- Email: [email protected]
Relaxor Ferroelectric Capacitors Embrace Polymorphic Nanodomains
the full potential of this approach. For now, it is a welcome and promising new tool to help advance organic photovoltaics and other device platforms based on organic semiconductors. 1. Fraunhofer Institute (2015). Photovoltaics Report. https://www.ise.fraunhofer.de. 2. Yuan, J., Zhang, Y., Zhou, L., Zhang, G., Yip, H.-L., Lau, T.-K., Lu, X., Zhu, C., Peng, H., Johnson, P.A., et al. (2019). Singlejunction organic solar cell with over 15%
efficiency using fused-ring acceptor with electron-deficient core. Joule 3, 1140–1151. 3. Meng, L., Zhang, Y., Wan, X., Li, C., Zhang, X., Wang, Y., Ke, X., Xiao, Z., Ding, L., Xia, R., et al. (2018). Organic and solution-processed tandem solar cells with 17.3% efficiency. Science 361, 1094–1098. 4. Lin, Y., Wang, J., Zhang, Z.G., Bai, H., Li, Y., Zhu, D., and Zhan, X. (2015). An electron acceptor challenging fullerenes for efficient polymer solar cells. Adv. Mater. 27, 1170–1174. 5. NREL (2019). Best Research-Cell Efficiencies. NREL. https://www.nrel.gov/.
6. Lami, V., Weu, A., Zhang, J., Chen, Y., Fei, Z., Heeney, M., Friend, R.H., and Vaynzof, Y. (2019). Visualizing the vertical energetic landscape in organic photovoltaics. Joule 3, this issue, 2513–2534. 7. Kahn, A. (2016). Fermi level, work function and vacuum level. Mater. Horiz. 3, 7–10. 8. Postcavage, W.J., Yoo, S., and Kippelen, B. (2008). Origin of the open-circuit voltage in multilayer heterojunction organic solar cells. Appl. Phys. Lett. 93, 193308. 9. Vandewal, K., Tvingstedt, K., Gadisa, A., Ingana¨s, O., and Manca, J.V. (2009). On the origin of the open-circuit voltage of polymer-fullerene solar cells. Nat. Mater. 8, 904–909.
Preview
Relaxor Ferroelectric Capacitors Embrace Polymorphic Nanodomains Xiaodong Jian,1 Xin Chen,1 and Q.M. Zhang1,* Among the energy storage devices, the dielectric capacitors possess the fastest charge/discharge speed and highest power density. However, their energy density is low. Recently in Science, Pan et al. demonstrated a relaxor ferroelectric ceramic thin film with polymorphic nanodomains that achieves an energy density of 112 J/cm3 with a high discharge/change efficiency. Dielectric capacitors store and regulate charges/electric energy and are widely used in electronic and electrical systems.1 In general, the polarization of the dielectric materials utilized in capacitors can be changed rapidly by external applied electric fields. In fact, among all the energy storage devices such as batteries, fuel cells, and supercapacitors, the dielectric capacitor is the one that can be charged and discharged rapidly, with a rate that can reach much less than microseconds.1 It is the fast discharge of the dielectric capacitor in releasing the stored electric energy that quickly turns on the bright flashlight of cameras and delivers electrical pulses to restore a normal heart rhythm in implantable
cardioverter-defibrillators (ICDs). The increased functionality and miniaturization of modern devices demands higher energy density and better charge/ discharge efficiency of dielectric capacitors than the state of the art. For example, a smaller dielectric capacitor that stores and delivers more electric energy efficiently can help shrink the size of smart phones and ICDs. Therefore, there is a great demand to increase the energy density of dielectric materials. Recently in Science, Pan et al. report the development of a dielectric ceramic thin film with a thinness of ca. 500 nm that possesses a high polarization level, approaching 1 C/m2 with a high dielec-
