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Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Technical Report

NREL/TP-5K00-72953

January 2019

Manufacturing and Reliability Science 

for CIGS Photovoltaics

Lorelle Mansfield

National Renewable Energy Laboratory
NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

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303-275-3000 • www.nrel.gov

Technical Report

NREL/TP-5K00-72953

January 2019

Manufacturing and Reliability Science 

for CIGS Photovoltaics

Lorelle Mansfield

National Renewable Energy Laboratory

Suggested Citation

Mansfield, Lorelle. 2019. Manufacturing and Reliability Science of CIGS Photovoltaics. 

Golden, CO: National Renewable Energy Laboratory. NREL/TP-5K00-72953.

https://www.nrel.gov/docs/fy19osti/72953.pdf.
NOTICE

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable 

Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding 

provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy 

Technologies Office. The views expressed herein do not necessarily represent the views of the DOE or the U.S. 

Government.

This report is available at no cost from the National Renewable 

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Cover Photos by Dennis Schroeder: (clockwise, left to right) NREL 51934, NREL 45897, NREL 42160, NREL 45891, NREL 48097, 

NREL 46526.

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1

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Final Report 

Project Title: Manufacturing and Reliability Science for CIGS Photovoltaics

Project Period: 1 Oct 2015 – 30 Sept 2018

Project Budget: $4,000,000

Submission Date: 30 September 2018

Recipient: NREL

Address: 15013 Denver West Pkwy., Golden, CO 80401

Agreement Number: SuNLaMP 30296

Awarding Agency: DOE EERE SETO PV subprogram

Working Partners: NA

Principal Investigator: Lorelle Mansfield

Scientist

Phone: 303-384-7884

Email: lorelle.mansfield@nrel.gov
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Executive Summary: The purpose of this program was to overcome the largest 

challenges to investor confidence and long product lifetime in CuInxGa1-xSe2 (CIGS)-

based photovoltaic products: metastability, shading-induced hot spots, and potentialinduced degradation (PID). Key findings were made in each of these areas by studying 

CIGS reliability at the cell level, which very few groups are currently doing. Metastability 

was thought to be a function of the CIGS absorber. We have challenged the state-of-theart by showing that the metastability seen in commercial products is likely to be caused 

by the buffer layer. Solar Cell Capacitance Simulator (SCAPS) device modeling confirmed 

that the buffer layer has a significant influence on metastability in CIGS devices, and it 

also led to a processing change—the introduction of CdS islands to Zn(O,S) buffer 

layers—that dramatically reduced metastability in CIGS solar cells. In the reverse-bias 

shading task, modeling showed us that 19% solar cells are possible with thin CIGS layers 

of 0.5 μm. We were able to fabricate 15.2% solar cells in this project, which is the highestreported efficiency of devices in the ultra-thin class. We also discovered that the best way 

to dissipate less power in reverse bias was to eliminate the intrinsic ZnO layer that is often 

used in CIGS devices. Lower power dissipation led to devices that allowed two times the 

maximum power-point current density in reverse without damage. PID is caused by the 

drift of Na+ ions from the back glass to the CIGS/Mo interface, followed by diffusion into 

the solar cells and to the CdS region. We found that PID can be slowed by using lowconductivity borosilicate glass that contains higher K and lower Na than soda-lime glass.

Based on significant progress in each of the three reliability challenges, the CIGS celllevel reliability project was very successful. We have also proved that module-level 

degradation mechanisms can be tested and solved at the cell level.

Background: The novelty of this work is evidenced by the few updates in the literature 

in the field of cell-level reliability. Of the three areas of study, metastability has the most 

activity. Several papers document techniques for measuring metastability, such as 

photoluminescence [7-10]. Most cite the Lany-Zunger VSe-VCu complex (LZ) [11] as an 

absorber defect that is likely responsible for metastable behavior. These are different from 

our work because we have shown the metastable behavior to be more buffer-related than 

absorber-related. Some studies did look at buffer changes such as surface treatments 

[12] and varying chemistry [13-15] to reduce metastability in devices with Zn(O,S) buffers. 

Oftentimes they still site the LS model for defect states in the CIGS at the buffer/absorber 

interface. One notable experiment is the addition of Si to the CIGS growth [16], which 

enables the elimination of the buffer layer and also reduces metastability. 

Studies related to partial-shading damage include those by Steve Johnston’s project, 

where sites likely to break down were identified using thermal imaging techniques [17-

19]. Another group looked at differences in reverse breakdown behavior depending on 

the buffer layer used and modeled it according to Fowler–Nordheim tunneling and also 

Poole–Frenkel conduction [20]. They think that Fowler–Nordheim tunneling is the main 

contributor to the breakdown current. This paper could be useful when we begin device 

modeling for reverse-bias behavior. Of course, there are also reports of partial-shading 

damage in modules [21, 22], and Marco Nardone was able to model the difference 

between bare and encapsulated modules [23]. Experimentally, we have shown that 

encapsulated devices break down at smaller reverse voltages, but that will not be 

reported publicly. Studies on ultra-thin devices are covered below in the Project Results 

and Discussion under Task 2. 
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Potential-induced degradation (PID) had few literature reports, and we are the main group 

studying it at the cell level. Several deal with PID test procedures for modules [24-26], 

documentation of failure in CdTe [27], and a review of module PID [28]. In-situ dark 

current-voltage measurements were performed on our cells, and maximum power 

calculations were done similar to reference [29] with the results submitted to the IEEE 

Journal of Photovoltaics for publication [30].

Introduction: As costs of Si-based modules have dropped rapidly, the projected large 

price advantage of CIGS over Si has not been realized. Without a substantial price 

difference between Si and CIGS modules, and long product lifetime required to achieve 

low levelized cost of electricity (LCOE), investors have little incentive to choose CIGS, the 

less mature technology. Thus, with a short product history, addressing product lifetime 

and reliability issues (or perceived reliability issues) is critical for CIGS. This program was 

significant because it investigated the three main challenges for reliability in CIGS 

modules. They correspond to the project tasks: Task 1: Metastability, Task 2: ReverseBias Shading, and Task 3: Potential-Induced Degradation. We took an innovative 

approach by investigating module-scale problems at the cell level and attempting to solve 

the problems at the cell level. We found ways to mitigate all three reliability challenges,

and they are detailed in the Project Results and Discussion section. The project 

milestones are listed in Table 1.
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Table 1 Milestones Year # Task # Milestone 

Milestone

Description

Planned 

End Date

Milestone 

Type: 

Annual or 

Quarterly

1 1 1

Outline for publication that draws conclusion whether datasets 

are consistent with hypothesis that metastability is controlled by 

the density of (VSe-VCu) defects and their population.

