STRATEGIC ENERGY TECHNOLOGY PLAN

Transcription

1 STRATEGIC ENERGY TECHNOLOGY PLAN Scientific Assessment in supprt f the Materials Radmap enabling Lw Carbn Energy Technlgies Phtvltaic Technlgy Authrs: Peter Rigby, (Rapprteur), Bertrand Filln, Andreas Gmbert, Jsé Herrer Rueda, Edwin Kiel, Enn Mellikv, Jef Prtmans, Ruud Schrpp, Ing A. Schwirtlich, Paul Warren JRC Crdinatin: A. Jäger-Waldau and E. Tzimas EUR EN

2 The missin f the JRC-IET is t prvide supprt t Cmmunity plicies related t bth nuclear and nn-nuclear energy in rder t ensure sustainable, secure and efficient energy prductin, distributin and use. Eurpean Cmmissin Jint Research Centre Institute fr Energy and Transprt Cntact infrmatin: Dr. Arnulf Jäger-Waldau Address: Via E. Fermi 2749, TP 450, Ispra(VA), Italia arnulf.jaeger-waldau@ec.eurpa.eu Tel.: Fax: Legal Ntice Neither the Eurpean Cmmissin nr any persn acting n behalf f the Cmmissin is respnsible fr the use which might be made f this publicatin. Eurpe Direct is a service t help yu find answers t yur questins abut the Eurpean Unin Freephne number (*): (*) Certain mbile telephne peratrs d nt allw access t numbers r these calls may be billed. A great deal f additinal infrmatin n the Eurpean Unin is available n the Internet. It can be accessed thrugh the Eurpa server JRC EUR EN ISBN ISSN di: /64679 Luxemburg: Publicatins Office f the Eurpean Unin Eurpean Unin, 2011 Reprductin is authrised prvided the surce is acknwledged Printed in the Netherlands

3 Preamble This scientific assessment serves as the basis fr a materials research radmap fr slar phtvltaic technlgy, itself an integral element f an verall "Materials Radmap Enabling Lw Carbn Technlgies", a Cmmissin Staff Wrking Dcument published in December The Materials Radmap aims at cntributing t strategic decisins n materials research funding at Eurpean and Member State levels and is aligned with the pririties f the Strategic Energy Technlgy Plan (SET-Plan). It is intended t serve as a guide fr develping specific research and develpment activities in the field f materials fr energy applicatins ver the next 10 years. This reprt prvides an in-depth analysis f the state-f-the-art and future challenges fr energy technlgy-related materials and the needs fr research activities t supprt the develpment f slar phtvltaic technlgy bth fr the 2020 and the 2050 market hrizns. It has been prduced by independent and renwned Eurpean materials scientists and energy technlgy experts, drawn frm academia, research institutes and industry, under the crdinatin the SET-Plan Infrmatin System (SETIS), which is managed by the Jint Research Centre (JRC) f the Eurpean Cmmissin. The cntents were presented and discussed at a dedicated hearing in which a wide pl f stakehlders participated, including representatives f the relevant technlgy platfrms, industry assciatins and the Jint Prgrammes f the Eurpean Energy Research Assciatins.

4 Chapter n PV Technlgy Fr the Radmapping Exercise n Materials fr the Eurpean Strategic Energy Technlgy Plan Mr. Peter Rigby, (Rapprteur) Dr. Bertrand Filln, Dr. Andreas Gmbert, Dr. Jsé Herrer Rueda, Dr. Edwin Kiel, Prf. Dr. Enn Mellikv, Prf. Jef Prtmans, Prf. Dr. Ruud Schrpp, Prf. Dr. Ing A. Schwirtlich, Dr. Paul Warren, 4

5 1. PHOTOVOLTAIC TECHNOLOGY Technlgy and System State f the Art The scpe f phtvltaic (PV) technlgy t be cvered in this scientific summary assessment paper is the PV Mdule and inverter. It will nt cver muntings and frames used fr installatin. Nr will it include energy strage systems and smart grids, hwever clse cllabratin with these sectrs will be mandatry in the future as the level f PV penetratin rises in the verall energy generatin mix. This paper is a synthesis f the varius designated expert s reprts that are prvided in attachment. Fr mre detail n the subjects and the assciated references please refer t these dcuments. Figure 1. Schematic f PV system cnnectin cnfiguratins The cmplexity f this assessment paper is that PV technlgy tday cvers several parallel technlgies that are either cmpeting r are cmplementary. They vary widely in terms f technlgical maturity, perfrmance, cst, materials availability and requirements. Hwever this dcument will review all the relevant PV technlgies (listed belw) and their develpment needs t meet the SET Plan bjectives fr 2020 in terms f energy prductin cst and materials availability. Crystalline silicn (c-si) Wafer based c-si, the mst mature PV technlgy, with high efficiency mdules suitable fr less price sensitive applicatins where area restrictins apply. Thin film inrganic PV (TFPV) Have the lwest mdule cst ptential in the near t mid term. There are three brad families Cadmium Telluride (CdTe) Is the current cst leader PV technlgy. There are sme cntested cncerns expressed ver the future easy availability f tellurium as well as the use f cadmium. Thin Film Silicn (TFSi) Amrphus Silicn / micr crystalline (TFSi) Acceptable efficiency cells require sphisticated multi junctin device architecture and manufacturing techniques and cntrl. Such multi junctin devices architecture will als cntribute t device stability. Cpper indium selenide (sulphide) / Cpper indium gallium di-selenide (sulphide) (CIS/CIGS) Is the PV technlgy which has achieved the highest lab based efficiencies f all TFPVs. The active absrber layer material system is the mst cmplex t manufacture which explains the efficiency gap between lab cells and industrial mdules. The material system wuld appear t lend itself t cheaper nn vacuum manufacturing prcesses. There are sme cncerns abut future availability f In, Ga and Se leading t a need fr nging research in substitute materials systems. 5

