Research ArticleStudy on the Electrical Injection Regeneration of IndustrializedB-Doped Czochralski Silicon PERC Solar Cells

Jiaxing Ye ,1,2 Bin Ai ,1 Jingsheng Jin,3 Depeng Qiu,1 Runxiong Liang,1 and Hui Shen1

1School of Materials Science and Engineering, Guangdong Provincial Key Laboratory of Photovoltaic Technology,Sun Yat-sen University, Guangzhou 510006, China2China National Electric Apparatus Research Institute Co. Ltd., Guangzhou 510300, China3Jinko Solar Holding Co. Ltd., Haining 314416, China

Correspondence should be addressed to Bin Ai; stsab@mail.sysu.edu.cn

Received 29 January 2019; Revised 8 April 2019; Accepted 11 April 2019; Published 20 June 2019

Academic Editor: Yanfa Yan

Copyright © 2019 Jiaxing Ye et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In this paper, 156mm × 156mm boron-doped Czochralski silicon (Cz-Si) wafers were fabricated into PERC solar cells by using theindustrial standard process; then, the as-prepared PERC solar cells were treated by the regeneration process using electricalinjection and heating and the effects of different regeneration processes (temperature, time, and injection current) on the anti-light-induced degradation (anti-LID) performance of the PERC solar cells were investigated. The results show that under thecondition of 10A injection current and 30min processing time, the optimal processing temperature is about 180°C for PERCsolar cells to obtain the best anti-LID performance. Under the conditions of a temperature of 180°C, an injection current of10A, and a processing time of 0-30min, the anti-LID performance of the PERC solar cells is enhanced with the increase in theprocessing time. When the processing time is 20 and 30min, the efficiency, the short-circuit current, and the open-circuitvoltage of the processed PERC solar cells are slightly higher than the initial values before the regeneration and remain stable inthe subsequent 12-hour light degradation process at 45°C and 1-sun illumination. At a temperature of 180°C and a processingtime of 30min, the injection current of 6A is enough to obtain a good regeneration effect, but the optimal injection current isaround 10A.

1. Introduction

Depending on the competitive advantages of low cost, highefficiency, long service life, mature process technology, andso on, boron-doped p-type crystalline silicon solar cells havefirmly occupied the dominant position in the globe photovol-taic market all along, but there exists the problem of light-induced degradation (LID) for such kind of solar cells andthis problem has severely hindered their development for along time. Thus, the investigation on the LID and its mitiga-tion of boron-doped p-type crystalline silicon solar cells hasbeen paid much attention all the time [1, 2]. In recent years,with the maturation of Al2O3 back passivation and laser abla-tion technology, more and more photovoltaic manufacturers

are gradually upgrading from producing conventional alumi-num back surface field (Al-BSF) solar cells to PERC (passiv-ated emitter and rear cell) solar cells with an efficiency of over20% [3, 4]. As compared with Al-BSF solar cells, the LID ofthe PERC solar cells is much severer and faster [5]. Therefore,the research on LID and its mitigation of PERC solar cells hasattracted great interest and high attention among the photo-voltaic community.

It is generally thought that the LID is caused by theformation of the boron-oxygen- (B-O-) related defects withrecombination activity in boron-doped p-type crystallinesilicon wafers when illuminated [1]. In 2006, Herguth et al.discovered that when boron-doped Cz-Si wafers wereinjected with carriers (illumination or electric injection)

HindawiInternational Journal of PhotoenergyVolume 2019, Article ID 5357370, 10 pageshttps://doi.org/10.1155/2019/5357370

while heated (60–200°C), B-O defects would undergo aregeneration reaction; that is to say, B-O defects would trans-form from the degraded state with recombination activity tothe regenerated state without recombination activity, and theloss of minority carrier lifetime caused by LID could be fullyrecovered. More importantly, the regenerated state of theB-O defects is stable under the working conditions of solarcells [6, 7].

