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

Conference Paper

NREL/CP-5K00-77483

September 2020

High Efficiency Silicon Module 

Degradation - From Atoms to Systems

Preprint

D.C. Jordan,1 D.B. Sulas-Kern,1 S. Johnston,1

H.R. Moutinho,1 C. Xiao,1 C.S. Jiang,1 M. Young,1

A.G. Norman,1 C. Deline,1 I. Repins,1 R. Bhoopathy,2

O. Kunz,2 Z. Hameiri,2 C. Sainsbury3

1 National Renewable Energy Laboratory

2 USNW Australia

3 Sinton Instruments

Presented at the 37th European Photovoltaic Solar Energy Conference and 

Exhibition (EU PVSEC 2020)

September 7-11, 2020
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

Golden, CO 80401

303-275-3000 • www.nrel.gov

Conference Paper

NREL/CP-5K00-77483

September 2020

High Efficiency Silicon Module 

Degradation - From Atoms to Systems

Preprint

D.C. Jordan,1 D.B. Sulas-Kern,1 S. Johnston,1

H.R. Moutinho,1 C. Xiao,1 C.S. Jiang,1 M. Young,1

A.G. Norman,1 C. Deline,1 I. Repins,1 R. Bhoopathy,2

O. Kunz,2 Z. Hameiri,2 C. Sainsbury3

1 National Renewable Energy Laboratory

2 USNW Australia

3 Sinton Instruments

Suggested Citation

Jordan, D.C., D.B. Sulas-Kern, S. Johnston, H.R. Moutinho, C. Xiao, C.S. Jiang, M. 

Young, A.G. Norman, C. Deline, I. Repins, R. Bhoopathy, O. Kunz, Z. Hameiri, C. 

Sainsbury. 2020. High Efficiency Silicon Module Degradation - From Atoms to Systems: 

Preprint. Golden, CO: National Renewable Energy Laboratory. NREL/CP-5K00-77483. 

https://www.nrel.gov/docs/fy20osti/77483.pdf. 
NOTICE

This work was authored in part 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 the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy (EERE) under Solar 

Energy Technologies Office (SETO) Agreement Number 30295. The views expressed herein do not necessarily 

represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by 

accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, 

irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for 

U.S. Government purposes.

This report is available at no cost from the National Renewable 

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

U.S. Department of Energy (DOE) reports produced after 1991 

and a growing number of pre-1991 documents are available 

free via www.OSTI.gov.

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

NREL 46526.

NREL prints on paper that contains recycled content.
HIGH EFFICIENCY MODULE DEGRADATION – FROM ATOMS TO SYSTEMS

D.C. Jordan*1, D.B. Sulas-Kern1, S. Johnston1, H.R. Moutinho1, C. Xiao1, C.S. Jiang1, M. Young1, A.G. Norman,1, C.

Deline1, I. Repins1, R. Bhoopathy2, O. Kunz2, Z. Hameiri2, C. Sainsbury3

1National Renewable Energy Laboratory (NREL), 15013 Denver West Parkway., Golden, CO, USA

2SPREE, UNSW Sydney, Kensington, NSW, 2052, Australia

3Sinton Instruments, Boulder, CO 80301 USA

ABSTRACT: For photovoltaics (PV) to be cost competitive with traditional energy sources, reliability is of critical 

importance. Historically, PV reliability has focused on the module packaging because degradation and failure modes 

were directly linked to the packaging. Today, in addition to module packaging, cell related reliability issues can 

increasingly be observed. We have investigated PV systems of high-efficiency modules such as silicon heterojunction 

(HJ) and passivated emitter and rear cell (PERC). System degradation of these technologies is found to be no worse 

than systems using conventional cell technologies. Module performance loss, for HJ and PERC technologies, shows

open-circuit voltage reduction indicative of cell level changes. For HJ modules, possible hydrogen concentration 

changes and a rougher interface between the amorphous silicon and the silicon is observed, although more samples are 

needed to confirm these findings. The PERC modules show hydrogen changes in the front and rear of the cell with

more changes pronounced at the front. Importantly, these two case studies demonstrate that cell level understanding is 

required to accurately predict module and system performance for high-efficiency technologies.

1 INTRODUCTION

Today photovoltaics (PV) systems are cost 

competitive with traditional energy sources, however, 

efficiency and reliability are of vital importance [1]. 