6 Lw Cncentratr PV (LCPV) Such systems typically use lenses t cncentrate the incident light n smaller area c-si r TFPV cells. High Cncentratr PV (HCPV) High Cncentratr PV (HCPV): Uses lenses r mirrrs t cncentrate the incident light n highlyefficient III-V multi-junctin slar cells. HCPV systems have great ptential fr lw cst electricity prductin in slar pwer statins with 1 t 100 MWp in cuntries with a large fractin f direct slar radiatin. Organic PV (OPV) Organic based thin film PV that have great ptential fr cst reductin in the medium t lng term, hwever a number f significant scientific / technlgical hurdles remain t be vercme. The figure 2 belw tracking best lab cell efficiencies shws that all the PV technlgies have been imprving ver recent years and is cntinuing t d s as science and technlgy cntinually push pen the envelpe. Figure 2. Evlutin f best research cell efficiencies 6

7 Nte gaps between best lab and prductin efficiencies Figure 3a. Efficiency gap between research lab and prductin (Surce Veec Phtn s PV prductin equipment cnference 2009) Figure 3b. Histrical evlutin f technlgy market share and future trends (Surce - Slar Generatin IV) It is imprtant t nte the fairly large gaps between best lab cell efficiencies and typical industrial prductin fr all PV technlgies (Figure 3a). These gaps are being cntinually narrwed, hwever it remains a pririty t develp cst effective, reliable prcesses and technlgy t minimise them. The evlutin f the different PV technlgies illustrated in figure 3b als is an indicatr f the early stage f maturity f the different PV technlgies. As a whle, the PV industry has shwn tremendus prgress in terms f cst reductin. Figure 4 shws the evlutin f c-si and TFPV prices functin f the cumulative manufacturing experience. can nte sme shrt term variatins abve and belw trend line. These are mainly due t the shrtage f crystalline silicn in recent times (nw reslved) as as brief perids f industry ver-capacity. This is nrmal especially fr an industry in its early develpment stages, but it is imprtant t nte that thanks t cntinuus research effrts and the effects scale, this price experience curve cnfirms a cnsistent trend f 22% reductin in mdule manufacturing csts fr every dubling f cumulative prductin. as a One the ply well f PV Figure 4. PV mdule price experience curve 7

8 Hwever, the mdule is nly part f the ttal cst picture. Additinal csts are intrduced with the inverter, the Balance f System csts (BOS), installatin and engineering / permitting. The mdule represents typically 50-60% f ttal installed systems csts (Figure 5). Simple reductin f mdule csts is f curse beneficial t the installed csts and investment, hwever imprvements n mdule efficiency will nt nly impact directly n the mdule csts but als n the BOS and installatin csts i.e. mdule plus BOS are equivalent t 70 80% f ttal investment csts. As demnstrated in figure 4, the trend has been fr mdule csts t cme dwn quickly and t cntinue t d s. As this happens, the nn-mdule BOS+Installat in 23% Inverter 10% c-si rftp Engineering and prcurement 7% Mdule 60% BOS+Installat in 32% TFPV rftp Engineering and prcurement 7% Surce - EPIA / Greenpeace, Slar Generatin VI Figure 5.. Cst breakdwn fr c-si and TFPV rftp systems Inverter 10% csts increase relatively thus increasing the relative impact and imprtance f the mdule efficiency. Fr this reasn it is imprtant t fcus n develpments that will ideally bth reduce directly the mdule csts and especially imprve its efficiency in rder t have the maximum impact n ttal installed cst and s the Levelised Cst f Electricity (LCOE). As utlined abve several PV technlgies have been develping in parallel. This can be viewed as an underlying strength since it allws the selectin f the ptimum PV technlgy as a functin f the lcal irradiatin prfile and the applicatin cnstraints. In additin, when ne technlgy is faced with material r technlgy cnstraints it allws ready substitutin by anther. Hwever, each PV technlgy des have its wn specific cst / perfrmance attributes implying that several but prbably nt all f the current PV technlgies will c-exist in the future. Actual applicatin cnditins will determine which nes will be the mst adpted thrugh their ffer f the ptimal slutin fr a given set f cnstraints (price sensitivity, space, weight, light cnditins, ambient temperatures, aesthetics, lngevity ). Since each f the PV technlgies (including even the mst mature c-si) is still explring the limits f its wn attributes, it wuld be premature tday t limit the future ptins. Cnsequently, when cnsidering the hrizns f 2020, 2030 and 2050 we need t cnsider the range f PV technlgies listed abve fr further develpment as it is difficult t fresee tday the ptimal slutin f tmrrw. KPIs In the case f PV, the materials fcus has t be with respect t their functinality in their activated frm. A PV device cmprises a series f discrete layers each with its wn typical functinalities such as light absrptin, semi cnducting, electr-ptical, ptical, abrasin resistance, cnductivity.. The materials actual functinality is mst ften due t a cmbinatin f the material, the manufacturing prcess and activatin steps assciated with that material and the behaviur f tw adjacent materials at their interface. It is therefre quite ften difficult (impssible) t islate the functinality fr measurement e.g. the semi cnducting active layer. Others will be relatively easier fr example Transparent Cnducting Oxide layers (TCOs) in terms f transparency and cnductivity. Hwever, even in these cases the interface behaviur will have a significant effect n the device perfrmance. Cnsequently in the fllwing pages KPIs fr individual materials will be indicated where pssible but in sme cases and ultimately in all cases it will be necessary t refer t verall device perfrmance and cst. Based n histrical data and lking t the future, we can set the fllwing PV system Key Perfrmance Indicatrs. Mdule 51% 8