It should be noted that previous researches on B-Odefect-induced degradation (BO-LID) and its mitigationwere almost carried out on lifetime samples (i.e., Cz-Si waferswith sawing damage being removed and the surface beingpassivated). However, boron-doped Cz-Si solar cells are verydifferent from boron-doped Cz-Si lifetime samples; thus, itis necessary to directly investigate the LID and its mitiga-tion of boron-doped Cz-Si solar cells, especially the newlyemerging boron-doped Cz-Si PERC solar cells. However,there is a lack of reports on such a subject in the litera-ture. Just as Basnyat et al. from the National RenewableEnergy Laboratory (NREL) of the United States describedin their paper in 2015, “Although a great deal of informa-tion is available on B-O effects in silicon, LID in solar cellhas not been understood fully. LID effect on crystalline sil-icon solar cells is studied by a small number of researchgroups, using comparatively small sets of samples. Eventhe results reported in literature show large diversity” [8].Although Herguth’s team at the University of Konstanzand Rein’s team at the Fraunhofer Institute for SolarEnergy Systems (ISES) first reported their research resultson the LID and regeneration of PERC solar cells in 2015[9–12], their studies were based on the PERC solar cellsprepared in laboratory; thus, their research results cannotrepresent those of industrialized PERC solar cells. Specifi-cally speaking, Herguth’s team studied the PERC solarcells with the back surface being passivated by SiOx/-SiNx:H, resulting in the open-circuit voltage (Voc) of thePERC solar cells even slightly lower than that of the Al-BSF solar cells [9, 10]. Rein’s team studied the PERC solarcells using LFC (laser-fired contact) technology to formlocal electrical contact with the wafer on the rear side[11, 12]. In fact, the industrialized PERC solar cells alluse an Al2O3 layer or a thin AlOx/thick SiNx:H cap layerto passivate the back surface and use laser ablation tech-nology to open electrical contact windows on the backpassivation layer. Finally, local back contact is formed onthe rear side by screen printing the Al paste and sintering.

In view of the lack of research on the LID and regenera-tion of the industrialized boron-doped Cz-Si PERC solarcells, this paper is aimed at addressing this inadequacy. Forregeneration treatment, there are two ways to inject carriersinto a solar cell, i.e., light injection and electrical injection.Since electrical injection has some unique advantages overlight injection, such as low equipment cost, energy saving,high injection level, and no light damage, electrical injec-tion and heating were used in this paper to regenerate theindustrialized boron-doped Cz-Si PERC solar cells, andthe effects of different regeneration process conditions(temperature, time, and injection current) on the anti-light-induced degradation (anti-LID) performance of the

PERC solar cells were systematically investigated for thefirst time and the experimental results were reasonablyexplained by using the new three-state model proposed byHallam et al. in 2016 [13]. The research results can be usedas an important reference or even directly applied by theindustry to further decrease or even completely removethe LID effect of the industrialized PERC solar cells, whichis very important considering that the whole photovoltaicindustry is transforming from producing conventionalAl-BSF solar cells to higher-efficiency PERC solar cells,and the PERC solar cells are gradually becoming themainstream products of the photovoltaic market.

2. Experiment

2.1. Sample Preparation. 156mm × 156mm boron-dopedCz-Si wafers with a round angle and a resistivity of about1Ω·cm were fabricated into PERC solar cells by using theindustrial standard process. The specific process includesthe following: removing the saw damage layer and texturingusing KOH solution, POCl3 diffusion at 850°C to form anemitter at about 85 Ω/□, removing back PN junction usingHF/HNO3 solution, thermal oxidation at 750°C to form a5nm oxide layer, depositing a 20 nm AlOx/140 nm SiNx pas-sivation layer on the back side of the silicon wafers byPECVD at 400°C, depositing about a 80nm SiNx antireflec-tion film on the front surface of the silicon wafers by PECVDat 450°C, laser grooving on the back passivation layer to formelectrical contact windows, screen printing the front andback electrodes, and sintering with temperature up to800°C. The initial efficiencies of the as-prepared PERC solarcells were in the range of 20.5% to 20.9%.

2.2. Experimental Methods. First, the I-V characteristics ofas-prepared PERC solar cells were measured. Subsequently,the PERC solar cells were regenerated using different electri-cal injection and heating conditions on self-developed equip-ment, which consists of a WXD-2620 heating stage whosetemperature can be regulated from room temperature to400°C, a JP8020D constant-current source with an outputcurrent range of 0-20A, and a self-assembled probe holderfor contacting the front electrode of a solar cell and a copperplate for contacting the back electrode of the solar cell. As thetemperature displayed on the heating stage controller cannotaccurately reflect the real temperature of a solar cell, it wasdetermined by both a contact platinum RTD (resistance tem-perature detector) and a noncontact infrared thermometer.Then, the I-V characteristics were measured again. Afterthat, the regenerated solar cells were degraded by light soak-ing for 12 h with a light intensity of 1000W/m2 at 45°C in aYQ-GF-SC4 solar cell LID box. During the 12h LID process,the PERC solar cells were taken out for I-V measurementevery 10min in the first hour and every 1 hour thereafter.All the I-V characteristic parameters of the solar cells weremeasured with a VS-6821M solar cell I-V tester under stan-dard test conditions (AM1.5 spectrum, 1000W/m2, 25°C).According to the claim of the manufacturer (IVT Corpora-tion of Singapore) of the VS-6821M solar cell I-V tester,the uncertainties of measurement results of short-circuit