Efficiency is important for obvious direct reasons, but has 

also an indirect benefit through reduced area, balance-ofsystems (BOS), labor, materials requirements etc. 

However, the cost competitiveness is achieved over the 

life of the system, thus, reliability may not be as obvious,

but can be equally important. Energy loss can be caused 

by underperformance and/or failures or disruptions at the 

system, module and cell level. Minimizing and 

understanding underperformance and failures at all levels 

are a vital part of PV reliability.

Traditionally, crystalline silicon (c-Si) system field 

degradation was dominated by losses in short-circuit 

current (ISC) or fill factor (FF), depending on the 

underlying degradation mechanism [2]. As cells and 

modules have evolved towards their theoretical efficiency 

limits, more cell-related phenomena, such as light induced 

degradation (LID) or light and elevated temperature 

induced degradation (LeTID), manifested through opencircuit voltage (VOC) losses, have been observed impacting 

modules and systems [3,4]. Despite the introduction of 

high-efficiency modules into the commercial market more 

than a decade ago, multi-year field studies of these 

technologies are not as common as desired [5,6]. 

In this paper we focus on two c-Si high-efficiency 

technologies, heterojunction (HJ) and passivated emitter 

and rear cell (PERC). We examine their performance loss 

from the system to the cell and nanoscale levels, linking 

overall energy output with fundamental materials changes 

during outdoor aging.

2 SYSTEM PERFORMANCE 

In the PV Fleet Performance Data Initiative time series 

data are collected across the USA to assess the overall PV 

fleet performance and distill regional trends [7]. Figure 1 

shows a cumulative distribution function of the 

performance loss rate by systems using high-efficiency 

modules such as PERC and HJ. The systems using PERC 

modules originated from one manufacturer. For 

comparison, conventional aluminum back surface field 

(Al-BSF) modules from the same manufacturer in a 

similar climate zone and mounting configuration are also 

shown. Each performance loss rate was determined from

AC power data using satellite data for irradiance and 

RdTools as the methodology [8]. The uncertainty of the 

performance loss rate is indicated for each system by a 

horizontal line of the respective color. At the median, the 

performance loss rate for the PERC systems is slightly 

smaller than the Al-BSF equivalent. The positive tail of the 

PERC systems may be caused by the substantially shorter 

exposure time, measurement uncertainty and possible 

start-up problems that are fixed in time. The HJ systems 

show a slightly smaller performance loss rate possibly 

aided by more systems installed in cooler climates. Given 

this limited data set we do not observe performance loss 

rates that are atypical or uneconomical. 

Figure 1: Cumulative distribution function of systems 

using PERC, Al-BSF and heterojunction cell technologies. 

Uncertainties of each performance loss rate is indicated by 

horizontal bar in respective colors. The average age for 

each category is given in the inset.

3 SILICON HETEROJUNCTION MODULES

Silicon heterojunction technology has received 

considerable attention not least because of record 

efficiency for c-Si cells [9]. As a commercial product, HJ 

are attractive because of fewer processing steps compared 

to a PERC manufacturing line, and advances in availability 

of low-cost high-quality n-type wafers, improvements in 

metallization etc. [10]. In the HJ structure, the n-type Si 

wafer is enveloped by a thin hydrogenated amorphous 

This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. 1
silicon (a-Si:H) layer and capped by a transparent 

conducting oxide (TCO) because of poor lateral 

conductivity of a-Si. Other attractive features for field 

performance include the low temperature coefficient and a

high bifacial factor [11]. Several field studies showed 

gradual Voc loss, hinting that cell changes take place, 

although the detected performance losses were generally 

within the warranty [12,13,14]. In this section we continue 

our investigation into the mechanisms of the VOC loss and 

small series resistance (RS) increase that we reported 

previously. The system under investigation was installed 

at the National Renewable Energy Laboratory (NREL), 

USA for ca. 10 years. In addition, to the fielded module 

we also had a control module that was kept indoors during 

the same time. 

Figure 2: EL imaging of the fielded module at forwardbias equivalent of ISC (a). One of the cells selected for 

enlarged cell imaging by high-current EL (b), PL (c), linescan PL/EL ratio (d) and low-/high-current ratio EL (e). 

Dark lock-in thermography of the same cell (f) and PL of 

a 3/4” cored piece from the cell (g). The blue circle 

highlights an area indicated by a darker region in El and 

PL but lighter contrast in the ratio image (d) and the area 

of the cored piece. 

