Upconversion for Photovoltaics – a Review of Materials, Devices and Concepts for Performance Enhancement

Upconversion of low-energy photons into high-energy photons increases the efficiency of photovoltaic devices by converting photons with energies below the absorption threshold of the solar cell into photons that can be utilized. In this review, an overview is provided of quantitative studies of the upconversion quantum yield of upconverter materials, and of the achieved efficiency enhancements in upconverting solar cell devices. Different materials and devices are compared based on well-defined figures-of-merit and the challenges to their accurate measurement are discussed. Internal upconversion quantum yields above 13% have been reported both for Er3+-based materials as well as for organic upconverters, using irradiance values below 0.4 W cm−2. On the upconverting solar cell device level, relative enhancements of the solar cells' short-circuit currents by up to 0.55% have been achieved. These values document progress by orders of magnitude achieved in the last years. However, they also show that the field of upconversion needs further development to become a relevant technology option in photovoltaics. Different options regarding how upconversion performance can be increased further in the future are outlined.

[1]  Judith Grimm,et al.  Upconversion spectroscopy and properties of NaYF4 doped with Er3+, Tm3+ and/or Yb3+ , 2006 .

[2]  Jennifer A. Dionne,et al.  Narrow-bandwidth solar upconversion: Case studies of existing systems and generalized fundamental limits , 2013 .

[3]  Jianzhang Zhao,et al.  Fluorene as π-conjugation linker in N^N Pt(II) bisacetylide complexes and their applications for triplet–triplet annihilation based upconversion , 2012 .

[4]  R. E. Thoma,et al.  The Sodium Fluoride-Lanthanide Trifluoride Systems , 1966 .

[5]  K. Krämer,et al.  Origin of the High Upconversion Green Luminescence Efficiency in β-NaYF4:2%Er3+,20%Yb3+ , 2011 .

[6]  F. V. van Veggel,et al.  Size-dependent maximization of upconversion efficiency of citrate-stabilized β-phase NaYF4:Yb(3+),Er(3+) crystals via annealing. , 2013, ACS applied materials & interfaces.

[7]  D. Sardar,et al.  Highly efficient NIR to NIR and VIS upconversion in Er3+ and Yb3+ doped in M2O2S (M = Gd, La, Y) , 2013 .

[8]  Wenfang Sun,et al.  Texaphyrin sensitized near-IR-to-visible photon upconversion. , 2014, Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology.

[9]  F. Auzel Upconversion and anti-Stokes processes with f and d ions in solids. , 2004, Chemical reviews.

[10]  Murad J Y Tayebjee,et al.  On the efficiency limit of triplet-triplet annihilation for photochemical upconversion. , 2010, Physical chemistry chemical physics : PCCP.

[11]  Markus P. Hehlen,et al.  Power dependence of upconversion luminescence in lanthanide and transition-metal-ion systems , 2000 .

[12]  D. Jaque,et al.  Upconversion emission obtained in Yb(3+)-Er(3+) doped fluoroindate glasses using silica microspheres as focusing lens. , 2013, Optics express.

[13]  Robert N. Schwartz,et al.  Infrared-to-visible upconversion in LaCl 3 :1% Er 3+ : Energy-level and line-strength calculations , 1997 .

[14]  P. Gibart,et al.  Below Band-Gap IR Response of Substrate-Free GaAs Solar Cells Using Two-Photon Up-Conversion , 1996 .

[15]  The upconversion properties of β-NaYF4:Yb3+(10%),Er3+(1%) microprisms under different excitation conditions , 2013 .

[16]  C. Ballif,et al.  Organic-inorganic halide perovskite/crystalline silicon four-terminal tandem solar cells. , 2015, Physical chemistry chemical physics : PCCP.

[17]  W. Cao,et al.  Enhancement of upconversion luminescence of Y 2O 3:Er 3+ nanocrystals by codoping Li +Zn 2+ , 2011 .

[18]  Yanli Ding,et al.  Enhancement on concentration quenching threshold and upconversion luminescence of β-NaYF4:Er3+/Yb3+ codoping with Li+ ions , 2014 .

[19]  W. Cao,et al.  Enhanced near-infrared to visible upconversion nanoparticles of Ho³⁺-Yb³⁺-F⁻ tri-doped TiO₂ and its application in dye-sensitized solar cells with 37% improvement in power conversion efficiency. , 2014, Inorganic chemistry.

