1、第八章 薄膜太陽能電池授課教師：黃俊杰薄膜太陽能電池的種類非晶硅(Amorphus Silicon, a-Si)微晶硅(Nanocrystalline Silicon，nc-Si，or Microcrystalline Silicon，uc-Si)CIS/CIGS(銅銦硒化物)CdTe(碲化鎘)GaAs Multijuction(多接面砷化鎵)色素敏化染料(Dye-Sensitized Solar Cell)有機導電高分子(Organic/polymer solar cells)太陽能電池市場現況太陽能電池效演進非晶硅(Amorphus Silicon, a-Si) 數據源：BP 2002、W

2、orld Nuclear Association是發展最完整的薄膜式太陽能電池。其結構通常為p-i-n（或n-i-p）偶及型式，p層跟n層主要座為建立內部電場，I層則由非晶系硅構成。非晶硅的優點在于對于可見光譜的吸光能力很強，而且利用濺鍍或是化學氣相沉積方式生成薄膜的生產方式成熟且成本低廉，材料成本相對于其他化合物半導體材料也便宜許多；不過缺點則有轉換效率低(約57%)，以及會產生嚴重的光劣化現象的問題，因此無法打入太陽能發電市場，而多應用于小功率的消費性電子產品市場。不過在新一代的非晶硅多接面太陽能電池(MultijuctionCell)已經能夠大幅改善純非晶硅太陽電池的缺點，轉換效率可提升

3、到68%，使用壽命也獲得提升。未在具有成本低廉的優勢之下，仍將是未薄膜太陽能電池的主流之一。CIS/CIGS(銅銦硒化物)CIS(CopperIndiumDiselenide)或是CIGS(CopperIndiumGalliumDiselenide)都屬于化合物半導體。這兩種材料的吸光(光譜)范圍很廣，而且穩定性也相當好。轉換效率方面，若是利用聚光裝置的輔助，目前轉換效率已經可達30%，標準環境測試下最高也已經可達到19.5%，足以媲美單晶硅太陽電池的最佳轉換效率。在大面積制程上，采用軟性塑料基板的最佳轉換效率也已經達到14.1%。由于穩定性和轉換效率都已經相當優異，因此被視為是未最有發展潛力

4、的薄膜太陽能電池種類之一。CdTe(碲化鎘)CdTe同樣屬于化合物半導體，電池轉換效率也不差：若使用耐高溫(600C)的硼玻璃作為基板轉換效率可達16%，而使用不耐高溫但是成本較低的鈉玻璃做基板也可達到12%的轉換效率，轉換效率遠優于非晶硅材料。此外，CdTe是二元化合物，在薄膜制程上遠較CIS或CIGS容易控制，再加上可應用多種快速成膜技術(如蒸鍍法)，模塊化生產容易，因此容易應用于大面積建材，目前已經有商業化產品在市場營銷，轉換效率約11%。不過，雖然CdTe技術有以上優點，但是因為鎘已經是各國管制的高污染性重金屬，因此此種材料技術未發展前景仍有陰影存在。染料敏化染料(Dye-Sensit

5、ized Solar Cell)染料敏化感染料電池是太陽能電池中相當新穎的技術，產品是由透明導電基板、二氧化鈦(TiO2)奈米微粒薄膜、染料(光敏化劑)、電解質和ITO電極所組成。此種太陽能電池的優點在于二氧化鈦和染料的材料成本都相對便宜，又可以利用印刷的方法大量制造，基板材料也可更多元化。不過目前主要缺點一是在于轉換效率仍然相當低(平均約在78%，實驗室產品可達10%)，且在UV照射和高熱下會出現嚴重的光劣化現象，二是在于封裝過程較為困難(主要是因為其中的電解質的影響)，因此目前仍然是以實驗室產品為主。然而，基于其低廉成本以及廣泛應用層面的吸引力，多家實驗機構仍然在積極進行技術的突破。有機導

