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Glasses for up- and down-conversion for PV applications

Glasses for up- and down-conversion for PV applications. Maurizio Ferrari maurizio.ferrari@ifn.cnr.it.

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Glasses for up- and down-conversion for PV applications

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  1. Glasses for up- and down-conversion for PV applications Maurizio Ferrari maurizio.ferrari@ifn.cnr.it Thi NgocLam Tran1,2,3, Lidia Zur4,1, Anna Lukowiak5, Alessandro Chiasera1, Yann G. Boucher6,7, Alessandro Vaccari8, Damiano Massella9,1, Cesare Meroni9,1, Francesco Enrichi4,10, Stefano Varas1, Cristina Armellini1, Andrea Chiappini1, Alessandro Carpentiero1, Davor Ristic11,12, Francesco Scotognella13,14, Silvia Pietralunga14, Stefano Taccheo15, Daniele Zonta2,1,16, Alexander Quandt17, Brigitte Boulard18, Dominik Dorosz19, Roberta Ramponi14, Giancarlo C. Righini4,20, Maurizio Ferrari1,4 1IFN-CNR CSMFO Lab. and FBK Photonics Unit via alla Cascata 56/C Povo, 38123 Trento, Italy 2Department of Civil, Environmental and Mechanical Engineering, Trento University Via Mesiano, 77, 38123 Trento, Italy 3Ho Chi Minh City University of Technical Education, 1 Vo Van Ngan Street, Linh Chieu Ward, Thu Duc District, Ho Chi Minh City, Viet Nam 4Centro di Studi e Ricerche “Enrico Fermi”, Piazza del Viminale 1, 00184 Roma, Italy 5Institute of Low Temperature and Structure Research PAS, Okolna St. 2, 50-422 Wroclaw, Poland 6CNRS FOTON (UMR 6082), CS 80518, 22305 Lannion, France 7École Nationale d’Ingénieurs de Brest, CS 73862, 29238 Brest Cedex 3, France 8FBK CMM-ARES Unit, Via Sommarive 18, 38123 Povo-Trento, Italy 9Department of Physics, Università di Trento, Via Sommarive 14, 38123 Povo-Trento, Italy 10Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, 971 87 Luleå, Sweden. 11Ruđer Bošković Institute, Division of Materials Physics, Laboratory for Molecular Physics, Bijenička c. 54, Zagreb, Croatia 12Center of Excellence for Advanced Materials and Sensing Devices, Research unit New Functional Materials, Bijenička c. 54, Zagreb, Croatia 13Center for Nano Science and Technology@PoliMi, Istituto Italiano di Tecnologia, via Giovanni Pascoli, 70/3, 20133, Milano, Italy 14IFN-CNR and Department of Physics, Politecnico di Milano, p.zza Leonardo da Vinci 32, 20133 Milano, Italy 15College of Engineering, Swansea University, Bay Campus, Swansea, UK 16Department of Civil and Environmental Engineering, University of Strathclyde, 75 Montrose Street, Glasgow, G11XJ, UK 17 MER group and DST-NRF Centre of Excellence in Strong Materials, School of Physics, University of the Witwatersrand, Private Bag 3, 2050 Johannesburg, South Africa 18Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, Université du Maine, Av. O. Messiaen, 72085 Le Mans cedex 09, France. 19AGH University of Science and Technology, 30 Mickiewicza Av., 30-059 Krakow, Poland 20MDF Lab. IFAC - CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy

  2. OUTLINE • Up- and down-conversion: definition • - differentmecanisms • importance of the host matrix • energytransferbetween rare-earth ions • short theory • efficiencyassessment • Some Applications • down converter layer for solarcells • choice of the RE couples: Pr3+/Yb3+ , Tb3+/Yb3+, Er3+/Yb3+systems • matrix effect: glass ceramic and cluster formation in single crystal

  3. Introduction Basically, down- and up-conversion correspond to a frequency conversion of the photons through a non-linear interaction. The up/down terms correspond to the "direction" of the frequency change. UV-visible to IR (and UV to visible) IR to visible Rare-earth (RE) doped luminescent materials usually show unique down-conversion and/or UC properties (many unfilled level in the 4f inner shell). It generally implies energy transfer between two RE ions that was first suggested by François Auzel in 1966.