[20]  Richard H. Friend,et al.  An improved experimental determination of external photoluminescence quantum efficiency , 1997 .

[21]  S. Fischer,et al.  Experimental analysis of upconversion with both coherent monochromatic irradiation and broad spectrum illumination , 2011 .

[22]  M. Tonelli,et al.  BaY2F8 doped with Er3+: An upconverter material for photovoltaic application , 2013 .

[23]  Pavel P. Fedorov,et al.  Oxysulfide optical ceramics doped by Nd3+ for one micron lasing , 2007 .

[24]  Shu-Hao Chang,et al.  Upconversion effects on the performance of near-infrared laser-driven polymer photovoltaic devices , 2012 .

[25]  S. A. Pollack,et al.  Ion‐pair upconversion pumped laser emission in Er3+ ions in YAG, YLF, SrF2, and CaF2 crystals , 1988 .

[26]  M. J. Weber,et al.  Probabilities for Radiative and Nonradiative Decay of Er 3 + in La F 3 , 1967 .

[27]  John-Christopher Boyer,et al.  Absolute quantum yield measurements of colloidal NaYF4: Er3+, Yb3+ upconverting nanoparticles. , 2010, Nanoscale.

[28]  J. Méndez‐Ramos,et al.  Dopant distribution in a Tm(3+)-Yb(3+) codoped silica based glass ceramic: an infrared-laser induced upconversion study. , 2004, The Journal of chemical physics.

[29]  M. McCann,et al.  Modifying the solar spectrum to enhance silicon solar cell efficiency—An overview of available materials , 2007 .

[30]  Jan Christoph Goldschmidt,et al.  Enhanced up-conversion for photovoltaics via concentrating integrated optics. , 2014, Optics express.

[31]  M. Grabolle,et al.  Relative and absolute determination of fluorescence quantum yields of transparent samples , 2013, Nature Protocols.

[32]  Hans U. Güdel,et al.  Strukturelle und spektroskopische Charakterisierung von lichtemittierenden Natriumlanthanoidtetrafluoriden , 2006 .

[33]  Helmut Schäfer,et al.  Synthesis and Optical Properties of KYF4/Yb, Er Nanocrystals, and their Surface Modification with Undoped KYF4 , 2008 .

[34]  Zhiguo Zhang,et al.  Upconversion Emission Enhancement in Yb3+/Er3+-Codoped Y2O3 Nanocrystals by Tridoping with Li+ Ions , 2008 .

[35]  W.G.J.H.M. van Sark,et al.  Enhanced near-infrared response of a-Si:H solar cells with β-NaYF4:Yb3+ (18%), Er3+ (2%) upconversion phosphors , 2010 .

[36]  F. W. Ostermayer,et al.  Infrared‐to‐Visible Conversion by Rare‐Earth Ions in Crystals , 1972 .

[37]  H. Güdel,et al.  Electronic energy-level structure, correlation crystal-field effects, and f-f transition intensities of Er{sup 3+} in Cs{sub 3}Lu{sub 2}Cl{sub 9} , 1998 .

[38]  A. Gurvich Luminescent screens for mammography , 1995 .

[39]  Shaomin Ji,et al.  Triplet–triplet annihilation based upconversion: from triplet sensitizers and triplet acceptors to upconversion quantum yields , 2011 .

[40]  M. Green,et al.  Improving solar cell efficiencies by up-conversion of sub-band-gap light , 2002 .

[41]  G. Ozin,et al.  Absolute quantum yields in NaYF4:Er,Yb upconverters – synthesis temperature and power dependence , 2012 .

[42]  Yalin Lu,et al.  Enhancing near-infrared solar cell response using upconverting transparentceramics , 2011 .

[43]  Y. Messaddeq,et al.  Infrared‐to‐visible CW frequency upconversion in Er3+‐doped fluoroindate glasses , 1996 .

[44]  F. Auzel Spectral Narrowing of Excitation Spectra in N-Photons Up-Conversion Processes by Energy Transfers , 1984, International Conference on Luminescence - 1984.

[45]  C. Weder,et al.  Low-power photon upconversion through triplet–triplet annihilation in polymers , 2012 .

[46]  P. Prasad,et al.  Upconversion Nanoparticles: Design, Nanochemistry, and Applications in Theranostics , 2014, Chemical reviews.

