PV BASICS PART (SOLAR CELLS - HIGH EFFICIENCY CONCEPTS IN SPV) Dr O.S SASTRY DIRECTOR, PV TESTING SOLAR ENERGY CENTRE PH 0124-2579213; Fax: 0124-2579207e.mail: sankar_sec@yahoo.co.uk LECTURE FORMAT • • • • • Basics of Semiconductors Solar Cell Device (P-N Junction) Fabrication Technologies of Silicon Solar Cell Concepts of High Efficiency Silicon Solar Cells Third Generation Concepts BASICS OF SEMICONDUCTORS MAJOR REQUIREMENTS FOR CELL MATERIAL Technical: ·       HIGH ABSORPTION COEFFICIENT LONG DIFFUSION LENGTH; SLOW RECOMBINAION BAND GAP GENERAL: ·       LOW COST MATERIALS WITH TAILORABLE PROPERTIES ·        ABUNDANT MATERIAL ·        CONVENIENCE OF SHAPES AND SIZES ·         SIMPLE AND INEXPENSIVE INTEGRATED PROCESSING FABRICATION & ECONOMICS RELATED: ·        MINIMUM MATERIAL / WATT ·        MINIMUM ENERGY INPUT/ OUTPUT WATT ·        ENERGY PAY BACK PERIOD < YEARS COST PAY BACK PERIOD< YEARS ·        LONG LIFE (> 20 Years) ·        COST (< $1/Watt) TYPICAL PARAMETERS Thin Films Eg(eV) α (cm-1) Life Time Recombination Diffusion (S) (cm/s) Velocity Length (µm) C-Si 1.1 102-104 > 10-4 > 103 >10 A-Si:H 1.1-2.0 > 104 < 10-6 > 106 < 0.1 GaAs 1.4 > 104 > 10-6 > 105 ~ 0.2 CdTe 1.45 > 104 ~ 10-5 > 104 ~ 0.4 Cu-In-Se 1.1 > 104 ~ 10-5 > 104 ~ 0.2 Cu-In-S 1.6 > 104 ~ 10-5 > 104 ~ 0.2 TRANSPORT EQUATIONS · Generation Rate G(x)= [ E∞ g (f) [1-R(E)] α(E) exp I-d(E)x]dE · I(V)=IS exp(eV nkT - 1) – IL V  V-IRS & I  I - V-IRS R sh POSSIBLE TFSC MATERIALS Single Elements: Si ( epi, mc, nc, mixed) Carbon (nanotubes, DLC) Binary alloys / Compounds: Cu2S, Cu2O Cu-C, CdTe, CdSe, GaP, GaAs, InP,ZnP , a-Si : H, Dye coated TiO2 Ternary Alloys / Compounds: Cu-In-S, Cu-In-Se CdZnSe , CdMnTe, Bi-Sb-S, Cu-Bi-s, Cu-Al-Te, Cu-Ga-Se, Ag-In-S, Pb-Ca-S, Ag-Ga-S, Ga-In-P, Ga-In-Sb ,and so on Organic Materials: Semiconducting Organics / Polymers and Dyes Chalcogenides: CdTe and CIGS glass CdTe TCO window alloy layer absorber metal contact highest efficiency tricky to deposit Cd toxic, In scarce SnO2 CdS CdSxTe1-x CdTe TCO window easily deposited Cd toxic, Te scarce absorber contact substrate Courtesy: UNSW ZnO CdS Cu (Ga,In) (Se,S)2 Mo glass CIGS Second Generation: thin-film (COST REDUCTION MAIN TARGET!) Advantages low materials cost large manufacturing unit fully integrated modules aesthetics, ruggedness? Thin-film Technologies Silicon amorphous microcrystalline polycrystalline Chalcogenide (polycrystalline) CIS, CIGS [Cu (In,Ga) (Se,S)2] CdTe Dye sensitised, Organics HIGH EFFICIENCIES ?? STABILITY ??? Courtesy: UNSW Efficiency- cost The generations Thin-film US$0.20/W 80 Efficiency,% ? US$0.10/W 100 high-efficien thin-film US$0.50/W abundant non-toxic Thermodynamic durable limit 60 US$1.00/W III 40 Present limit 20 I II 100 200 300 US$3.50/W 400 Cost, US$/m2 Courtesy: UNSW 500 Third generation options 100% circulators 74% 68% 58% 54% 49% 44% 39% 31% 0% tandem (n ) hot carrier tandem (n = 6) thermal, thermoPV, thermionics tandem (n = 3) impurity PV & band, up-converters impact ionisation tandem (n = 