  4. Rare-earth ions down-conversion mechanisms - Quantum cutting (QC) (e) A B B • QC on a single ion A by sequential emission of two photons. (b)-(d) QC by a pair of rare-earth ions via (partial) energy transfer (resonant or not resonant) from ion A to ion B indicated by (1) and (2) (e) QC by single-step cooperative energy transfer for ion A to 2 ions B (less efficient than sequential energy transfer). R. T. Wegh, H. Donker, K. D. Oskam, A. Meijerink, J. Lumin. 82 (1999) 93.

  5. Rare-earth ions down-conversion mechanisms - Down shifting (DS) (a) (b) (c) (a) and (b) DS on a single ion A. (c) DS by a pair of rare-earth ions via energy transfer from ion A to ion B. The difference in energy of the 2 photons is dissipated by phonons.

  6. (b) (c) (d) (a) Rare-earth ions up-conversion mechanisms efficiency:  = 10-3 = 10-5  = 10-6  = 10-8 (in) (YF3:Yb:Er) (SrF2:Er) (YF3:Yb:Tb) (YbPO4) • APTE (Photon Addition by Energy Transfer): closely approaches full resonance case (b) 2-step absorption process. It involves excitated state absorption (ESA) (c) cooperative sensitization (d) cooperative luminescence (a) and (c) are often mistaken one for another but they show different rise times; instantaneous for (c) whereas the APTE rise-time reflects population accumulation in the excited state. F. Auzel, « Spectroscopy properties of rare-earth in optical materials , Material Sciences G. Liu and B. Jacquier (Eds)

  7. Choice of the rare-earth host • Low phonon energy to reduce non radiative mechanisms • High RE solubility Beyond critical concentrations, RE ions tend to form precipitates in most solid hosts. These can either take the form of clusters of rare-earth ions, or can be compounds or alloys formed with one component of the host matrix. • large bandgap (UV transparency) • large Stokes shift (less reabsorption) • high transparency …..and ease and cost of fabrication! phonon energy  single crystal Glass-Ceramics (GC) Glass RE in crystal environnement + optical properties of a glass

  8. Choice of the rare-earth host * formation of cluster depending on the RE radius. Can be avoided by charge compensation by adding LiF or NaF or by forming SrF2-CaF2 solid solutions

  9. Theory of Energy Transfer between RE The Förster-Dexter theory (FRET) developed the basic theory of sensitized luminescence in solids based on the ion-ion interactions produced by electric multipoles. The evaluation of the ET transfer probability W is related to the overlap integral between donor emission and acceptor absorption cross-section spectra. For D-D interaction, W depends on distance R between Donor and Acceptor: RC is the critical transfer distance between the luminescent ions, D the intracenter lifetime of Donor excited level. The Inokuti–Hirayama model has succeeded in describing the non exponential fluorescent decay for energy transfer assumed to occur within a single donor-acceptor pair: average distance between ions NA the concentrations of acceptor, 0 the intrinsic radiation lifetime (without transfer) and (1-3/s) is a Gamma function. (n)=(n-1)! The values s = 6, 8, 10 denote the electric D-D, D-Q and Q-Q interactions between the ions (D=dipole, Q = quadrupole). Neglect of higher-order interaction processes involving more than two ions is reasonable for the low concentrations. T. Förster, “Zwischenmolekulare Energiewanderung und Fluoreszenz,” Ann.Phys. (Leipzig) 2, (1948) 55-75 D. L. Dexter, “A theory of sensitized luminescence in solids,” J. Chem. Phys. 21 (1953) 836-850 M. Inokuti, F. Hirayama, “Influence of energy transfer by the exchange mechanism on donor luminescence,” J. Chem. Phys. 43 (1965) 1978

  10. Down conversion efficiency The energy transfer efficiency (ETE) is obtained from the mean decay time of Donor ion (D) with and without Acceptor (A). non single exponential decay The total internal quantum efficiency QE (photon emitted/ photon absorbed) is given by: with D and A the luminescent quantum efficiency of Donor and Acceptor

  11. Down conversion efficiency The energy transfer efficiency (ETE) is obtained from the mean decay time of Donor ion (D) with and without Acceptor (A). non single exponential decay The total internal quantum efficiency QE (photon emitted/ photon absorbed) is given by: with D and A the luminescent quantum efficiency of Donor and Acceptor The total external QE takes into account light reflection at the surface of the layer, ratio of light absorbed. The external QE is always lower than the internal QE. It is not possible to evaluatethe conversion efficiency only on the base of the luminescence spectra. The real QE is less than the calculated value because of scattering of the emitted light.