3/31/2016 Quarterly

1 3 2

Demonstrate that small-cell module test coupons show no 

degradation under standard damp-heat test (85°C, 85% relative 

humidity, 1000 hours) and have electrical leads appropriate for 

PID stress and electrical testing.

6/30/2016 Quarterly

1 2 3

Demonstrate an improved state-of-the-art thin device exhibiting 

>15% efficiency at <0.5-μm CIGS absorber thickness. Device 

should exhibit larger reverse current flow at a fixed reverse 

voltage compared to the standard 2.5-μm-thick device.

Quantify, on a research-cell scale, the magnitude of metastability 

and PID in CIGS devices, and identify routes to mitigate these 

effects.

9/30/2016 Annual

2 1 1

Identify at least one CIGS metastability mechanism by 

demonstrating at least one absorber-processing variation and at 

least one buffer-processing variation that significantly affects 

metastability.

12/31/2016 Quarterly

2 2 2

Using unencapsulated scribed partner absorbers, document 

individual cell voltage at which damage from shading occurs, i.e.,

Vdamage.

3/31/2017 Quarterly

2 3 3 Identify at least two populations resulting in differing amounts of 

PID in CIGS cells. 6/30/2017 Quarterly

2 2 4

Demonstrate high-efficiency (>15%) research cell that flows at 

least Imp in reverse current at a reverse voltage bias of Vdamage or 

less.

Submit at least three publications to peer-reviewed journals.

9/30/2017 Annual

3 2 1

Using encapsulated NREL cells, document individual cell reverse 

voltage at which damage from shading occurs, Vdamage, and 

current density allowed before damage occurs. 

12/31/2017 Quarterly

3 1 2

Show that buffer metastability is reduced in devices with Cd 

partial-electrolyte (CdPE) treatment plus Zn(O,S) buffer layer 

when compared to devices with only a Zn(O,S) buffer layer. 

3/31/2018 Quarterly

3 3 3

Confirm the hypothesis that migrating Na is the cause of PID and 

that K mitigates PID because it migrates less than Na. Stress 

samples with at least three different alkali levels or incorporation 

methods, including at least one K-containing sample and one Nacontaining sample. 

6/30/2018 Quarterly
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3 1 4

Provide specific process and device design guidelines to 

eliminate or significantly reduce metastability, shading 

degradation, and PID in CIGS. Two out of three of the following 

metrics should be achieved:

• (Task 1) Reduce metastability to a change in VOC less than or 

equal to 1 mV over the time period of 500 s to 1200 s of light 

soaking. State-of-the-art: The most-stable devices with 

Zn(O,S) buffers had a change in VOC of 1.8 mV to 2.5 mV over 

the time period of 500 s to 1200 s of light soaking.

• (Task 2) Encapsulated devices should allow 1.5 x JMPP to flow 

in reverse-bias without damage. State-of-the-art: Greater than 

62% of encapsulated mini-modules were damaged by reverse 

currents less than 1.5 x JMPP. To measure progress, the 

behavior of encapsulated standard NREL devices will be 

measured in Q1.

• (Task 3) Limit PID to 7% relative change in efficiency after 25 

hours of accelerated stressing in the most damaging 

configuration of back-grounded with +1000 V applied to 

devices. State-of-the-art: Devices on soda-lime glass degrade 

by 100% (from original efficiency to 0% efficiency) after 25 

hours of accelerated stressing in the most damaging 

configuration.

Publication and/or documentation of communication of these 

results to an industrial partner, preferably, with results on 

implementation.

9/30/2018 Annual
6

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Project Results and Discussion:

Task 1 Metastability – Summary

Some commercial CIGS modules show large changes in current-voltage (JV) parameters 

with light soaking. Although such changes do not necessarily indicate a performance 

problem, the associated uncertainty may be disadvantageous in a highly competitive 

market. Thus, it is beneficial to understand the origin of large metastabilities to define 

what processing changes might diminish metastability without impacting other desirable 

aspects of high-performance devices. We have attempted to reproduce large 

metastabilities such as those in some commercial products through both absorber and 

buffer processing variations in small devices. Although variations of both types were 

found to affect metastability, only buffer variations could reproduce large metastability in 

high-efficiency devices. Device modeling confirms that buffer effects alone are sufficient 

to explain the large metastability seen in these devices. The device model has guided us 

toward a processing change that reduces metastability without increasing current loss in 

the buffer.

Background

In CIGS cells and modules, changes in JV behavior with light exposure are most typically 

observed to be metastable, (i.e., the change can be reversed by periods of dark storage) 

and positive (i.e., module efficiency increases with time). Some products are observed to 

undergo large metastable increases in fill factor and voltage with light exposure. Figure 1

shows an example of parameter changes with light soaking in a commercial CIGS 

module. JV parameters are shown as a function of one-sun light-soaking time at 50oC. 

Buffer Variations

Several works have reported 

larger JV metastability in 

CIGS with non-CdS buffers

compared to CdS buffers [31-

35]. Results from this study 

support that trend. Figure 2

shows the change in opencircuit voltage (Voc) with light 

soaking for an experiment 

involving only buffer 

variations. Data from all 45 

different samples are shown, 

with the mean value for each 

buffer type marked with an 

“X.” 

Figure 1: Power, Voc, and fill factor as a function of 1-sun light-soak 

time for an example of a commercial CIGS module.
7

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Absorber Variations

The goal was to induce large metastable device 

behavior via multiple variations in absorber 

processing, without changing the CdS buffer. 37 

samples incorporating processing variations were 

expected to affect metastable defect concentration. 

However, for high-efficiency samples (i.e., efficiency 

> 15%), large metastability did not occur. This result 

is shown by the gray + signs in Figure 3. On the other

hand, some absorber process variations resulted in 

low-efficiency devices with significant metastability. 

The low-efficiency, metastable devices occurred for 

process variations that produced low carrier density. 

The black circles in Figure 3, read to the bottom axis, 

show how the metastable change in Voc anticorrelates with zero-bias, dark-state carrier density 

(p). 