2 International Journal of Photoenergy

current Isc, open-circuit voltage Voc, fill factor FF, and effi-ciency η in the confidence level of 95.4% are 4.99%, 0.51%,0.48%, and 5.00%, respectively. In order to compare theregeneration and anti-LID effects of the PERC solar cellsregenerated by using different conditions, all the graphs inthis paper use the relative values (At/Ainitial) of the I-V char-acteristic parameters (η, Voc, Isc, and FF) as the vertical axis.

3. Results and Discussion

3.1. Influences of Heating Temperature on the RegenerationEffect. Figure 1 shows the time dependence of the efficiencyη versus initial efficiency of the PERC solar cells before andafter regenerationandduring the subsequent12 hLIDprocess,which were regenerated by using 10A injection current at dif-ferent temperatures (160, 180, 200, 220, 240, and 260°C) for30min. As shown in Figure 1, when the processing tempera-ture is 260°C, theηof thePERCsolar cell decreases slightly afterthe regeneration. In contrast, the η of the PERC solar cellincreases markedly after the regeneration at other processingtemperatures. After the 12 h LID, the efficiencies of the PERCsolar cells regenerated at lower temperatures (160 and 180°C)are higher than the initial values before regeneration, whereasthe efficiencies of the PERC solar cells regenerated at highertemperatures (200, 220, 240, and 260°C) are lower than the ini-tial values.Moreover, thedecay rateofη increaseswith increas-ing processing temperature, but the efficiencies of theregenerated PERC solar cells are all higher than that of the ref-erence (untreated) sample.

Figure 2 shows a histogram describing the relative varia-tion of η of the PERC solar cells with processing temperaturebefore and after regeneration with 10A injection current for30min, as well as before and after the subsequent 12 h LID.As shown in Figure 2, when the processing temperature isbetween 160 and 240°C, the efficiencies of the regeneratedPERC solar cells are all higher than the initial values andthe increment of η decreases with increasing temperature.When the temperature increases to 260°C, the increment ofη becomes negative. After the 12h LID, the decay rate of ηof the PERC solar cell regenerated at 180°C relative to thevalue before LID is lowest, which in fact corresponds to an

increment rate of 0.15%. Furthermore, the decay rateincreases with increasing processing temperature. Thus, thebest anti-LID performance cannot be achieved by using toohigh or too low processing temperature. According to ourexperimental results, the optimal processing temperature isaround 180°C for obtaining the best anti-LID performance.

The above results can be explained by the new three-statemodel of the B-O defects proposed by Hallam et al. in 2016[13]. According to the new three-state model [13], there arethree configurations of B-O defects in boron-doped Cz-Siwafers which are the annealed state (A) without recombina-tion activity, degraded state (B) with recombination activity,and passivated state (C) without recombination activity.They can transform into each other by the following reactionformula:

It can be seen that there exist four kinds of reactionsbetween the three configurations; they are the degradationreaction from the annealed state (A) to the degraded state(B) (the reaction rate is expressed as KAB), the annealingreaction from the degraded state (B) to the annealed state(A) (the reaction rate is expressed as KBA), the passivationreaction from the degraded state (B) to the passivated state(C) (the reaction rate is expressed as KBC), and the

destabilization reaction from the passivated state (C) to thedegraded state (B) (the reaction rate is expressed as KCB).All the four reaction rates increase with increasing tempera-ture, in which KAB has a minimum increase rate and KBAhas a maximum increase rate, whereas both KBC and KCBhave a moderate increase rate but KBC is several orders ofmagnitude larger than KCB. The temperature-dependentcurves of KAB and KBA intersect at about 180°C, whereas

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Figure 1: The variation of efficiency η relative to the initial value ofthe PERC solar cells with time which were regenerated by using 10Ainjection current at different temperatures (160, 180, 200, 220, 240,and 260°C) for 30min before and after regeneration and during thesubsequent 12 h LID.

Annealed state (A) degraded state (B) passivated state (C).minority carrier injection

annealing in dark

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3International Journal of Photoenergy

the temperature-dependent curves of KBC and KBA intersectat around 320°C. In the temperature range of 120-320°C,the regeneration reaction rate KBC is the largest among thefour reaction rates (see reference [13] for details).

