Relationship between electroluminescence images and power type parameters of defective silicon solar cells

Transcription

1 Availabl onlin Journal of Chmical and Pharmacutical Rsarch, 2014, 6(6): Rsarch Articl ISSN : CODEN(USA) : JCPRC5 Rlationship btwn lctroluminscnc imags and powr typ paramtrs of dfctiv silicon solar clls Liai Gao, Xusong Suo, Jingrn Zhou, Ya Zhang and Limin Huo * Collg of Mchanical and Elctrical Enginring, Agricultural Univrsity of Hbi, Baoding, China ABSTRACT Basd on Elctroluminscnc (EL) thory, th solar cll dtction systm wr built by th particular wavlngth nar-infrard CCD imaging dvic, which mainly includd th camra obscura, computr imaging analysis softwar and constant currnt sourc, finally compltd th nar-infrard imag dtction of solar clls in a dark room. A numbr of th sam batch of solar clls wr dividd into normal or rcssiv dfctiv clls through EL dtction, thn w could gt th appropriat clls of th opn circuit voltag, short-circuit currnt, powr and othr paramtrs by standard solar powr tstr for powr tst. Finally w could gt that th dfcts would affct th powr typ paramtrs of th solar cll, manwhil EL tchnology is provd to b an accurat masurmnt to dtct solar clls. It could provid a broad ida for furthr dsign of th powr tst quipmnt. Kywords: Solar clls, lctroluminscnc, hiddn dfcts, Powr typ Paramtrs, rlationship. INTRODUCTION With th rapid dvlopmnt of tchnology and conomy, solar nrgy has bn gradually got th attntion of many countris, and also got a bttr dvlopmnt and utilization. Global photovoltaic industry was dvloping vry rapidly; manwhil th domstic solar cll industry scal has bn xpandd. But a dfct in a solar cll has a grat influnc on th battry photolctric convrsion fficincy, xtrnal dfcts was asy to dtct, but micro-cracks of intrnal was difficult to idntify only by th human y. How to ffctivly dtct th crack of th silicon solar clls in th procss of industrial production, and find out th caus of th dfct of tchnology as soon as possibl, which was a ky problm for th dvlopmnt of solar cll industry. Now, thr ar thr mthods for solar clls dfct dtction in industrial productions, which includ artificial visual dtction [1], th infrard dtction [2] and CCD dtction [3]. Infrard imag tchnology was usd to th battry componnts for dfct dtction, which could achiv four kind of dfct dtction, such as fragmnts, virtual wlding, brokn gat and crackd through th analysis and procssing componnts of lctroluminscnt imag [4]. A dtction mthod was proposd basd on cll physical dfcts, and applid for a patnt on crack dtction quipmnt [5]. This quipmnt was mainly composd of lasr sourc and th lasr controllr, rotating mirror and controllr, rflctor, a CCD camra, scannr, cargo and computr composition, it could dtct th dfct of battry componnts through th analysis of th infrard imag of procssing scanning for. But most of th tsting quipmnt only masurd singl indx, and nd many vn rpat tst quipmnt, it is not conduciv to th rapid dtction of solar clls dfcts. As th imag of dfct dtction and powr paramtrs dtction quipmnt intgration, th fficincy of cll production tsting would improv gratly. Basd on th lctroluminscnt dtction principl, th Solar Panls on-lin dtction systm was dsignd and assmbld, first usd th CCD camra to captur th EL imag, th micro-cracks of crystallin silicon solar clls wr dtctd by th nar-infrard CCD camra, such as th cracks, off-grid, non-uniform rsistanc, flowr slic. Thn w 1609