2296 Joule 3, 2294–2302, October 16, 2019 ª 2019 Elsevier Inc.
tric breakdown strength (~5 MV/cm) and low leakage current (~10 6 A/cm2 under 1.5 MV/cm).2 As a result, the ceramic thin films deliver an energy density of 112 J/cm3, approaching that of supercapacitors, with 80% of discharge/charge efficiency. In general, the energy density Ue stored in a dielectric can be deduced from the polarization P change with external electric field E; e.g., Z Ue =
Pm
E dp;
(Equation 1)
Pr
where Pr and Pm are the initial (E = 0) and final (at Em) polarizations, respectively (see illustration in Figure 1A). Hence, in order to achieve a high Ue, a dielectric should possess a high Pm and high Em at which the dielectric reaches Pm. Among various dielectrics, the ferroelectric ceramics are the ones that possess the highest Pm.1,3 In their investigation, Pan et al. selected BiFeO3 (BFO) as a main component, which generates a large Pm, ~100 mC/cm2, which is among the highest in known leadfree ferroelectrics.3 However, in normal ferroelectrics, the polarization forms
1Department
of Electrical Engineering and Materials Research Institute, Pennsylvania State University, University Park, PA, 16802, USA *Correspondence: [email protected] https://doi.org/10.1016/j.joule.2019.09.008
In ferroelectrics, multi-phase coexistence has been widely employed to enhance the functional properties. One well-known example is the morphotropic phase boundary (MPB) in Pb(ZrTi)O3 piezoceramics in which the highest piezoelectric response was achieved near MPB.4 The reason for the remarkable enhancement of electromechanical performance is the reduction of energy barriers for polar-vector switching due to increased polarization switching pathways and reduced polar-vector switching angles near MPB, similar to the approach employed by Pan et al.2
Figure 1. Polarization-Electric Field Loops of Ferroelectric Materials (A) Schematic of Pm , Pr , and U e in ferroelectric polarization-electric field (PE) loop. (B) Schematic of loss in the charge/discharge of a ferroelectric material. (C) PE loop of ferroelectrics with micrometer-size domains. (D) PE loop of RFE with nanodomains. (E) PE loop of RFE with polymorphic nanodomains. (C), (D), and (E) have been reprinted with permission from Pan et al. 2 Copyright 2019 AAAS.
large polar domains (>0.1 mm in size).3 The high nucleation barrier in switching the polarization causes a large polarization hysteresis with a high Pr (see illustration in Figure 1C). The presence of a remnant polarization Pr reduces the amount of energy that can be delivered to a load. Relaxor ferroelectrics (RFE), in contrast, consist of nano-polar-domains, which possess very low or, if properly designed, zero polarization switching barriers, leading to near-zero Pr. Hence, converting the normal ferroelectric into RFE can reduce or even eliminate this polarization hysteresis as well as result in a near-zero Pr. In BFO-based RFE such as BFO-STO, the RFE contains nano-polar-domains of local rhombohedral (R) symmetry embedded in a cubic matrix, which still exhibits remnant polarization hystere-
sis, reducing the discharge/charge efficiency and hence lowering Ue (see Figure 1D). Here, Pan et al. proposes a RFE with polymorphic nanodomains by introducing BaTiO3 to form a ternary solid solution of BFO-BTO-STO (BEBSTO). In such a polymorphic nanodomain RFE, BFO and BTO generate coexisting R and T (tetragonal) FE phases and STO breaks long-range FE ordering in BFO-BTO to generate nano-polar-domains. By finely tuning the composition of the ternary solid solution, guided by phase-field simulation, Pan et al. show that the BEBSTO has the coexistence of R- and T-nanopolar-domains, which greatly expands the numbers of switching pathways. As a result, the energy barriers for the polarization switching in such a polymorphic nanodomain RFE become near zero, leading to a near-zero Pr (see illustration in Figure 1E).