In the temperature range of 180-320°C, KBC > KBA > KABand the difference between KBC and KBA decreases with theincrease in temperature; therefore, when regenerated at thistemperature range, a large part of the degraded states withrecombination activity would transform into passivatedstates; meanwhile, a small part of the degraded states wouldtransform into annealed states and a proportion of theannealed states to the passivated states would increase withrising temperature. Because the passivated states can onlybe transformed from the degraded states rather than fromthe annealing states, once annealing states are formed duringthe regeneration process, these annealing states would trans-form into the degraded states under the solar cell workingconditions, resulting in the LID of the solar cells. Our evalu-ation criterion on the regeneration effect is that the ratio ofthe stable efficiency after 12 h LID to the initial efficiency ofthe PERC solar cell before regeneration should be maxi-mized. That is to say, only the regeneration condition underwhich the highest content of the passivated states is obtainedcan be regarded as the best. Therefore, in order to make asmuch B-O defects as possible transform into the passivatedstates, the temperature interval of 120-180°C which corre-sponds to the condition of KBC > KAB > KBA should be cho-sen in performing regeneration treatment. In thetemperature range of 120-180°C, the difference betweenKBC and KAB increases with increasing temperature, whichmeans that higher temperatures can accelerate the passiv-ation reaction. Therefore, under the condition of limitedregeneration time, the regeneration at about 180°C canachieve the best regeneration effect.

Figures 3(a)–3(c) show the time dependence of Isc, Voc,and FF of the PERC solar cells versus the initial values beforeand after regeneration and during the subsequent 12 h LID,which were regenerated by using 10A injection current at

different temperatures (160, 180, 200, 220, 240, and 260°C)for 30min, respectively. As shown in Figures 3(a) and 3(b),Isc and Voc basically have the same change tendency with η.Except for 260°C, the Isc and Voc of the PERC solar cellsregenerated at other temperatures are all higher than the ini-tial values. After 12 h LID, the processing temperatures corre-sponding to the Isc value higher than the initial value are160°C and 180°C, whereas the processing temperatures cor-responding to the Voc value higher than the initial value are160, 180, and 200°C. This result suggests that the larger decayof Isc results in η of the PERC solar cell regenerated at 200°Cbeing lower than its initial value. In addition, when the pro-cessing temperature is higher than 180°C, the decay rates ofIsc and Voc relative to the initial values increase with theincreasing temperature. It can be seen from Figure 3(c) that,after 12 h LID, the decay rates of FF of the regenerated PERCsolar cells show an increasing tendency with the increase inthe processing temperature. Specifically speaking, the decayrates of FF of the PERC solar cells regenerated at lower tem-peratures (160°C, 180°C, and 200°C) are lower than those ofthe reference sample, whereas the decay rates of FF of thePERC solar cells regenerated at higher temperatures (220°C,240°C, and 260°C) are higher than those of the reference sam-ple. This result shows that too high temperature cannotimprove the regeneration effect of the PERC solar cells butdegrade their anti-LID performance.

3.2. Influences of Processing Time on the Regeneration Effect.Figure 4 shows the time dependence of efficiency η versusthe initial value of the PERC solar cells before and afterregeneration and during the subsequent 12 h LID, whichwere regenerated by using 10A injection current at 180°Cfor different times (0, 2, 5, 10, 20, and 30min). As shown inFigure 4, when the regeneration time is less than or equal to10min, the η of the regenerated PERC solar cells decreasesmarkedly and the decay rates of the η decrease with increas-ing processing time. Specifically speaking, the decay rates of ηcorresponding to the processing times of 2, 5, and 10min are

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Figure 2: The histogram of the relative change of efficiencies of the PERC solar cells with processing temperature before and afterregeneration with 10A injection current for 30min, as well as before and after the subsequent 12 h LID.

4 International Journal of Photoenergy

4.87%, 4.07%, and 2.77%, respectively. For comparison, thePERC solar cells regenerated for 20 and 30min and thereference sample have no obvious decay in efficiency.Moreover, the η of the PERC solar cells regenerated for20 and 30min increases slightly. These results show thatthe η of the PERC solar cells may decay when the regen-eration time is shorter, whereas the η of the PERC solarcells may recover and even exceed the initial values whenthe regeneration time is longer.

