CdSeCdS量子点敏化TiO2太阳能电池研究

1、Core/shell CdSe/CdS Quantum Dots Sensitized Solar CellsYu XiaoyunYu XiaoyunInstructor: Prof. Kuang Daibin Instructor: Prof. Kuang Daibin 1. Instruction2. Method3. Result and Discussion4. ConclusionContentsINTRODUCTION Dye sensitized solar cells (DSSCs)： low cost, energy savingp light conversion effi

2、ciency() up to 11 % p 31% Schockley-Queisser balance limit Sensitized Solar CellsQDs sensitized solar cells (QDSSCs)： visible light absorption tunable band gap high extinction coefficientsthermodynamic efficiency limit up to 44 %Electron injection：CdSe(VB) CdSe (CB) TiO2(CB) hSx/S2- Pt TCOexternal c

3、ircuitStructure and Functional PrincipleFabrication of sensitized electrodesLinker assisted adsorption： High QDs size Controllability Low QDs coveragePoor electronic transport property of linker molecules Low (1%)CBD or SILAR Method： Highest is 4.22% QDs size is uncontrollable Complex fabrication pr

4、ocessHydrothermal Fabrication New： Facile one step synthesis Narrow QDs size distribution High coverage up to 3.10%EthanolP25TiO2pasteTiO2electrode+ +Cd(Ac)2TGANa2SeSO3H2OSensitized electrodeAcquire QDs solutionQDSSCQDs powderMethodRESULT AND DISCUSSIONTemperature/D/nm602.11002.41402.81603.820304050

5、6070140oC100oC60oC160oC2 / degreeCdSintensity / a.u.CdSe2030405060702 /(degree)200oC180oCintensity / a.u.Cd10S5.71Se4.29XRD Measurement160 Hexagonal Cd10S5.71Se4.292030405060701h3h6h9hIntensity / a.u.2 / degree12hCdSCdSetime/hD/nm12.733.363.894.0124.1CdSeCdSeCdSCdS1h only CdSe3h core/shell CdSe/CdS

6、Reaction at 140-160 for over 3h will obtain CdSe/CdS Core/Shell QDsXRD MeasurementFormation of Core/Shell QDs100， TGA is stable，Only CdSe QDs140-160， TGA gradually decompose，First the CdSe core，then the CdS shell180， TGA rapidly decompose，S2- and Se2- reacted with Cd2+ at the same timeTEM ImagesA nu

7、mber of QDs homogeneously covered onto the surface of TiO2 Fluorescence Emission Spectra450500550600650700PL Intensity / a.u.Wavelength/ nm QDs QDs-TiO2Most of the exited electrons in the QDs can be injected into TiO2 successfully, and recombine via a nonradiative transition.FTIR Spectra4000 3500 30

8、00 2500 2000 1500 1000 500020406080100Transmittance %Wavenumber / cm-1 I: Free TG A: Free TG A II: C dSe-TG A-Ti O: C dSe-TG A-Ti O2 2 60 60o oC C III: C dSe/ C dSe-TG A-Ti O: C dSe/ C dSe-TG A-Ti O2 2 160 160o oC C1720256513851628138011202978129511701720 cm-11628+1385cm-1TGA binds to the surface of

9、 TiO2 using COOH2565cm-1disappearTGA combines the QDs through the Cd-S bondFunctions of TGA Molecules stabilizer: controls the formation of water-soluble QDs. linker: links the QDs onto the TiO2 surface. sulfur source: the decomposition of TGA trigger the formation of the CdS shell.Reaction Temperat

10、ure & Solar CellsCellJSC / mA.cm-2VOC / mVFF/%601.643400.340.191002.283600.370.301404.40 5200.43 0.99 1605.435200.421.191802.474700.220.254004505005506006507000.40.50.60.70.80.91.0AbsorbanceWavelength / nm 60oC 100oC 140oC 160oC 180oCa)01002003004005006000123456Current density / Am cm-2Voltage /

11、 mV 60oC 100oC 140oC 160oC 180oCb)Band Gap Analysis A step-like structure band edge separate the hole and the electron thus offering a high driving force for electron injection from QDs to TiO2. CdS shell protected the QDs from photo-oxidative degradation , resulting in low surface defect. TEM Image

12、sZnS TreatmentAnnealing Time/sZnSLattice Spacing/nmCrystal FormQDs Size/nm0noncrystalline0.338Cubic4300crystalline0.338Cubic4450crystalline0.361Hexagonal6-7ZnS Treatment & Solar cellsElectrodeJSC/mA cm-2VOC/ mVFF/%QDs-0s6.906200.502.16ZnS-0s7.326100.472.09ZnS-300s11.426100.453.10ZnS-450s13.62540

13、0.292.10pThe transition of as-deposited amorphous ZnS to crystalline ZnS after 300 second annealing plays an important role in cell efficiency.pOver long annealing leads to high absorption of light but destroyed the core/shell structure of QDs, resulting in a high JSC but low light conversion efficiency. ZnS & annealingZnS capping layer could act as a passivation between the QDs and the electrolyte, thus prevented the excited electron from recombining directly with the redox couple.ConclusionsAdvantages: One step synthesis High QD size controllability Hig