2 compard th EL imags with th imags undr visibl light. Powr paramtrs of th dfctiv solar clls was tstd, and w got that th paramtrs such as opn-circuit voltag, short-circuit currnt, voltag of maximum powr point, currnt of maximum powr point I m, fficincy, so as to gt th rlationship btwn all kinds of dfcts in solar clls EL imags and powr paramtrs. So if w could us th corrsponding rlationship for production monitoring and of solar clls dfct dtction in th industrial production, It could not only rduc th damag rat, improv th product grad ffctivly, but also could rduc th cost of silicon matrial and th production cost at th sam tim, so as to improv th markt comptitivnss of th componnt. EXPERIMENTAL SECTION 1 Exprimnt principl 1.1 Solar clls lctroluminscnt principl If w put th positiv lctricity to PN junction of solar panls, nrgy will b rlasd in th form of photons bcaus of th rcombination of lctron and hol. Elctroluminscnt spctra has a crtain light intnsity at 700 nm to 1200 nm rang, th imag could b capturd by CCD imaging dvic. But for th brokn part, th capturd imag prsnt a clar spots in dfct part bcaus of non-rcombination phnomnon of lctrons and hols For silicon solar clls snding out th nar infrard wavlngth of 1150 nm whn nrgizd, so w can gt crystallin silicon solar clls of lctroluminscnt imag by using th nar infrard camra [6]. From th infrard imag th battry slic of hiddn dfcts can b intuitiv analysis, and th hiddn dfcts ar unabl to distinguish in visibl light workrs. In viw of th common silicon solar battry, th rlationship btwn th numbr of th carrir and th corrsponding diffusion lngth ar as th formula [7]: V m = N n (0) xp( x / L ) dx = n (0) L 0 p p (1) Among of th formula, n p(0) is th numbr of xcss carrirs in silicon matrial, L is th ffctiv diffusion lngth. Undr th condition of fixd numbr of minority carrir, lctroluminscnc intnsity is proportional to th ffctiv diffusion lngth of minority carrir. Th rlationship btwn minority carrir diffusion lngth ffctivly and its longvity is as follows: L = τ (2) D So whn th silicon cll is switchd to forward biasd of th powr, th lctroluminscnt intnsity dpnds on th silicon matrial intrnal minority carrir liftim, th CCD camra is th intgration of xposur for lctroluminscnt intnsity within th xposur tim, th xprssion is: N v = t Ev 0 dx (3) Whn th powr is connctd to offst, silicon clls will radiat about 1150 nm wavlngth of invisibl light, so w can us nar-infrard camra photographs to gt th lctroluminscnt imag, this systm adopts th high rsolution of rfrigration CCD industrial camra. 1.2 Th solar cll powr paramtrs Th basic paramtrs of Solar clls includ short-circuit currnt and opn-circuit voltag, maximum powr and fill factor and photolctric convrsion fficincy. Faturs good solar cll which has obtain highr powr output of solar clls, and th short circuit currnt and opn circuit voltag and fill factor ar also biggr. Convrsion fficincy is usd to indicat th dgr of light nrgy convrt into lctrical nrgy. It is anothr important masur indx of th solar cll prformanc, which is proportional to th maximum powr. For crystallin silicon, uppr limit of convrsion fficincy in thory is 27%, rsarch and dvlopmnt phas is 24.2%, but in th production scal is only 18%. For th low cost of amorphous silicon solar clls, uppr limit convrsion fficincy in thory is 25.5%, but solar cll convrsion fficincy is only 12% whn th typ is 10 cm * 10 cm. According to statistics, th actual convrsion fficincy is 50% ~ 70% of its thortical fficincy for th actual production of solar clls. Th convrsion fficincy in common silicon solar cll is only about 18% [8]. Th sction hadings ar in boldfac capital and lowrcas lttrs. Scond lvl 1610