[47]  H. Moos,et al.  MULTIPHONON ORBIT-LATTICE RELAXATION OF EXCITED STATES OF RARE-EARTH IONS IN CRYSTALS. , 1968 .

[48]  Maxwell J. Crossley,et al.  Efficiency Enhancement of Organic and Thin-Film Silicon Solar Cells with Photochemical Upconversion , 2012 .

[49]  Akio Yasuda,et al.  Blue-green up-conversion: noncoherent excitation by NIR light. , 2007, Angewandte Chemie.

[50]  Jae-Hong Kim,et al.  Upconversion under polychromatic excitation: Y2SiO5:Pr3+, Li+ converts violet, cyan, green, and yellow light into UVC , 2013 .

[51]  Paras N. Prasad,et al.  (α-NaYbF4:Tm(3+))/CaF2 core/shell nanoparticles with efficient near-infrared to near-infrared upconversion for high-contrast deep tissue bioimaging. , 2012, ACS nano.

[52]  Th. Förster Zwischenmolekulare Energiewanderung und Fluoreszenz , 1948 .

[53]  K. Krämer,et al.  Novel materials doped with trivalent lanthanides and transition metal ions showing near-infrared to visible photon upconversion , 2005 .

[54]  M. Green,et al.  Luminescent layers for enhanced silicon solar cell performance: Up-conversion , 2006 .

[55]  Yaoming Xiao,et al.  Application of upconversion luminescence in dye-sensitized solar cells , 2011 .

[56]  Naoteru Matsubara,et al.  Achievement of More Than 25% Conversion Efficiency With Crystalline Silicon Heterojunction Solar Cell , 2014, IEEE Journal of Photovoltaics.

[57]  Markus P. Hehlen,et al.  Hexagonal Sodium Yttrium Fluoride Based Green and Blue Emitting Upconversion Phosphors , 2004 .

[58]  M. Green,et al.  Efficiency enhancement of solar cells by luminescent up-conversion of sunlight , 2006 .

[59]  Tsuyoshi Kano,et al.  NaLnF4 : Yb3 + , Er3 + ( Ln : Y , Gd , La ) : Efficient Green‐Emitting Infrared‐Excited Phosphors , 1972 .

[60]  I. Ladany,et al.  Rare-earth-doped oxysulfides for GaAs-pumped luminescent devices , 1971 .

[61]  A. Eychmüller,et al.  Absolute photoluminescence quantum yields of IR26 and IR-emissive Cd(1-x)Hg(x)Te and PbS quantum dots--method- and material-inherent challenges. , 2015, Nanoscale.

[62]  U. Rodríguez-Mendoza,et al.  Upconversion mechanisms in rare-earth doped glasses to improve the efficiency of silicon solar cells , 2011 .

[63]  R. Mulet,et al.  Improving triplet-triplet-annihilation based upconversion systems by tuning their topological structure. , 2014, The Journal of chemical physics.

[64]  B. Richards,et al.  Broadband photoluminescent quantum yield optimisation of Er3+-doped β-NaYF4 for upconversion in silicon solar cells , 2014 .

[65]  Felix N. Castellano,et al.  Photon upconversion based on sensitized triplet-triplet annihilation , 2010 .

[66]  Wei Guo,et al.  An upconversion NaYF4:Yb3+,Er3+/TiO2 core–shell nanoparticle photoelectrode for improved efficiencies of dye-sensitized solar cells , 2013 .

[67]  G. Dieke,et al.  The Spectra of the Doubly and Triply Ionized Rare Earths , 1963 .

[68]  N. Menyuk,et al.  NaYF4 : Yb,Er—an efficient upconversion phosphor , 1972 .

[69]  B. van der Ende,et al.  Lanthanide ions as spectral converters for solar cells. , 2009, Physical chemistry chemical physics : PCCP.

[70]  W. Cao,et al.  Shell thickness dependence of upconversion luminescence of β-NaYF4:Yb, Er/β-NaYF4 core-shell nanocrystals. , 2013, Optics letters.

[71]  J. Williams,et al.  Energy Upconversion via Triplet Fusion in Super Yellow PPV Films Doped with Palladium Tetraphenyltetrabenzoporphyrin: a Comprehensive Investigation of Exciton Dynamics , 2013 .

