S.Loheeswaran, K.Balashangar & P.Ravirajan* Department of Physics, University of Jaffna, Sri Lanka *p_ravirajan@jfn.ac.lk, pravirajan@gmail.com EFFECT OF ALUMINA COATING IN HYBRID NANOCRYSTALLINE TITANIUM DIOXIDE / POLYMER SOLAR CELL Acknowledgements HETC Project Thanks for equipment Thanks for equipment Thanks for financial assistance • World energy consumption is expected to rise by more than 50 % over the next two decades. (Source: U.S. Department of Energy) • Since the oil energy sources are finite and release unwanted waste products into the environment, alternative energy sources are in increasing demand (wind, hydro, solar (thermal and photovoltaic). • photovoltaic is the best, because they  convert light energy directly into electricity.  do not require any cooling water system.  require little maintenance.  have no moving parts.  are silent in operations. Why Solar cells? 1 Dye sensitized nanocrystalline solar cells Polymer blend solar cells Hybrid polymer/nanocrystal solar cells Molecular film solar cells Major classes of solar cells 2 •Power conversion efficiency 24% in lab. •High cost for production. •limited material availability. •The current price for solar energy is approximately five times higher than electricity obtained from fossil Nanotechnology may bring the cost down SoftHard Advantages • Low cost on large scale industrial production • Low weight • Low material requirements • Ease of manufacture • Mechanical flexibility • Large field of application •Solar Energy Windows Let the Light Shine In encapsulant metal deposition solution deposition su b st ra te Solution Metal Deposition deposition Su bs tr at e Encapsulation 5 Why polymer based Solar Cell ?Why polymer based Solar Cell ? • However, there are constrains such as poor stability, low efficiency for commercialisation and . Material engineering in the nanometre scale 6 Why Metal Oxides/Polymer Solar Cells? Organic solar cells typically made from electron and hole transporting polymers offered highest reported Power Conversion Efficiency. But compared to inorganic materials,  electron mobility of photoactive polymers is extremely low.  stability of photoactive polymers is poor. Hybrid metal oxide/ polymer solar cells Nanocrystalline metal oxides can be used as alternative electron acceptors in donor-acceptor solar cells: • Effective acceptor materials (TiO2, ZnO, SnO2 ) for photoinduced charge transfer from conjugated polymers. • Reasonable electron mobility. • Stability in air. • Ease of fabrication and low cost. • Control of morphology due to the metal oxides. Device performance mainly influenced by 1) Photo-generation rate 2) Quality of interfaces - by modifying the electronic properties of the interface we can able to control the interfacial charge transfer rates 7 DonorAcceptor Electrodes DonorAcceptor Cathode CB VB LUMO HOMO Anode Acceptor Donor 1 1. Absorption of light 2 2 2. Creation of electron-hole pair 3 3 3. Dissociation of electron-hole pair 5. Recombination of charges e- 6. Collection of charges h+ 6 6 5 Photovoltaic effect in hybrid metal oxide/polymer solar cells 4. Transport of charges e- 4 h+ Exciton diffusion length ~ 5-20 nm 8 Au electrode (thermal evaporated) Polymer dip & spin coated (~120 nm) Porous metal-oxide film spin-coated and sintered (~200 nm) Dense compact metal-oxide film ITO - transparent electrode Glass spray pyrolysis (~ 30 nm) PEDOT:PSS (spin-coated) + - 1 cm 1 cm Optimised device structure for Metal oxide/polymer solar cells 9 Device fabrication at the Department of Physics, UoJ Fume hood Nano-enclosure Glove box Programmable spin coater Thermal Evaporator Furnace Modifying the Nano-interface with Alumina coating Modifying the interface Nano Alumina layer Polymer Porous TiO2 1. Concerning the interfacial energetics in a hybrid polymer / TiO2 structure, treatment with alumina coating suppressing the interfacial recombination. 