3 hadings ar typd as part of th succding paragraph (lik th subsction hading of this paragraph). All manuscripts must b in English, also th tabl and figur txts; othrwis w cannot publish your papr. Plas kp a scond copy of your manuscript in your offic. Whn rciving th papr, w assum that th corrsponding authors grant us th copyright to us th papr for th book or journal in qustion. Whn rciving th papr, w assum that th corrsponding authors grant us th copyright to us th papr for th book or journal in qustion. Whn rciving th papr, w assum that th corrsponding authors grant us th copyright to us. 2 th solar clls dfct dtcting systm 2.1 Th dsign of EL dtcting systm This systm mainly consists of thr parts: solar panls Camra obscura, computr, and constant-currnt sourc. Th masurd solar panls wr placd in an opaqu tst cas, switchd on constant dirct currnt that carris on adjustmnt siz according to th siz of th panls. And th solar panls can mit infrard light, using th principl of photolctric convrsion. Plac an infrard industrial camra in th black cas and th panls can b usd for ral-tim monitoring and singl fram collction. Industrial camra conncts with computr by USB. Th stand or fall of panls can b dirctly obsrvd from th scrn and it`s convnint for usrs to oprat [9]. Th framwork of th EL dtcting systm is shown in Figur 1. CCD camra Camra obscura EL imag lns computr solar cll Dirct Powr Fig.1 Th EL dtcting systm Th CCD imag snsor is mad of silicon matrials, bing high snsitiv to th nar infrard. Spctral rspons can b xtndd to about 1.0 um. Whn you obsrvd in a closd darkroom, you cannot s th infrard wavlngths but th imag can b prsnt in th monitor clarly. So using nar infrard imaging mthod by CCD snsor and th surfac of th CCD imaging chip, you can mak with lctroluminscnt imag of crystallin silicon solar clls. Thr ar many indicators to tst quality of CCD, such as th ffctiv numbr of pixls, th siz, snsitivity, and signal-to-nois ratio, tc. Th two important indicators ar ffctiv numbr of pixls and th CCD siz.th camra is dsignd with SONY413 chip with th function of rfrigration and pixls of 6.1 million. And th siz of pixls is 7.8 um * 7.8 um, which is twic as larg as ordinary common 1.44 million pixls. In ordr to mak th choic of corrsponding lns, th siz of th tsting quipmnt should b count out by calculating th distanc of th light path in th black box, and th siz of dtcting clls. Bsids, a filtr is installd at th lns which can filtr out th visibl light to prvnt intrfrnc. Du to th wavlngth of visibl light rang is 380 nm to 645 nm, and silicon solar cll could snd out a wavlngth of 1150 nm nar-infrard at th tim of lctricity, w dsignd camra obscura for tsting [10, 11]. Thr ar thr parts in th camra obscura, CCD camra fixd fram, th mirror support, Adjustabl voltag powr supply with constant currnt and solar nrgy battry componnts. W could gt th nar-infrard imags by using CCD camra whn loading positiv bias voltag to battry componnts through th adjustabl voltag constant currnt sourc. Tst panls ar loadd by th opning and closing Windows controlld of th cylindr, at th sam tim blocking th visibl light. Th dark room installd in solar cll production procss middl prssur of ach link, with th nds of th production procss for dtcting dfcts and powr tst. During th tst lctroluminscnt driv mod using Panls connctd to th constant dc sourc,th siz of th currnt can b adjustd according to th masurd of th spcifications of th panl accordingly. Th adjustmnt rang of gnral voltag was adjustd from 0 to 60 V in th production lin, currnt rang from 0 to 10 A. Th smallr production sit has, th smallr siz of th obscura should hav. In ordr to achiv gratr siz dtction, plan optical rflctor could b us to achiv infrard way, so as to adapt to diffrnt sizs of panls. 2.2 construction of th powr tsting platform 1611

4 W choos solar modul tstr as powr tst quipmnt which manufacturd by Taiwan instrumnt lctronics co., LTD., th modl is PROVA200. It consists of th tstr host, computr, display parts. Solar modul tstr is a kind of solar battry and componnt tst spcial quipmnt with high rliability, high prcision. Som paramtrs such as I-V curv, P -V curvs, short-circuit currnt I sc, opn-circuit voltagv oc, voltag of maximum powr point m, currnt I of maximum powr point m, fficincy.at th sam tim it can also display th corrsponding currnt, voltag and powr paramtrs of arbitrary point on th curv. Using this instrumnt, it not only guarant th accuracy of th masurmnt rsults,but also guarant th masuring rang of th linar rror within %. Th structur of powr tsting platform ar shown in figur 2. V Puls xnon data procssor solar clls Fig.2 Powr tsting platform 3 Exprimntal procdurs Som clls wr slctd as th xprimntal sampls for doing EL dfct tsting. All of thm wr com from th sam xprimntal batchs of th sam production lin. W slctd svntn pics clls with hiddn dfctiv from th sampl, which hav som dfcts such as th cracks, off-grid, non-uniform rsistanc, flowr slic. And diffrnt clls hav diffrnt ffcts on powr. In ordr to analyz th influnc of ths dfcts, w filtr out two solar clls with flowr slic as latr powr tst comparison sampls from th svntn dfctiv clls. Thn two dfctiv clls and two normal clls randomly ar slctd to do EL tsts rspctivly. In ordr to nsur th consistncy of th tsting data, firstly w r-wld th sam lngth and cross-sctional ara for th tsting lins; unify th positiv and ngativ link lins for tst sampl. This nsurs that th tst hav th sam conditions. Th tst tim of EL common lin is 8-15 sconds; powr-on tst clls will bring currnt fluctuations if th tst tim is too long, so w adopt a mthod of rlativly larg currnt (3A), and accurat short-tim tst (3S). In ordr to rflct th invisibl dfcts affct powr of solar clls, a normal cll is slctd to do an arthing tratmnt, simulating th condition of outdoor installation and long running. Th xprimntal rsults of th EL tsting imag ar shown in Figur 3. A Dfct solar cll1 1 B Dfct solar cll1 2 C Normal solar cll D Earthing solar cll Fig.3 EL tst imag RESULTS AND DISCUSSION 1612