[72]  Ralph H. Page,et al.  Upconversion-pumped luminescence efficiency of rare-earth-doped hosts sensitized with trivalent ytterbium , 1997 .

[73]  A. García-Adeva Spectroscopy, upconversion dynamics, and applications of Er3+-doped low-phonon materials , 2007, 0707.1434.

[74]  B. Richards,et al.  Self-absorption in upconverter luminescent layers: impact on quantum yield measurements and on designing optimized photovoltaic devices. , 2014, Optics letters.

[75]  R. Macfarlane,et al.  Green infrared‐pumped erbium upconversion laser , 1987 .

[76]  A. Shalav,et al.  Enhancing the Near-Infrared Spectral Response of Silicon Optoelectronic Devices via Up-Conversion , 2007, IEEE Transactions on Electron Devices.

[77]  Judith Grimm,et al.  Highly efficient near-infrared to visible up-conversion process in NaYF4:Er3+,Yb3+ , 2005 .

[78]  N. J. Johnson,et al.  Lanthanide-based heteroepitaxial core-shell nanostructures: compressive versus tensile strain asymmetry. , 2014, ACS nano.

[79]  J. M. Gardner,et al.  Anchoring Energy Acceptors to Nanostructured ZrO2 Enhances Photon Upconversion by Sensitized Triplet–Triplet Annihilation Under Simulated Solar Flux , 2013 .

[80]  H. Güdel,et al.  Anomalous power dependence of sensitized upconversion luminescence , 2005 .

[81]  W.G.J.H.M. van Sark,et al.  Upconverter solar cells: materials and applications , 2011 .

[82]  Gan-Moog Chow,et al.  Water -soluble NaYF4:Yb,Er (Tm)/NaYF4/Polymer Core/Shell/Shell nanoparticles with significant enhancement of upconversion fluorescence , 2007 .

[83]  Ultra-high photoluminescent quantum yield of β-NaYF4: 10% Er3+ via broadband excitation of upconversion for photovoltaic devices. , 2012, Optics express.

[84]  M. Wermuth,et al.  Up-conversion processes of 5d transition metal ions in crystals , 1999 .

[85]  S. Fischer,et al.  Increasing Upconversion by Plasmon Resonance in Metal Nanoparticles—A Combined Simulation Analysis , 2012, IEEE Journal of Photovoltaics.

[86]  S. Ivanova,et al.  Strong 1.53 μm to NIR-VIS-UV upconversion in Er-doped fluoride glass for high-efficiency solar cells , 2009 .

[87]  Guohong Zhou,et al.  Power conversion efficiency enhancement in silicon solar cell from solution processed transparent upconversion film , 2012 .

[88]  G. H. Bauer,et al.  Enhancement of silicon solar cell efficiency by upconversion: Optical and electrical characterization , 2010 .

[89]  B. Richards,et al.  Optimizing infrared to near infrared upconversion quantum yield of β-NaYF4:Er3+ in fluoropolymer matrix for photovoltaic devices , 2013 .

[90]  F. Auzel,et al.  Materials and devices using double-pumped-phosphors with energy transfer , 1973 .

[91]  R. Schropp,et al.  Increased Upconversion Response in a-Si:H Solar Cells With Broad-Band Light , 2013, IEEE Journal of Photovoltaics.

[92]  Florian Hallermann,et al.  Plasmon enhanced upconversion luminescence near gold nanoparticles-simulation and analysis of the interactions. , 2012, Optics express.

[93]  I. R. Martín,et al.  Enhanced energy upconversion and super-resolved focused spot generation in Tm 3+ -Yb 3+ codoped glass using silica microspheres , 2013 .

[94]  Tymish Y. Ohulchanskyy,et al.  Enhanced upconversion emission in colloidal (NaYF4:Er(3+))/NaYF4 core/shell nanoparticles excited at 1523 nm. , 2014, Optics letters.

[95]  M. Yoshimura,et al.  Size-dependent upconversion luminescence and quenching mechanism of LiYF 4 : Er 3+ /Yb 3+ nanocrystals with oleate ligand adsorbed , 2013 .

[96]  Francisco Sanz-Rodríguez,et al.  Temperature sensing using fluorescent nanothermometers. , 2010, ACS nano.

[97]  Xueyuan Chen,et al.  Upconversion nanoparticles in biological labeling, imaging, and therapy. , 2010, The Analyst.