An anti-correlation between carrier 

density and metastable change in Voc

is to be expected from the modest 

metastable defect concentrations 

reported. Specifically, following the 

derivation of Obereigner, the change in 

Voc, ∆Voc, can be derived to be

 ΔVVoooo ≈ AAAAAA

2qq

ln �1 + Δ ppmmmmmmmm

ppssh aaaaaaaa

�,

where k is Boltzmann’s constant, T is 

temperature, q is the electron charge, 

A is the diode quality factor, pshallow is 

the shallow acceptor density, and

∆pmeta is the change with light-soaking 

and a subsequent increase with light 

soaking due to metastable defects. The 

solid line in Figure 3 is a least-squares 

fit using the form of this equation and 

pmeta as the fit parameter. The 

extracted value for ∆pmeta is 8.5×1014

cm-3, in approximate agreement with the low 1015 cm-3 values of ∆pmeta observed in the 

literature. The correlation coefficient is 0.6, implying that this relationship explains most 

of the variation in metastability in the dataset. 

Figure 2: Voltage metastability in CIGS 

devices for different buffer deposition 

chemistries, with mean value marked 

as “X.”

Figure 3: Metastable change in Voc as a function of 

dark carrier density (lower axis, black circles) or 

stabilized device efficiency (upper axis, gray +’s). The 

solid line is a least-squares fit to the carrier-density 

data.
8

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JV Curves and Device Modeling of Buffer Variations

JV curves exhibiting metastability 

were modeled to determine what 

ranges of materials parameters 

might reasonably lead to the 

observed effects. A few 

representative JV curves from this 

study were chosen for modeling and 

are shown in Figure 4 as solid lines. 

Because the CdS devices are much 

more stable, Figure 4 contains only

one experimental JV curve for this 

device, whereas both relaxed-state 

and light-soaked curves are shown 

for the other devices. 

Device modeling was used to 

understand the possible origins of 

the observed behaviors, using Solar 

Cell Capacitance Simulator (SCAPS)

software [36]. Literature or measured materials properties values were used to describe 

each layer. The values employed in the SCAPS model are well-documented in the paper 

(drafted, to be submitted) so that other groups may use them to replicate our results and 

compare to their own devices. Four ZnOS parameters—free-electron density, deep-trap

density, buffer/absorber surface recombination velocity, and buffer/absorber conductionband offset—were varied to fit the experimental JV curves. These modeled JV curves are 

overlaid with the experimental data in Figure 4. The modeled curves reproduce the

features of the experimental data (including inflection, voltage, and fill factor increases 

with light soaking) and curve shape. Thus, it is concluded that buffer effects alone are 

sufficient to explain the large metastability seen in these devices.

Figure 4: Measured JV curves (solid lines) and modeled 

JV curves (dashed lines with x’s) for samples with different 

buffer variations.
9

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Implications for Processing Changes

The insights provided by the SCAPS device 

model have suggested some processing 

changes that might mitigate metastability. One 

such change has been proven experimentally. 

Tiny islands of CdS were deposited adjacent to 

the buffer layer. These islands enable hole 

injection into the buffer layer, and thus, they 

decrease metastability without increasing 

buffer absorption. Figure 5a compares 

quantum efficiency (QE) from devices with a 

standard CdS buffer, one with a standard 

Zn(O,S) buffer, and a third with a Zn(O,S) 

buffer with CdS islands. The addition of the 

CdS islands does not appreciably decrease the 

blue response of the device. Figures 5b and 5c 

compare the change in VOC of these three 

devices as a function of time, over two different 

timescales. From the small change in VOC of 

the devices with Zn(O,S) + CdS islands (red

traces), it can be seen that the presence of the 

CdS islands dramatically decreases 

metastability.

During the course of this project, we have 

made excellent progress in understanding 

CIGS device metastability. We have 

challenged the long-held theory that 

metastability is solely a function of defects in 

the CIGS absorber by proving that the 

metastability seen in commercial products is 

likely to be caused by the buffer layer. Our 

discovery has been supported by SCAPS 

device modeling and confirmed by 

experimental devices. A dramatic reduction of 

metastability in CIGS solar cells was realized 

by introducing CdS islands adjacent to Zn(O,S) 

buffer layers. 

a)

b)

c)

Figure 5: Comparison of devices with three 

different buffer designs, in terms of a) QE, b) 

voltage increase over 20 minutes of light soak, 

and c) voltage increase 500–1200 seconds 

after initial exposure.
10

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Task 2 Reverse-Bias Shading – Summary

Partial shading can degrade module performance by forcing reverse current through the 

shaded cells. Our original hypothesis was that fabricating devices with a thinner CIGS 

layer would confine the electric field and allow the reverse current to flow at lower 

voltages, thus reducing the power dissipated and the likelihood of damage. We modeled 

thin devices to determine how to attain the highest efficiency and were able to fabricate 

devices with 0.49-μm CIGS that had 15.2% efficiency. However, reverse-bias behavior 

was not significantly improved. Taking a cue from previous reverse biasing of Zn(O,S) 

devices, we improved reverse-bias behavior in CdS devices by removing the i-ZnO layer 

from the device stack. Both the CdS devices without i-ZnO and the Zn(O,S) devices were 

able to survive twice the maximum power-point current in reverse without damage. 

Background

Partial shading can degrade module performance by 

forcing reverse current through the shaded cells. 

Silverman et al. found that modules lost 4%–7% of 

their maximum power due to shunting caused by 

partial shade [21]. The damage is observed as visible 

“worm trails” in Figure 6. We have been able to 

reproduce this damage in small-area cells by 

subjecting them to reverse bias in the dark.

Thin CIGS Devices – Modeling and Performance

It is difficult to evaluate changes to current and voltage 

separately by device fabrication trials, especially 

when determining how Ga content should change through the device thickness. 

Therefore, we used device modeling to investigate the effect of Ga content in ultra-thin 

CIGS devices. We first wanted to determine the optimum “height” of the Ga/(Ga+In) 

(Ga/III) at the rear of the film near the CIGS/Mo interface, which can act as an electron 

reflector at the back of the device. In Figure 7a, at a thickness of 2 μm, the efficiency can 

be greater than 20% for rear Ga/III ratio of 0.3 and higher, with the best efficiency coming 

from rear Ga/III = 0.6. For thinner CIGS films, the highest efficiencies also occur at rear 

Ga/III = 0.6, but the efficiency numbers are lower. This modeling indicates that it is 

Figure 6: Image of visible damage 

(“worm trails”) to a CIGS module 

caused by partial shading.

