Dye-sensitized Solar Cells - Materials and Interfaces Lars Kloo Dept. of Chemistry School of Chemical Sciences & Engineering KTH Royal Institute of Technology Stockholm, SWEDEN
Energy in the future WEO 2008 2009 : ca. 16 TW, momentaneous yearly averaged rate of consumption ( cf. 4.1 x 10 20 J/ y; 2006 it was 13 TW) 2050 : Estimated to 28 TW Perspective : 1 new 1 GW nuclear reactor per day for 30 years… … BUT, less than 1 hour of solar light 2
The alternatives Thus, we need 12 TW 3
Energy and latitude Solar light in different regions: SE: 871 kWh m -2 y -1 (= 242 W m -2 ) GE: 1014 kWh m -2 y -1 ES: 1586 kWh m -2 y -1 Optimal angle in SE: 44°(S): 1079 kWh m -2 y -1 Latitude of Moscow ≈ Stockholm 4
Energy from the Sun • Photosynthesis → biomass/ biofuels – Efficiency < 1% • Solar heat: – Water heating (domestic): Efficiency ≤ 70% – Elektricity: Conc solar light (CSP), turbines, etc: Efficiency ≤ 20% • Solar electricity (solar cells) – Direct conversion: Efficiency ≤ 20% Common problem: S TORAGE ! 5
Solar cell technologies p-CIGS – Thin film CdTe/CdS – Thin film Solid solution of Cu(In,Ga)Se 2 (1-3 µm) Too expensive !!! Power excellent – Energy not optimal !!! Si Amorf, polycryst. or monocryst New and promising technologies … 6
Cost & efficiency improvmenents I. Si-based II. Thin-film III. ??? Target: < 0.5 €/ W p or > 20% efficiency at < 100 €/ m 2 7
Grätzel cells ≅ DSC Cited 7,800 times; Feb 19, 2012 Current world record (lab cells): ≈ 13% 8
The electrochemical cell Cell = 2 electrodes + electrolyte 9
DSC function Resistance Sensitizer Redox electrolyte TiO 2 TCO 10
A note on kinetics e - fs µ s E e - CB > ns ms e - < ms VB Semi- Dye Electrolyte conductor ”a molecular diode”
Multicomponent cell Semiconductor-based cell DSC: Absorption & charge transport separated !!! 12
Pro’s & con’s + • ’Kitchen chemistry’ ( i.e. easy to make) • Inexpensive (glass substrate the most expensive) • Relatively high efficiency • Also works in diffuse light ( i.e. indoor, cloudy days, etc. ) - • Complex, interlinked reactions (tuning required!) • Stability • Competition from other technologies 13
Estetic Toyota (Jpn) Sony (Jpn) Dyesol (Aus) 14
Useful? Profs. Segawa & Uchida, Tokyo Univ., Japan (among 10 best of 35 … ) 15
Simple: Three parts only ! 16
Photoelectrode (Part 1: Semiconductor) Step 1: Nanostructured semiconductor 300 nm TiO 2 -particles, d ≈ 25 nm 1 cm 2 contains ≈ 10 13 particles (huge surface – nano !) 17
Photoelectrode (Part 2: Sensitizer) Sensitizing dye Step 2: The dye 18
Counter electrode A pencil offers the graphite … Catalytical material Catalytic platinum (Pt) Graphite Conducting polymers Nanoporous carbon 19
Electrolyte • Organic solvent (ethanol etc .) • Dissolved redox couple ( eg. I - / I 3 - ) 20
A DSC in about 15 min Voltage Current µ A V The DSC obtained: • ≈ 0,5 V photovoltage • Lousy current • ≈ 0.5% efficiency … 21
CMD www.moleculardevices.se 22
CMD at KTH ”Materials & Fundamentals” CMD: > 30 researchers 23
CMD Cited > 300 times in a year 24
The cells Lab cells Monolithic cells (Swerea IVF AB) 25
CMD: Electrode materials Working Electrode - Metal oxide semiconductors Counter Electrode - Metals - Carbon materials - Semiconductors - Polymers Sensitizer - Metal coordination complexes - Organic dyes - Semiconductor Quantum-Dots 26
CMD: Electrolyte Solvents - Ionic liquids - ISILs Redox Couple - Halogens - Organic molecules Additives - Solid-state mediators - Cations - Lewis bases 27
The electrolyte An electrolyte is a chemical system that provides an electrolytic contact between the solar cell electrodes 28
Types Electrolytes Gel-like Solid Liquid (quasi-solid) 29
Organic solvents Name Formula Meltin Boiling Viscosity, g Point, cp o C Point o C H 2 O Water 0 100 0.89 CH 3 CH 2 OH Ethanol -114 78 1.08 CH 3 CN 0.33(30 o C) Acetonitrile -44 82 Problems: • Evaporation CH 3 (CH 2 ) 3 CN Valeronitrile -96 139 0.78(19 o C) • Chemical stability • Electrochemical stability Glutaronitrile -29 287 5.3 • Temperatur range • Toxicity CH 3 OCH 2 CH 2 CN 3-Methoxy- -63 164 1.1 • … propionitrile Propylene carbonate -49 241 2.5 γ -Butyrolactone -44 204 1.7 L. Kloo et al., Dalton Trans. 2 0 1 1 , 40 , 10289 (Perspective) 30