[98]  M. Lastusaari,et al.  Enhancement of blue upconversion luminescence in hexagonal NaYF4:Yb,Tm by using K and Sc ions , 2013, Journal of Nanoparticle Research.

[99]  M. J. Weber,et al.  Radiative and Multiphonon Relaxation of Rare-Earth Ions in Y 2 O 3 , 1968 .

[100]  Heiko Steinkemper,et al.  Absolute upconversion quantum yield of β-NaYF4 doped with Er3+ and external quantum efficiency of upconverter solar cell devices under broad-band excitation considering spectral mismatch corrections , 2014 .

[101]  Gordon G Wallace,et al.  Dye-Sensitized Solar Cell with Integrated Triplet-Triplet Annihilation Upconversion System. , 2013, The journal of physical chemistry letters.

[102]  Jianzhang Zhao,et al.  Thienyl-substituted BODIPYs with strong visible light-absorption and long-lived triplet excited states as organic triplet sensitizers for triplet–triplet annihilation upconversion , 2012 .

[103]  R. Afzal,et al.  Intensity‐dependent upconversion efficiencies of Er3+ ions in heavy‐metal fluoride glass , 1991 .

[104]  Wei Li,et al.  Direct imaging the upconversion nanocrystal core/shell structure at the subnanometer level: shell thickness dependence in upconverting optical properties. , 2012, Nano letters.

[105]  Jianzhang Zhao,et al.  Strongly emissive long-lived 3IL excited state of coumarins in cyclometalated Ir(III) complexes used as triplet photosensitizers and application in triplet-triplet annihilation upconversion. , 2014, Dalton transactions.

[106]  Wei Huang,et al.  Enhancing solar cell efficiency: the search for luminescent materials as spectral converters. , 2013, Chemical Society reviews.

[107]  W. Liu,et al.  Upconversion induced enhancement of dye sensitized solar cells based on core-shell structured β-NaYF4:Er3+, Yb3+@SiO2 nanoparticles. , 2014, Nanoscale.

[108]  S. Baluschev,et al.  A general approach for non-coherently excited annihilation up-conversion: transforming the solar-spectrum , 2008 .

[109]  Timothy W. Schmidt,et al.  Photochemical upconversion: present status and prospects for its application to solar energy conversion , 2015 .

[110]  J. Guillemoles,et al.  Upconversion of 1.54 μm radiation in Er3+ doped fluoride-based materials for c-Si solar cell with improved efficiency , 2011 .

[111]  Hehlen,et al.  Upconversion in Er3+-dimer systems: Trends within the series Cs3Er2X9 (X=Cl,Br,I). , 1994, Physical review. B, Condensed matter.

[112]  J. Ohwaki,et al.  High‐efficiency infrared‐to‐visible upconversion of Er3+ in BaCl2 , 1993 .

[113]  R. Scheps Upconversion laser processes , 1996 .

[114]  M. Wermuth,et al.  Mechanisms of near-infrared to visible upconversion in CsCdBr3:Ho3+ , 1998 .

[115]  I. R. Martín,et al.  Experimental enhancement of the photocurrent in a solar cell using upconversion process in fluoroindate glasses exciting at 1480 nm , 2013 .

[116]  Jan C. Hummelen,et al.  Broadband dye-sensitized upconversion of near-infrared light , 2012, Nature Photonics.

[117]  Yongsheng Zhu,et al.  Super-intense white upconversion emission of Yb2O3 polycrystals and its application on luminescence converter of dye-sensitized solar cells. , 2013, Optics letters.

[118]  Maxwell J. Crossley,et al.  Improving the light-harvesting of amorphous silicon solar cells with photochemical upconversion , 2012 .

[119]  Bryce S. Richards,et al.  Bifacial n-type silicon solar cells for upconversion applications , 2014 .

[120]  Cunhai Dong,et al.  Self-focusing by Ostwald ripening: a strategy for layer-by-layer epitaxial growth on upconverting nanocrystals. , 2012, Journal of the American Chemical Society.

[121]  W.G.J.H.M. van Sark,et al.  Towards upconversion for amorphous silicon solar cells , 2010 .

[122]  H Berthou,et al.  Optical-fiber temperature sensor based on upconversion-excited fluorescence. , 1990, Optics letters.

