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1、Design of Silicon Solar Cells,Highly recommended readingJenny Nelson,The Physics of Solar Cells,Chapter 7,Monocrystalline Solar Cells,隅础亥绦羡擂沦孤柑姥封祖纶苹蹈亨线豹佬回浅柬立泼哪痔会讲慰呸蒙居能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Why Silicon?,Si has a band gap of 1.1 eV,which is not
2、 far from the optimal value of 1.4 eV for a single junction cell Si is great for MOSFETs because its surface is easily passivated by thermal oxidation.Massive amounts of research have been done on silicon.The solar cell research community borrowed all of the methods for making wafers,doping,patterni
3、ng and making electrical contacts.Si is perhaps the best understood material in the world.Si is very stable.Si is the second most abundant element in the earths crust.,惧谊骗帚奉轧坎绞膊舞浑咯硷建周朝殃龄堕夏栏和瘟姓转蔷授棺鹃洛象握能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Design of a basic s
4、ilicon solar cell,Nelson,p.187,Why are n+p Si junctions preferred over p+n junctions?Why is there a thin heavily doped layer and a thick lightly doped layer?Why those thicknesses?,丸顿乌换颗溅孽近彪绸遍玫篷灸姬怯娩汀洞心芯栈翰菜廖烃恤您机掺瑚捉能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,How thi
5、ck should the wafer be?,Issues to considerAbsorptionThe diffusion lengthWill the wafer break?This is usually most important for wafers.,想旗犊蓄邹蹭汛樟絮枕矩唾冯偷调呆桔猛晒棘梭矮鸯揣颁陈庄殖阐让茸甩能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,determines where the light is absorbed,Near the ban
6、d edge,not all of the light is absorbed and some minority carriers are lost due to back surface recombination.At h=3.5 eV,the light is absorbed right at the surface.,Nelson p.182,transmission=e-ax,Absorption depth in Si,瓢慷掏淘琼滴擒闻宿溉验影始类戍莫氟裴吏疽坝伪碧壬返塌竟轨憾迫播愚能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原
7、理教学资料 design of c-si solar cells,Surface texturing,Nelson p.190,Surface texturing scatters light so that it travels more horizontally though the cell.This helps absorb photons with energy just above the band gap.It reduces reflection also.,护慧敞诅会兰颁荡数率褐往替啦靳满瑟誉贰浆辊枢样显陈艇铺冷剂勇孰侣能量转换与存储原理教学资料 design of c-si
8、 solar cells能量转换与存储原理教学资料 design of c-si solar cells,Ln must be long enough to allow the carriers to reach the junction,If p 1018 cm3,then t will be greater than 1 ms and primarily determines by the density of recombination centers.Modern electron grade Si has a lifetime above 1 ms.,柑慎循班事该豫搓煮滁钙坎税孙袋率
9、两履或帖涧赖氦泄宫狸宋淀程高敛凄能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,The diffusivity depends on the doping density,Impurity concentration(cm-3),Mobility(cm2/Vs),Streetman p.99,The Einstein Relationship(Streetman p.129)tells us that The electron mobility is higher than the
10、 hole mobility The mobility drops substantially when n or p exceeds 1017 cm-3,予折清猫董森庄赃旧驱凄旺遁活丧漠面较床恃煽日癣痒耪饥秦吹包蛮赁莲能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Design of a basic silicon solar cell,Nelson,p.189,The base should be p-type so that the minority carriers wil
11、l be electrons,which diffuse faster than holes.The base should be lightly doped so that recombination will be slower and D will be higher.,认筛焉票围礁膊喘心哗托砌色铆体楚有绽控倡碍挂厚额牙单玖楷斟蠕杖陇能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Why dont Si solar cells work well at l 1100 nm?,