2) down-converters single cell Third generation options 100% circulators 74% 68% 58% 54% 49% 44% 39% 31% 0% tandem (n ) hot carrier tandem (n = 6) thermal, thermoPV, thermionics tandem (n = 3) impurity PV & band, up-converters impact ionisation tandem (n = 2) down-converters single cell Si-based tandems A M G E ffic ie n c y Free choice or Si cell Sunlight Decreasing band gap F r e e c h o ic e S i b o t to m c e ll % 40 5 % % 45% 33% 30 29% 20 10 0 Intrinsic radiative and Auger losses included N u m b e r o f c e lls Fabrication of Si quantum dots SiOx, SiyNx, SiCx SiO2, Si3N4, SiC 100nm Zacharias et al., APL 80, 661, 2002 Si quantum dot photoluminescence 100nm Third generation options 100% circulators 74% 68% 58% 54% 49% 44% 39% 31% 0% tandem (n ) hot carrier tandem (n = 6) thermal, thermoPV, thermionics tandem (n = 3) impurity PV & band, up-converters impact ionisation tandem (n = 2) down-converters single cell Hot-carrier cell concept quantum dot Courtesy: UNSW absorber Ta Efficiency > cell tandem hole contact electron contact Efficiency (%) 80 Tc InN tunneling contact Si 60 40 hot carriers absorber 20 cold carriers 0.0 0.5 1.0 1.5 2.0 Bandgap (eV) 2.5 3.0 100nm Third generation options Courtesy: UNSW 100% circulators 74% 68% 58% 54% 49% 44% 39% 31% 0% tandem (n ) hot carrier tandem (n = 6) thermal, thermoPV, thermionics tandem (n = 3) impurity PV & band, up-converters impact ionisation tandem (n = 2) down-converters single cell Luque & Marti, PRL 78, 5014 (1997) Third generation options PbSe 100% circulators 74% 68% 58% 54% 49% 44% 39% 31% tandem (n ) hot carrier tandem (n = 6) thermal, thermoPV, thermionics tandem (n = 3) impurity PV & band, up-converters impact ionisation tandem (n = 2) down-converters single cell 0% Schaller & Klimov, Phys.Rev.Lett.92,186601(2004); Ellingson et al., Nano.Lett.5, 865(2005) END PART-III THANK YOU !! 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Connection Box Crucibles Aluminum (frames) PEG Process gas SOLAR CELL (SILICON) FABRICATION TECHNOLOGY QUARTZ (SiO2)SAND METALLAZRY GRADE -Si SOLAR GRADE -Si SINGLE CRYSTAL INGOT WAFERING DOPING (p-n JUNCTION FORMATION) TEXTURIZATION AND AR COATING BACK SURFACE METALLIZATION FRONT SURFACE GRIDDING TESTING STRINGING MODULE LAMINATION MINIMUM MATERIAL LOSS DURING PROCESSING ENERGY CONSUMPTION COST PAY... ti o n Si Si 용융체 Melt S ilic o n SILICON RIBBON m e lt CASTING Cast mc-Si solar cells END PART- II CONCEPTS OF HIGH EFFICIENCY SILICON SOLAR CELLS (LOSSES IN SOLAR CELLS) LOSSES IN SOLAR CELLS • THERMODYNAMICAL • OPTICAL • ELECTRICAL Solar Radiation Spectrum Spectral Distribution of Extraterrestrial Radiation • In addition to the total energy in the solar spectrum (i.e the solar constant), it is useful... cell Industrial Silicon Solar Cells (for 1 sun) (Cell size 125 mm x 125 mm square/pseudo square) Ag contacts SiNx:H ARC n+emitter p-silicon base ρ = 0. 