After 12h LID, the reference sample shows significantdegradation, with the decay rate of η relative to the valuebefore the LID up to 7.54%. However, the decay rates of ηof the regenerated PERC solar cells decrease remarkably with

increasing processing time; specifically speaking, the decayrates of η corresponding to processing times of 2, 5, 10, 20,and 30min are 1.27%, 0.84%, -0.05%, -0.08%, and -0.15%,respectively. In particular, the PERC solar cells regeneratedfor 20 and 30min even have a slight increase in efficiencywith respect to the initial values before regeneration.

Figure 5 shows a histogram describing the relative varia-tion of η of the PERC solar cells with processing time beforeand after regeneration with 10A injection current at 180°C,as well as before and after the subsequent 12 h LID. As shownin Figure 5, the degradation of the reference sample is severerthan those of regenerated PERC solar cells after 12 h LID.With the increase in regeneration time, both the decay rates

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Figure 3: The time dependence of Isc, Voc, and FF of the PERC solar cells versus the initial values regenerated by using 10A injection currentat different temperatures (160, 180, 200, 220, 240, and 260°C) for 30min before and after regeneration and during the subsequent 12 h LID:(a) Isc t /Isc initial ; (b) Voc t /Voc initial ; (c) FF t /FF initial .

5International Journal of Photoenergy

of η after/before regeneration and those after/before 12 hLID gradually decrease and the decay rates of the latterare far below those of the former. In addition, when theregeneration time is longer than 10min, efficiencies ofthe PERC solar cells after 12 h LID are higher than thosebefore the LID process. Thus, the anti-LID performancesof PERC solar cells are enhanced with the increase inprocessing time.

According to the new three-state model proposed byHallam et al. [13], BO defects have three composition forms,i.e., the annealed state without recombination activity, thedegraded state with recombination activity, and the passiv-ated state without recombination activity. The specific LIDsituations of boron-doped Cz-Si PERC solar cells are deter-mined by the concentrations of three defect states and theprocessing conditions. For the case given in this paper, beforethe regeneration, the BO defects in the as-prepared PERCsolar cells mainly exist in the form of the annealed state, witha small amount of BO defects in the degraded state. Since theannealed state can only transform into the degraded stateinstead of the passivated state, the generation rate of thedegraded state defects is much higher than that of the passiv-ated state defects at the initial stage of the regeneration,which would result in a decrease in the bulk-carrier lifetimeand efficiency of the solar cells. The amount of the degradedstate defects increases with increasing processing time, sothat the regeneration reaction would dominate at themiddle-late stage of regeneration, and the concentration ofthe passivated state defects would increase with the increasein processing time. When the processing time is long enough,most of the annealed state and degraded state defects couldconvert into stable passivated state defects, which would leadto the recovery of the bulk-carrier lifetime and efficiency,making the regenerated PERC solar cells possess anti-LIDperformance.

Figures 6(a)–6(c) show the time dependence of Isc, Voc,and FF of the PERC solar cells versus the initial values beforeand after regeneration and during the subsequent 12h LID,which were regenerated by using 10A injection current at180°C for different times (0, 2, 5, 10, 20, and 30min, respec-tively). As shown in Figures 6(a) and 6(b), Isc and Voc basi-cally have the same change tendency with η, and Isc andVoc of the PERC solar cells regenerated for 20 and 30minnearly have no distinct decay with respect to the initial valueand almost remain stable in the subsequent 12 h LID. How-ever, Isc and Voc of the PERC solar cells regenerated for lessthan or equal to 10min have marked decay relative to the ini-tial value, but their anti-LID performances are better thanthat of the reference sample during the subsequent 12hLID and the anti-LID performances improve with theincrease in regeneration time. In addition, during the 12 hLID, the relative values of Isc of the PERC solar cells show arising tendency with fluctuation, while those of Voc remainstable. The relative values of the FF before and after theregeneration basically have the same change tendency withthose of η, Isc, and Voc. The decay rates of FF of the PERCsolar cells regenerated for less than or equal to 10min arehigher than that of the reference sample, while the FF valuesof the PERC solar cell regenerated for 20 or 30min are evenslightly higher than the initial values before regeneration.During the 12h LID, the decay rate of FF shows a differenttrend from those of η, Isc, and Voc. Specifically speaking,when the regeneration time is less than or equal to 10min,the decay rates of FF are larger than that of the reference sam-ple, while the decay rates of FF of the PERC solar cells regen-erated for 20 or 30min are less than that of the referencesample. The above experimental results can be explained asfollows: with the increase in the regeneration time, morerecombination-active defects are passivated, which resultsin the increase in bulk-carrier lifetime and rise in η, Isc, andVoc of the PERC solar cells. Since FF is not only affected bythe bulk-carrier lifetime but also affected by other factorssuch as series and parallel resistance, the FF would show adifferent change tendency from η, Isc, and Voc.