Ionic liquids Definition: ”Liquid consisting of only ions and with a melting point < 100 ° C” a) cations R R R N N S R P R R R' N N R' R R R' H/R'' R b) anions Hal - , PF 6 - , BF 4 - , OTf - , NO 3 - , N(CN) 2 - , SCN - , Co(CO) 4 - 31
Ionic liquids Advantages: • No vapour pressurs (almost) • Non-explosive / non-flammable • Thermally & electrochemically very stable • Good solvent for both salts and organics • … not yet toxic … 32
Academically interesting but useless ... Last lecture … 33
Murky crystal ball ... 34
Reasonable performance Intensity I sc V oc Efficiency Fillfactor (W/m 2 ) (mA/cm 2 ) (V) (%) 250 3.0 0.70 0.69 6.0 250 2.5 0.74 0.66 4.9 1000 11.1 0.75 0.60 5.0 1000 8.6 0.77 0.56 3.7 Composition of electrolyte 0.2 M I 2 0.1 M GuanSCN 0.5 M NMBI 2 M n -BuMeIm + I - BuMeIm + N(CN) 2 -
The world record for ILs
Does not solve all problems 16 14 12 AN ( 0 .0 3 M I 2 ) sc (mA/ cm 2 ) 10 I L low ( 0 .0 3 M I 2 ) 8 6 J N N 4 B N N N N 2 EMI TCB 0 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Light intensity (Wcm -2 ) Mass-transport problems already at 1/ 5 Sun L. Kloo et al. , Dalton Trans. 2 0 0 8 , 38 , 2655 (Perspective) 37
ISILs Low viscosity High ion mobility Low vapor pressure High long-term High chemical and durability electrochemical stability 38
New redox systems R 3+/2+ I - /I 3 - R R Br - /Br 3 - N N N Pseudohalogens Co N N Interhalogens N R R Sulfur-based systems Metal complexes R N N S - N N S N N N S N N N N N T - T 2 39
D35 Dye + Co-based redox system A. Hagfeldt, L. Sun et al ., JACS 2 0 1 0 , 132, 16714 Later: M. Grätzel et al. made the current 13% world record using a similar system (Science 2011) N.B. Not one single component can be changed at a time !!! 40
Sulfur-based alternatives S S S S TTF N N N N N N N S S S S S S McMT BMT 41
Energy in the Future PEDOT CE First ever all ‘organic’ DSC Sensitizer Redox Couple H. Tian, L. Sun, L. Kloo et al ., Angew. Chem. Int. Ed. 2 0 1 0 , 49, 7328 & JACS 2 0 1 1 , 133 , 9413 N.B. Not one single component can be changed at a time !!! 42
Counter electrode effect 0.65 FF: 0.50 η = 6.0% 14 12 O O O O O O 10 J sc (m A/ cm 2 ) S S S S S 8 n O O O O 6 PEDOT 4 350 Pt 2 300 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 250 -Z'' (Ohm ) V oc (V) 200 150 PEDOT 100 Pt 50 0 PEDOT CE shows considerably lower 0 100 200 300 400 500 600 700 800 charge-transfer resistance Z' (Ohm) 43
Hybrid systems X.Yang, L. Sun, L. Kloo et al ., RSC Advances 2 0 1 2 , in print Presence of S 2- suppresses the formation of coloured I 3 - Efficiency > 9%
CMD: Fundamentals Working Electrode - Dye coordination - Dye organization Regeneration - Mechanism of regeneration 45
On the myth about SAM SAM = Self-assembled monolayer http: / / people.bath.ac.uk/ pysabw/ research/ scell/ dssc.htm
The sensitizing dye COO(TBA) (ABT)OOC N Anchoring groups N (e - injection) +II/+III Ru COOH COOH N N NCS NCS Site(?) of re-generation Good dyes have : (reduction) • match energetic condition • broad absorption N 719 • high extinction coefficient • good charge separation ( cf . Kodak)
Towards organic dyes η = 5.1% N3 D5 LUMO N719 HOMO From Organometallic to Organic
Adsorption isotherms Adsorption isotherms by depletion method 4 10 -5 N719 (EtOH) Z907 (MeCN/ t -BuOH 1:1) 3 10 -5 ads [mmol/electrode] 2 10 -5 n 1 10 -5 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 C eq [mM]
AFM: A problem indicator AFM (in electrolyte) 100 µm 2 TiO 2 under 24h: a) t = 0h b) t = 3h c) t= 24h d) After rinsing Aggregation / Precipitation Langmuir ( 2 0 1 0 ) Collaboration: Rob Atkin, Univ. of Newcastle
The NICISS technique NICISS = Neutral Impact Collision Ion Scattering Spectroscopy Collaboration: Gunther Andersson, Flinders Univ.
The NICISS technique N C 15000 O Br P intensity [counts/h/nA] 10000 1.50 molal 0.41 molal 0.20 molal 5000 0.05 molal 0.03 molal 0.01 molal solvent 0 2 3 4 5 6 7 8 TOF [µs] Allows element-specific depth profiling at interfaces Depths up to ~ 20 nm with a few Å resolution
Recommend
More recommend