6、電高分子(Organic/polymer solar cells)有機導電高分子太陽能電池是直接利用有機高分子半導體薄膜(通常厚約為100nm)作為感光和發電材料。此種技術共有兩大優點，一在于薄膜制程容易(可用噴墨、浸泡涂布等方式)，而且可利用化學合成技術改變分子結構，以提升效率，另一優點是采用軟性塑料作為基板材料，因此質輕，且具有高的可撓性。目前市面上已經有多家公司推出產品，應用在可攜式電子產品如NB、PDA的戶外充電上面，市場領導者則是美國Konarka公司。不過，由于轉換效率過低(約45%)的最大缺點，因此此種太陽能電池的未發展市場應該是結合電子產品的整合性應用，而非大規模的太陽能發電。

7、非晶硅薄膜太陽電池構造Need of raw materialThin-film solar cells非晶硅薄膜太陽電池制造程(玻璃基材)非晶硅薄膜太陽電池制造程(玻璃基材)Thin film Si:H challengesIncreasing deposition rate (from 0.1 nm/s to 10 nm/s!), including compatible doped layersEnhance the Isc (absorption, light trapping)Improving stabilized device performanceUnderstanding f

8、undamental physics: low Voc, shunt behavior, light-induced defect creation非晶硅薄膜太陽電池“Amorphous Si:H Thin-film Solar Cell”UniSolar and薄膜太陽能電池 CIGS薄膜電池此型有種：一種含銅銦硒三元素（簡稱CISe），一種含銅銦鎵硒四元素（簡稱CIGS）。由于其高光電效及低材成本，被許多人看好。在實驗室完成的CIGS光電池，光電效最高可達約19.88，就模塊而言，最高亦可達約13(CISe約10%)。CIGS隨著銦鎵含的同，其光吸收范圍可從1.02ev至1.68ev，此項

9、特征可加以用于多層堆棧模塊，已近一步提升電池組織效能。此外由于高吸光效（104105-1），所需光電材厚需超過1m，99以上的光子均可被吸收，因此一般粗估產制造時，所需半導體原物可能僅只US$0.03/W。薄膜太陽能電池 CIGS薄膜電池CIGS太陽能電池組件結構演進CIGS太陽能電池組件制作程CIGS太陽能電池-真空制程真空涂布制程- Co-evaporation真空涂布制程- SputteringCIGS太陽能電池-非真空制程非真空涂布制程- electrodeposition非真空涂布制程-Metal Oxide InkCIS薄膜太陽電池“Copper Indium Diselenide

10、 Thin-film Solar Cell ”245-kW rooftop, thin-film CIS-based solar electric array, Camarillo, California (Shell Solar Industries.)85-kW thin-film CIS-based BIPV facade, North Wales, UK結論各型太陽能電池的市場需求將與日遽增，且各技術皆以低成本和提高光電轉換效為研究方向。其中又以薄膜太陽能電池為現階段最具有取代硅晶太陽能電池的可能。薄膜太陽電池中，CIGS是目前具有最高效的電池之一?，F階段CIGS電池主要產技術仍以真空

11、制程技術為主，但難以克服大面積及低成本的問題。 CIGS非真空制程技術雖具有低成本以及提高材使用的優點，但各方式具有難以克服的關鍵問題皆仍待解決。如CIGS晶成長等。結瓶頸CIGS薄膜太陽能電池雖具有高效、低成本、大面積與可撓性等潛優勢，但還有許多需要克服的問題接踵而：制程復雜、技術選擇百家爭鳴，且供應相當分歧，各站并無制式化設備放大制程之均質性佳，變化大 dopant ratio thin window layer Low Voc resulting in increased area loss系統化的研究與實驗據十分缺乏許多關鍵點無定，如：組成成分、結構、晶界、各層間之接口等關鍵原的缺乏