Figure 7: (a) Efficiency versus rear Ga/(Ga+In) and (b) efficiency versus bandgap-gradient start for three 

different film thicknesses. Insets show, by red arrows, the portion of the bandgap that is changing.
11

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possible to achieve 19% efficiency for 0.5-μm devices. The device model also leads to 

the conclusion that the rear Ga/III of the 0.5-μm CIGS films should be at least 0.5 to 0.6. 

This is a difference in Ga/III of at least 0.3 over the rest of the film. In general, the efficiency 

is also increased when the start of the bandgap-gradient is farther from the film surface

(Figure 7b). The dependency of efficiency on bandgap-gradient start depth is particularly 

strong for the ultra-thin CIGS films with a thickness of 0.5 μm. Optimization would result 

in a very thin layer of high-Ga CIGS. It also means that the rear Ga gradient should be as 

steep as possible to increase the device efficiency. More than 19% efficiency could be 

achieved if the bandgap-gradient start depth is greater than 0.35, or stated alternatively, 

if the high-Ga region is less than 0.15 μm thick.

To aid in fabricating the Ga gradients that were modeled, we developed a prediction tool 

for Ga gradients. As shown above, the gradients are important to device performance, 

and they vary as a function of growth recipe. Predicting Ga profiles using classic diffusion 

equations is not possible for a couple of reasons. First, In and Ga atoms occupy the same 

lattice sites—thus, they diffuse interdependently. Second, there is not yet a detailed 

experimental knowledge of the chemical potential as a function of composition that

describes this interaction. We showed how diffusion equations can be modified to account 

for site sharing between In and Ga atoms [37]. The analysis was implemented in an Excel 

spreadsheet, and outputs predicted Cu, In, and Ga profiles for entered deposition recipes. 

A single set of diffusion coefficients and activation energies was chosen such that 

simulated elemental profiles track with published data and our own experiments.

Device modeling and diffusion 

modeling guided our attempt to 

achieve high-efficiency ultra-thin 

CIGS solar cells. The best devices 

from this study are plotted in Figure 

8, along with best results from some 

other studies [1-6]. The devices most 

similar to ours in performance are 

from Kim et al., with efficiency of 

13.7% at 0.5 μm [6]. Vermang et al. 

used rear passivation to attain 

devices of 13.5% efficiency at 0.4 μm 

[3]. In our experiments, we did not 

use additional passivation like 

Vermang’s, light-management 

schemes as reviewed by Schmid 

[38], or the increasingly popular postdeposition alkali treatments. This 

indicates that even higher device performance is possible. We were able to increase the 

efficiency of our ultra-thin CIGS for thicknesses between 0.43 and 0.65 μm. Our best cell

was measured at 15.15% efficiency and had a CIGS thickness of 0.49 μm. It had the 

highest voltage of our samples at 0.733 V, plus good current at 26.4 mA/cm2 and fill factor 

of 78.2%. The official JV measurement was taken by NREL’s Solar Cell/Module 

Performance Group. Full details can be found in reference [39].

Figure 8: Efficiency versus thickness for several previous 

studies [1-6] on ultra-thin CIGS. The best efficiencies from 

this study are shown by red triangles pointing toward the 

upper right.
12

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Reverse-Bias Behavior

We reverse-biased devices with a variety 

of Cu(In,Ga)Se2 absorber thicknesses 

from 0.4 μm to 2.5 μm, with the 

expectation that larger reverse current 

would be allowed to flow at lower voltages. 

Our initial experiments showed promise. 

However, as the efficiency of thin devices 

was improved, the reverse current allowed 

at a given voltage decreased. To display 

this phenomenon, we tried several 

different metrics. Originally, we calculated 

reverse breakdown voltage after the 

method of Puttnins et al. [40], but our CdS 

devices did not always show a turn-on 

voltage in reverse before becoming 

damaged. We also looked at voltages to 

reach a given current density, such as

maximum power-point current (Jmpp) or -30 mA/cm2. The best metric was to calculate the 

power dissipated (P = I * V) for those devices that reached the Jmpp in reverse. This makes 

sense as a comparison between devices because we can easily understand that more 

power dissipated will indicate device damage. The power in mW versus CIGS absorber 

thickness is shown in Figure 9. The orange box is to indicate that most of the devices are 

within that power range regardless of thickness. We should note that not all devices were 

able to allow Jmpp in reverse without damage and the devices that failed are not on the 

graph.

Processing Changes

We did discover one processing change that improved reverse-bias behavior. Lee et al. 

showed that Zn(O,S) buffers were able to allow more current flow in reverse at lower 

voltages [22]. We saw similar results in our Zn(O,S) devices and wanted to find out if 

the i-ZnO and AZO layers affected the device’s ability to reach Jmpp in reverse bias. 

Comparisons of the device stacks of Zn(O,S) and CdS devices are shown in Figure 10. 

We did several iterations of CdS devices with thinner i-ZnO layers, with AZO only (no iZnO layer), and with thicker AZO layer. A comparison of the power dissipated at Jmpp in 

reverse for CdS with AZO only, standard CdS with 

bi-layer ZnO, and Zn(O,S) devices is shown in 

Figure 11a. The orange box is the same power 

range as in Figure 9, indicating the common range 

of power dissipated at Jmpp for standard CdS 

devices. This set does not include devices that were 

damaged before reaching Jmpp in reverse, which 

was about 50% of the CdS devices. We are pleased 

to report that devices without an i-ZnO layer—the 

CdS with AZO only and the Zn(O,S) devices—were 

consistently able to reach Jmpp (and even 2×Jmpp, 

Figure 11b) in reverse bias without damage.

Figure 9: Power dissipated at Jmpp in reverse bias 

versus CIGS film thickness.

Figure 10: Diagrams of (a) Zn(O,S) 

and (b) CdS device stacks. The buffer 

layers are indicated with arrows.
13

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The reverse-bias and partial-shading task led to some important conclusions. Device 

models confirmed that 19% devices are possible with 0.5-μm CIGS layers. We were able 

to fabricate 15.2%-efficiency devices with thin absorber layers, significantly improving 

upon the previous efficiency of ultra-thin CIGS devices. With these best-in-class devices, 

we also found that the reverse-bias characteristics do not depend on absorber thickness. 