3.3. Influences of Injection Current on the Regeneration Effect.Figures 7(a)–7(d) show the time dependence of η, Isc, Voc,and FF of the PERC solar cells versus the initial values regen-erated by using different injection currents (6, 8, 10, 12, 14,16, and 18A) at 180°C for 30min before and after the regen-eration and during the subsequent 12 h LID, respectively. Asshown in Figure 7, η, Isc, Voc, and FF of the PERC solar cellsregenerated by using different injection currents at 180°C for30min are all higher than the initial values before the regen-eration. During the 12 h LID, Isc shows a mild fluctuation,while Voc shows a slight decrease tendency and FF decreaseswith fluctuation; as a result, η shows a slight decline tendencywith fluctuation. After 12 h LID, Isc and Voc of the PERCsolar cells regenerated with different injection currents areall higher than the initial values before the regeneration,while only the FF values of the PERC solar cells regeneratedby using 10A, 16A, and 18A are higher than the initialvalues; consequently, efficiencies of the PERC solar cellsregenerated by the current other than 12A are higher than

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Figure 4: The time dependence of efficiency η versus the initialvalue of the PERC solar cells before and after regeneration byusing 10A injection current at 180°C for different times (0, 2, 5,10, 20, and 30min) and during the subsequent 12 h LID.

6 International Journal of Photoenergy

the initial values. The above results show that under the con-dition of 180°C and 30min, the injection current of 6A is bigenough to obtain a good regeneration effect, and raising theinjection current does not necessarily improve the regenera-tion effect. Given the processing temperature and time, thebest regeneration effect seems to correspond to an optimuminjection current. According to our experimental results,the optimal injection current corresponding to the condi-tions of 180°C and 30min is around 10A. Of course, it stillneeds further investigation to achieve the best regenerationeffect by decreasing the processing time meanwhile increas-ing the injection current.

In the studied parameter range, the optimum regenera-tion condition corresponds to the treatment with 10A injec-tion current for 30min at 180°C. Under such an optimumregeneration condition, the ratio of the efficiency during12 h LID to the initial efficiency reaches the maximum valueof 1.019 at 6 h light soaking and a stabilized value of 1.012at 12h light soaking (see Figure 7(a)). It seems that thefluctuation of efficiency with time could be attributed tothe nature of reversible reaction between the three config-urations of B-O defects and a mixture of three states beinggenerally reached. The reason why the efficiencies of suit-ably regenerated PERC solar cells after 12 h LID exceedthe initial efficiency is that we did not perform annealingtreatment (200°C, 30min) in the dark to make all the B-Odefects convert into annealing states before measuring theinitial efficiency. The majority of degraded state defects con-tained in the as-prepared PERC solar cells transform intopassivated states after suitable regeneration which results inthe rising of efficiency.

It was reported that “a very fast regeneration process lessthan 10 s at 230°C and 2.7-sun illumination can be realized.”However, this conclusion was drawn from the research onthe lifetime samples which were well gettering (POCl3 getter-ing at 840°C), well hydrogenated (PECVD-SiNx:H on bothsides), suitably fired, and completely degraded (200°C

annealing for 10min in the dark) [14, 15]. More importantly,the authors did not provide the direct proof of the stability ofthe optimally regenerated lifetime sample under solar cellworking conditions [14, 15]. Obviously, this fast regenerationcondition is not in good agreement with ours. The reason isas follows: (1) PECVD-SiNx:H and electrode firing processconditions used for fabricating PERC solar cells in the indus-try are optimized to maximize the efficiencies of the PERCsolar cells, which are different from the optimum fabricationcondition of the lifetime sample. In addition, no 200°Cannealing in the dark was performed on the as-preparedPERC solar cells before regeneration. (2) The judging criteriaon the optimum regeneration condition are also different.Specifically speaking, the optimum light injection regenera-tion condition was determined by fully recovering the life-time of completely degraded sample under the illuminationand heating condition, whereas our judging standard is tomaximize the ratio of the stable efficiency of a regeneratedsolar cell after 12 h LID (45°C, 1-sun illumination) to the ini-tial efficiency before regeneration, which means that only theregeneration condition under which the highest content ofpassivated states is obtained can be regarded as the opti-mum one. Moreover, the reason why the optimum regen-eration can be achieved at 180°C has also been given areasonable explanation according to the new three-statemodel proposed by Hallam et al. (see Section 3.1 fordetails). (3) Because the manufacturing process and archi-tecture of a solar cell have complex and important influ-ence on the regeneration and LID process, theconclusions drawn on the regeneration and LID of lifetimesamples cannot be directly applied to those of the solarcells [16] and the conclusions given by this paper are onlyvalid for the industrialized PERC solar cells.