[123]  Yi Wang,et al.  3-Dimensional photonic crystal surface enhanced upconversion emission for improved near-infrared photoresponse. , 2014, Nanoscale.

[124]  F. A. Saunders,et al.  New Regularities in the Spectra of the Alkaline Earths , 1925 .

[125]  Paras N. Prasad,et al.  Intense visible and near-infrared upconversion photoluminescence in colloidal LiYF₄:Er³+ nanocrystals under excitation at 1490 nm. , 2011, ACS nano.

[126]  Markus Pollnau,et al.  Near-infrared to visible upconversion in Er 3+ doped Cs 3 Lu 2 Cl 9 , Cs 3 Lu 2 Br 9 , and Cs 3 Y 2 I 9 excited at 1.54 µm , 1999 .

[127]  Leopoldo L. Martin,et al.  Study of the focusing effect of silica microspheres on the upconversion of Er3+–Yb3+ codoped glass ceramics , 2013 .

[128]  Gavin Conibeer,et al.  Theoretical and experimental evaluation of silicon photonic structures for enhanced erbium up-conversion luminescence , 2013 .

[129]  N. Bloembergen,et al.  Solid State Infrared Quantum Counters , 1959 .

[130]  Craig M. Johnson,et al.  Limiting efficiency of generalized realistic c-Si solar cells coupled to ideal up-converters , 2012 .

[131]  Demetra A. Chengelis,et al.  A strategy to protect and sensitize near-infrared luminescent Nd3+ and Yb3+: organic tropolonate ligands for the sensitization of Ln(3+)-doped NaYF4 nanocrystals. , 2007, Journal of the American Chemical Society.

[132]  K. Krämer,et al.  Broad-band Cr5+-sensitized Er3+ luminescence in YVO4 , 2003 .

[133]  R. A. Buchanan,et al.  Rare Earth Oxysulfide X-Ray Phosphors , 1970 .

[134]  Yongsheng Chen,et al.  The size-dependent upconversion luminescence properties of β-NaYF4: Yb3+,Ho3+ microprisms , 2012 .

[135]  A. Polman,et al.  Field enhancement in metallic subwavelength aperture arrays probed by erbium upconversion luminescence. , 2009, Optics express.

[136]  Timothy W. Schmidt,et al.  Highly efficient photochemical upconversion in a quasi-solid organogel , 2015 .

[137]  K. Ghiggino,et al.  Photon Upconversion by Triplet-Triplet Annihilation in Ru(bpy)(3)- and DPA-Functionalized Polymers , 2013 .

[138]  Jan Christoph Goldschmidt,et al.  Upconversion quantum yield of Er3+-doped β-NaYF4 and Gd2O2S: The effects of host lattice, Er3+ doping, and excitation spectrum bandwidth , 2014 .

[139]  S. Fischer,et al.  Relation between Excitation Power Density and Er3+ Doping Yielding the Highest Absolute Upconversion Quantum Yield , 2014 .

[140]  A. Meijerink,et al.  Infrared to near-infrared and visible upconversion mechanisms in LiYF4: Yb3+, Ho3+ , 2014 .

[141]  B. Richards,et al.  Measurement procedure for absolute broadband infrared up-conversion photoluminescent quantum yields: correcting for absorption/re-emission. , 2014, The Review of scientific instruments.

[142]  Madhab Pokhrel,et al.  Intense visible and near infrared upconversion in M2O2S: Er (M=Y, Gd, La) phosphor under 1550 nm excitation , 2012 .

[143]  A. Shalav,et al.  Application of NaYF 4 : Er 3 + up-converting phosphors for enhanced near-infrared silicon solar cell response , 2005 .

[144]  J. Demas,et al.  Measurement of photoluminescence quantum yields. Review , 1971 .

[145]  V. K. Rai,et al.  Visible upconversion and infrared luminescence investigations of Al2O3 powders doped with Er3+, Yb3+ and Zn2+ ions , 2009 .

[146]  Bryce S. Richards,et al.  Upconverter Silicon Solar Cell Devices for Efficient Utilization of Sub-Band-Gap Photons Under Concentrated Solar Radiation , 2014, IEEE Journal of Photovoltaics.

[147]  F. Lahoz Ho(3+)-doped nanophase glass ceramics for efficiency enhancement in silicon solar cells. , 2008, Optics letters.