We discovered that the best way to dissipate less power in reverse bias was to eliminate 

the intrinsic ZnO layer that is often used in CIGS devices. Lower power dissipation led to 

devices that allowed 2×Jmpp in reverse current without damage.

Task 3 Potential-Induced Degradation – Background

Studying potential-induced degradation (PID) can add value to photovoltaic (PV) modules 

by helping to accurately predict power output and mitigate degradation. CIGS absorbers 

are known to benefit from alkali-metal dopants, which can diffuse out from soda-lime glass 

(SLG) substrates to enhance carrier concentration and reduce recombination [41]. On the 

other hand, transport of Na+ from SLG into the semiconductors is the cause of PID in Si, 

CdTe, and CIGS modules [28]. Therefore, alkali metals can both benefit and deteriorate 

PV performance, depending on their particular distribution and bonding. Careful study of 

these characteristics is needed to optimize the initial efficiency and degradation of CIGS 

modules.

Samples

To study CIGS PID, a method for packaging seven small-area solar cells (0.42 cm2 each) 

into module-like encapsulated samples was developed [42]. Standard CIGS device 

stacks were grown on various substrates: SLG, two borosilicate glasses (BSG), and SLG 

with an Al2O3 diffusion barrier. A KF post-deposition treatment (PDT) was additionally 

performed on SLG substrates. KF PDTs are known to enhance initial efficiency [41], but 

studies have connected alkali metals with degradation in damp heat [41], so more work 

is needed to understand how KF PDTs affect power produced over the lifetime of the PV 

module. The present study also employed K-rich borosilicate glass substrates instead of 

Na-rich SLG as a means to achieve comparable initial performance with reduced PID. 

Figure 11: (a) Power at Jmpp versus device type and (b) power at 2×Jmpp versus device type. The 

orange box in (a) indicates the common range of power dissipated at Jmpp for standard CdS devices.
14

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Multiple BSGs were explored at first, and Schott D263 BSG was the best of all 

investigated because of its high K content and thermal expansion coefficient of 7×10-6 K -1, which was well-matched to that of CIGS (~7–9×10-6 K-1). The SLG with an Al2O3

diffusion barrier was chosen to be similar to substrates used in industry.

Diffusion (85°C; no bias)

Before PID studies were performed, thermal anneals were examined as control 

samples—these samples endured long-term exposure to 85°C without bias. Independent 

of the thermal anneals’ duration, samples of every type exhibited a decrease in carrier 

concentration by 2x to 3x (Figure 12). As expected, this coincided with small VOC and 

efficiency reductions. These changes may be 

attributable to diffusion, possibly through a 

redistribution of alkali metals. Na is smaller 

than K, so it should have a higher diffusivity at 

85°C. Na’s smaller atomic radius should also 

make its grain-interior defect formation 

energies more favorable than K, likely making 

it a more active dopant [41]. For these reasons, 

the redistribution of Na may dominate the 

observed carrier concentration and efficiency 

losses after thermal diffusion.

Drift and Diffusion (-1000 V and 85°C)

Previous studies of CIGS PID have shown that

it is crucial to separate moisture and potential 

effects [28], so the present study employed 

encapsulation. Bias can be applied across the 

substrate glass or the cover glass, and both 

have been shown to cause PID [28]. In this 

study, four configurations were initially tested 

on SLG substrates: positive or negative 1000 

V, in each case applied either across the

substrate or across the cover glass. Bias 

across the cover glass with both polarities had 

little or no effect after 100 h of stress. Applying 

positive bias to the cells with the back of the 

substrate grounded, which establishes an 

electric field from the device toward the back (and should drive Na+ the same direction), 

did not cause PID in 100 h, and may have even improved performance. Applying negative 

bias to the cells to establish an electric field from the back toward the device (driving Na+

from the substrate into the device) caused catastrophic PID. In some cases, the PID 

(efficiency and carrier concentration losses) could be recovered by reversing the voltage 

polarity, in agreement with former reports [28]. However, the drops in efficiency and 

carrier concentration associated with thermal diffusion (Figure 13) were not restored by 

the polarity switch. The most damaging configuration (-1000 V on the substrate) was 

carried on for the rest of the experiments.

Figure 12: (a) Carrier concentration and (b) 

efficiency means and standard deviations 

(error bars) as a function of time at 85°C and 

10% relative humidity (no bias) for SLG (gray 

squares), SLG + KF PDT (black squares), 

BSG (orange circles), and repeated BSG 

(red circles) substrates.
15

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Initial PV performance of the BSG devices 

was almost as good as the standard SLG 

devices (Figure 12) because high levels of K 

diffused out from the BSG into the growing 

absorbers (Figure 13). This caused the 

absorber K secondary-ion mass spectrometry 

(SIMS) signal on BSG substrates to be similar 

to the absorber Na SIMS signal on SLG 

substrates. This relatively high apparent 

concentration of K established majoritycarrier hole concentrations approaching those 

established by Na on SLG substrates (Figure 

12). In this way, K can achieve similar effects 

to Na with respect to absorbers’ initial PV 

performance. The SLG PID absorber had 

increased Na after 25 h of PID, and likewise, 

the BSG PID sample had more K in the 

absorber than the BSG control. However, the 

gain in BSG absorber K was less pronounced 

than the Na gain on SLG due to the BSG’s 35x 

lower leakage current. The present results 

suggest that PID occurred through harm to 

the p-n junction itself (SIMS not shown [43])—

as opposed to ZnO corrosion, which has been 

observed in previous CIGS PID studies [28]. 

ZnO corrosion is much faster in the presence of moisture, highlighting the importance of 

encapsulation for PID testing.

After 25 h of stress, the SLG and KF PDT (not shown) samples exhibited catastrophic

PID to 0% efficiency, while the BSG and SLG/Al2O3 substrates suffered much less 

degradation (Figure 14). Much longer stressing durations were carried on, and slow PID 

was observed out to 700 h. Figure 14 summarizes the contrast in stability among the 

samples: on average, the SLG, SLG/Al2O3, and BSG solar cells degraded to <50% of 

their initial efficiency within 6, 30, and 500 h, respectively.