Due to the scarcity of reports on light injection regen-eration and anti-LID performance of industrial PERC solarcells, we cannot compare our research results with thoseby light injection regeneration. However, in our opinion,

Regeneration processing time

After degradation processAfter regeneration process

−1.00%

0.00%

1.00%

2.00%

3.00%

4.00%

5.00%

6.00%

7.00%

8.00%

9.00%

−1.00%

0.00%

1.00%

2.00%

3.00%

4.00%

5.00%

6.00%

7.00%

8.00%

9.00%

(�휂in

itial−�휂t=

0)/�휂

initi

al

(�휂t=

0−�휂t=

12h)/

�휂t=

0

Reference 2min 5min 10min 20min 30min

Figure 5: The processing time-dependent histogram of the relative change of η of the PERC solar cells before and after regeneration with 10Ainjection current at 180°C, as well as before and after the subsequent 12 h LID.

7International Journal of Photoenergy

this work is worthy of being published for the followingreasons: (1) electrical injection has some significantadvantages over light injection, such as more simpleequipment thus leading to lower equipment cost, higherenergy utilization efficiency (without electricity-to-lightand light-to-electricity conversion), and higher injectionlevel without worry of light damage. (2) Since the electricinjection regeneration apparatus can be made into a batchprocessing equipment [17], there is no problem to inte-grate a 30min anti-LID batch processing procedure intoa solar cell manufacturing process, because themanufacturing process also uses other time-consumingbatch processing procedures such as the diffusion processand PECVD-SiNx:H process. (3) From the point of viewof the mechanism, whether light injection or electric

injection, they are just the methods to introduce nonequi-librium minority carriers (i.e., electrons) into boron-dopedCz-Si wafers. The injected electrons can combine thenearby hydrogen ions (H+) to form hydrogen atoms, andhydrogen atoms can diffuse more quickly when heatedand thus can effectively passivate the defects with recombi-nation activity. It is thought that moderate temperature,higher injection level, and higher hydrogen concentrationcan give a better regeneration effect [14, 15]. Unlike lightinjection, electric injection will not bring damages in asolar cell at high injection levels; thus, the electric injectionshould have a better regeneration effect than the lightinjection. (4) Different from the most of previous studieson LID and regeneration which were mainly characterizedby lifetime or Voc, all the illuminated I-V characteristic

0.96

0.97

0.98

0.99

1.00

1.01

I sc(t

)/Isc

(initi

al)

After regeneration(at 10A/30min)

Time (h)Before regeneration

Degradation at 45°C/1sun

0min2min 20min

30min

10min

5min

0 1 2 3 4 5 6 7 8 9 10 11 12 13

(a)

0.96

0.97

0.98

0.99

1.00

1.01

Voc

(t)/V

oc(in

itial

)

After regeneration(at 10A/30min)

Time (h)Before regeneration

Degradation at 45°C/1sun

0min2min 20min

30min

10min

5min

0 1 2 3 4 5 6 7 8 9 10 11 12 13

(b)

0.985

0.990

0.995

1.000

1.005

1.010

FF(t

)/FF (in

itial

)

After regeneration(at 10A/30min)

Time (h)Before regeneration

Degradation at 45°C/1sun

0min2min 20min

30min

10min

5min

0 1 2 3 4 5 6 7 8 9 10 11 12 13

(c)

Figure 6: The time dependence of Isc, Voc, and FF of the PERC solar cells versus the initial values regenerated by using 10Ainjection current at 180°C for different times (0, 2, 5, 10, 20, and 30min) before and after regeneration and during the subsequent 12 hLID: (a) Isc t /Isc initial ; (b) Voc t /Voc initial ; (c) FF t /FF initial .

8 International Journal of Photoenergy

parameters (η, Voc, Isc, and FF) are used in this paper tocharacterize the regeneration and anti-LID performanceof the industrialized PERC solar cells. In addition, theresearch results can be used as an important reference ordirectly used by the industry to further decrease orcompletely eliminate the LID problems of the industrial-ized PERC solar cells.

