Nanomaterials For Solar Energy Conversion Shankar
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Nanomaterials for Solar Energy Conversion. Presented in International Conference. Describes Opportunities & Challenges in Photochemical solar cells. Demonstrates TRIZ Innovative Problem Solving approach.
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Nanomaterials For Solar Energy Conversion Shankar
- 1. Nanomaterials Innovations for efficient solar energy conversion Opportunities Bottlenecks Challenges Joint Indo-US Workshop on Scalable Nanomaterials for Enhanced Energy Transport & Conversion Thursday, 21 August 2008, JFWTC, GE Bangalore Shankar M Venugopal Asst General Manager – Advanced Materials Tata Chemicals Innovation Centre Nature-inspired solar-energy conversion Strategy Nanomaterials for Solar conversion - Shankar 2
- 2. 1 Efficiency Crystalline Silicon 0.5 DSSC Image source – STI Australia Nanomaterials for Solar conversion - Shankar 3 0 0.2 0.5 Cost 1 Photo electro chemical Solar Cell Nanostructured Solar Cell Dye-sensitized Solar Cell Light Glass TCO Absorbed dye with TiO2 10 – 20 µm I- I3 - Electrolyte I- I3- TCO / Pt Glass Nanomaterials for Solar conversion - Shankar 4
- 3. Photo electro chemical Solar Cell Kinetic Solar Cell •No built-in electric field •Different rate constants for electron extraction (via diffusion) and electron recombination Carrier transport I- I3- •Only majority carriers within cell I- I3- •Less sensitive to defects, impurities •Allows “less pure” materials Nanomaterials for Solar conversion - Shankar 5 Nanoporous Transport r semiconductor Re s te g ve El tin co ar ec es m bin rv tH tro Ha at gh de ion t Li s gh Li Physics Materials Nanomaterials for solar energy conversion Challenges Opportunities Qu Sc a nt a le um O up s t TC Co do ts Efficiency Nanotubes Nanomaterials for Solar conversion - Shankar 6
- 4. Light Harvesters capture solar photons Generate Excitons Excito Nano n split nanop at article TiO2 with surfac e Electro adsorbed n injec into TiO ted dye 2 I- I3- molecules I- I3- ted injec Each n exp o electr apping n tr millio ents ev Nanomaterials for Solar conversion - Shankar 7 Nano TiO2 – Heart of the Device Provides large SA for adsorption of light harvesters Nano TiO2 with adsorbed dye molecules I- I3- I- I3- Electron transport by trap-limited diffusion Nanomaterials for Solar conversion - Shankar 8
- 5. Nano Solar Cell – Time scales Life time of the Dye molecule’s excited state: ~ ns molecule’ Dye + Photon Dye+ + e- e- injection time to TiO2: ~ fs Regeneration of oxidized dye: ~ ns At Dye – Electrolyte interface 3I- + 2Dye+ I3- + 2Dye At TiO2 – Electrolyte interface I- I3- I- + 2e- I3 - For efficient charge extraction e- I- I3- lifetime: > 20 µs (for a 10 microns film) At counter electrode Pt electrode Nanomaterials for Solar conversion - Shankar 9 I3- + 2e- 3I- TRIZ Functional Map of Nano Solar Energy Converter Transmission Sun Excitation Circuit TCO VIS Abs Counter Electrode UV Abs Transmission Aggregation Circuit Transfer e- e- recombination Evaporation e- recombination Corrode Dye e- recombination Electrolyte e- recombination e- recombination Substrate e- supply Circuit Transfer e- Nano-TiO2 Heat Nanomaterials for Solar conversion - Shankar (+)ve interaction 10 (-)ve interaction
- 6. Underlying TRIZ Technical Contradictions What is to be What is holding us Element Present What is desired? improved? back? High transmittivity & TCO ITO electrical conductivity Light transmittivity low conductivity loss in transmittivity Electrical conductivity due to light scattering Organic Light harvester molecules absorb entire spectrum Aggregation, selective (Dye) (Ru-based) of incident radiation # Absorbed photons absorption convert all absorbed photon energy into excitons # Excitons generated Recombination Nanoporous conduct electron away Transfer of e from dye photoelectrode Nano TiO2 immediately Electron mobility to TiO2 Iodine based conduct hole away Hole mobility (liquid Electrolyte redox couple immediately electrolyte) volatility, leakage supply electrons Chemical stability, Counter Pt on continuously, not react electron donating corrosive nature of electrode glass/TCO with electrolytes ability Nanomaterials for Solar conversion - Shankar electrolytes and cost 11 Nanoporous Transport r semiconductor Re s te g ve El tin co ar ec es m bin rv tH tro Ha at gh de ion t Li s gh Li Physics Materials Nanomaterials for solar energy conversion Challenges Opportunities Qu Sc a nt a le um O up s t TC Co do ts Efficiency Nanotubes Nanomaterials for Solar conversion - Shankar 12
- 7. Nano Solar Cell - Materials Glass TCO ITO Nanoparticles TiO2 Adsorbed Ru-based dye molecule molecules I- I3- Electrolyte Iodine-based redox couple I- - I -3 I- I3- Counter electrode TCO, Pt Substrate Glass Nanomaterials for Solar conversion - Shankar 13 Nano Solar Cell Materials Current Materials Limitations ITO 50% Cost, Indium scarce TiO2 Nanowires, NT Ru-based 30% cost, molecules Ruthenium scarce I- I3- Iodine-based redox Leakage, Volatility, couple Corrosive I- I3- TCO, Pt Pt – corrosion resistant but expensive Glass Mfg, Scale-up Nanomaterials for Solar conversion - Shankar 14
