《新能源材料与技术》课程教学课件（讲稿）L3 Solar energy and conversion technologies（2/2）

新能源材料手技术Renewable Energy: Materials and TechnologiesL3: Solar Energy and Conversion Technologies (II)- Dye Sensitized Solar Cells (DSSC) (2, 3)Dr Yimin Chaoy.chao@uea.ac.ukwww.uea.ac.uk/chemistry/people/faculty/chao

新能源材料与技术 Renewable Energy: Materials and Technologies L3: Solar Energy and Conversion Technologies (II) - Dye Sensitized Solar Cells (DSSC) (2, 3) Dr Yimin Chao y.chao@uea.ac.uk www.uea.ac.uk/chemistry/people/faculty/chao

SynopsisLecture1ABluffer'sGuidetoPhotophysics andPhotochemistryLecture2Whymakedye-sensitized(andotherexcitonic)solarcells?“Classic"Dye-SensitizedSolarCells(DSSCs)Lecture3Recentdevelopments-p-TypeDSSCs,perovskiteDsSCs,OPVsCommercialization

Synopsis Lecture 1 A Bluffer’s Guide to Photophysics and Photochemistry Lecture 2 Why make dye-sensitized (and other excitonic) solar cells? “Classic” Dye-Sensitized Solar Cells (DSSCs) Lecture 3 Recent developments – p-Type DSSCs, perovskite DSSCs, OPVs Commercialization 46

Semiconductorsolarcellscanbeupto44%efficientDye-sensitizedsolarcellsareonly10to15%efficientWhyConsiderDSSCs?

Why Consider DSSCs? Semiconductor solar cells can be up to 44% efficient Dye-sensitized solar cells are only 10 to 15% efficient 47

Cost-Si currently $0.50 to$1per watt.Predicted$0.36perwatt(2017)DSSC-mayhit$0.30perwatt.Lowlightperformance-Si,GaAsetcworkbestwithsolarconcentratorsDssCs stillworkoncloudydays(andindoors)Transparency-DssCs can be incorporated into coloured windowsAlso-lightweight,canbeflexible,betterhightemperatureperformance

Cost – Si currently $0.50 to $1 per watt. Predicted $0.36 per watt (2017) DSSC – may hit $0.30 per watt. Low light performance – Si, GaAs etc work best with solar concentrators DSSCs still work on cloudy days (and indoors) Transparency – DSSCs can be incorporated into coloured windows Also – lightweight, can be flexible, better high temperature performance 48

What isDyeSensitization?Electron injection,efficiencyPinjConductionband4E=2.5eV4E=3.2eVSensitizerValenceband3.2eVis390nm,2.5evis495nmWideband gap semiconductor(e.g. TiO2, SnO2)Excited stateof adye absorbingvisible lighttransfers electrons toawidebandgap(UVabsorbing)semiconductorFirst use-Vogel, 1870s, photography. Understanding developed from1960sonwards

What is Dye Sensitization? Conduction band Valence band ΔE = 3.2 eV Wide band gap semiconductor (e.g. TiO2, SnO2) ΔE = 2.5 eV 3.2 eV is 390 nm, 2.5 eV is 495 nm Sensitizer Excited state of a dye absorbing visible light transfers electrons to a wide band gap (UV absorbing) semiconductor First use – Vogel, 1870s, photography. Understanding developed from 1960s onwards. Electron injection, efficiency Φinj 49

EarlyDevelopmentsChemical modification of atitanium (rv) oxideelectrode to give stable dyesensitisation withouta supersensitiserofroeofonHOFig, 2Pbotocurrent-time characteristics for a derivatised TiOelectrode held at 1.2 V (versus SSE) and illuminated with lightfrom a 150-w Xe lamp passing through a 450-nm interferencefilter.Arrowsrepresent time of light switching gon and off.Steady-CO2Hstatecurrentwas70nAcmPhotocurrentsDyechemicallybindsto TiO,crystalSystemaimedatwateroxidationSurprisingly low Φini = 0.25%Goodenough,butnotgood enough(boomboom)J.B.Goodenough et alNature,1979.280.571

Early Developments J. B. Goodenough et al Nature, 1979, 280, 571 • Dye chemically binds to TiO2 crystal • System aimed at water oxidation • Surprisingly low Φinj = 0.25% • Goodenough, but not good enough (boom boom) Photocurrents 50

GratzelSmall changes can get big improvements!M.Gratzeletal,J.Am.Chem.Soc.1985,107,2988e3CO.HOHCO2HTiO2OHCO2HO0CO2H450500550400600[Ru(dcbpy)3]2+onTiO2colloids/nmPhotocurrentactionspectra中ini=60%(oxidationofaqueoushydroquinone)IPCEat460nm=44%(A) = [Ru(dcbpy)3J2+Compared to [Ru(bpy),]2+ IPCE =2.5%(B) = [Ru(bpy)3J2+IPCE=incidentphotontocurrentefficiency(C) = no sensitizer对苯二酚，Hydroquinone

Grätzel Small changes can get big improvements! M. Grätzel et al, J. Am. Chem. Soc.,1985, 107, 2988 Φinj = 60% IPCE at 460 nm = 44% Compared to [Ru(bpy)3] 2+ IPCE = 2.5% [Ru(dcbpy)3] 2+ on TiO2 colloids Photocurrent action spectra (oxidation of aqueous hydroquinone) (A) = [Ru(dcbpy)3] 2+ (B) = [Ru(bpy)3] 2+ (C) = no sensitizer IPCE = incident photon to current efficiency TTiO2 e- e- 对苯二酚 51 , Hydroquinone

GratzelPartllB.O'ReganandMichaelGratzelNature1991,353,737HO.0HO.CTiO,nanoparticles sinteredat450ConconductingglassDvewithbroadabsorptionprofile+ExRedoxelectrolyte(l-/l)inorganicsolvent (iodine)+Pt cathode4005006007008OCA-nn

Grätzel Part II B. O’Regan and Michael Grätzel Nature 1991, 353, 737 Dye with broad absorption profile TiO2 nanoparticles sintered at 450 °C on conducting glass + + Redox electrolyte (I- /I3 - ) in organic solvent (iodine) + Pt cathode 52

TheFirst DSSCDye-Sensitized SolarCell (DSSC)LUMOhCB3/ 15RedoxpotentialHOMOelectrolyteTiO2FTOPtDyeTiO2DyeOInGratzel'sfirstexample:IPCE(520nm)80to97%Overallefficiency-7.1to7.9%(simulated solarspectrum)12%indiffusedaylightDyeshighlystableundertheconditions

The First DSSC In Grätzel’s first example: IPCE (520 nm) 80 to 97% Overall efficiency – 7.1 to 7.9% (simulated solar spectrum) 12% in diffuse daylight Dyes highly stable under the conditions 53

OfficialRecord-2006to2012CO2HL.Y.Hanetal11.1%(simulatedsolarspectrum)HO2CN-C-SN749-theblackdyeOnTiO2,1-/l3redoxelectrolyteLightscatteringof TiO,electrodeoptimizedCNDeoxycholicacidcoabsorbentusedHO,CCOH=SHO"OHCO2HHO20CSimilarresultsobtainedwithN3/N719andarangeofotherdyesHOCO2H

Official Record – 2006 to 2012 11.1% (simulated solar spectrum) N749 – the black dye On TiO2, I- /I3 - redox electrolyte Light scattering of TiO2 electrode optimized Deoxycholic acid coabsorbent used Similar results obtained with N3/N719 and a range of other dyes L. Y. Han et al 54