Besides the energy density Ue, the discharge/charge efficiency, as pointed out by Pan et al., is another critical factor when using dielectrics in practical devices. As illustrated in Figure 1B, the difference between the input electric energy density (Equation 1 for the red curve) and the discharged energy density (Equation 1 for the green curve) is the energy loss, and high efficiency means a low loss. The loss wastes energy and causes heating of the capacitor. In ferroelectrics, in addition to the polarization hysteresis loss, there are dielectric losses associated with the delayed polarization response to the applied field and conduction loss (leakage current), which can be very large when the electric field is high (such as >1 MV/cm for ceramics).5,6 Pan et al. present results showing that including BTO, which has a larger bandgap and chemical stability compared with BFO, significantly reduces conductivity at high fields (2.5 3 10 12 S/cm at 1.5 MV/cm) for the polymorphic nanodomain RFE compared with 8.7 3 10 11 S/cm of the regular RFE. This also results in a higher breakdown field (4.9 MV/cm to 5.30 MV/cm) compared to that of the regular RFE (3.2 MV/cm). All of these contribute to the high energy density of 112 J/cm3 with a discharge/charge efficiency of 80%
Joule 3, 2294–2302, October 16, 2019 2297
Figure 2. Schematic Illustration of Energy Densities in Ferroelectric (Including RFE) and Antiferroelectric
for the polymorphic nanodomain RFE BEBSTO. It is noted that besides the normal ferroelectric (including RFE), antiferroelectric (AFE) ceramics also present interesting dielectrics for high energy density with high efficiency.7,8 As illustrated in Figure 2, for the same Pm and Em, AFE can store even higher energy density than FEs. The polymorphic nanodomain approach by Pan et al. may also be applied in AFE to eliminate the polarization hysteresis and achieve high efficiency. Overall, the exciting re-
sults of Pan et al. as well as the potential of these approaches leading to even higher-energy-density dielectrics present great opportunities to develop these dielectrics for practical high-energy-density capacitors,2,7–9 if one can successfully address the challenge of transitioning these thin ceramic films to high-performance multilayer ceramics capacitors, required for practical applications.10
ACKNOWLEDGMENTS This work was supported by the Office of Naval Research, United States, grant no. N00014-19-1-2028. 1. Nalwa, H.S. (1999). Handbook of low and high dielectric constant materials and their applications, two-volume set (Elsevier). 2. Pan, H., Li, F., Liu, Y., Zhang, Q., Wang, M., Lan, S., Zheng, Y., Ma, J., Gu, L., Shen, Y., et al. (2019). Ultrahigh-energy density lead-free dielectric films via polymorphic nanodomain design. Science 365, 578–582. 3. Lines, M.E., and Glass, A.M. (2001). Principles and applications of ferroelectrics
and related materials (Oxford University Press). 4. W. Heywang, K. Lubitz, and W. Wersing, eds. (2008). In Piezoelectricity: evolution and future of a technology, Volume 114 (Springer Science & Business Media). 5. Wu, S., Li, W., Lin, M., Burlingame, Q., Chen, Q., Payzant, A., Xiao, K., and Zhang, Q.M. (2013). Aromatic polythiourea dielectrics with ultrahigh breakdown field strength, low dielectric loss, and high electric energy density. Adv. Mater. 25, 1734–1738. 6. Kao, K.C. (2004). Dielectric phenomena in solids (Elsevier). 7. Xu, B., I´n˜iguez, J., and Bellaiche, L. (2017). Designing lead-free antiferroelectrics for energy storage. Nat. Commun. 8, 15682. 8. Peng, B.L., Zhang, Q., Li, X., Sun, T.Y., Fan, H.Q., Ke, S.M., Ye, M., Wang, Y., Lu, W., Niu, H.B., et al. (2015). Giant electric energy density in epitaxial lead-free thin films with coexistence of ferroelectrics and antiferroelectrics. Adv. Electron. Mater. 1, 1500052. 9. Palneedi, H., Peddigari, M., Hwang, G.T., Jeong, D.Y., and Ryu, J. (2018). High-performance dielectric ceramic films for energy storage capacitors: progress and outlook. Adv. Funct. Mater. 28, 1803665. 10. Pan, M.J., and Randall, C.A. (2010). A Brief Introduction to Ceramic Capacitors. IEEE Elec. Insul. Mag. 26, 44.
Preview
Solving the Soiling Problem for Solar Power Systems Russell K. Jones1,* In this issue of Joule, Ilse et al. have presented a comprehensive look at soiling losses seen in photovoltaic systems around the world and quantified the threshold allowable cost for some commonly proposed mitigation measures. Their analysis shows significant differences in economic feasibility of mitigation measures in regional markets based on their soiling rates.
That soiling is considered an important problem for the PV industry is an indicator of the success of the industry, coming from a technology with niche applications and considered by mainstream utility players as too expensive to be significant less than a decade
ago, to being the largest source of new energy generation in the world today.1 When photovoltaic (PV) module prices were $4/watt, that was the main problem to be solved. Now, any problem affecting the field performance and long-term reliability of de-