Figure 2(a) shows an electroluminescence (EL) image 

of one of the fielded modules at forward-bias equivalent of 

ISC (+3.8A). A few cracked cells can be observed that were 

caused during transport to various characterization 

laboratories. These cells are not the causes of the observed 

degradation, as we have shown in previous 

characterization and can be ignored for the subsequent

discussion. The blue highlighted cell is one example that 

is further explored with high-current EL and 

photoluminescence (PL) in Fig. 2(b)-(c). Regions across 

the cell that are dark in EL and bright in PL indicate

resistance issues, and regions that are dark in both imaging 

techniques indicate degradation of material quality. 

Figure 3: EL imaging of the fielded module at forwardbias equivalent of ISC (a). One of the cells selected for 

enlarged cell imaging by high-current EL (b), PL (c), linescan PL/EL ratio (d) and low-/high-current ratio EL (e). 

Dark lock-in thermography of the same cell (f) and PL of 

a 3/4” cored piece from the cell (g). The blue circle 

highlights the area of the cored piece (e). 

Figure 2(d) displays the same cell as the ratio between 

line-scan PL and EL that enhances RS defects (brighter 

areas), while suppressing the lifetime related defects due 

to an inversion in luminescence intensity as reported in 

[15]. The ratio of low-/high-current EL is shown in Fig. 

2(e), where low current is 0.1 times the forward-bias 

equivalent of ISC. Similar to the line-scan PL example in 

Fig. 2(d), darker regions show less resistive impact. Dark 

lock-in thermography (DLIT) is another non-destructive 

characterization tool that shows cooler regions on the leftThis report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. 2
hand side of the cell in Fig. 2(f) commensurate with the 

resistive areas that receive less current flow. The blue 

circle indicates an area that was physically removed from 

the cell for further materials characterization [16]. The 

successful extraction from the module is corroborated by 

the PL image of the cored section in Fig. 2(g). It is 

conceivable that the different regions across the cell 

visible in Fig. 2 may have different underlying degradation 

mechanisms.

The equivalent images for the control module are 

displayed in Fig. 3. It can be noted that the two ratio 

images, Fig. 3(d)-(e), show a generally darker shade than 

the fielded module, indicative of overall lower resistance. 

Additionally, it should be noted that at the same current 

injection, the luminescence intensity in the control module 

was approximately twice that of the fielded module, 

consistent with higher VOC (lower loss) in the control. One 

of the cells that we further investigated is indicated by a 

blue rectangle, and the cored piece is indicated by a blue 

circle. 

Figure 4: Scanning spreading resistance microscopy 

(SSRM) of cored pieces from the control (left) and fielded 

module (right). The average value for each sample is 

indicated by the cross. 

Figure 5: Hydrogen concentration from dynamic

secondary ion mass spectroscopy traces for a fielded, 

control and a control sample that was heated to 1750C for 

20 hours (a). The maximum of hydrogen concentration 

derivative for control and fielded samples (b).

Because the TCO is integral for lateral conductivity in the 

HJ structure, we investigated whether the resistance of the 

TCO contributes to the overall higher RS by scanning 

spreading resistance microscopy (SSRM). SSRM is a twoterminal resistance mapping technique based on an atomic 

force microscope (AFM). Because of the small probe 

contact area from the AFM tip, the current route decreases 

quickly away from the tip. Therefore, the resistance is 

dominated by the local TCO regardless of the current path 

through the underlying Si device. The results from several 

pieces of the fielded and control sample are depicted in 

Fig. 4. Substantial variation within a given sample can be 

seen for both sets of pieces, however no statistically 

significant difference between the fielded module and the 

control module can be discerned [17]. Thus, it appears that 

the conductivity of the TCO did not degrade during the 10-

year field exposure, despite the apparent increase in Rs at 

the module level.

Several cored samples from the fielded and control 

module were investigated by dynamic secondary ion mass 

spectroscopy (d-SIMS). Figure 5(a) shows the hydrogen 

(H) concentration for a fielded (blue diamonds), a control 

(red circles) and a control sample that was heated to 1750C 

for 20 hours (grey squares). Because of the texturing of the 

Si wafer, the sample orientation relative to the d-SIMS 

sputtering beam can have considerable impact on the 

profile shape and location of the profile maximum. 

