2THE SOLAR CHALLENGEWith a projected global population of 12 billion by 2050 coupled with moderate economic growth, the total global energy consumption is estimated to be ~28 TW. Current global use is ~11 TW.To cap CO2 at 550 ppm (twice the pre-industrial level), most of this additional energy needs to come from carbon-free sources.Solar energy is the largest non-carbon-based energy source (100,000 TW).However, it has to be converted at reasonably low cost.
3Solar cells Large sized buildings-Silicon Dye sensitized solar cells Portable electronics and Small-medium sized buildings
4Mimicking Plant system -In terms of Activity & Structure for Energy devices Solar CellMetal complex in PSI and PSIIharvest lightFuel CellMetal complex in PSI andPSII catalyze water splittingto generate electronsEfficient harvesting, synergistic performance, combined activityEfficient transfer
5Materials & Development Integration of biological macromolecules with nanostructured organic and inorganic materialsBio-nano InterfaceInterface EngineeringOrganic/OrganicMetalOxide /OrganicInorganic / OrganicNano InterfacesSolar CellOrganic/QDs Solar CellFuel CellSensorDevice TestingInorganic/ biometaloxide/bioBio- Solar CellBio- Fuel CellBio- SensorMATERIALS SYNTHESIS,ExtractionOrganicInorganicBiomoleculesNanostructureMaterials & DevelopmentStructure-Function Relationship Investigation
6Evolution of Solar devices Solar cellssiliconPolycrystalline(CuInS2, CuInGaSe2, CuInSe2)Dye sensitized solar cell, Quantum dot sensitized solar cellII-VI compoundsCdTeIII-V compoundsGaA, InPCells that generate free electron – hole pairCells that generate bound electron-hole pairOrganic solar cellPolymer solar cellHybrid solar cellsIIIIIIBio solar cell ?IVArtificial photosynthesisBio-involved systemEvolution of Solar devicesOur area of researchCombination of biological and inorganic (metal oxide)components to create solar cell
7Three important components in the current generation of solar cells EfficiencyElectrolyteSensitizerPhotoelectrodeCostSize
8Structural importance and Mechanism of Natural molecules The key to obtain such rapid electron ransfer is to endow the dye with a suitable anchoring group, such as a carboxylate or phosphonate substituent or a catechol moiety, through which the sensitizer is firmly grafted onto the surface of the Titania.Proton coupled electron transfer Mechanism in Chemical Dye (DSSCs)The surface dipole is generated by proton transfer from the carboxylate groups of the sensitizer to the oxide charging the solid positively and leaving an excess negative charge on the dye.
9Bio-sensitized Solar Cell (BSSC) Seeram Ramakrishna, V Bio-sensitized Solar Cell (BSSC) Seeram Ramakrishna, V. RenugopalakrishnanElectrolyteSensitizerSemiconductorBiomoleculesRenugopalakrishnan., et al. submitted toNature nano
10Biomolecules as sensitizers MacromoleculesProteinsBacteriorhodospinSimple moleculesWorld climate & Energy Event. 1-5 December Rio de Janerio, BrazilTea catechins (fruit extracts).Cyanin 3-glycosidePNAS | April 4, 2006 | vol 103 | no 14 |Photosystem I & IIJChemEd.chem.wisc.edu.Vol 75 No.6 June 1998Chlorophyll aJ.Phy. Chem. 1993, 97,CarotenoidsChemical Physics Letters 439(2007)J.Phys.Chem. B, Vol No.2,2005
13bR as a potential sensitizer 2 ms70 ms0.5 ms500 fs8-10 msECCPL550N550M412O640H+inH+outPhotoisomerized to13-cisa 9-cis pathway4-5potonatedall-transRetinal Quantum Efficiency in methanol %Retinal Quantum Efficiency in BR – %De- and reprotonatedSchiff base
14Postulated Mechanism of bR in Solar cell Photoexcitation of the sensitizer resulted in the changes in protonation state of acidic and basic groups in the protein.They produce a transmembrane potential gradient that causesinjection of an electron into the conduction band of the oxide and transport through the metaloxides to the collection electrode.Hence, the principle of bR in solar device is based on bR proton coupled electron transfer upon photoexcitationPROTON coupled Electron transfer
15Binding of bR to TiO2 and ZnO IEP = 9.5TiO2 anatase, 1 0 0IEP = 6.0
16Role of Cl- ions in bR triple mutant MD, 0 nsMD, 1 nsMD, 4 ns
17Importance of Femtosecond electron injection 2 ms70 ms0.5 ms500 fs8-10 msECCPL550N550M412bO640H+inH+outPhotoisomerized to13-cisa 9-cis pathway4-5Protonatedall-transRetinal Quantum Efficiency in methanol15.0%Retinal Quantum Efficiency in BR%De- and reprotonatedSchiff baseNorbert Hampp, Chem Rev., Vol. 100, , 2000.Norbert Hampp, et al., J. Phys. Chem B., Vol. 106, , 2002.