2298 Joule 3, 2294–2302, October 16, 2019 ª 2019 Elsevier Inc.
ployed PV systems is serious business indeed. As the PV industry was poised to make the transition to really large-scale deployment, forward thinkers in the industry began to anticipate the new issues of scale that would soon emerge and engage the international PV community to understand and mitigate those issues. Particularly, the formation of the PV Quality Assurance Task Force (PVQAT) was initially spearheaded by Sarah Kurtz of NREL (now at the University of California at Merced) and Michio Kondo of AIST in Japan, leading the
1King
Abdullah City for Atomic and Renewable Energy (K$A$CARE), Riyadh, Saudi Arabia
*Correspondence: [email protected] https://doi.org/10.1016/j.joule.2019.09.011
efficiency using fused-ring acceptor with electron-deficient core. Joule 3, 1140–1151. 3. Meng, L., Zhang, Y., Wan, X., Li, C., Zhang, X., Wang, Y., Ke, X., Xiao, Z., Ding, L., Xia, R., et al. (2018). Organic and solution-processed tandem solar cells with 17.3% efficiency. Science 361, 1094–1098. 4. Lin, Y., Wang, J., Zhang, Z.G., Bai, H., Li, Y., Zhu, D., and Zhan, X. (2015). An electron acceptor challenging fullerenes for efficient polymer solar cells. Adv. Mater. 27, 1170–1174. 5. NREL (2019). Best Research-Cell Efficiencies. NREL. https://www.nrel.gov/.
6. Lami, V., Weu, A., Zhang, J., Chen, Y., Fei, Z., Heeney, M., Friend, R.H., and Vaynzof, Y. (2019). Visualizing the vertical energetic landscape in organic photovoltaics. Joule 3, this issue, 2513–2534. 7. Kahn, A. (2016). Fermi level, work function and vacuum level. Mater. Horiz. 3, 7–10. 8. Postcavage, W.J., Yoo, S., and Kippelen, B. (2008). Origin of the open-circuit voltage in multilayer heterojunction organic solar cells. Appl. Phys. Lett. 93, 193308. 9. Vandewal, K., Tvingstedt, K., Gadisa, A., Ingana¨s, O., and Manca, J.V. (2009). On the origin of the open-circuit voltage of polymer-fullerene solar cells. Nat. Mater. 8, 904–909.
Preview
Relaxor Ferroelectric Capacitors Embrace Polymorphic Nanodomains Xiaodong Jian,1 Xin Chen,1 and Q.M. Zhang1,* Among the energy storage devices, the dielectric capacitors possess the fastest charge/discharge speed and highest power density. However, their energy density is low. Recently in Science, Pan et al. demonstrated a relaxor ferroelectric ceramic thin film with polymorphic nanodomains that achieves an energy density of 112 J/cm3 with a high discharge/change efficiency. Dielectric capacitors store and regulate charges/electric energy and are widely used in electronic and electrical systems.1 In general, the polarization of the dielectric materials utilized in capacitors can be changed rapidly by external applied electric fields. In fact, among all the energy storage devices such as batteries, fuel cells, and supercapacitors, the dielectric capacitor is the one that can be charged and discharged rapidly, with a rate that can reach much less than microseconds.1 It is the fast discharge of the dielectric capacitor in releasing the stored electric energy that quickly turns on the bright flashlight of cameras and delivers electrical pulses to restore a normal heart rhythm in implantable
cardioverter-defibrillators (ICDs). The increased functionality and miniaturization of modern devices demands higher energy density and better charge/ discharge efficiency of dielectric capacitors than the state of the art. For example, a smaller dielectric capacitor that stores and delivers more electric energy efficiently can help shrink the size of smart phones and ICDs. Therefore, there is a great demand to increase the energy density of dielectric materials. Recently in Science, Pan et al. report the development of a dielectric ceramic thin film with a thinness of ca. 500 nm that possesses a high polarization level, approaching 1 C/m2 with a high dielec-