9 PV perfrmance targets Typical electricitygeneratin csts in Suthern Eurpe (2) (Eurs/kWh) Typical turn-key system prices (Eurs/Wp) (1) ,30-0,60 0,16-0,36 0,10-0,20 0,08-0,19 <0,07 0,03 5 2,26-3,41-1,30-2,08 <1,20 0,5 Typical PV mdule efficiencies (%) Crystalline Silicn 13-18% 15-20% 16-21% 18-23% 30% >30% Thin Films (inrganic) 5-11% 6-12% 8-14% 10-18% 20% >20% Cncentratr PV 20% 20-25% 35-40% 40-50% 50-60% <60% OPV > Nvel PV technlgies Will need t be cmpetitive with status qu PV systems Inverter life time (years) >25 >25 >25 Guaranteed perfrmance utput (years) (3) Inrganic OPV 10 >20 >30 System Energy Pay-back time (years) ,5 0,4 0,25 Surce: Implementatin plan fr the strategic research agenda / SEII May EU PV Technlgy Platfrm / EPIA - AT Kearney (1) Price f system depends n technlgy imprvements as well as market maturity (industry infrastucture and admin csts) (2) LCOE varies with financing cst and lcatin. Suthern EU lcatins cnsidered range frm 1500kWh/m 2 (e.g. Tuluse) t 2000 kwh/m 2 (e.g. Syracusa). (3) Refers t highest perfrmance guarantees required frm the industry but actual figures required will be applicatin dependent. Table 1. Key Perfrmance Indicatrs fr PV systems Inherent t all materials develpments effective and sustainable resurce use shuld be cnsidered. Recycling will be dealt with in greater depth in sectin 1.2. Cradle t cradle apprach and design fr recycling shuld be an underlying theme fr prpsed develpments where materials can have an influence r enable. Pririties fr implementatin f research results In view f its innate attributes, PV has an assured future in cntributing t sciety s lng term energy and envirnmental sustainability needs; hwever at present it is still largely relying n external incentives such as Feed in Tariffs t be ecnmically viable. It is f the utmst pririty t the industry and sciety that PV becmes an attractive ratinal investment pprtunity in as shrt a time frame as pssible withut the need fr such incentives. Once this tipping pint has been reached we can expect a self-fuelled rapid deplyment f PV fr bth residential and industrial sectrs alike. Reaching this threshld early will be pssible prvided that the right effrts in research and manufacturing scale effects are implemented. Figure 6 illustrates schematically the pririties f the implementatin bjectives fr PV ver the cming 40 years. The abslute verarching pririty between nw and 2020 is t bring dwn the cst f PV electricity generatin. Installed cst reductin based n imprving current PV technlgies will be the key enabler t reach ecnmic autnmy. Grid parity fr retail electricity Cst Reductin & imprved perfrmance c-si, TFPV and CPV technlgies Grid parity fr peak and bulk electricity Supply chain balance fr materials Substitute sustainable PV materials systems Optimisatin f c-si, TFPV and CPV technlgies By % f electricity supplied by renewables. PV becmes cheapest and mst sustainable surce f energy Recycling EOL PV systems Incremental cst / perfrmance imprvements n TFPV and CPV technlgies Intrductin f Nvel PV high perfrmance technlgies Figure 6. Schematic f PV industry s research pririties / implementatin challenges 9

10 Hwever, success will bring new challenges in terms f materials availability particularly fr the advanced thin film PV technlgies. Intensive research int new substitute materials systems with n resurce limitatins will need t be initiated in the next 10 years s that they may be ready fr implementatin befre Due t the life time f PV devices, it is nt expected that significant vlumes f end-f life PV mdules will require recycling befre 2030, hwever effective recycling f prductin scrap will be an imprtant element t ensure sufficient materials availability. 10