4. Conclusion

The PERC solar cells were fabricated by using the industrialstandard process and treated by using different regeneration(electrical injection and heating) conditions, and the effects

of the regeneration conditions (temperature, time, and injec-tion current) on the anti-LID performance of as-preparedPERC solar cells were studied. The results show that the Isc,Voc, and η of the PERC solar cell regenerated at 180°C underthe condition of 10A injection current and 30min processingtime have the lowest degradation rate relative to the valuesbefore LID, which in fact corresponds to the maximumincrement. When the processing time is less or equal to10min under the condition of 180°C and 10A injection cur-rent, the η, Isc, and Voc of the regenerated PERC solar cellswith respect to the initial values before the regenerationdecays markedly, but during the subsequent 12 h LID, theiranti-LID performances are better than that of the reference

0.920.930.940.950.960.970.980.991.001.011.021.03

Reference6A8A10A

12A14A16A18A

After regeneration(at 10A/30min)

Time (h)Before regeneration

Degradation at 45°C/1sun

0 1 2 3 4 5 6 7 8 9 10 11 12 13

�휂(t

)/�휂(t

=ini

tial)

(a)

0.95

0.96

0.97

0.98

0.99

1.00

1.01

I sc(t

)/Isc

(initi

al)

Reference6A8A10A

12A14A16A18A

After regeneration(at 10A/30min)

Time (h)Before regeneration

Degradation at 45°C/1sun

0 1 2 3 4 5 6 7 8 9 10 11 12 13

(b)

0.96

0.97

0.98

0.99

1.00

1.01

Voc

(t)/V

oc(in

itial

)

Reference6A8A10A

12A14A16A18A

After regeneration(at 10A/30min)

Time (h)Before regeneration

Degradation at 45°C/1sun

0 1 2 3 4 5 6 7 8 9 10 11 12 13

(c)

0.980

0.985

0.990

0.995

1.000

1.005

1.010FF

(t)/F

F (initi

al)

Reference6A8A10A

12A14A16A18A

After regeneration(at 180°C/20min)

Time (h)Before regeneration

Degradation at 45°C/1sun

0 1 2 3 4 5 6 7 8 9 10 11 12 13

(d)

Figure 7: The time dependence of I-V characteristic parameters of the PERC solar cells versus the initial values regenerated by using differentinjection currents (6, 8, 10, 12, 14, 16, and 18A) at 180°C for 30min before and after regeneration and during the subsequent 12 h LID: (a)η t /η initial ; (b) Isc t /Isc initial ; (c) Voc t /Voc initial ; (d) FF t /FF initial .

9International Journal of Photoenergy

sample and their anti-LID performances improve with theincreasing processing time. When the processing time is 20or 30min, the η, Isc, and Voc of the regenerated PERC solarcells increase slightly relative to the initial values before theregeneration and basically remain stable during the subse-quent 12h LID. Under the condition of 180°C and 30min,6A injection current is enough to obtain a good regenerationeffect, but the optimum injection current at such a conditionis around 10A.

Data Availability

The data used to support the findings of this study areincluded within the paper. The raw data measured with aVS-6821M solar cell I-V tester are provided as supplemen-tary materials.

Conflicts of Interest

The authors declare that there is no conflict of interestsregarding the publication of this paper.

Acknowledgments

This work was supported by the National Natural ScienceFoundation of China (Grant no. 61774171) and theSpecial Scientific Research Program of Guangzhou (Grantno. 201607020032).

Supplementary Materials

The supplementary material is the raw data measured with aVS-6821M solar cell I-V tester before and after regenerationtreatment and during the subsequent 12 h LID processshown in Section 3.1, Section 3.2, and Section 3.3 of themanuscript. (Supplementary Materials)

References

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[13] B. Hallam, M. Abbott, N. Nampalli, P. Hamer, andS. Wenham, “Influence of the formation- and passivation rateof boron-oxygen defects for mitigating carrier-induced degra-dation in silicon within a hydrogen-based model,” Journal ofApplied Physics, vol. 119, no. 6, article 065701, 2016.

[14] S. Wilking, J. Engelhardt, S. Ebert, C. Beckh, A. Herguth, andG. Hahn, “High speed regeneration of BO-defects : improvinglong-term solar cell performance within seconds,” in Proceed-ings of the 29th European Photovoltaic Solar Energy Conferenceand Exhibition (EUPVSEC), pp. 366–372, Amsterdam,Netherlands, 2014.

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