[148]  Stefan Andersson-Engels,et al.  High-resolution fluorescence diffuse optical tomography developed with nonlinear upconverting nanoparticles. , 2012, ACS nano.

[149]  D. L. Dexter A Theory of Sensitized Luminescence in Solids , 1953 .

[150]  Joseph P. Dinnocenzo,et al.  Low-power green-to-blue and blue-to-UV upconversion in rigid polymer films , 2009 .

[151]  Alberto Salleo,et al.  Plasmon-Enhanced Upconversion. , 2014, The journal of physical chemistry letters.

[152]  S. Fischer,et al.  Highly Efficient IR to NIR Upconversion in Gd2O2S: Er3+ for Photovoltaic Applications , 2013 .

[153]  F. Ortica,et al.  New molecular pairs for low power non-coherent triplet–triplet annihilation based upconversion: dependence on the triplet energies of sensitizer and emitter , 2013 .

[154]  S. Glunz,et al.  Neodymium‐doped fluorochlorozirconate glasses as an upconversion model system for high efficiency solar cells , 2008 .

[155]  Tymish Y. Ohulchanskyy,et al.  Use of colloidal upconversion nanocrystals for energy relay solar cell light harvesting in the near-infrared region , 2012 .

[156]  J. Luther,et al.  Absolute Photoluminescence Quantum Yields of IR-26 Dye, PbS, and PbSe Quantum Dots , 2010 .

[157]  Oliver Benson,et al.  Plasmon-enhanced upconversion in single NaYF4:Yb3+/Er3+ codoped nanocrystals. , 2010, Nano letters.

[158]  Cunhai Dong,et al.  Ln(3+)-doped nanoparticles for upconversion and magnetic resonance imaging: some critical notes on recent progress and some aspects to be considered. , 2012, Nanoscale.

[159]  Taeghwan Hyeon,et al.  Upconverting nanoparticles: a versatile platform for wide-field two-photon microscopy and multi-modal in vivo imaging. , 2015, Chemical Society reviews.

[160]  Jianzhang Zhao,et al.  Visible light-harvesting trans bis(alkylphosphine) platinum(II)-alkynyl complexes showing long-lived triplet excited states as triplet photosensitizers for triplet-triplet annihilation upconversion. , 2013, Dalton transactions.

[161]  Mauro Tonelli,et al.  Record efficient upconverter solar cell devices with optimized bifacial silicon solar cells and monocrystalline BaY2F8:30% Er3+ upconverter , 2015 .

[162]  G. Wegner,et al.  Up-conversion fluorescence: noncoherent excitation by sunlight. , 2006, Physical review letters.

[163]  J. M. Gardner,et al.  Photon Upconversion on Dye-Sensitized Nanostructured ZrO2 Films , 2011 .

[164]  P. Ramasamy,et al.  Combined plasmonic and upconversion rear reflectors for efficient dye-sensitized solar cells. , 2014, Chemical communications.

[165]  Jennifer A. Dionne,et al.  Narrow-bandwidth solar upconversion: Case studies of existing systems and generalized fundamental limits , 2012, 1212.6477.

[166]  T. Behnke,et al.  Critical review of the determination of photoluminescence quantum yields of luminescent reporters , 2014, Analytical and Bioanalytical Chemistry.

[167]  Shaomin Ji,et al.  Ruthenium(II) polyimine complexes with a long-lived 3IL excited state or a 3MLCT/3 IL equilibrium: efficient triplet sensitizers for low-power upconversion. , 2011, Angewandte Chemie.

[168]  S. Fischer,et al.  Increased upconversion quantum yield in photonic structures due to local field enhancement and modification of the local density of states--a simulation-based analysis. , 2013, Optics express.

[169]  V. Badescu An extended model for upconversion in solar cells , 2008 .

[170]  Maxwell J. Crossley,et al.  Photochemical Upconversion Enhanced Solar Cells: Effect of a Back Reflector , 2012 .

[171]  M. Haase,et al.  Highly Efficient Multicolour Upconversion Emission in Transparent Colloids of Lanthanide‐Doped NaYF4 Nanocrystals , 2004 .

[172]  En Ma,et al.  Synthesis and Characterization of Highly Efficient Near-Infrared Upconversion Sc3+/Er3+/Yb3+ Tridoped NaYF4 , 2010 .