New trends in organic materials based solar cells

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1 ew trends in organic materials based solar cells Prof. Frank üesch Funktionspolymere Empa 8600 Dübendorf

2 Semiconductors silicon germanium In organic single crystals and amophous powders Cu Se CI(G)S

3 Silicon crystal structure energy band gap 1eV electron energy levels of a Si atom energy bands of a Si crystal

4 Molecular crystal Energie band gap 1eV merocyanine dye energy levels of a molecule energy «bands» of a molecular crystal

5 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

6 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)

7 Development of organic solar cells 10 8 amorphous silicon Mitsubishi Chemical Heliatek Heliatek Solarmer Solarmer Konarka Heliatek Solarmer PCE (%) 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

8 Polymer bulk-heterojunction concept Solarmer

9 Small molecule multilayer architecture Heliatek

10 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)

11 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 Cl - + H Cl H 4 [C 2 H 5 OH] Yield: 86% + ClO - Cl 4 + Cl n n ClO ClO 4 - T. Geiger et al., Macromol. Rapid Commun. 2008, 29, Cl 8

12 Polymeric cyanine dye films ClO 4 silicon 1.5 absorbance solar emission Irradiation density (W/m 2 nm) wavelength (nm) 12

13 Ultrathin absorber layers e ClO 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, Hany R. et al., Prog. Photovoltaics 2011, 19,

14 Ionic dyes for organic solar cells Empa licensed

15 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, % V + 4V1min + 4V3min + 4V8min + 4V13min + 4V20min + 4V25min after5min after15min after30min after45min after75min after105min after125min after175min after225min positive biasing Wavelength, nm H. Benmansour, F. A. Castro, M. agel, J. Heier, R. Hany, F. üesch, Chimia, 2007, 61 (12) 787.

16 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.

17 Lifetime of organic solar cells M. Jorgensen et al., Adv. Mater. 2012, 24, Suren A. Gevorgyan et al., Solar Energy Materials & SolarCells, 95 (2011) Ma terials Sci ence & Technolog y

18 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

19 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,

20 ew developments in dye sensitized solar cells 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

21 «Transparent" dye sensitized solar cells photovoltaic windows flexible, transparent PV active films tandem solar cells absorption of squaraine dyes UV Vis IR 1.6 AM modeling synthesis LUMO HOMO Spectral Irradiance / Wm -2 nm Dyes in solution A / a.u Synthesis solar cell fabrication wavelenght / nm demonstrators O - O HO O + visible red IR T. Geiger et al., Adv. Funct. Mater. 2009, 19,

22 Verkehrshaus der Schweiz (2012)

23 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:

24 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)

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26 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)