2. TiO2 film with the alumina coating improves the polymer uptake due to the more basic surface of the alumina coated porous TiO2 film than the bare film. Strategy for further optimisation 10 Absorbance 11 400 500 600 700 800 0.00 0.05 0.10 0.15 0.20 0.25 0.30 With Alumina coating (TiO2/Al2O3 d/P3HTd) Without Alumina coating (TiO2/P3HTd) A bs or ba nc e( O D ) Wavelength (nm) J-V characterization under solar simulator with AM1.5 filter -0.2 0.0 0.2 0.4 0.6 0.8 1.0 -5 0 5 10 ITO/Dense TiO2/Porous TiO2/Al2O3 d/P3HTd/P3HTs/PEDOT:PSS/AU Control Device Alumina treated device Champion device C ur re nt d en si ty (m A /c m 2 ) Voltage (V) Device Jsc (mA/cm2) Voc (mV) FF Efficiency (%) Without Alumina coated device 3.53 0.35 0.26 0.40 Alumina coated device 5.46 0.45 0.28 0.86 Best device 7.12 0.45 0.28 1.12 -1.0 -0.5 0.0 0.5 1.0 10-2 10-1 100 101 102 ITO/Dense TiO2/Porous TiO2/Al2O3 d/P3HTd/P3HTs/PEDOT:PSS/AU Champion device Alumina treated device Control Device C ur re nt d en si ty (m A /c m 2 ) Voltage (V) 12 Absorbance 13 400 500 600 700 800 0.00 0.05 0.10 0.15 0.20 0.25 0.30 With Alumina coating (TiO2/Al2O3 d/P3HTd) Without Alumina coating (TiO2/P3HTd) A bs or ba nc e( O D ) Wavelength (nm) 14 Conclusion Due to better polymer uptake by alumina coated electrode, the alumina coated device shows increase short circuit current density compared to devices with uncoated electrode. The increase in VOC for alumina coated device is attributed to the suppression of interfacial recombination by the insulating alumina layer. Due to better attachment of polymer on alumina coated surface and suppression of interfacial recombination, the amount of charge carriers produced in the active layer reaching the top electrode are increased. Thus the alumina coating improves the overall power conversion efficiency over 100 %. 15 Thank You Nanotechnology work at the Department of Physics, University of Jaffna Title of the Projects, Status and Principle investigator(PI) Source Amount LKR List of Major equipments received under these grants Optoelectronic properties of hybrid Metal oxide / Polymer Nano–composites (Revised title since May 2005) - Completed Dr. L. Jeyanathan (PI) (2000 – 2005) Dr. S. Sivaraya  (2000 – 2008) Dr. P. Ravirajan (2005 – 2008)  NRC Sri Lanka   11,000,000 (100,000US$)   Turbo Molecular Pump, Closed Cycled Cryostat, Compressor, Tube Furnace, Photoluminescence Spectrometer assembly Hot Electron Spectroscopic Studies of indirect tunnel barriers-Completed Dr. S. Sivaraya  (2004 – 2005) TWAS Italy 770,000 (7,000 US$)   Source Measure Unit Low cost solar cells based on Nanocrystalline titanium dioxide and vegetable dyes – Completed Prof. P. Ravirajan (PI) (2006 – 2009) IFS Sweden 1,100,000 (10,000 US$) Solar Simulator, Digital Scope Fabrication and Characterization of Hybrid organic / metal oxides Nanostructured photovoltaic devices – Completed Prof. P. Ravirajan (PI) (2006 – 2009) NRC, Sri Lanka     8,350,00 (75,000 US$)   Thermal Evaporator, Programmable Spin processor, Pulsed Laser, Monochromator Characterization of Nanostructured polymer / Fullerene solar cells under sun light – Completed Prof. P. Ravirajan (PI) (2007 – 2011) NSF Sri Lanka 1,900,000 (17,000 US$) Glove box Improving the performance of Hybrid Nanocrystalline Titanium Dioxide (TiO2) / Polymer solar cell using interface modifiers – In progress. Prof. P. Ravirajan (PI) (2011 – 2014) NRC Sri Lanka   8,000,000 (72,000 US$)   Box furnace Fume cupboards Thickness monitor Nano-enclosure UV Visible sectrometer  Research grants of over 300,000 US$ (33 million rupees) had been won by the staff for the following Research Projects Please visit http://www.jfn.ac.lk/physics for more detail 16 PowerPoint Presentation Slide 2 Why Solar cells? Major classes of solar cells Slide 5 Why Metal Oxides/Polymer Solar Cells? Slide 7 Slide 8 Slide 9 Modifying the Nano-interface with Alumina coating Absorbance Slide 12 Slide 13 Slide 14 Slide 15 Slide 16