- 8. Nanoporous Transport r semiconductor Re te g es El tin co v ar ec es m bin rv tH tro Ha at gh de ion t Li s gh Li Physics Materials Nanomaterials for solar energy conversion Challenges Opportunities Qu Sc a nt a le um O up s t TC Co do ts Efficiency Nanotubes Nanomaterials for Solar conversion - Shankar 15 Materials Innovation Opportunities Current Materials New Materials ITO SnO2:F, ZnO:Al TiO2 Nanowires, NT Ru-based Cu-based molecules Molecules, QDs I- I3- Iodine-based Solvent-free ionic redox couple liq with I melt I- I3- TCO, Pt Nano Pt Glass Polymer, metal Nanomaterials for Solar conversion - Shankar 16
- 9. Component Current New Material Performance Why? Material Improvement Substrate Glass Flexible polymer, Easy Roll-to-roll metal sheets manufacturability processing Lower Mfg cost Top Electrode TCO - ITO TCO – doped tin Lower cost Free of oxide and Zinc expensive oxide indium Light Organic dye Cu-based dyes Lower cost Free of Harvester molecules, Quantum Dots Design flexibility expensive Ru-based Ruthenium, Size-tunable absorption Semiconductor Nanoporous Nanotubes, Higher collector Guided e- TiO2 Nanowires TiO2 current efficiency transport, less recombination Electrolyte Iodide-tri Solvent-free RT Imp Stability Less leakage, iodide redox ionic liquid with volatility couple iodide melt Counter Platinized Nano Pt, Graphite, Lower cost Less Pt or No Pt electrode glass carbon, Aluminum electrode Nanomaterials for Solar 17 conversion - Shankar Nanotube dye-sensitized solar cell Tube-to-tube spacing Wall thickness Tube length Wall roughness TiO2 Nanowires array Pore diameter • Similar e-transport time • Longer e-recombination time • Higher collector efficiency Nanomaterials for Solar conversion - Shankar 18 Source – Peidong Yang group, UC Berkeley,
- 10. Ru-free dye molecules An element of surprise—efficient copper-functionalized dye-sensitized solar cells – w Takeru Bessho,a Edwin C. Constable,*b Michael Graetzel, a Ana Hernandez Redondo,b Catherine E. Housecroft,b William Kylberg,b Md. Solar conversion - Markus Neuburgerb and Nanomaterials for K. Nazeeruddin,a Shankar 19 Silvia Schaffnerb. Chem Comm 2008 Design of light harvesters • Increase light absorption cross-section • Suppress interface recombination • Longer wavelengths – red & beyond • Organic dye molecules + QDs (CdSe, CdTe) + Nanometals P.V. Kamat, Meeting the Clean Energy Demand Solar conversion - Shankar Nanomaterials for 20 J. Phys. Chem. C, Vol. 111, No. 7, 2007
- 11. Materials Degradation Challenges Degradation ITO, SnO2:F Corrosion Shift of energy levels, surface TiO2 states, loss of contact – particle, substrate, Pt absorption, photocatalysis Ru-based Loss of ligand, I- I3- Molecules – aggregation, desorption e.g N3 dye I- I3- Iodine-based Solvent degradation, redox couple dissolving water / oxygen, conversion of I2 to IO3- TCO, Pt Release of Pt, adsorption of species Nanomaterials for Solar conversion - Shankar 21 Glass Mechanical breaking Nano Solar Cells Technology – Active Players • Materials • Processing Equipment • Technology Consulting Solaronix is a Swiss shareholder company located in Aubonne, near Lake Geneva. The company was founded in 1993 by the twin brothers Andreas & Toby Meyer. 11 Aurora Avenue Queanbeyan NSW Australia Nanomaterials for Solar conversion - Shankar 22 Global Headquarters: Lowell, Massachusetts, USA R&D Subsidiaries: Linz, Austria & Zug, Switzerland
- 12. Research Focus • Maximize harvesting of sunlight - Nano light harvesters, QDs • Improved electron transport - TiO2- 1-D Nanostructures • Indium-free TCO – max cost savings • Flexible substrates – low-temp sintering • Non-corrosive electrolytes • Counter electrode – No or less Pt Nanomaterials for Solar 23 conversion - Shankar Nanoporous Transport r semiconductor Re s te g ve El tin co ar ec es m bin rv tH tro Ha at gh de ion t Li s gh Li Physics Materials Nanomaterials for solar energy conversion Challenges Opportunities Qu Sc a nt a le um O up s t TC Co do ts Efficiency Nanotubes Nanomaterials for Solar conversion - Shankar 24
- 13. Thank you Photovoltaic shingles (in blue) - 500 square feet produce three kilowatts during peak sunlight, (Courtesy of United Solar Ovonic.) Nanomaterials for Solar conversion - Shankar 25 Nanomaterials for Solar conversion - Shankar 26
- 14. Nanoporous Transport r semiconductor Re te g es El tin co v ar ec es m bin rv tH tro Ha at gh de ion t Li s gh Li Physics Materials Nanomaterials for solar energy conversion Challenges Opportunities Qu Sc a nt a le um O up s t TC Co do ts Efficiency Nanotubes Nanomaterials for Solar conversion - Shankar 27