12、銦元素也是一項潛在隱憂，銦的天然蘊藏相當有限，國外曾計算，如以效10的電池計算，人如全面使用CIGS光電池發電供應能源，可能只有光景可，銦的天然蘊藏相當有限，國外曾計算，如以效10的電池計算，人如全面使用CIGS光電池發電供應能源，可能只有光景地熱CdTe Film DepositionCdTe Film DepositionCdTe Film DepositionRooftopCdTe薄膜太陽電池“Cadmium TellurideThin-film Solar Cell”Katzenbach Juwi Memmingen SAGSAGFirst Solar -CdTe RooftopC-S

13、i Technology in Historic Perspective全球PV前十大廠商臺灣太陽光電產業鏈分布概況太陽光電產值預期達成規模光電高分子太陽能電池特征發展不久原理:利用不同氧化還原型聚合物的不同氧化還原位勢,在導電材料(電極)表面進行多層復合,外層聚合物的還原電為較高,電子轉移方向只能由內層向外層轉移;另一電極正好相反奈米晶色素增感solar cellDSSC進展Why organic solar cell? Ease of fabrication for large area from solutionTransparentConformal and flexibleLow c

14、ost of manufacturingDye-Sensitized Solar CellMechanisms of the DSSCh :photon absorptiona :electron injectionb :recombinationc : e- transport and collection at conducting substrate d :I- oxidatione :I3- reductionf :ion transportBasic mechanisms in a DSSCI/I3- redox electrolytedyehTiO2TCOCounter elect

15、rodeabcdef2e- + I33I-3I-I3- + 2e-E-An Introduction to its Principle, Materials, Processes, and Recent R&DsDye-sensitized Solar Cell(DSSC):Principle ofDye-Sensitized Solar cellsDye-Sensitized Solar CellLow photocurrent could be the result ofInefficient light harvesting by the dyeInefficient charge in

16、jection into TiO2Inefficient collection of injection electronGratzel, Nature, 2001Special Features of a DSSCSemiconductor not excited directlyPhoto carrier generation & transportation arewell separated the probability of recombination can be drastically reduced.Positive charge transportvia ion trans

17、port in the electrolyte, rather than hole conditionNo electric field, electron transfer has been described as diffusionJn= nnEcb+ q DnnNanoparticle structureTCOCounter electrodeTiO2/ dye / electrolyte(I-/I3-)glasse-0Performance of Photovoltaic and Dye-sensitized Solar CellsType of cellEfficiency %(c

18、ell)Efficiency %(module)Research and technology needsCrystalline silicon2410-15Higher production yields, lowering of cost and energy contentMulti-crystalline silicon189-12Lower manufacturing cost and complexityAmorphous silicon137Lower production costs, increase production volume and stabilityDye-se

19、nsitized nano-structured materials10-117Improve efficiency and high-temperature stability, scale up production-Their functions, principles, characteristics, materials, processes, and recent R&DsPart II:Major Components in a DSSC The TCO Electrode -one of the major components in a DSSC Role of the TC

20、O electrode in a DSSCElectronstransportation and collectionCharacteristicsHightransmittance in visible region()Highelectrical conductivity()Thermal endurance ()Corrosion resistanceEnergy level not higher than nanoparticle oxide() present the issue still for improvinge-ITRCommon Materials and Process

21、es of the TCO Electrodes Materials:ITO, ZnS, ZnO, SnO2(energy gap higher than photo energy in visible region)Processes:Sputtering depositionPlasma ion assisted depositionRef (3)Recent R&Ds of TCO Electrode in DSSCMethod improvingContentsEvaluationRef.Design*Oxide/metal/oxide structure1/ tot= 2/ oxid

22、e+ 1/ metal Ref.(465)Material* TiO2 replace ITO* AgCu replace Ag as metal interlayer Thermal enduranceRe. f(7)Ref. (8)Processes*Heat treatment*PIAD ; TAvoid high tempRef. (9) Ref. (10)Analysis*Multi-layer combination appropriate arrangement of the n & t of each layerR ; TOptic simulationRef. (11) Re