11 Scenaris and market size Over the years, the IEA, the EC, the EPIA and independent market frecasters have all regularly increased their predictins f the glbal PV market size. The given example is the Sarasin Bank frecasts which cnsistently increased its 2020 PV scenari in successive years. This highlights the inherent difficulty f evaluating and defining such scenaris in an early stage high grwth industry. Figure 7. Evlutin f PV market estimates Sarasin Bank (surce Stefan Nwak) When cnsidering the PV market ptential and the pressures placed n the materials supply chain, it is essential t cnsider the wrld market. Tday Eurpe is leading the way with mre than 70% f the installed PV capacity. Hwever this will mst likely change ver the next years. A recent study n the ptential f the Sun Belt cuntries (between 35N and 35S) where the innate drivers in favur f PV are extremely high, suggests that in a Paradigm Shift scenari, the PV ptential in such regins wuld be fr an installed base f 1,100 GWp by In additin, significant grwth is expected in ppulus il-resurce-pr cuntries such as India and China. The scenaris suggested in this technlgy chapter differ slightly frm thse riginally prpsed by the EC when defining the prject. The wrld wide annual PV installatins in 2010 are nw cnfirmed t have been 16.6 GWp (13.2 GWp in Eurpe), with estimates fr a ttal installed PV base f 39.5 GWp wrld wide f which 29.2 GWp is in Eurpe. The EC prpsed figure in the lw case scenari f 84 GWp in 2020 in Eurpe (cming n dubt frm the NREAPs) wuld appear unduly cnservative as it implies an average annual reductin f installatin levels f 15 20%. Instead we wuld prpse an annual psitive prgressin per annum until 2020 and slwing dwn prgressively after that as PV fills its rightful place in the energy mix. In the case f the high scenari, rather than intrduce a cmpletely new set f figures, we prpse t refer t the EPIA s Paradigm shift scenari (Table 2). We wuld g further and suggest that prvided that the R&D effrts prpsed in this dcument are successful, we wuld expect the PV industry t be able t meet the requirements necessary fr the paradigm shift scenari, but this f curse assumes that the ther cnditins are als met as utlined in the EPIA reprt LOW SCENARIO Cumulative GWp 39, Annual GWp/yr 16, Rati f cumulative PV installatins Wrld/Eurpe 1,35 2,5 3,9 - - HIGH SCENARIO Cumulative GWp 39, Annual GWp/yr 16, Rati f cumulative PV installatins Wrld/Eurpe 1, ,9 - - Table 2. Summary f prpsed wrld wide scenaris (Surce EPIA/Greenpeace Slar Generatin IV) Althugh the Eurpean PV end user market is dminant tday, it is expected that the centre f gravity will prgressively shift t ther regins as csts cme dwn, making PV mre affrdable fr develping regins with great ptential (refer t the EPIA s Sunbelt Study). This represents fresh challenges, but great exprt pprtunities fr the cst and technlgy leaders. A final pint is that in spite f Eurpe s high installatin rates, this is nt necessarily reflected in the surce f manufactured devices. In the last 2-3 years, China and Taiwan have becme dminant frces wrld wide in the 11

12 manufacture f c-si cells and t a lesser extent mdules. The reasns fr this rapid evlutin g beynd a simplistic cmparative f labur csts. Further develpment f cutting edge technlgy in rhyme with prgressive public industrial plicy will be needed t ensure that PV is stabilised as a high value added industry in Eurpe Main Challenges fr PV Technlgies Materials can be viewed as key enablers in any PV system. In verall terms the key challenges fr materials are twfld: T design and manufacture PV systems that are efficient enugh and cheap enugh t meet the grid parity targets (initially residential retail and ultimately utility scale base lad) within the next few years as defined in Table 2. A materials supply chain that is able t supply sufficient quantities f the required elements (refer t sectin 1.2). Mdule design and chice f materials that lend themselves t cst effective recycling. Develping standardised perfrmance testing and reliability/ageing test prtcls that will prvide cnfidence (and s bankability) fr PV devices emplying newly develped materials in a wide range f perating cnditins (frm Eurpe t Sunbelt envirnments). Each PV technlgy has its wn specific challenges and will be utlined in the fllwing sectins Crystalline-Si Figure 8. c-si cell / detail f tp metalisatin cllectr Surce: Schtt Present value chain : Cell prcessing Wafer Cutting/Separatin Saw damage remval + texturing POCl 3 Diffusin Parasitic Junctin Remval PECVD SiNx:H ARC layer Screen Printed Metallisatin C-firing Surname + Name imec/restricted Figure 9a & 9b. Value chain fr c-si manufacturing Crystalline Si with 80% f tday s PV market is the mst mature f all the PV technlgies having benefited frm mre than 30 years f develpment. It is a beacn f what can be achieved in terms f reducing csts and raising efficiency. The manufacturing prcesses are well established but still have cnsiderable ptential fr imprvement. 12