However, these samples were aligned with similar sample 

orientation for best comparison. The fielded sample 

exhibits a secondary peak especially compared to the 

control sample trace. The heated control sample also 

appears to exhibit a shoulder that could indicate a 

secondary peak. We plan to continue d-SIMS studies to 

further determine the degree to which the secondary peak 

is related to texturing effects versus whether a real redistribution of hydrogen occurs to account for the change 

in H profile that we observe.

To determine the location of the secondary H 

concentration peak, the derivative for all unheated control 

samples is contrasted against samples from the fielded 

module in Fig. 5(b). The depth of H concentration for the 

fielded samples is statistically significant and less than for 

the unheated control samples at a p-value of 0.01. 

However, the sample orientation was not the same for all 

samples. Therefore, despite the significance, more 

samples and careful alignment of the incident sputtering 

beam with respect to the pyramid texture orientation are 

required to confirm this difference, which could indicate a 

possible H re-distribution in the sample. 

Finally, Fig. 6 displays high-resolution transmission 

electron microscopy (TEM) images of the fielded and 

control module that show the physical structure of the 

electrical junction. The a-Si:H layer is sandwiched 

between the c-Si wafer and the multicrystalline TCO. The 

root mean square (RMS) roughness of the a-Si:H/c-Si 

interface indicates that the interface may be rougher for the 

fielded sample compared to the control and recent highefficiency cells [18]. However, the TEM contrast,

especially for the fielded module is not as high as desired 

because surface texture the facets on the Si wafer are not 

exactly parallel to the {111} planes and made alignment in 

This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. 3
the TEM difficult. Therefore, more cross-sectional 

samples will be characterized to corroborate the current 

findings and their role in the energy loss in these types of 

modules. Yet, this case study is a good demonstration how 

cell phenomena at the atomic level can have considerable 

impact at the macroscopic level. 

Figure 6: Cross section transmission electron microscopy 

images of the fielded (a) and the control module (b). The 

root mean square (RMS) roughness at the a-Si:H/Si 

interface is also given.

4 PERC MODULES

The second case study of the synergistic nature of cell, 

module and system level involves PERC modules from a 

different manufacturer. Although the PERC structure was 

first reported in 1989 it has found its way into commercial 

products only in the last decade [19]. Monofacial PERC, 

bifacial PERC, and Al-BSF modules and equivalent 

strings of the same type were installed at NREL for 2-3 

years. Both PERC modules were packaged in a glass-glass 

construction whereas the Al-BSF had a glass-backsheet 

construction. A bifacial PERC control module was kept 

indoors during the same time. Performance loss rates for 

individual current-voltage parameters are shown in Fig. 7. 

The maximum power (PMAX) loss for the Al-BSF module 

is in the typical historical range and the loss is roughly

divided between short-circuit current (ISC) and fill factor 

(FF) depending on the underlying degradation mechanism. 

In addition, no open-circuit voltage (VOC) loss is also 

typically observed for this technology. The monofacial 

PERC module shows similar PMAX loss as the Al-BSF 

module but VOC loss is now clearly visible. 

The bifacial PERC module also shows VOC loss but 

exhibits additional ISC and FF loss leading to a slightly 

higher overall performance loss. Indoor measurements 

(filled symbols) confirm the outdoor measurements (open 

symbols). Lifetime curves taken from Suns-VOC

measurements for these 3 modules are shown in Fig. 7(b). 

At Pmax the lifetime between the modules is very similar 

but at higher injection levels the PERC modules show 

considerably lower lifetimes corroborating the VOC loss. 

EL and PL imaging, Fig. 8, shows no obvious defects 

such as cracked cells, thus the VOC loss may indicate again 

cell level problems. The bifacial module exhibits resistive 

regions (red circle) and areas of material quality issue 

(blue circle) similar to the HJ modules. In contrast, the 

monofacial module shows mostly resistive areas indicated

by slight darkening in areas of the EL but more uniformly 

bright in PL. Subsequently, samples from these modules 

were cored for further materials characterization. Because 

of the glass-glass package, the extraction was more 

challenging than for glass-backsheet constructions

resulting in smaller samples. However, the areas were 

large enough to allow for d-SIMS measurements.

Figure 7: Performance loss rates for Al-BSF, monofacial 

PERC and bifacial PERC modules and strings from 

manufacturer B (a). Lifetime curves obtained from SunsVOC measurements (b).