  12. Down conversion to improve solar cells efficiency

  13. Si band gap 1100 nm~1,05eV 350-550nm Potential gain for down- and upconversion for Si solar cell Silicon Photovoltaic devices are able to convert only a portion of solar spectrum. green part: energy conversion of the absorbed part of the solar spectrum for a c-Si solar red part: the extra energy conversion if every photon with E > 2Eg results in 2 NIR photons beige part: energy gain if every pair of photons with 0.5Eg < E< Eg is converted to 1NIR photon. Note that the figure considers no other losses than spectral mismatch losses

  14. Potential gain for down- and upconversion for Si solar cell Break the Shockley-Queisser limit to the energy conversion: from 30% to 36.6% (theoretical value)

  15. Potential gain for down- and upconversion for Si solar cell Donor:absorbs incident photons from the sun and transferitsenergy to the acceptor rare-earth : Pr3+, Tm3+relativelystrong absorption in the blue Er3+ : manymean or weak absorption bands in the UV-blue-green Ce3+ in the UV Acceptor:emits the photons thatwillbeabsorbed by the PV cell Yb3+ : single excited state - Emission at ~1000 nm absorbed by Si solarcellwithoutanylosses Sensitizer: added to improve the capture of incident photons (especially in the UV) since the 4f-4f absorption cross section of RE is low. Transfer its energy to the donor. Example Ce3+, Gd3+ : broad and intense UV 4f-5d absorption band

  16. Selected NIR quantum-cutting materials co-doped with Ln3+ – Yb3+ for PV applications review article : X. Huang et al,, « Enhancing solar cell efficiency: the search for luminescent materials as spectral converters » Chem. Soc. Rev. 42 (2013) 173-201

  17. QC using a single ion Initial work on down conversion materials was aimed at the conversion of one UV photon in two visible photons: • Cascade emission or energy transfer by steps, from the 1S0 level of Pr3+ [1];. • Energy transfer by steps, from 6GJ levels of the Gd3+[2] QC in YF3:Pr3+ 185 nm photon is absorbed and the energy is transfered into the 1S0 state. emission of a blue (1S01I6) (408 nm) and red (3P03H6) (620 nm) photon, with an EQE of 140 15%. QC in LiYF4: Gd3+ 194-196 and 200-204nm photon is absorbed From the 6GJlevels emission of a red photon (6GJ 6PJ) followed by emission of an UV photon (6PJ 8S7/2) Pr3+ [1] W.W. Piper, J.A. de Luca, F.S. Ham, J. Lumin. «Cascade fluorescent decay in Pr3+-doped fluorides: Achievement of a quantum yieldgreaterthanunity for emission of visible light » 8 (4) (1974) 344-348. [2] R. T. Wegh et al, Vacuum-ultraviolet spectroscopy and quantum cutting for Gd3+ in LiYF4» Phys. Rev. B 56 (21) (1997) 13841.

  18. Down conversion with Tb3+/ Yb3+ Two red photon @ 980 nm One green photon @ 488nm

  19. Down-converters Silica-Hafnia glass ceramics • Low phonon energy ( 700 cm-1) • Rare earth solubility • Combine spectroscopic properties of the crystal with optical properties of the glass • Determine the efficiency of the process • Optimize the rare earth ions content

  20. TEM images • Spinodaldemixing • Validation of the process: Incorporation of hafnia nanocrystals in the waveguide • Nanocrystals identified as monoclinic HfO2 • Size of about 3-4 nm

  21. Decay curves analysis Energy transfer efficiency between Tb3+ and Yb3+ : The relation between the transfer efficiency and the effective quantum efficiency is linear and is defined as: ηEQE = ηTb-r(1-ηTb-Yb)+2ηTb-Yb where the quantum efficiency for Tb3+ions, ηTb-r, is set equal to 1. Decay curves of the luminescence from the 5D4 metastable state of Tb3+ ions for the first samples series under excitation at 355 nm.

  22. Tb3+/ Yb3+ down conversion efficiency Transfer efficiency and effective quantum efficiency as a function of Yb3+ molar concentration for A samples where Tb3+ content is fixed at 0.5 mol% • For compositions with Tb3+ content kept constant at 0.5 mol% and increasing Yb3+ molar concentration, we observed that: • the Tb-Yb energy transfer efficiency increases with the increase of the molar ratio Yb/Tb; • the energy transfer efficiency does not exceed 24-25%.