5 Powr tst ar carrid on th solar cll with dfcts rspctivly, In ordr to nsur data consistncy, w chos th tst with th sam tim, th sam plac, th sam location for th clls, as wll as th installation angl of th sun. W also chos th cloudy wathr so as to rflct th gratr dgr of influnc on powr. Th Powr tst curv th clls as shown in Figur 4. A Dfct solar cll 1 B Dfct solar cll 2 C Normal solar cll Fig.4 Powr tst curv D Earthing solar cll Th rsults of tst prformanc ar shown in Tabl 1. Tabl 1 th tst prformanc of solar cll typ Dfct ara Tst tmpratur( ) opn-circuit voltag (V) short-circuit currnt (ma) max powr (mw) A Dfct1 12.5% B Dfct2 18.7% C Normal 0% D Earthin g Simulation th outdoor Th corrspondnc btwn th EL imag and th powr can b obtaind from ths tst rsults. Th following conclusions can b obtaind from th tabl 1: 1Th dfcts such as th cracks, off-grid, and non-uniform rsistanc, flowr slic hav diffrnt dgrs of impact on th solar cll whn compard th dfct clls to th common clls. Th short-circuit currnt, fficincy ar both dcrasd, and it has lss impact on th opn circuit voltag. 2 In ordr to liminat th outdoor nvironmntal impacts for th clls (such as ovrburdn), w could adopt ras, automatic claning and othr mthods. Bfor laving factory th hiddn dfcts must b dtctd, othrwis th impact will b long. 3 Bcaus of th corrspondnc btwn th powr and th EL imag, possibl dfcts can b analyzd by th photoluminscnc xprimnts of th clls. This mthod is fastr than convntional dirct masurmnt, and it has broad prospct. CONCLUSION Nar-infrard imaging xprimnts ar carrid out in polycrystallin silicon solar cll using th lctroluminscnt principl, and compard th visibl light imag with EL imags of th polycrystallin silicon solar cll in th sam position, EL imags accuratly dtct th dfcts of th solar cll, such as th cracks, off-grid, non-uniform rsistanc, flowr slic. and ths dfcts ar th micro-cracks and could not obsrvd in visibl light, thn using standard solar 1613

6 battry tstr, masurd som paramtrs such as I-V curv of th clls, short-circuit currnt and opn-circuit voltag, maximum powr, and got th prliminary corrsponding rlationship btwn cll EL imag and powr paramtrs. Tst rsults confirm th xistnc of dfcts mak polycrystallin silicon solar cll fficincy dcrasd significantly. Bcaus of th corrsponding rlationship, w would analysis th battry slic of possibl dfcts through th lctroluminscnt xprimnt. If gray lvl analysis, statistical analysis of infrard photosnsitiv points on imag procssing could b usd in latr xprimnt, mak it to intgrat th EL tstr and powr tstr and othr production quipmnt. W can judg th typs of dfct through th powr charactristic curv, finally to rduc th silicon matrial consuming, cost savings, and improv th markt comptitivnss. Acknowldgmnts This work was supportd by a grant from th high school scintific and tchnological rsarch outstanding youth fund projct in Hbi provinc (QN ) and th planning projcts of Scinc and Tchnology Dpartmnt of Hbi Provinc( ). REFERENCES [1] R Ahmd; MPF Sutcliff. War, 2000, 244, [2] B Souhil; L Rinhold. Journal of Nondstructiv Eval, 2007, 26(1), 1-9. [3] P Lavalir; A D. Sands; F Panlla. Intrnational Journal of Fatigu, 2009, 31(2), [4] YF Ding; HB Li; CQ Zhang. Solar Enrgy, 2010(2), [5] Q Li; WS Wang; C Ma. Dtction. Optics&Lasr Tchnology, 2010, 42, [6] XS Suo; L Gao; N Wang; CJ Li; RM Zhao, DN Zhang,,Journal of Chins Agricultural Mchanization, 2010,10(5), [7] J Xiao; L Xu; JM Cao. Modrn Scintific Instrumnts, 2012,11(5), [8] LA Gao;M Chng;J Tang. Tlkomnika -Indonsian Journal of Elctrical Enginring, 2013,11(9), [9]D Sandip; Chaudhuri; K Sandp; Bhattacharya, N Raghu. Mandal, C Krishna., Applid Physics Lttrs, 2014, 104(19), [10] CJ Li; SG Zhang; ZJ Cai; XS Suo; YS Jia. Journal of Chins Agricultural Mchanization,2013,34(2): [11] D Kohlr; A Zuschlag; G Hahn. Solar Enrgy Matrials and Solar Clls, 2014,120(1), [12] R Bhattacharj; IM Hung. Matrials Chmistry and Physics, 2014, 143(2),