This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. 4
Figure 8: EL (a, c) and PL (b, d) images for bifacial (top) 

and monofacial (bottom) PERC modules. Red and blue 

circles indicate resistive problems (dark in EL and bright 

in PL) and material issues (dark in EL and PL),

respectively.

The hydrogen concentration is shown for the bifacial 

control (grey squares), the fielded bifacial (red circles), 

and the fielded monofacial module (blue diamonds) from 

the front in Fig. 9(a) and the back in Fig. 9(b). The sample 

orientation for all samples was fixed with respect to the 

fingers to minimize texturing artifacts, and the 

concentration normalized to the maxima. At the front

surface, the bifacial control sample shows a pronounced H 

peak that slowly declines into the bulk of the cell. In 

contrast, fielded bifacial sample shows a secondary peak 

and a much broader distribution into the bulk. The 

monofacial sample shows a broader peak and distributions 

that is broader than the bifacial control but not as wide as 

the fielded bifacial sample. This data suggests that H may 

diffuse into the bulk of the cell. At the back, we see a 

similar pattern for all 3 samples, although not as 

pronounced as on the front of the cell. This further 

suggests that H may be re-distributed in the fielded 

modules compared to the control module.

Figure 9: D-SIMS traces of H concentration for the PERC 

module from the front (a) and the back (b).

6 CONCLUSIONS

We have investigated PV systems comprised of highefficiency modules such HJ and PERC. System 

degradation of these technologies was found to be no 

worse than systems using conventional cell technologies. 

Module performance loss for both technologies show VOC

loss indicating cell level changes. For HJ, possible 

hydrogen distribution changes and a rougher a-Si:H/c-Si 

interface were observed, although more samples need to 

be analyzed to confirm these findings. The PERC modules 

similarly appear to show hydrogen changes in the front and 

rear of the cell, although the changes appear more 

pronounced at the front. More samples are needed to 

validate these findings. Finally, these two case studies 

demonstrate that cell and materials level understanding is 

helpful performance for high-efficiency technologies. 

7 ACKNOWLEDGEMENTS

The authors would like to thank the PV Fleet group, 

Michael Deceglie, Kevin Anderson, Kirsten Perry, Robert 

White, Martin Green, Stefan DeWolf, Zach Holman, 

Mariana Bertoni, Robert Flottenmesh, Katherine Jordan. 

This work was authored in part by Alliance for Sustainable 

Energy, LLC, the manager and operator of the National 

Renewable Energy Laboratory for the U.S. Department of 

Energy (DOE) under Contract No. DE-AC36-

08GO28308. Funding provided by the U.S. Department of 

Energy’s Office of Energy Efficiency and Renewable 

Energy (EERE) under Solar Energy Technologies Office 

This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. 5
(SETO) Agreement Number 30295. The views expressed 

in the article do not necessarily represent the views of the 

DOE or the U.S. Government. The U.S. Government 

retains and the publisher, by accepting the article for 

publication, acknowledges that the U.S. Government 

retains a nonexclusive, paid-up, irrevocable, worldwide 

[1] EIA (2020). Annual Energy Outlook 2020 with 

Projections to 2050. (No. AEO2020).

[2] D.C. Jordan, J.H. Wohlgemuth, S.R Kurtz, 

Technology and Climate Trends in PV Module 

Degradation, 27th European Photovoltaic Solar 

Energy Conference, Frankfurt, Germany, (2012), 

3118 - 3124.

[3] B. Hallam, M. Abbott, J. Bilbao, P. Hamer N. 

Gorman, M. Kim, D. Chen, K. Hammerton, D. Payne, 

C. Chan,N. Nampalli, S. Wenham., Energy Procedia, 

92, (2016), 42 ¬ 51

[4] F. Kersten, P. Engelhart, H.-C. Ploigt, A. 

Stekolnikov, T. Lindner, F. Stenzel, M. Bartzsch, A. 

Szpeth, K. Petter, J. Heitmann, J.W. Müller, A New 

mc-Si Degradation Effect called LeTID, 42nd IEEE 

Photovoltaic Specialists Conference, New Orleans, 

LA, 2015

[5] D.C. Jordan, C. Deline, M. Deceglie, T.J. Silverman, 

W. Luo, PV Degradation – Mounting & Temperature, 

46th IEEE Photovoltaic Specialists Conference, 

Chicago, IL, USA, 2019. 

