Teaching the concept of energy using analogies between solar energy converters

Transcription

1 Teaching the concept of using analogies between solar converters TPI-15 / ELTE Zoltán Csernovszky Kölcsey Ferenc High School, Budapest Physics Teaching PhD School, Eötvös University

2 LIGHT Interactions Photon-Electron Solar Energy Converters Dye sensitized solar cell n-p junction Solar Cell Photo- Synthesis Raspberry Cell Electron Transports Analogies Energy Levels Analogue Processes Pedagogical Applications Project Works Interdisciplinarity

3 Absorption of a photon by an electron Molecular systems Crystal lattices Ionisation 1 Photon absorption by an electron Thermalisation 4 Excitation 1 of the electron Generation of an electron hole pair Dissociation 1 Photoinduced homolytic cleavage 2 A B + hυ A + B Energy storage inside the molecule 2 Photo-induced transfer of electron 5 Principle of photovoltaic systems 3 : A B + hυ A: + B + PHOTOSYNTHESIS DSSC 5 N-P JUNCTION SC 5 SEMICONDUCTORS SOLAR CELLS

4 Conversion of photon s : Photosynthesis Water Carbon-dioxide Photon s Solar Chemical Glucose Dioxygen 6CO 2 + 6H 2 O + hυ C 6 H 12 O 6 + 6O 2 Photolysis (H 2 O) + hυ 1 2 O 2 + 2e + 2H +

5 Conversion of photon s : semiconductors 1 Solar Electrical Absorption of an electron and generation of an electronhole pair in a semiconductor. The band gap determines how much is needed to excite the electron that it can participate in conduction. The excitation of an electron into the CB results also a hole in the VB. Thus, both the electron and hole can participate in conduction 3. Two types of semiconductors

6 Conversion of photon s : CB n VB CB p VB Before joining After joining diffusion Exposed charges are unable to move Solar Electrical single n-p junction solar cells Photostability or sensitivity to the visible spectrum? Solar spectrum at sea level diffusion Energy bands of a single n-p junction Formation of an electric field in depletion region OPTIMAL GAP VISIBLE

7 Conversion of photon s : Dye-sensitized solar cells 1 Separatation of functions in a DSCC Main steps and electron transfer in a DSCC

8 Pedagogical applications 1: electron transport analogies A Depletion region SC n-type (CB) Anode Outer circle SC Cathode SC p-type Dye /Anode TiO 2 /Anode DSSC FTO glass /Anode Outer circle Cathode Electrolyte Photosystem II Chlorophyll aii e- transport chain Chlorophyll ai Photosystem I e- transport chain PHSY Final receptor

9 Pedagogical Applications 2: Energy levels analogies Relative levels diagrams Photosynthesis DSSC TiO2 /N719 elte_hyplin_redoxpot.docx Single n-p junction SC

10 Pedagogical Applications 3: Analogue Processes STEP PHOTOSYNTHESIS n-p JUNCTION SC DSSC Excitation Charge separation Electron transport Photosystem II (chlorophyll all) Photosystem I (chlorophyll ai) Dissociation water (photolysis): 2H 2 O (O 2 +4e )+ 4H + PS II e - transport chain PS I ReactionCenter Final Acceptor e VB + hν e CB e - / h + generation: e VB + AC e CB + h + VB Depletion n-typesc CB p-typesc VB GRDye + hν EXDye Oxydation of Dye: EXDye e SC,CB + Dye + Dye TiO 2 FTO Cathode Electrolyte Regeneration -LDR Reduction of electroncarrier NADP+ to NADPH -Calvin Cycle/ Step 2: Reduction of CO 2 (Reactions using e - from NADPH/ ATP.) -Calvin Cycle /Step 3: Regeneration of RuBP. e - / h + recombination e CB+h + VB e VB+AC + VB Iodine regeneration: I 3 + 2e 3I. Dye Regeneration: 2 Dye + + 3I 2GRDye + I 3

11 Pedagogical Applications : Raspberry Cell Project Works The realization of a DSSC is an exciting way for teachers to place the notion of into an interdisciplinary context. You can examine a new type of solar cells and underline the similarities between photovoltaic systems and photosynthesis. Build your own Raspberry Cell elte_hyplink_raspcell_proj.docx Explore its photovoltaic properties Compare to a classical Solar Cell elte_hyplink_bac_physics.docx Use different dyes Explore voltage and photostability Examine the effect of light-source type Compare spectral responses Projects Steps - elte_hypl_pr_steps.docx Pedagogical Objectives Correlations to Hungarian Standards elte_hyplink_corr.docx PROJECT WORKS

12 CONCLUSION To help an interdisciplinary energetical approach of these solar converters we showed - 3 comparative figures to follow their electron transports - 3 relative levels figures to strenghten the analogy - a recap-table to follow the main steps of processes - a Pedagogical Application to build and examine your own Raspberry Cell Solar Energy Absorption Charge Separation Electron Regeneration Electron Transport Chemical Energy Electrical Energy Stockage Sources Externes/ To Go Further: elte_hyplink_sources.docx