5-3 Ώ cm, CZ-Si, Area= 7 8-1 40cm2: η = 1 2-1 5%(1sun) FABRICATION TECHNOLOGIES OF SILICON SOLAR CELL PV Value Chain – c-Si and Thin Films Modules Key materials required for module Design, tools & equipments Glass Silver paste Wire SiC Tedler Aluminium EVA/PVB... power point current and voltage (In, Vm), and a series and a parallel resistance (Rs, Rsh) • Solar Cell Efficiency η – output = Im Vm = I siVIL FT input Σ nhv Σ nhv depends on quantum efficiency of creation of carriers, effectiveness of separation of carriers before recombination and collection of the separated carriers • Highest Theoretical Homo-junction ~ 30% Hetero-junction ~ 42% 36 Tandem Multi-gap... ENERGY CONSUMPTION COST PAY BACK PERIOD : About 20 TO 30% : ~ 3 kWh/Wp : < 5 YEARS Material Flo a t- z one pulling P u ll ro d R o ta tio n & L ift Fe ed rod holder Feed ro d (po ly s ilic o n) G a s c o n v e c tio n Melting interf a c e C ry s ta l ro d RF hea ting c o il Moltem z o ne Freez ing interf a c e S ing le c rys ta l s ilic on Q u a rtz c ru c ib le S i m e lt L iq u id c o n v e c tio n R a...SOLAR CELL DEVICE (p-n JUNCTION) • A solar cell is a p-n junction semiconductor device • When p and n type semiconductors are brought together the Fermi levels try to come to the same level This results in band bending to maintain the charge equilibrium • When SUN radiation incidents on such junction, current is generated due to creation of electron... band bending drives the light generated charge carriers down the electric field gradient, pushes in to the load In this way both voltage and current, hence power are generated Understanding Operation of Solar Cell Reflection Absorption Generation Separation Collection Section View of a Solar Cell SOLAR CELL • o o o o • Solar Cell operations depend on : Absorption of light to create electron-hole pairs... would be received in the absence of the atmosphere • A standard spectral irradiance curve based on high altitude and space measurements is shown here which is found to be similar to the 5777K blackbody spectrum • From this figure following observations are made: – The peak solar intensity is 2028.8 w/m2 at a wavelength of 0.48 µm – The solar spectrum varies from 0.2 – 3.0 µm, – The energy in various spectral... varies from 0.2 – 3.0 µm, – The energy in various spectral ranges is as follows: Wavelength Energy (W/m2) Percent Ultravoilet Visible Infrared 0.2 – 0.38µm) 88 6 (0.38 – 0.78 µm) 656 48 (0.78 – 3.0 µm) 623 46 LOSSES AT DIFFERENT COMPONENTS Burried Contact Silicon Solar cells Green et al (1988) ... ~10nm ~20 nm M Tanaka, et al., 3rd WCPVEC, Osaka, 11-18, 20 03 25 12. 5 8.3May6 .25 Estimated S (cm/sec) THIRD GENERATION CONCEPTS First generation cells Larger Si wafer area than ICs 150 -20 0 µm... solar intensity is 20 28.8 w/m2 at a wavelength of 0.48 µm – The solar spectrum varies from 0 .2 – 3.0 µm, – The energy in various spectral ranges is as follows: Wavelength Energy (W/m2) Percent Ultravoilet... 30 29 % 20 10 0 Intrinsic radiative and Auger losses included N u m b e r o f c e lls Fabrication of Si quantum dots SiOx, SiyNx, SiCx SiO2, Si3N4, SiC 100nm Zacharias et al., APL 80, 661, 20 02