  23. Pr3+/ Yb3+down conversion efficiency B.Dieudonné, B. Boulard, G. Alombert-Goget, A. Chiasera, Y. Gao, S. Kodjikian , M. Ferrari “Up- and Down-conversion in Yb3+-Pr3+ co-doped fluoride glasses and glass ceramics” Journal of Non-Crystalline Solids 377 (2013) pp. 105-109. doi:10.1016/j.jnoncrysol.2012.12.025 ZLAG parent glass single crystalline phase LaF3-ZrF4 system

  24. Pr3+/ Yb3+down conversion efficiency Schematic energy level diagram of Pr3+ and Yb3+ ions explaining the energy transfer process between the dopants.Two IR photons can be obtained upon absorption of one blue photon via two sequential resonant ET steps from Pr3+ to Yb3+: Pr3+ (3P1 1G4) ; Yb3+ (2F7/2 → 2F5/2) and Pr3+ (1G4 3H4) ; Yb3+ (2F7/2 → 2F5/2).

  25. Pr3+/ Yb3+down conversion efficiency Decay curves corresponding to the 3P0 state of Pr3+ ions monitored at 478 nm under 440 nm excitation for different Yb3+ concentrations. The inset shows the dependence of the average decay time  as a function of the Yb3+ concentration.

  26. Pr3+/ Yb3+down conversion efficiency in different hosts ETE (%) same doping 0.5Pr3+ x Yb3+ Yb3+ content (mol%) • The ETE of ZLAG and InF3-based glasses is almost equal to the one obtained in K3YF10 and higher that the one obtained in oxyfluoride germanate glass [2]). • The ETE of ZBLA is less than ZLAG but close to YF3 • CaF2 matrix exhibits the highest ETE, obtained even for low Yb3+ content (1mol%) [1] D. Serrano, A. Braud, J.-L. Doualan, P. Camy, A. Benayad, V. Ménard, R. Moncorgé, Optical Material, (2010). [2] G. Lakshminarayana, Jianrong Qiu,  Journal of Alloys and Compounds 481, 582–589 (2009).

  27. Up-conversion in single ions: Er3+ doped host Green emission of Er3+ is one of the most famous up-conversion process. it is attributed to excited-state absorption (ESA) through a multi-step process. different pumping schemes of Er3+ 800 nm 980 nm Er3+ ZBLAN fiber excited @ 800nm 800nm: Er3+ pumping to the 4I9/2 state following by nonradiative decay to the metastable 4I13/2 state. Then successive excitation by other pump photons to the 2H11/2 and 4S3/2 states. After that decay to the ground state 4I15/2 with green emission. 980nm: successive resonant absorption from ground state and excited state 4I11/2 to 4F7/2. After non radiative decayto 2H11/2 and 4S3/2 states ……. Two-photon process

  28. Conclusion 1 The sun is hot HarvestingSolar Energy is the onlysolution to meet the worldwidedemand (need?) forenergy vs. Efficiency < 0.1% Efficiency > 10%

  29. Major loss mechanism solar cell Conclusion 2 • Thermalization loss • Transparancy loss Shockley-Queisser efficiency limit Si Solar Cell: 30% Figure taken from B.S. Richards, Solar Energy Materials & Solar Cells 90, 2329-2337 (2006)

  30. Solutions? Adapt the solar cell: Tandem solar cells (up to 40% efficient) Multiple exciton generation Adapt the solar spectrum: Upconversion of IR to NIR (recovery of lost IR photons) Downconversion of UV/VIS to NIR (doubling of e-h pairs, reduction of lost excess photon energy) Conclusion 3 S. Kurtz et al. J. Cryst. Growth 298 (2007) 748

  31. Adapt the solar spectrum Transparency losses → Upconversion Thermalisation losses → Downconversion Conclusion 4

  32. Prime candidates for spectral conversion: Conclusion 5

  33. Conclusion 6 • We have seenthat: • The energytransferfrom RE3+ (RE = Pr, Tm, Er) to Yb 3+is efficient in matrices withlow phonon energy but the efficiency of down-conversion in solarcellislimitedbecause of: • concentration quenching of Yb3+ and/or back energytransfer • low absorption of RE ions •  better use RE-doped materialwithstrongbroad band absorption like high band gap semi-conductors (SnO2) or add Ag nanoparticules F. Enrichi, C. Armellini, G. Battaglin, F. Belluomo, S. Belmokhtar, A. Bouajaj, E. Cattaruzza, M. Ferrari, F. Gonella, A. Lukowiak, M. Mardegan, S. Polizzi, E. Pontoglio, G.C. Righini, C. Sada, E. Trave, L. Zur “Silver doping of silica-hafnia waveguides containing Tb3+/Yb3+ rare earths for downconversion in PV solar cells” Optical Materials 60 (2016) pp. 264-269

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