13 The principal advantages tday are that c-si has the highest prductin mdule perfrmance f all flat plate PV mdules and the principal semi cnducting material (silicn) has n intrinsic material availability issues, althugh f curse industrial investment in refining and wafering capacity will need t keep pace with the market. New cell architectures, such as heter-junctin technlgies riginally develped in Japan, are just nw starting t be cnsidered by the rest f the c-si cmmunity. Key challenges fr c-si cells / mdules The current ply crystalline silicn refining prcesses require a high level f energy input. S a key cncern is t reduce the energy input per Wp f utput. In this respect, new prcess rutes with high saving ptential (e.g. plasma/segregatin purificatin, Fluidized Bed Reactr) shuld be investigated t develp feedstck materials. In parallel, new prcess rutes shuld be investigated t develp direct epitaxial grwth f silicn wafers nt substrates frm gaseus phase (silanes, trichlrsilanes, plysilanes r plychlrsilanes ). The resulting material will need t have a very lw defect cncentratin leading t carrier lifetimes f at least 3 times the layer thickness The refined ply-silicn needs t have a cst f less than 20 Eurs/kg as sn as pssible. New technlgies are required t prduce slar grade plysilicn. There needs t be a better understanding n the interactin between metallic impurities, grain bundaries and intra-grain defects in relatin t the thermal histry f the ingt and wafer fr multi crystalline Si. This infrmatin is highly relevant t estimate the technical and ecnmic viability f Slar-Si feedstck btained frm alternative rutes like UMG-Si Ingt crystallisatin has a number f areas fr imprvement e.g.: Figure 10. Life time pattern f an ingt crss sectin, (A. Müller, J. Henker, DGKK Jahrestagung, , Bremen) Crucible material, cating etc. and prcess develpment t inert material (Si3N4)and reusable crucibles. Re-usable crucibles. Imprvements in silicn yield by aviding cntaminatin znes arund multi-ingts. Optimizatin f ingt vlume and gemetry Maintain the purity f the feed stck t the ingt and wafer. Imprvement f feedstck yield. 13

14 Materials / / 2050 mc-/ mn ingts xygen [cm -3 ] < 7,5 * < 5 * < 2 * < 2 * carbn [cm -3 ] < 1 * < 5 * < 2 * < dislcatin density [cm -2 ] < 10 6 < 10 5 < 10 4 < 10 3 (mn r multi) metals [ppbw] 100 < 50 < 20 <10 Crucibles residual metal imurities [ppm] 100 < 50 inert inert releasing agent [ppmw] 30 < 10 inert inert minrity carrier diffusin length [µm] > Table 3. Plycrystalline KPIs Blcking and crpping f ingts The current prcess has challenges fr gemetrical accuracy and surface quality. Minimizatin f cutting lsses Fully autmated in-line prductin frm feedstck and crucible preparatin, t ingt blcking and crpping. Cntinuus flw f materials in prductin, silicn as well as cnsumables The blck surface quality shuld shw a gd finish after cutting directly, aviding additinal plishing r ther surface treatments. Gemetrical tlerance + 0,1 mm Lw surface damage t minimize breakage in later prcesses (micr-cracks < 20 µm) Wafering Silicn lsses due t the slicing prcess and SiC slurries are the tw majr cst items in wafers. Recycling is used t save csts, hwever fr very thin wafers this technlgy has limits. The challenges in wafering technlgy can be summarised: Reductin f the Si-cnsumptin by thickness reductin. This impses challenges n thin wafer slicing and understanding f breakage thrughut the cell and mdule prcess. Wafer separatin at thin thicknesses. Reductin f slurry csts and imprvement f TTV and surface defects. Reductin f kerf lss t << 100 µm fr thinner wafers (< 100 µm). Nvel technlgies t prduce thin wafers f < 100 µm thickness and a TTV f < 10 µm up t Cntrl f surface defect mrphlgy t < 10 µm, sufficient fr structural etching but aviding relevant breakage. Reductin f chemicals fr cleaning and recycling. Further thickness reductin t 5 µm 10 µm with nvel technlgy while keeping the quality level (in implantatin, prus silicn, epitaxial grwth) in the timeframe 2020 / 30. The scpe up t 2050 is a cmbinatin f silicn substrate preparatin with key elements f the slar cell, like heter-junctin technlgies with thin films which are starting already t make inrads Slar cell technlgy: Substitutin f Ag (Cu, Al, thers). Substitutin f thermal and chemical prcesses by laser based prcess (surface structuring, lcal diffusin, firing). Imprved surface passivatin with alternative materials, multi layer structures etc, Investigating alternative lwer cst depsitin technlgies t PE-CVD fr rear emitters. This culd include ALD, nn vacuum as well as thers. Because f easier breakage the handling and prcessing f very thin wafers is crucial. Nvel technlgies have t be develped. Thin wafer based cells will need imprved light management / ptical engineering fr efficiencies f > 20 %. Up- r dwn-cnversin requires nvel semicnductr materials, band gap tailring in silicn. Greater develpment f new cell architectures such as heter-junctin technlgies (HIT) Prductin lines with a thrughput f > 5000 Wafer/h are required Chemicals fr crystalline slar cells: The specificatin f the chemicals (HF, HCl, HNO3, acidic acid, KOH, NaOH) shuld be adapted t acceptable levels. Reductin f the verall use f vlume chemicals t reduce transprtatin and recycling effrt Dpant materials: Lw cst prcesses and dpant materials that can be applied easily and result in hmgeneus dpant distributin and cncentratin in vlume prductin are required. Nvel laser based lcal diffusin prcesses require specially designed substances 14