2296 Joule 3, 2294–2302, October 16, 2019 ª 2019 Elsevier Inc.
tric breakdown strength (~5 MV/cm) and low leakage current (~10 6 A/cm2 under 1.5 MV/cm).2 As a result, the ceramic thin films deliver an energy density of 112 J/cm3, approaching that of supercapacitors, with 80% of discharge/charge efficiency. In general, the energy density Ue stored in a dielectric can be deduced from the polarization P change with external electric field E; e.g., Z Ue =
Pm
E dp;
(Equation 1)
Pr
where Pr and Pm are the initial (E = 0) and final (at Em) polarizations, respectively (see illustration in Figure 1A). Hence, in order to achieve a high Ue, a dielectric should possess a high Pm and high Em at which the dielectric reaches Pm. Among various dielectrics, the ferroelectric ceramics are the ones that possess the highest Pm.1,3 In their investigation, Pan et al. selected BiFeO3 (BFO) as a main component, which generates a large Pm, ~100 mC/cm2, which is among the highest in known leadfree ferroelectrics.3 However, in normal ferroelectrics, the polarization forms
1Department
of Electrical Engineering and Materials Research Institute, Pennsylvania State University, University Park, PA, 16802, USA *Correspondence: [email protected] https://doi.org/10.1016/j.joule.2019.09.008
In ferroelectrics, multi-phase coexistence has been widely employed to enhance the functional properties. One well-known example is the morphotropic phase boundary (MPB) in Pb(ZrTi)O3 piezoceramics in which the highest piezoelectric response was achieved near MPB.4 The reason for the remarkable enhancement of electromechanical performance is the reduction of energy barriers for polar-vector switching due to increased polarization switching pathways and reduced polar-vector switching angles near MPB, similar to the approach employed by Pan et al.2
Figure 1. Polarization-Electric Field Loops of Ferroelectric Materials (A) Schematic of Pm , Pr , and U e in ferroelectric polarization-electric field (PE) loop. (B) Schematic of loss in the charge/discharge of a ferroelectric material. (C) PE loop of ferroelectrics with micrometer-size domains. (D) PE loop of RFE with nanodomains. (E) PE loop of RFE with polymorphic nanodomains. (C), (D), and (E) have been reprinted with permission from Pan et al. 2 Copyright 2019 AAAS.
large polar domains (>0.1 mm in size).3 The high nucleation barrier in switching the polarization causes a large polarization hysteresis with a high Pr (see illustration in Figure 1C). The presence of a remnant polarization Pr reduces the amount of energy that can be delivered to a load. Relaxor ferroelectrics (RFE), in contrast, consist of nano-polar-domains, which possess very low or, if properly designed, zero polarization switching barriers, leading to near-zero Pr. Hence, converting the normal ferroelectric into RFE can reduce or even eliminate this polarization hysteresis as well as result in a near-zero Pr. In BFO-based RFE such as BFO-STO, the RFE contains nano-polar-domains of local rhombohedral (R) symmetry embedded in a cubic matrix, which still exhibits remnant polarization hystere-
sis, reducing the discharge/charge efficiency and hence lowering Ue (see Figure 1D). Here, Pan et al. proposes a RFE with polymorphic nanodomains by introducing BaTiO3 to form a ternary solid solution of BFO-BTO-STO (BEBSTO). In such a polymorphic nanodomain RFE, BFO and BTO generate coexisting R and T (tetragonal) FE phases and STO breaks long-range FE ordering in BFO-BTO to generate nano-polar-domains. By finely tuning the composition of the ternary solid solution, guided by phase-field simulation, Pan et al. show that the BEBSTO has the coexistence of R- and T-nanopolar-domains, which greatly expands the numbers of switching pathways. As a result, the energy barriers for the polarization switching in such a polymorphic nanodomain RFE become near zero, leading to a near-zero Pr (see illustration in Figure 1E).
Besides the energy density Ue, the discharge/charge efficiency, as pointed out by Pan et al., is another critical factor when using dielectrics in practical devices. As illustrated in Figure 1B, the difference between the input electric energy density (Equation 1 for the red curve) and the discharged energy density (Equation 1 for the green curve) is the energy loss, and high efficiency means a low loss. The loss wastes energy and causes heating of the capacitor. In ferroelectrics, in addition to the polarization hysteresis loss, there are dielectric losses associated with the delayed polarization response to the applied field and conduction loss (leakage current), which can be very large when the electric field is high (such as >1 MV/cm for ceramics).5,6 Pan et al. present results showing that including BTO, which has a larger bandgap and chemical stability compared with BFO, significantly reduces conductivity at high fields (2.5 3 10 12 S/cm at 1.5 MV/cm) for the polymorphic nanodomain RFE compared with 8.7 3 10 11 S/cm of the regular RFE. This also results in a higher breakdown field (4.9 MV/cm to 5.30 MV/cm) compared to that of the regular RFE (3.2 MV/cm). All of these contribute to the high energy density of 112 J/cm3 with a discharge/charge efficiency of 80%