PID was also compared on the basis of Coulombs transferred. After physically driving 

equal amounts of cations into the devices, the SLG, BSG, and SLG/Al2O3 showed 

different trends. BSG substrates had the least PID with respect to time, but the SLG/Al2O3

substrates had the least PID with respect to Coulombs transferred. The Al2O3 diffusion 

barrier did not alter the leakage current of SLG substrates, and the Na driven through the 

Al2O3 diffusion barrier initially improved carrier concentration and efficiency. After 15 h (or 

0.05 C), too much Na had accumulated and PID occurred. The Al2O3 samples may have 

different slopes than SLG in Figure 14 and Figure 15 because they received more time 

at 85°C, light soaking, and bias sweeping, all of which can reverse PID [25]. The BSG 

samples also had much longer durations at 85°C, so roughly 24x more diffusion should 

Figure 13: (a) Na and (b) K SIMS intensity with 

depth through the cored device stack for the 

SLG (triangles) control (black) and PID (red) 

and BSG (circles) control (gray) and PID 

(orange) samples. PID duration was 25 h.
16

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

have occurred relative to SLG. Diffusion could be reducing the K+ accumulation in the 

junction that high bias causes, which could also explain the recovery after PID that has 

been reported to occur even at room temperature [44]. The possibility of test-specific 

degradation in Figure 14 and Figure 15 must be checked in future work by approximating 

field conditions more closely (e.g., combining high-voltage stress with light soaking and 

device bias).

Processing Changes

This study examined the effect of switching from SLG to BSG substrates on PID of CIGS. 

The high K levels in BSG led to increased K in the absorber layer, which led to initial PV 

performance similar to devices on standard SLG substrates. High-voltage stressing led 

to catastrophic PID of solar cells on SLG substrates after just 6 h. In contrast, solar cells 

on BSG substrates required 500 h of stress for catastrophic PID. The SLG PID was 

associated with increased Na in the absorber, especially near the buffer interface. The 

less-conductive BSG had reduced leakage current, which diminished PID. 

Unencapsulated experiments have observed ZnO corrosion-based PID, but 

encapsulated PID is due to physical accumulation of ions in the junction. These cations 

initiate PID by compensating to reduce charge-carrier concentration, built-in voltage, VOC, 

and efficiency, although catastrophic PID could also relate to shunting or interface 

recombination. In contrast to the PID-diminishing BSG substrates, SLG with Al2O3

diffusion barriers reduced PID without altering leakage current. Further experiments are 

needed on SLG with Al2O3 diffusion barriers with added alkali to increase the device 

efficiencies. 

Figure 15: (a) Efficiency means and standard 

deviations (error bars) and (b) champions as a 

function of time at -1000 V bias, 85°C, and 10% 

relative humidity for SLG (black squares), 

SLG/Al2O3 (gray squares), and BSG (red circles).

Figure 14: (a) Efficiency means and standard 

deviations (error bars) and (b) champions as a 

function of cumulative charge transferred at -

1000 V bias, 85°C, and 10% relative humidity for 

SLG (black squares), SLG/Al2O3 (gray squares),

and BSG (red circles) substrates.
17

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

These laboratory studies emulated field PID using smaller sample areas and shorter 

timescales. PID of encapsulated CIGS was due to alkali-metal ion drift from the glass 

substrate, followed by catastrophic accumulation of alkali metal in the junction. These 

findings indicate that PID testing can be accelerated by using a basis of Coulombs 

transferred. Similar studies of CdTe modules in the Photovoltaic Quality Assurance Task 

Force (PVQAT) project have shown that Coulombs transferred in the chamber for a given 

power-loss level relate well to Coulombs transferred in the field. For this project, two 

methods for mitigating PID were identified: using less-conductive glass and using a 

diffusion barrier on the glass to limit initial absorber alkali-metal content. Our results show 

that less-conductive BSG substrates reduce the Coulomb transfer rate and offer a 

processing solution for dramatically reducing PID.

Conclusions: Most milestones in the project were met, although some took slightly 

longer to complete than others. In particular, fabricating an ultra-thin CIGS solar cell with 

efficiency of 15% was more difficult than expected. This caused the annual milestones

1.2.3 and 2.2.4 to be completed later in the project than planned. Reducing metastability 

by using a Cd partial-electrolyte before the Zn(O,S) buffer layer was an unmet Quarterly 

Performance Indicator (QPI). We were able to do this once earlier in the project, but we 

were unable to replicate the results. The QPI dealing with reverse-biasing encapsulated 

NREL cells (3.2.1) also did not go as planned because NREL devices tended to break 

down at the grid lines unlike our partner cells, which did not have grids.

This project did demonstrate that investigating cell-level reliability is an effective way to 

solve module reliability problems. We were able to reduce metastability by adding CdS 

islands to our Zn(O,S) buffers. Reverse-bias damage was mitigated by removing the iZnO layer from devices, when using either a Zn(O,S) buffer or a CdS buffer. Potentialinduced degradation was also slowed by replacing the soda-lime back glass with a lowNa, high-K borosilicate glass. These changes could be implemented in modules to help 

solve the three main reliability problems in CIGS PV.

Budget and Schedule:

Path Forward: Open questions still exist in the field of cell-level reliability. We found that 

CdS islands reduce the metastability of CIGS devices with Zn(O,S). However, we did not 

explore other materials that may be able to perform a similar function. Reducing the Cd 

in the device stack is always a priority, so there are research opportunities in finding 

materials that can inject holes into the Zn(O,S) buffer layer, or alternative buffer layers 

that would provide stability without the use of Cd. The definition of metastability used in 

this project was of reversible changes. Other degradation mechanisms, such as 

irreversible performance decreases caused by heat and light-soaking, could be studied 

in a similar fashion. Reverse-bias behavior in solar cells is not commonly explored, and 

the field could benefit from having a device module that attempts to describe it. This would 

allow predictions of reverse-bias behavior in modified device structures before the actual 
18

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

fabrication occurs. Another area for study in PID is whether or not a device with only K 

and no Na will degrade as quickly as the devices on soda-lime glass. In addition, the 

front-grounded PID stress configuration should be explored because it has also been 

identified as a cause of degradation in modules. Finally, the framework we have used for 

studying cell-level reliability and using it to solve module-level problems could be 

expanded to other solar cell technologies. This is by no means an exhaustive list, but 

there is certainly room for additional discoveries in the little-studied field of cell-level 

reliability.