15 slar cells Materials / / 2050 dpants /diffusin POCl 3, H 3 PO 4 selective emitters by different diffusin lcally prcessed dpants with laser induced technlgies and dpants, diffusin dped catings with laser indused diffusin laser based hybrid prcesses etchants Wet etch: HF, HNO 3, HF hybride laser induced vapr etch hybride laser induced vapr etch hybride laser induced vapr etch metalizatin, cnductive pastes Ag w/ lead n lwer Ag based leadfree n high Cu/ Al instead f Ag printable, dispensible Si, sheet resistane sheet resistant emitters, printable, dispensible Si, graphite- (nanparticle) emitters, lw bw high prductin speed (>3000 wafers/h) substrate size > 15,6 cm x 15,6 cm CO < 0,01 $/Wp lw stresshigh aspect rati graphite- (nanparticle) based pastes (inks) n high sheet resistant emitters with gd cnductivity, lw stress based paste n high sheet resistant emitters with gd cnductivity, lw stress barriers < cntact resistance applicatin fr thin, very < resistivity thin Si-wafers r ribbns > adhesin strength nvel materials See part n nvel inrganic technlgies - the develpment is related t layers which shuld alw up- r dwncnversin and the develpment f high-quality based materials (Si-QDs, Si-nanwires, SiGeSn- Table 4. KPIs c-si dpants, etchants, metalisatin, barriers, nvel materials Metallizatin: Substitutes fr the lead cntaining frits. Substitutes fr silver as cnductive metal inside the pastes. Develpment f new cntact materials and applicatin prcesses based n nan- silicn particles (Innvalight), LRD (laser reactive depsitin, Nangram technlgy) graphite, fullerenes, graphenes, cyclsilanes r ther materials that belng t the 5 mst abundant elements n earth. Develpment f nn-cntact fine line metalisatin techniques (aersl, ink jet..). Adapted cntact materials fr high sheet resistant emitters. Lw cntact resistivity pastes. Lw stress at the cntact silicn interface. Lw shadwing and high aspect ratis in cntact lines. Stability against humidity ingress, UV and temperature variatins. Develpment f cntact materials and technlgies t intercnnect slar cells inside a mdule based n metal plymer cmpunds r ther new slutins. Materials / / 2050 Finger width µm [20] µm [20], [34] backside cntacts backside cntacts Table 5. KPIs fr metalisatin Mdule prductin cst reductin: System prices are expected t decline t /Wp by Related prductin csts shuld be reduced t abut 1 /Wp t make this pssible. Target mdule prductin csts will need t be abut 0.50 /Wp. Cntinuus fully autmated prductin (lay up, tabbing, stringing, laminatin, framing J-bx applicatin testing). Imprvement f handling and prcessing in mdule preparatin with very thin slar cells Savings in materials csts f abut 50 % is required. Cheaper thinner films If pssible, substitutin f EVA by cheaper materials with mre favurable prperties. Encapsulatin and backsheet material has t be cnsidered tgether. Very thin frnt sheet-glass (< 0,4 mm) t reduce the prcess time and the ttal weight f the mdule. The structural strength frm backsheet r the substructure. Mdules t be cnsidered as integral part f the system. Cntinuus and pssibly direct cnversin f materials t mdule, minimizing prcess steps acrss the whle supply chain Encapsulatin materials: 15

16 Chemically stability under envirnmental cnditins. Easy and fast t prcess mdule laminatin time 1 3 min, instead abut 30 min. High transparency > 95 % including frnt sheet (see table 4). Optimized refractive index, fitted t frnt sheet and slar cells Back sheet material: Chemically stable under envirnmental cnditins. Easy and fast t prcess Supprts easy recycling. Preferably frm natural surces. Thin glass is ne bvius candidate Integrated structural supprt functin and intercnnectin f slar cells Easily adptable t supprt structure f the PV generatr Frnt sheet materials: Very thin frnt glass t imprve transmissin and reduce weight. Durable flexible (flur)plymer sheets with high light transmissin, cntrlled humidity ingress (barrier layers) and UV stability at lw cst ARC material: Durability Tuch tlerant t different materials, n staining Scratch & weather resistance Intercnnectr materials: Sft material t avid stress in cntacts. Substitute f ribbn intercnnectrs by new materials, especially fr back cntact cells. Lw resistivity t avid big crss sectins that wuld avid thermal expansin issues. Back sheet with integrated structured cnductive intercnnectin layer. Defined cntact frmatin within mdule lay-up, integrated in laminatin prcess. Intercnnectin f very thin slar cells with high efficiencies, i.e. high currents. Lw resistivity intercnnectin f mdules with large dimensins and high pwer, e.g. 1 kw mdules [26]. mdules Materials / / 2050 encapsulants EVA, PVB, Inmers, chemically inert plymers, chemically inert plymers, chemically inert plymers, transmissin including n develpment f any n develpment f any n develpment f any frntsheet 88-93,9 % chemical under peratins chemical under peratins chemical under cnditins that culd react cnditins that culd react peratins cnditins that with slar cell materials, transmissin > 95 %, AR with slar cell materials, transmissin > 95 %, AR culd react with slar cell materials, transmissin > cating n frntsheet easy cating n frntsheet easy 95 %, AR cating n recycling recycling frntsheet easy recycling backsheet PET- PVF laminate, Inert plymer, intergrated strng supprt structur, mechanically and sme water vapr cell intercnnectin, electrically integrated part ingress, relatively integrated supprt integrated wiring, frm f the system, represents impermeable fr acidic structure, fr mechanical natural surces, sandwich acid, n integrated cell stability, lw heat capacity the interface t the intercnnectin fr fast laminatin laminate, easy t recycle system. frntsheet lw irn patterned better transmissin with better transmissin with better transmissin with tempered glass, 3,2 mm thin frnt glass 2 mm ultra thin frnt glass < 0,5-6 mm, a small thickness, AR cating, ultra thin frnt glass < 0,5 percentage (5-10 %) scratch resistant, weather mm thickness, AR AR cated prf mm thickness, AR cating cating intercnnectrs H-pattern cells integrated wiring f back intercnnectin by cells are devices put n a cnnected withcu- cntact cells, e.g. MWT cnductive layer in ribbns with Sn/Pb cells with metalized cating, µm plymer backsheet, new supprting backsheet with rigit circuit bard frming thick, 1,5-2,4 mm wide, slder cntacts and prcess separate electrical interface an interface t the system reliabilty assessment lifetime 20 years lifetime > 25 years lifetime > 30 years lifetime > 35 years r easy and cheap t exchange Table 5. KPIs fr encapsulants, backsheets, frnt sheets, intercnnectrs, reliability 16