Joule 3, 2294–2302, October 16, 2019 2297
Figure 2. Schematic Illustration of Energy Densities in Ferroelectric (Including RFE) and Antiferroelectric
for the polymorphic nanodomain RFE BEBSTO. It is noted that besides the normal ferroelectric (including RFE), antiferroelectric (AFE) ceramics also present interesting dielectrics for high energy density with high efficiency.7,8 As illustrated in Figure 2, for the same Pm and Em, AFE can store even higher energy density than FEs. The polymorphic nanodomain approach by Pan et al. may also be applied in AFE to eliminate the polarization hysteresis and achieve high efficiency. Overall, the exciting re-
sults of Pan et al. as well as the potential of these approaches leading to even higher-energy-density dielectrics present great opportunities to develop these dielectrics for practical high-energy-density capacitors,2,7–9 if one can successfully address the challenge of transitioning these thin ceramic films to high-performance multilayer ceramics capacitors, required for practical applications.10
ACKNOWLEDGMENTS This work was supported by the Office of Naval Research, United States, grant no. N00014-19-1-2028. 1. Nalwa, H.S. (1999). Handbook of low and high dielectric constant materials and their applications, two-volume set (Elsevier). 2. Pan, H., Li, F., Liu, Y., Zhang, Q., Wang, M., Lan, S., Zheng, Y., Ma, J., Gu, L., Shen, Y., et al. (2019). Ultrahigh-energy density lead-free dielectric films via polymorphic nanodomain design. Science 365, 578–582. 3. Lines, M.E., and Glass, A.M. (2001). Principles and applications of ferroelectrics
and related materials (Oxford University Press). 4. W. Heywang, K. Lubitz, and W. Wersing, eds. (2008). In Piezoelectricity: evolution and future of a technology, Volume 114 (Springer Science & Business Media). 5. Wu, S., Li, W., Lin, M., Burlingame, Q., Chen, Q., Payzant, A., Xiao, K., and Zhang, Q.M. (2013). Aromatic polythiourea dielectrics with ultrahigh breakdown field strength, low dielectric loss, and high electric energy density. Adv. Mater. 25, 1734–1738. 6. Kao, K.C. (2004). Dielectric phenomena in solids (Elsevier). 7. Xu, B., I´n˜iguez, J., and Bellaiche, L. (2017). Designing lead-free antiferroelectrics for energy storage. Nat. Commun. 8, 15682. 8. Peng, B.L., Zhang, Q., Li, X., Sun, T.Y., Fan, H.Q., Ke, S.M., Ye, M., Wang, Y., Lu, W., Niu, H.B., et al. (2015). Giant electric energy density in epitaxial lead-free thin films with coexistence of ferroelectrics and antiferroelectrics. Adv. Electron. Mater. 1, 1500052. 9. Palneedi, H., Peddigari, M., Hwang, G.T., Jeong, D.Y., and Ryu, J. (2018). High-performance dielectric ceramic films for energy storage capacitors: progress and outlook. Adv. Funct. Mater. 28, 1803665. 10. Pan, M.J., and Randall, C.A. (2010). A Brief Introduction to Ceramic Capacitors. IEEE Elec. Insul. Mag. 26, 44.
Preview
Solving the Soiling Problem for Solar Power Systems Russell K. Jones1,* In this issue of Joule, Ilse et al. have presented a comprehensive look at soiling losses seen in photovoltaic systems around the world and quantified the threshold allowable cost for some commonly proposed mitigation measures. Their analysis shows significant differences in economic feasibility of mitigation measures in regional markets based on their soiling rates.
That soiling is considered an important problem for the PV industry is an indicator of the success of the industry, coming from a technology with niche applications and considered by mainstream utility players as too expensive to be significant less than a decade
ago, to being the largest source of new energy generation in the world today.1 When photovoltaic (PV) module prices were $4/watt, that was the main problem to be solved. Now, any problem affecting the field performance and long-term reliability of de-
2298 Joule 3, 2294–2302, October 16, 2019 ª 2019 Elsevier Inc.
ployed PV systems is serious business indeed. As the PV industry was poised to make the transition to really large-scale deployment, forward thinkers in the industry began to anticipate the new issues of scale that would soon emerge and engage the international PV community to understand and mitigate those issues. Particularly, the formation of the PV Quality Assurance Task Force (PVQAT) was initially spearheaded by Sarah Kurtz of NREL (now at the University of California at Merced) and Michio Kondo of AIST in Japan, leading the
1King
Abdullah City for Atomic and Renewable Energy (K$A$CARE), Riyadh, Saudi Arabia
*Correspondence: [email protected] https://doi.org/10.1016/j.joule.2019.09.011