23、f. (12)Incident =Reflection + Transmittance +AbsorptionPassage of Light Through a Material related torefractive index,thickness, particle sizeDepend onEgParticle size effectInterference effectdSubstraten1nsn0Nano-material transmit lightMicro-material scatter lightRef (14)Ref (13)dyedye -one of the m

24、ajor components in a DSSC Role of dye in a DSSCPhotoexciting & injecting electrons into the conduction band of the oxide CharacteristicsAbsorb all light below 900nm ()Molecular dispersion in nanostructure oxide ()Carry attachment group(eg. carboxylate or phosphonate) tofirmly graft to the oxide surf

25、aceThe Energy level ofexcited state higher than conduction band of oxide The redox potential sufficient high to be regenerated via electron from the electrolyteSustain high cycle usageTiO2Ru2+Ru2+*Ru3+e-e-hCommon Materials of the DyeGeneral structure: ML2X2( L: 2.2-ipyridyl-4,4-dicarboxylic;M: Ru or

26、 Os;X: halide,-CN,-SCN )N3Absorption Spectrum of N3 and dark grayDark grayAM1.5 solar spectrum400500600700800900nmA00.51.01.52.0N3Dark grayRef (14)Recent R&Ds of Dye in DSSCMethod improvingContentsEvaluationRef.Design*Mix different dyes Broadband absorptionRef. (15)Material*Different types of ligand

27、Explore:e- donation process, charge recombination, sensitizer regenerationRef. (16)Oxide Film-one of the major components in a DSSCRole of the oxide in a DSSCReceive electrons from the dyeEfficient transport electrons in the media CharacteristicsUltra fine structure(nm-crystal, mesoporous) interconn

28、ected ()Good electrical conduction properties ()Conduction band edge is more negative than HUMO of the dye ultra fine structure enable.TiO2 nanoparticlesRef (17)Ref (3)IPCE%001000.15300800nm300800nmSingle crystal anataseNanocrystal anataseCommon Materials and Processes of the Oxide filmMaterial:TiO2

29、(cheap, non-toxic), ZnO, Fe2O3, Nb2O5, WO3, Ta2O5, CdS, CdSeCommon processes:TiO2filmTiO2particles (Finely divided monodispersed colloidal)Coating,sinteringTi saultProcess parameters:Precursor chemistryHydrothermal growth TempBinder additionSintering conditionControl: hydrolysis and condensation kin

30、eticsFactors influence properties:Material contentChemical compositionStructureSurface morphologyGrain size, porosity pore size distributionCrystalline form (anatase,rutile.)Hydrolysissolvent+binder(1-20m)Electron Transport in the DSSC- An important factor affecting IPCEDe in the porous film De in t

31、he bulk crystalMulti-trapping model: electron transport is mediated by the conduction band and is interrupted by trapping.The traps could be formed byoxygen defects,amorphous layer on the particle surface,chemical surrounding, andlattice mismatch at boundaries.Injection electrons are slow down by tr

32、apping at the surface of the particle andmay back reaction through combination with I3- iron.Ref (18)Recent R&Ds of the Oxide Film in DSSCMethod improvingContentsEvaluationRef.Design & process*Nanocrystallite(TiO2,SnO2, ZnO.) coated with the shells of material(Al2O3,MgO, ZnO)*Column ZnO film (struct

33、ure scale 100-500nm ) -electrodeposition, non- equilibrium growth on wurtzite crystal*addition of larger particle TiO2Voc; IPCEscatteringscattering( optical path length)Ref. (19)Ref. (20)Ref. (21)Analysis*SPV(surface photo voltage measurement)*Decay kinetics(nanosecond transient absorption)Detect electron injection processRef. (22)Ref. (23)Band positions of semiconductorsThe Electrolyte -o