17 CdTe mdules CdTe manufacturing can be divided int tw brad categries: a) High temperature (550C) CSS, CSVT and variatins b) Lwer temperature (<400C) HVE, Sputtering, Electr depsitin, MOCVD.. Imprtant Cmpnents and steps. Glass-TCO cated Active layer depsitin: prcess depending Annealing steps: Junctin activatin & back cntact frmatin Mdules: Scribing /patterning and intercnnects/encapsulatin Figure 11. CdTe cell cnfiguratin and manufacturing value chain (J.Hererr-Rueda) Typically the higher depsitin temperatures have higher efficiencies, but limit the chice f substrates t use. Varius TCOs have been prpsed fr CdTe hwever the mst prevalent tday is F:SnO 2 (FTO). ITO and AZO have been tried. Cd 2 SnO 4 is als a candidate, but btaining Cd cntaining sputtering targets is prblematic fr EHS reasns. Key challenges fr CdTe mdules The key is fr cst reductin thrugh manufacturing prductivity, materials usage and technlgy (increased mdule efficiency) imprvements. In the medium term it will be desirable t have tandem junctin cell structures cmbining CIGS and OPV cells. Materials csts Back glass 11% EVA 7% Cntact bx 11% Frnt glass 11% ITO 17% Surce Cu band 2% Back cntact 4% Chisels 2% 35% CdTe ZnTe:Cu 35% CdTe CdS 2µm Active materials +TCO 55% f ttal csts Figure 12. Materials cst breakdwn fr CdTe mdules 17

18 Active layers The active materials and TCO layers represent 55% f the bill f materials. It will be necessary t reduce the amunt f materials used (thinner layers 1 μm) and increase the efficiency f the device (pssibly thrugh graded materials) Glass Frnt glass represents 11% f csts. There are tw types f frnt glass currently available a) Brsilicate Higher temperature Higher transmissin Higher cst b) Sda Lime Lwer temperature therm-physical prperties (hwever adequate fr all current PV technlgy prcesses) Pssible surce f impurities (Na migratin in the lng term t absrber and TCO layers applicable t CdTe and ther TFPVs) Adequate ptical prperties fr current applicatins: lng term effects (Nte that lw irn glass has similar prperties t brsilicate) Brsilicate glass is typically used in the lab envirnment due t its intrinsic attributes, but in cmmercial prductin mre than 99% f the glass used will be sda lime glass. S althugh sda lime glass meets present PV technlgy requirements there is a case t be made fr the future fr imprved glass prperties and cntrlling the cst CdTe / CdS layers A better understanding is required f nucleatin & grain grwth kinetics interface and diffusin prperties rle f impurities: define ptimum material (lw cst but high perfrmance) band-gap engineering fr advanced devices Ideally this shuld be achieved with lw temperature depsitin and industrially cmpatible activatin prcess (dry, fast, cntrl, ambient, etc.) Back cntact Dry (vacuum) in-line prcessing: N chemical etching Alternative materials and prcesses fr higher efficiency and lnger stability KPIs - CdTe Industrial manufactured mdule efficiency Industrial manufacturing cst % Eurs/W p < 1 0,5 0,3 1,0 graded absrbers and CdTe layer thickness μm 1,8 1,5 minimisatin f Cd / Hg CdS layer thickness μm 0,1 0,1 0,1 0,1 Al layer thickness μm 0,3 Alternative back cntact Depsitin temperatures ºC =/< 350 Nn vacuum printable depsitin prcesses Table 6. KPIs fr CdTe 18

