ew trends in organic materials based solar cells Prof. Frank üesch Funktionspolymere Empa 8600 Dübendorf
Semiconductors silicon germanium In organic single crystals and amophous powders Cu Se CI(G)S
Silicon crystal structure energy band gap 1eV electron energy levels of a Si atom energy bands of a Si crystal
Molecular crystal Energie band gap 1eV merocyanine dye energy levels of a molecule energy «bands» of a molecular crystal
Properties of organic semiconductors Organic semiconductors are soft and ductile Organic semiconductors have narrow absorption bands Organic semiconductors, in particular dyes have high absorption coefficients exceeding those of inorganic semiconductors by 100 times The properties of organic semiconductors can be tuned almost arbitrarily (absorption, solubility, crystallinity) Organic semiconductors are normally insulators. Conductivity can be achieved by chemical/physical doping. Organic semiconductors have a low charge carrier mobility, which is smaller by 3 to 6 orders of magnitude compared to inorganic semiconductors 5
Organic donor-acceptor junction Hans Meier, Bamberg 1960 acceptor material donor material zur Elektrode interface conduction band V acceptor material to the electrode valence band donor material Q. Tang, organic solar cell with 1% PCE (1986)
Development of organic solar cells 10 8 amorphous silicon Mitsubishi Chemical Heliatek Heliatek Solarmer Solarmer Konarka Heliatek Solarmer PCE (%) 6 4 2 Kodak Univ. Princeton Univ. Santa Barbara Univ. Princeton Univ. Los Angeles Univ. Groningen Univ. Linz Cavendish Laboratory Siemens Univ. Linz Konarka Heliatek Univ. Santa Barbara Plextronix REL, Konarka, Univ. Linz small molecules (dyes) polymers 0 1986 1998 2000 2002 2004 2006 2008 2010 2012 7
Polymer bulk-heterojunction concept Solarmer
Small molecule multilayer architecture Heliatek
Photographic dyes as organic semiconductors for solar cells Extremely strong absorption arrow absorption bands from the UV to the IR Synthesis is known (upscaling possible) Cost efficient (about 1% of polymer materials) Well soluble (compatible with roll to roll processing)
Synthesis of cyanine polymers H 2 H 2 O H H 1) ao 2 / HCl H 2 H 2 2) SnCl 2 / HCl H H Yield: 85% Yield: 52% 1 2 H H 2 + O 1) O S O - ClO + 4 ClO - 4 [CH 3 COOH] 2) 4 aclo 3 4 Yield: 72% Yield: 68% 4 O O O [Pyridine] Yield: 91% ClO 4-5 P1 n n + ClO 4 - ClO 4-7 + Cl - + H Cl H 4 [C 2 H 5 OH] Yield: 86% + ClO - Cl 4 + Cl n n ClO 4-6 + ClO 4 - T. Geiger et al., Macromol. Rapid Commun. 2008, 29, 651 658 Cl 8
Polymeric cyanine dye films ClO 4 silicon 1.5 absorbance solar emission 1.0 0.5 Irradiation density (W/m 2 nm) 400 600 800 1000 1200 wavelength (nm) 12
Ultrathin absorber layers e ClO 4 - + CyC C 60 photon + Pol transp. electrode electron donor ~20 nm electron acceptor aluminium pristine - Pol doped 0.02 mol/mol OBF 4 absorption Bilayer device Fan B., Castro F. A., Heier J., Hany R., üesch F., Org. Electron., 11, 2010, 583-588 Hany R. et al., Prog. Photovoltaics 2011, 19, 851-857
Ionic dyes for organic solar cells Empa licensed
Effect of counterions in bilayer cyanine devices I Al ITO ITO The device is biased for a certain time, then IPCE is taken (at V=0) Cy-ClO 4 (70 nm) MEH-PPV (30 nm) PEDOT:PSS (90 nm) IPCE, % 10 8 6 4 0V + 4V1min + 4V3min + 4V8min + 4V13min + 4V20min + 4V25min after5min after15min after30min after45min after75min after105min after125min after175min after225min positive biasing 2 400 500 600 700 800 15 0 Wavelength, nm H. Benmansour, F. A. Castro, M. agel, J. Heier, R. Hany, F. üesch, Chimia, 2007, 61 (12) 787.
Formation of ionic junctions no biasing positive biasing PEDOT: PSS Al PEDOT: PSS Al MEH-PPV Cy-ClO 4 MEH-PPV Cy-ClO 4 only reductive charge transfer observed mainly oxidative charge transfer H. Benmansour, F. A. Castro, M. agel, J. Heier, R. Hany, F. üesch, Chimia, 2007, 61 (12) 787.
Lifetime of organic solar cells M. Jorgensen et al., Adv. Mater. 2012, 24, 580 612 Suren A. Gevorgyan et al., Solar Energy Materials & SolarCells, 95 (2011)1398 1416. Ma terials Sci ence & Technolog y
R2R processing Low costs by high throughput (small depreciation) -> R2R fabrication of substrates -> R2R of the photoactive layers -> R2R production of encapsulation layers Flexible substrates are needed -> cheap barrier layers -> cost efficient, flexible and transparent electrode -> integrated bus bars first pruducts: charging bag solar cell from Konarka
Development of fabric electrodes (CTI project) W. Kylberg, F. A. de Castro, P. Chabrecek, U. Sonderegger, B. Tsu-Te Chu, F. üesch, R. Hany, Advanced Materials 2011, 23, 1015-1019 19
ew developments in dye sensitized solar cells 24.02.12 - The Interdisciplinary Committee of the World Cultural Council has selected Prof. Michael Grätzel as the winner of the ALBERT EISTEI World Award of Science 2012
«Transparent" dye sensitized solar cells photovoltaic windows flexible, transparent PV active films tandem solar cells absorption of squaraine dyes 1.8 1.4 UV Vis IR 1.6 AM1.5 1.2 1.4 modeling synthesis LUMO HOMO Spectral Irradiance / Wm -2 nm -1 1.2 1.0 0.8 0.6 0.4 0.2 Dyes in solution 1.0 0.8 0.6 0.4 A / a.u. 0.0 0.2 Synthesis solar cell fabrication -0.2 0.0 300 400 500 600 700 800 900 1000 wavelenght / nm demonstrators O - O HO O + visible red IR T. Geiger et al., Adv. Funct. Mater. 2009, 19, 2720 2727
Verkehrshaus der Schweiz (2012) http://youtu.be/ukljkqw7zrs
ovel redox mediators 12.3% using porphyrin dye Aswani Yella et al., SCIECE VOL 334 (4), p. 629, 2011 Jun-Ho Yum et al., nature communications 3:631 2011
ew electrolyte systems liquid small vapor pressure good ion diffusion I - 1 sun 0.3 sun 0.1 sun Irradiation with 0.8 sun/ 60 C Stability tests at 60 o C conducted by Toyota Research(Asin) R. Harikisun, H. Desilvestro / Solar Energy 85 (2011) 1179 1188
Acknowldgement Empa (Dübendorf) Roland Hany Jakob Heier Hui Zhang Gaëtan Wicht Daniel Rentsch Matthias agel Hadjar Benmansour (left) Fernando Castro (left) William Kylberg (left) Fan Bin (left) Solaronix Tobi Meyer Andreas Meyer EPFL Jacques. E. Moser Jelissa de Jonghe Michael Grätzel Yum Ho Thomas Geiger Iulia Shcherbakova Fahimeh afezarefi Simon Kuster (left) Simone Hochleitner (left)