Publications Resulting from This Work: Not all of the publications resulting from the 

project work were able to be referenced in the text. Those already referenced will appear

again in the following references list. Some of the included references are collaborations 

between two SuNLaMP projects.

A. M. C. Alonso-Garcia, P. Hacke, S. Glynn, C. P. Muzzillo, and L. M. Mansfield, 

“Analysis of Potential-Induced Degradation in Soda-Lime Glass and BorosilicateGlass Cu(In,Ga)Se2 Samples,” IEEE Journal of Photovoltaics, 2018. Submitted.

B. M. A. Contreras, P. Hacke, and I. Repins, “Development of Cu(In,Ga)Se2 Test 

Coupons for Potential Induced Degradation Studies,” Paper in 2016 IEEE 43rd 

Photovoltaic Specialists Conference (PVSC), Portland, OR, 5–10 June 2016, pp. 

0857–0862.

C. S. Glynn, I. Repins, J. Burst, C. Beall, K. Bowers, and L. Mansfield, “Selective 

Excitation of Window and Buffer Layers in Chalcopyrite Devices and Modules,” Thin 

Solid Films, Vol. 655, pp. 70–76, 2018. 

D. S. P. Harvey, H. Guthrey, C. P. Muzzillo, L. Mansfield, G. Teeter, P. Hacke, S. 

Johnston, and M. Al-Jassim, “Investigating PID Shunting in Polycrystalline CIGS 

Devices via Multi-Scale, Multi-Technique Characterization,” IEEE Journal of 

Photovoltaics, 2018. Submitted.

E. S. Johnston, E. Palmiotti, A. Gerber, L. Mansfield, T. J. Silverman, M. Al-Jassim, and 

A. Rockett, “Identifying Reverse-bias Breakdown Sites in CuInxGa(1-x)Se2 Photovoltaic 

Modules,” Paper in IEEE PVSC, Washington, D.C., 2017.

F. S. Johnston, D. Sulas, E. Palmiotti, A. Gerber, H. Guthrey, L. Mansfield, T. J. 

Silverman, M. Al-Jassim, and A. Rockett, “Thin-Film Module Reverse-Bias Breakdown 

Sites Identified by Thermal Imaging,” Paper in WCPEC-7/IEEE PVSC, Waikaloa, HI, 

June 10–15, 2018.

G. L. M. Mansfield, A. Kanevce, S. P. Harvey, K. Bowers, C. Beall, S. Glynn, and I. L. 

Repins, “Efficiency Increased to 15.2% for Ultra-Thin Cu(In,Ga)Se2 Solar Cells,” 

Progress in Photovoltaics: Research and Applications, Vol. 26, No. 11, pp. 949–954, 

2018. https://doi.org/10.1002/pip.3033

H. H. R. Moutinho, B. To, C. S. Jiang, C. Xiao, C. Muzzillo, P. Hacke, J. Moseley, J. 

Tynan, N. G. Dhere, L. Mansfield, M. M. Al-Jassim, and S. Johnston, “Artifact-Free 

Coring Procedures for Removing Samples from Photovoltaic Modules for Microscopic 

Analysis,” Paper in WCPEC-7/IEEE PVSC, Waikaloa, HI, June 10–15, 2018.

I. C. P. Muzzillo, S. Glynn, P. Hacke, H. R. Moutinho, M. R. Young, G. Teeter, I. L. 

Repins, and L. M. Mansfield, “Potential-Induced Degradation of Cu(In,Ga)Se2 Solar 

Cells: Alkali Metal Drift and Diffusion Effects,” IEEE Journal of Photovoltaics, Vol. 8, 

No. 5, pp. 1337–1342, 2018. http://dx.doi.org/10.1109/JPHOTOV.2018.2858549
19

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

J. E. Palmiotti, S. Johnston, A. Gerber, H. Guthrey, A. Rockett, L. Mansfield, T. J. 

Silverman, and M. Al-Jassim, “Identification and Analysis of Partial Shading 

Breakdown Sites in CuInxGa(1-x)Se2 Modules,” Solar Energy, Vol. 161, pp. 1–5, 2018. 

http://dx.doi.org/10.1016/j.solener.2017.12.019

K. I. L. Repins, S. Harvey, K. Bowers, S. Glynn, and L. M. Mansfield, “Predicting Ga and 

Cu Profiles in Co-evaporated Cu(In,Ga)Se2 Using Modified Diffusion Equations and a 

Spreadsheet,” MRS Advances, pp. 1–6, 2017. http://dx.doi.org/10.1557/adv.2017.350

L. T. J. Silverman, L. Mansfield, I. Repins, and S. Kurtz, “Damage in Monolithic Thin-Film 

Photovoltaic Modules Due to Partial Shade,” IEEE Journal of Photovoltaics, Vol. 6, 

No. 5, pp. 1333–1338, 2016. http://dx.doi.org/10.1109/JPHOTOV.2016.2591330

Publications most closely related to previous work in CIGS or CZTS

a. J. Bailey, D. Poplavskyy, G. Zapalac, L. Mansfield, and W. Shafarman, “VoltageInduced Charge Redistribution in Cu(In,Ga)Se2 Devices Studied with High-Speed 

Capacitance-Voltage Profiling,” IEEE Journal of Photovoltaics, 2018. Accepted with 

minor revisions.

b. M. Bär, I. Repins, L. Weinhardt, J. H. Alsmeier, S. Pookpanratana, M. Blum, W. Yang, 

C. Heske, R. G. Wilks, and R. Noufi, “Zn-Se-Cd-S Interlayer Formation at the 

CdS/Cu2ZnSnSe4 Thin-Film Solar Cell Interface,” ACS Energy Letters, Vol. 2, No. 7, 

pp. 1632–1640, 2017. http://dx.doi.org/10.1021/acsenergylett.7b00140

c. R. L. Garris, S. Johnston, J. V. Li, H. L. Guthrey, K. Ramanathan, and L. M. Mansfield, 

“Electrical Characterization and Comparison of CIGS Solar Cells Made with Different 

Structures and Fabrication Techniques,” Solar Energy Materials and Solar Cells, Vol. 