19 Thin Film Si PV TFSi grew rapidly during the plysilicn shrtage and thanks t the availability f turn key prductin lines frm Oerlikn, AMAT and ULVAC. At present single junctin, tandem and multi junctin cell structures are vying with each ther n cst Vs efficiency fr having the mst attractive value prpsitin amng the TFSi technlgies. Current stabilized ttal area prductin mdule efficiencies are in the range f %. The efficiency gap between lab and fab has been reduced frm 30% t abut 15% thanks t larger sized mdules, advanced mnlithic intercnnectin and imprved unifrmity. Figure 13. Cell structure fr tandem junctin TFSi cell In principle there are n materials availability issues. The key challenges fr TFSi are: As fr ther PV technlgies the key challenges fr TFSi are cst reductin and perfrmance imprvement. Materials represents 40-60% f present TFSi mdule manufacturing csts, these can be reduced by: Prductivity and thrughput Increased depsitin rate withut lss f quality. Alternatives t plasma based depsitin Develpment f cntinuus rll t rll (R2R) prcesses n flexible substrates Lwer cst packaging slutins Envirnmental aspects There is a need fr envirnmentally friendly exhaust gas abatement. The reactr etch cleaning gases have a greenhuse effect, s requires replacements f SF 6 and NF 3 by F 2 which will at the same time reduce csts Better materials usage required t reduce csts fr: Surce gases (SiH 4 ) imprving utilizatin and cycling f feed gases Sputter targets this can include new reactrs / rtary targets and develpment f alternative techniques fr cntact and electr-ptical layers Gases (DEZ) Reductin f Ag and/r In usage Glass substrates TCO (tday SnO2:F) cated glass wuld seem t be a bttleneck, but this is mainly due t investment in suitable plants by glass makers. The difficulty fr the glass maker is t achieve critical mass in terms f manufacturing vlumes; fr which a large PV market is required Transparent cnducting layers New transparent cnducting materials will need t be investigated. These will need t be high transmissin, lw sheet resistivity, and light trapping; fast and cst effective n line prductin at glass cmpanies, als including advanced antireflectin catings Encapsulants The cst f encapsulants needs t be reduced whilst maintaining the perfrmance. Easy and fast laminatin prcess (materials and equipment) The efficiency imprvements can be addressed by Develpment f higher efficiency devices (single and multi junctin) with lng term target f up t 40% efficiency Enhanced quality nancrystalline and amrphus silicn and allys. 19

20 Dped layers with less parasitic absrptin. Enhanced light trapping techniques Reductin f the light-induced defect creatin. Dped layers with less parasitic absrptin. Advanced light trapping techniques including TCO and alternatives Nvel cntacting and intercnnectin methds Nvel cncepts such as QDs, up- / dwn cnverters, plasmnics, phtnics and nan 3-D gemetries KPIs - TFSi Prd n mdule efficiency (rigid) % Prd n mdule efficiency (flex) % 11 Best stable cell efficiency % > 17 > 20 Best stable mdule efficiency % > 15 > 20 Mdule cst (rigid) Eurs/Wp < 0,65 0,3 0,3 Mdule cst (flex) Eurs/Wp < 0.5 Life time Years =/>40 Energy Pay Back Time Years 0,5 0,3 0,3 Table 7. KPIs fr TFSi CIS/CIGS Transparent cnductive xide Buffer layer (n type) Absrber layer (p type) Back cntact Substrate ZnO:Al r ZnO:B (0.5-1 µm) by sputtering r MOCVD i-zno ( nm) by sputtering r MOCVD CdS, ZnS, In 2 S 3 ( nm) by CBD Cu(In,Ga)Se 2 (2-3 µm) M (0.5-1 µm) by sputtering Glass, metal, plymer Figure 14. Cell structure CIGS cell (B.Filln) This is in part due t the cmplexity f the ternary / quaternary material systems emplyed and still requires cnsiderable wrk t ptimise the manufacturing prcesses r fr their simplificatin. CIGS PV technlgy has shwn the highest perfrmance levels bth in the lab (17,6% n flexible plyimide and 20,3% n glass) and in prductin (11-12%) with capability demnstratin f 13,8 % n 1 m 2 areas. Hwever CIGS is the least mature f the three TFPV technlgies and the gap between best cell results and regular prductin is als the highest. It is interesting and f great cncern t nte that as with CdTe mdules, much f the technlgy has Figure 15. Prductin figures fr CIGS been develped in Eurpe, whereas the larger industrial players are in fact likely t be in Japan r the USA in the immediate future. Referring t figure 15, the wrld wide prductin fr CIGS is likely t pass frm circa 150 MWp prductin in 2009 t 1.5 GWp by the end f Althugh nt an immediate threat, there are cncerns abut the future ready availability f indium and gallium. The unique character fr CIGS is the depsitin and activatin f the active absrber layer. There are tw techniques fr depsitin in regular prductin tday; c-evapratin and sputtering refer t figure 16. Similar efficiencies are btained in prductin with bth techniques. Hwever these vacuum based techniques are Others CIS/CIGS cell prductin Phtn Internatinal, G. Hering, 134, July Nanslar Odersun Helivlt SlPwer (USA) Ascent Slar (USA) Avancis (Ge) Sulfurcell Slartechnik (Ge) MiaSle (USA) Hnda Sltec (Jp) Würth Slar (Ge) Glbal Slar (USA) Slibr (Ge) 220 MW 600 MW Slyndra (USA) Slar Frntier (Jp)