18Construction of band diagram bR-TiO2 system 0.0-1.0eVe--2.0-3.8e--3.0LUMO?-4.01.6 eV-4.03.78 eVHOMO-5.03.2 eVTriple Mutant bR-5.4-6.0bRHOMOMismatching solar spectrumLow band gap materials preferred to harvest more solar energy1.2 eVIR-52%Vis-36%UV-12%+e-e-+-7.0TiO2
20Possible modes of orientation of bR Tatke, Renugopalakrishnan, Prabhakaran, Nanotech. 115, S684-S690,
21Computational study – Dipole moment The dipole moment vector of bR aligns to the exterior-cytoplasm axis (vertical) upon formation of the physiological trimer.A monomer of bR is shown as ribbons colored from blue (N-terminus) to red (C-terminus) and with its retinal chromophore in purple ball-and-stick representation.The monomer dipole moment vector, which has a magnitude of 265 D, is shown as a grey arrow, while that of the trimer to which this monomer belongs, with a value of 125 D, appears in Sienna brown.
22Comparison of 3 Glu bR with Wild type at AM 1.5We notice that 3 Glu bR is quite responsive
23Measurement at high concentration of 3 Glu bR (4mg/ml) at pH 8 Air Mass 1.5 solar spectrumConversion efficiency: 0.02%Isc: mA/cm2Cell Area: 1 cm2Electrolyte: LiI/KCl in Distilled water
24Effect of ZnO and TiO2 on the efficiency of biosensitized solar cell Solar=40mW/cm2Area= 0.5 cm2controlEff = 0.0TiO2-bREff = 0.02%Isc = 0.09mA/cm2ZnO-bREff = 0.03%Isc = 0.056mA/cm2ZnOControlTiO2ZnOBinding of anodes and biomolecules is associated with surface charges and pH.IEP of TiO2 and ZnO are reported to be 6 and 9.5 respectively,[i] whereas the bacteriorhodopsin (bR), has ca. 4.5.[ii]ZnO may be the suitable candidate for the immobilization of low IEP proteins[i]. Topoglidis, E., Cass, A. E. G., Regan, B. O. & Durrant. J. R. Immobilisation and bioelectrochemistry of proteins on nanoporous TiO2 and ZnO films. J. Elect. Chem. 517, (2001).[ii]. Hartley, P., Matsumoto, M. & Mulvaney, P. Determination of the Surface Potential of Two-Dimensional Crystals of Bacteriorhodopsin by AFM. Langmuir 14, (1998).
25Biosolar CellsSolar intensity=40 mW/cm2Cell area= 0.5 cm2TiO2-bRh ~ 0.02%Jsc ~ 0.1 mA/cm2VOC ~ 0.6VZnO-bRh ~ 0.03%JSC ~ 0.06 mA/cm2VOC ~ 0.4VTiO2 + electrolyte (no sensitizer-control)h = 0.0The first prototype of protein- (bacteriorhodopsin) interface with TiO2 solar cell has been demonstrated!
28TiO2 film electrode solar cell produced a short-circuit photocurrent density (JSC) of mA/cm2 whereas wild type bR adsorbed TiO2 cell showed only mA/cm2 as JSC. However, for both the type of bR, the open-circuit photovoltage (VOC) was about 0.39 V. The experimental results confirmed that both wt bR and 3Glu bR respond to the light illumination, however, the triple mutant (3Glu) showed up better photoelectric performance (JSC of mA/cm2) compared to wild type bR ( mA/cm2), which is likely due to more efficiently assembling and binding nature of the mutated protein (3Glu) to the TiO2
29Energy Loss in the Various Steps in the Solar Cascade The Shockley-Queisser limit rests on the assumption that one photon can produce only one electron-hole pair in the presence of a single energy gap. However, this limit can be violated if one photon can lead to multiple electron-hole pairs or excitons Another related issue is the effect of a band gap distribution on the cell efficiency. These important problems can be addressed by calculating the electronic structure of the protein chromophore with reliable first principles methods.The coupling of the excited protein with the substrate causes energy dissipation. In order to optimize the charge transfer efficiency, reliable first principles calculations are needed to simulate the energy losses.A mathematical theory for the electrolyte phase between the electrodes in the BSSC is another important tool we plan to develop in order to control various energy losses.
30An understanding and mastering interactions and charge transfer at the protein-substrate interface Finding a bR mutant that absorbs light in the right part of the spectrum, that enhances charge separation, and that ejects electrons to be captured by wide-gap semiconductors Finding an optimal non-invasive electrolyte for recharging the protein Developing mathematical models to predict ultimate efficiency, allowing for multiple exciton production and intermediate band light-adsorption processes, and practical efficiency, taking into account non-radiative losses in the semiconductor/br/electrolyte microstructure.