[6] M.G. Deceglie , T.J. Silverman, S.W. Johnston, J.A. 

Rand , M.J. Reed, R. Flottemesch, I.L. Repins, Light 

and Elevated Temperature Induced Degradation 

(LeTID) in a Utility-Scale Photovoltaic System, 

IEEE Journal of Photovoltaics, 10 (4) (2020), 1084.

[7] C. Deline, R. White, M. Muller, K. Anderson, K. 

Perry, M. Deceglie, L. Simpson, D. Jordan, M. 

Bolinger PV Fleet Performance Data Initiative

Program and Methodology, 46th IEEE Photovoltaic 

Specialists Conference, Chicago, IL, USA, 2019.

[8] D. Jordan, C. Deline, S. Kurtz, G. Kimball, M. 

Anderson, Robust PV Degradation Methodology and 

Application, IEEE Journal of Photovoltaics, 8(2) 

(2018), 525-531.

[9] K. Yoshikawa, H. Kawasaki,W. Yoshida, T. Irie, K. 

Konishi, K. Nakano, T. Uto, D. Adachi, M. 

Kanematsu, H. Uzu, K. Yamamoto, “Silicon 

heterojunction solar cell with interdigitated back 

contacts for a photoconversion efficiency over 26%”, 

Nature Energy, 2, (2017), 17032.

[10] C. Ballif, M. Boccard, A. Descoeudres, C. Allebé, A. 

Faes, O. Dupré, J. Haschke, P.-J. Ribeyron, M. 

license to publish or reproduce the published form of this 

work, or allow others to do so, for U.S. Government 

purposes.

8 REFERENCES

Despeisse, Solving all bottlenecks for silicon

heterojunction technology, PV International, (2019).

[11] S. DeWolf, A. Descoeudres, Z.C. Holman, C. Ballif, 

High-efficiency Silicon Heterojunction Solar Cells: 

A Review, Green, 2 (2012), 7–24

[12] D.C. Jordan , C. Deline , S. Johnston, S.R. Rummel, 

B.Sekulic, P. Hacke , S.R. Kurtz , K.O. Davis , E.J.

Schneller , X.Sun , M.A. Alam, R.A. Sinton, Silicon 

Heterojunction System Field Performance, IEEE 

Journal of Photovoltaics, 8(1), (2018), 177 182.

[13] T. Ishii, A. Masuda, Annual degradation rates of 

recent crystalline silicon photovoltaic modules, 

Progress in Photovoltaics, 25(12), (2017), 953967.

[14] W. Luo, Y. Sheng K., P. Hacke, D. Jordan, L. Zhao, 

S. Ramakrishna, A.G. Aberle, T. Reindl, Analysis of 

the long-term performance degradation of crystalline 

silicon photovoltaic modules in tropical climates, 

Journal of Photovoltaics, 9(1), (2019), 266 ¬ 271.

[15] I. Zafirovska, M. K. Juhl, J. W. Weber, J. Wong, T. 

Trupke, “Detection of Finger Interruptions in Silicon 

Solar Cells Using Line Scan Photoluminescence 

Imaging,” IEEE Journal Photovoltaics, 7(6), (2017), 

1496–1502.

[16] H. Moutinho, B. To, D. Sulas-Kern, C.S. Jiang, M. 

Al-Jassim, S. Johnston, Advances in Coring 

Procedures of Silicon Photovoltaic Modules, 47th

IEEE Photovoltaic Specialists Conference, virtual, 

2020.

[17] C.-S. Jiang, D.B. Sulas-Kern, H.R. Moutinho, D.C. 

Jordan, C. Xiao, S. Johnston, and M.M. Al-Jassim, 

Local resistance measurement for degradations of cSi heterojunction with intrinsic thin layer (HIT) solar 

modules, 47th IEEE Photovoltaic Specialists 

Conference, virtual, 2020.

[18] X. Ru, M. Qu, J. Wang, T. Ruan, M. Yang, F. Peng, 

W. Long, K. Zheng, H. Yan, X. Xu, 25.11% 

efficiency silicon heterojunction solar cell with low 

deposition rate intrinsic amorphous silicon buffer 

layers, Solar Energy Materials and Solar Cells, 215, 

(2020). 

[19] M.A. Green, The Passivated Emitterand Rear Cell

(PERC): From conception to mass production, Solar 

Energy Materials & Solar Cells, 143, (2015), 190-

197.

This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications. 6