174, pp. 77–83, 2018. https://doi.org/10.1016/j.solmat.2017.08.027

d. R. L. Garris, L. M. Mansfield, B. Egaas, and K. Ramanathan, “Low-Cd CIGS Solar 

Cells Made with a Hybrid CdS/Zn(O,S) Buffer Layer,” IEEE Journal of Photovoltaics, 

Vol. 7, No. 1, pp. 281–285, 2017. http://dx.doi.org/10.1109/JPHOTOV.2016.2617041

e. M. D. Heinemann, M. F. A. M. van Hest, M. Contreras, J. D. Perkins, A. Zakutayev, 

C. A. Kaufmann, T. Unold, D. S. Ginley, and J. J. Berry, “Amorphous Oxides as 

Electron Transport Layers in Cu(In,Ga)Se2 Superstrate Devices,” Physica Status 

Solidi (A) Applications and Materials Science, Vol. 214, No. 5, 2017. 

10.1002/pssa.201600870

f. H. Hempel, R. Eichberger, I. Repins, and T. Unold, “The Effect of Cu-Zn Disorder on 

Charge Carrier Mobility and Life Time in Cu2ZnSnSe4,” Submitted to Thin Solid Films, 

2018. 

g. H. Hempel, A. Redinger, I. Repins, C. Moisan, G. Larramona, G. Dennler, M. 

Handwerg, S. F. Fischer, R. Eichberger, and T. Unold, “Intragrain Charge Transport 

in Kesterite Thin Films—Limits Arising from Carrier Localization,” Journal of Applied 

Physics, Vol. 120, No. 17, pp. 175302, 2016. http://dx.doi.org/10.1063/1.4965868

h. S. A. Jensen, S. Glynn, A. Kanevce, P. Dippo, J. V. Li, D. H. Levi and D. Kuciauskas, 

“Beneficial Effect of Post-Deposition Treatment in High-Efficiency Cu(In,Ga)Se2 Solar 

Cells through Reduced Potential Fluctuations,” Journal of Applied Physics, Vol. 120, 

No. 6, 2016. http://dx.doi.org/10.1063/1.4960344

i. S. A. Jensen, A. Kanevce, L. M. Mansfield, S. Glynn, S. Lany, and D. Kuciauskas, 

“Optically Induced Metastability in Cu(In,Ga)Se2,” Scientific Reports, Vol. 7, No. 1, pp. 

s41598–41017, 2017. http://dx.doi.org/10.1038/s41598-017-14344-6
20

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

j. C. S. Jiang, L. M. Mansfield, S. Glynn, C. Xiao, R. Garris, S. Christensen, and M. M. 

Al-Jassim, “Effect of Window-Layer Materials on p-n Junction Location in 

Cu(In,Ga)Se2 Solar Cells,” IEEE Journal of Photovoltaics, 2018. Accepted

k. L. M. Mansfield, B. To, R. C. Reedy, M. R. Young, K. Bowers, and K. Ramanathan, 

“Investigation of Sb-Containing Precursors for Cu(In,Ga)Se2 Thin Films through 

Design of Experiments,” Paper in 2016 IEEE 43rd Photovoltaic Specialists 

Conference (PVSC), 5–10 June 2016, pp. 1157–1162, 

l. M. Mezher, L. M. Mansfield, K. Horsley, M. Blum, R. Wieting, L. Weinhardt, K. 

Ramanathan, and C. Heske, “KF Post-Deposition Treatment of Industrial Cu(In, 

Ga)(S,Se)2 Thin-Film Surfaces: Modifying the Chemical and Electronic Structure,” 

Applied Physics Letters, Vol. 111, No. 7, pp. 071601, 2017. 

http://dx.doi.org/10.1063/1.4998445

m. C. P. Muzzillo, J. V. Li, L. M. Mansfield, K. Ramanathan, and T. J. Anderson, “Surface 

and Bulk Effects of K in Highly Efficient Cu1-xKxInSe2 Solar Cells,” Solar Energy 

Materials and Solar Cells, Vol. 185, pp. 45–53, 2018. 

http://dx.doi.org/10.1016/j.solmat.2018.05.013

n. M. C. P., P. J. D., T. H. Ming, G. Wei and A. Tim, “Revealing the Beneficial Role of K 

in Grain Interiors, Grain Boundaries, and at the Buffer Interface for Highly Efficient

CuInSe2 Solar Cells,” Progress in Photovoltaics: Research and Applications, Vol. 26, 

No. 10, pp. 825–834, 2018. http://dx.doi.org/doi:10.1002/pip.3022

o. S. Paul, R. Lopez, I. L. Repins, and J. V. Li, “Study of Charge Transport Properties in 

a ZnO/CdS/Cu(In,Ga)Se2 Solar Cell via Admittance Spectroscopy,” Journal of 

Vacuum Science and Technology B: Nanotechnology and Microelectronics, Vol. 36, 

No. 2, 2018. http://dx.doi.org/10.1116/1.5013046

p. I. Repins, L. Mansfield, A. Kanevce, S. A. Jensen, D. Kuciauskas, S. Glynn, T. Barnes, 

W. Metzger, J. Burst, C. S. Jiang, P. Dippo, S. Harvey, G. Teeter, C. Perkins, B. 

Egaas, A. Zakutayev, J. H. Alsmeier, T. Lusky, L. Korte, R. G. Wilks, M. Bar, Y. Yan, 

S. Lany, P. Zawadzki, J. S. Park, and S. Wei, “Wild Band Edges: The Role of Bandgap 

Grading and Band-Edge Fluctuations in High-Efficiency Chalcogenide Devices,” 

Paper Vol. 2016-November, pp. 309–314.

q. L. T. Schelhas, K. H. Stone, S. P. Harvey, D. Zakhidov, A. Salleo, G. Teeter, I. L. 

Repins, and M. F. Toney, “Point Defects in Cu2ZnSnSe4 (CZTSe): Resonant X-Ray 

Diffraction Study of the Low-Temperature Order/Disorder Transition,” Physica Status 

Solidi (B) Basic Research, Vol. 254, No. 9, 2017. 

http://dx.doi.org/10.1002/pssb.201700156

r. K. H. Stone, S. T. Christensen, S. P. Harvey, G. Teeter, I. L. Repins, and M. F. Toney, 

“Quantifying Point Defects in Cu2ZnSn(S,Se)4 Thin Films using Resonant X-Ray 

Diffraction,” Applied Physics Letters, Vol. 109, No. 16, pp. 161901, 2016. 

http://dx.doi.org/10.1063/1.4964738

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21

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

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