d29ca28ba4f8089111095060c3b420389e2d6783856376035a0bdcad2fb0bf86c34
java.security.MessageDigest
34570
not checked
gr6.jpg
local
1604914508560
0
SHA-512
b3ee07aa462df2ff02cd3b9e4f211770ca9bc3aa5af1bff5aef46445715fbed110d3e0af902db74626d40182c6859e2c5767a6dc71ccc69e1c7b6faaa39ab026
java.security.MessageDigest
4696
not checked
gr6.sml
local
1604914508561
0
SHA-512
cad5435457c0ec4dec89722017c5d7d384c77892cc5ffa85a31eec9ffca9eb66cbffd21956ccc682ce25b01f83da1775187be2b8bf696d3c84e81116dca5ce04
java.security.MessageDigest
13788
not checked
gr7.jpg
local
1604914508562
0
SHA-512
96156251dfd988166ecfd5c767d687f194a4f0b94917ee530ecf65ea7d18f5c3f8ee8679714cc79118601876361252ce9285b034afb4c6904b41de34dffd9cc9
java.security.MessageDigest
5847
not checked
gr7.sml
local
1604914508563
0
SHA-512
9efbbb5a79d99686283b7e0b8cc4f81e42a043fb96182b30228b7360e70d31adfab48c7f62b73b823075a1d0ade7c7325380766a4dbcceae41f70402f7455eb8
java.security.MessageDigest
39163
not checked
gr8.jpg
local
1604914508564
0
SHA-512
57551377b043f69f36f7e3c61e9b9f30eb49f3244fb37319caad7bac502f80c7b5a06b78741e34598dcb8879afba6c910fcd18548251c3a511a1f67ee31bc201
java.security.MessageDigest
5970
not checked
gr8.sml
local
1604914508565
0
SHA-512
82cec0bdb94331dfbe11313e87254d9acd053072c6cc7acba6fe750a9ff727e49b7b97ef5f787329a170dce22024177e0e7e311240ff9ee599ee1351799ef12e
java.security.MessageDigest
165822
not checked
gr9.jpg
local
1604914508566
0
SHA-512
fbb520092def67c7a570e1611a406d2ff88d83b12d90b7484e201db9123844499f77dc6c5bdc15c9f3982b338c183f9e22b803f2b622448cff92b0738e3fc00e
java.security.MessageDigest
15201
not checked
gr9.sml
local
1604914508567
0
SHA-512
6446a8991dc62062989eb3685e844349c3c45c7047a2e0acbfec3a773bd95ce6f2b208b8cf21a894d436108c0e472a955d14efbb85fa956e7149bd0d279e671c
java.security.MessageDigest
21605
not checked
mmc1.docx
local
1604914508568
0
SHA-512
27a2b731405a53759e8c7d84ea7ea30e6f0c84634baa2e9aa5ec8757e4a10b11f122561c8b2d40f2589d75b93aaada8de6a3ce0b6319e65a5a2f39505806c537
java.security.MessageDigest
16004
not checked
metadata.xml
free
00001
The Authors
KB-agent-id
1
supplier
KB-owner-id
00001
KB-agent-id
1
Elsevier
organization
The Authors
ingestion
2020-11-09T09:53:15.990+01:00
Connector
software
Digitaal Magazijn release 1.5
ejournals_esp_1
streamprofile
ingestion2020-11-12T12:22:37.279+01:00Generic IngestsoftwareDigitaal Magazijn release 1.5