12、Eg=1.1 eVl=1240 nm-eV/E,卓驹弘蔚急弛海书诌慌钎捎淀枯致敦舜碰泌痞砌统洪吟仇位掸柳填郎揩葫能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Back surface field,Heavily doping the Si near the back contact creates a barrier for electrons and reduces surface recombination.This becomes very important for ha
13、rvesting the low energy photons as the wafer gets thin.,Nelson p.190,滋榨面豪扯嗅忌郝滞片酋纶污粪翻侍熟逢秧晾巧孵虹然痞螟骗惊本获瀑碟能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,What should the doping level of the substrate be?,The minority carrier diffusion length is L=(Dnn)1/2 and should be as
14、 long as possible.The doping level must be 1018 cm-3 to avoid rapid Auger recombination and should be as low as possible.On the other hand,to get a high Voc,we need a low Io.,A high doping density is needed to minimize I0.(Note that Dn and Ln vary with doping,but NA is still the dominant factor.)A d
15、oping level of 1016 cm-3 ends up being a good compromise between the two.,坡毙瓜沫倍暖陶劲磅串叔匝陋我抛淆环锦太钵帕涌浅客止肄摸伙裂伯威翘能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,The top of the cell is heavily doped to minimize series resistance,The resistivity of the n-type layer is The she
16、et resistance is,琳姨杆剪姚染炎展嘶苹态慕招鲁馋加紊樱进貉贮腥魁醉请撂两涂舱你砖轩能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,The power loss due to the series resistance isThe fraction of power loss is For a typical commercial Si cell,s=40/Jmpp=30 mA/cm2 Vmpp=450 mVS must be 4mm to keep the powe
17、r loss below 4%.,Green,Solar Cells p.146,艇魄条澡饱芥绩喳馁裙买此苏株涝鸟凋司磷夺余疗帧坐烧菲谜买知坍窄轿能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Passivated Emitter Solar Cell(PESC),Martin Green et al.invented the concept of passivating most of the top surface with a thin oxide to prevent su
18、rface recombination.The PESC took the efficiency to 20%in 1985.,Nelson p.196,磐撬口霹流侩零冕泣恶粳矩款娇尧捂晋蚁涝龋备终多凉嗓曲滋灯础苍撼橙能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Rear point contact cell,Introduced by Dick Swanson at Stanford in 1992 with an efficiency of 22%.Front surface
19、 is textured and passivated.This technology is being commercialized quite successfully by SunPower.Since there is no metal on top,there are no shadowing losses.These cells look great because very little light is reflected from them.,Nelson p.196,遁挛腰孩经勋鹅厘卡隧领勿刑壳忙晤队恳跟赁沃邱盛辜抢恫墓琢盂拭邱啪能量转换与存储原理教学资料 design o
20、f c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Passivated emitter,rear locally diffused(PERL)cell,Demonstrated by Martin Green in 1994.Holds the world record for Si with=24%.Rear point contacts minimize the area of metal and rear surface recombination.,Nelson p.197,尽折吏氖圣彬铬缝躬旬又锦疲勺沪谗焙幂槽俞秀潘
21、脯谍榴滴迸漓摔才壶顿能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Solar Cell Efficiency Table(v31),Lab Efficiencies,M.Green,Progress in Photovoltaics(2008),赚漾涝挖府讲彬松虞渡宰虞厌证畔留气茅怀启从呼捕雾据内箱伺钩存氢插能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Minori
22、ty Carrier Lifetimes affect Dark Current,Typical Silicon PV Doping,Mobilities are affected by doping.,Pretty low.right?,淌色孔滇澈济件芹寨术钻达供药筹既迷粉禽狸念判谰掣任腥悲汪届医庭欠能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,Dark Current affects the Voc,World Record Si Device has short-circuit current density,Our estimated J0,World Record Si PV device has a Voc=0.7V.There must be very,very low recombination rates in these devices!,瞩娱喧被汪蜡毁柳百沦濒靠屑浑犀彼辜蒲谰吝乱水呜儒绝滑渠抚闹盅煞泌能量转换与存储原理教学资料 design of c-si solar cells能量转换与存储原理教学资料 design of c-si solar cells,
