organic solar cells michele.maggini@unipd.it Humanitys core - PowerPoint PPT Presentation

organic solar cells michele.maggini@unipd.it

Humanity’s core problems in 2050 • Energy • Water • Food • Environment • Poverty • War • Disease • Education 2009 6.8 billion people • Democracy 2050 8-10 billion people • Population

happy life

third generation solar cells polymer/fullerene solar cells (PFSC) polymer/nanocrystal solar cells (PNSC) photoelectrochemical cells (DSSC) DSSC PFSC PNSC

efficiency 7.6% , claimed by Solarmer Energy, Inc. on Dec. 2, 2009 (Source: NREL) 5

n polymer inks n S S S

semiconducting polymers A. Heeger, A. McDiarmid, H. Shirakawa

polymer-C 60 blends light-absorbing semiconducting polymer (MEH-PPV) Transfer times in the range of 100 fs e – Quantum efficiency approaching unity Brabec, Zerza, Cerullo, De Silvestri, Luzzati, Hummelen, Sariciftci Chem. Phys. Lett. 2001 340 , 232 N.S. Sariciftci, L. Smilowitz, A.J. Heeger, F. Wudl Science 258 , 1474 (1992) G. Yu, J. Gao, J.C. Hummelen, F. Wudl, A.J. Heeger Science 270 , 1789 (1995)

synthesis of PCBM PCBM J. C. Hummelen et al. JOC 1995 , 60 , 532 G. Dennler, C.J. Brabec Adv. Mater. 2009 , 21 , 1323

molecular bulk-heterojunction a material with charge-separating junctions everywhere at nanometer length scale donor absorbs light generating an exciton that must diffuse to the D/A interface to split. Electrons travel to the back electrode. R.H. Friend et al. Nature 1995 , 376 , 498 Holes travel to the front electrode . A.J. Heeger et al. Science 1995 , 270 , 1789 J. Roncali Acc. Chem. Res. 2009 , 42 , 1719

bulk-heterojunction - + Aluminum LiF Active layer ITO PEDOT PSS Glass/plastic light S.E. Shaheen et al. Appl. Phys. Lett. 2001, 78, 841 (  eff = 2.5% ) C.J. Brabec et al. Appl. Phys. Lett. 2002, 80, 1288 (  eff = 3.3% ) G. Li et al. Nat. Mater. 2005, 4, 864 (  eff = 4.4%) W. Ma et al. Adv. Funct. Mater. 2005, 15, 1617 (  eff = 5% ) J. Y. Kim et al., Science 2007, 317, 222 (  eff = 6.5% , multijunction) S. H. Park et al. Nature Photonics 2009, 3, 297 (  eff = 6.1% ) H.-Y. Chen et al. Nature Photonics 2009, 3, 649 (  eff = 6.77% )

motivation The promise of organic photovoltaics is an ultra- low-cost technology with solar cells that could be fabricated in a continuous processing and implemented on flexible substrates. The actual challenge of OPV is to increase the efficiency and reliability Would a low-cost, lower performance OPV technology be a sustainable solution?

cost Balance of system @ 70 €/m 2 1000 h of sun a year Source: G. Dennler et al. Adv. Mater. 2009 , 21 , 1323

cost Source: www.energy.eu

Source: N. Camaioni, Bologna

Improve ordering Enhance mobility Extend the absorption

lock the nanoscale morphology ▲ after cooling to room T after cooling to room T and ◊ a further cycle from 22 to 50 °C 0,60 1 -2 ) 0,55 Voc (V) j sc (mA cm 0,50 0,1 0,45 0,40 3 0,35  (%) 2 FF P in : 20 mW cm -2 . Room T 0,30 1  (%) PHT/ 3 j sc × 10 4 V oc (V) FF 0,25 0 20 30 40 50 60 70 20 30 40 50 60 70 (A cm -2 ) Temperature (°C) Temperature (°C) 3:2 8.6 0.76 0.28 0.82 PTH/ 3 , 3:2 WR, 1 °C/min 2.50 2.5 0.63 0.35 before thermal treatment 5.6 0.68 0.19 0.32 3:1 after thermal treatment 8.2 0.59 0.31 0.68 J. Mater. Chem. 2002 , 12 , 2065; Adv. Mater. 2002 , 14 , 1735 (N. Camaioni – ISOF-CNR)

absorption P3HT P3HT: band-gap too large; missing more than half of solar spectrum Opportunity for improvement (factor of ca. 2) using polymer with smaller band-gap

bandgap engineering

low bandgap polymers R. Po, M. Maggini, N. Camaioni J. Phys. Chem. C 2010 , 114 , 695

(holes in the polymer  band, electrons in PCBM LUMO) j sc : short-circuit current density J SC V OC V oc : open-circuit voltage  = FF FF : fill factor P 0  : photovoltaic conversion efficiency Source: A. Heeger – Linz 2008

polymer-fullerene solar cells present status: 4-6% efficiency with P3HT or PCDTBT New device architectures (optical spacer) Opportunity: 25%-50% improvement New polymers for matching the solar spectrum ( energy gap engineering ) Opportunity:  2 improvement Better charge percolation and collection ( optimize morphology ) Opportunity: 25% improvement Increase open circuit voltage ( deeper HOMO for the polymer or raise the fullerene LUMO ) Opportunity: 50% improvement Multijunction (tandem) solar cells Opportunity: 50% improvement Achieve all the advances in the same cell: 1.25  2  1.25  1.5  1.5 = 7 Source: A. Heeger Linz 2008

the dream

acknowledgements acknowledgements E. Menna T. Carofiglio A.Venturi E. Rossi FIRB RBNE033KMA S. Silvestrini Fabbrica Italiana Sintetici SpA P. Maity MISCHA