1 Sanggyu Yim Kookmin University Molecular Thin Films and Small-Molecule Organic Photovoltaics 진공학회 2011 하계학술대회 Tutorial.

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1 1 Sanggyu Yim Kookmin University Molecular Thin Films and Small-Molecule Organic Photovoltaics 진공학회 2011 하계학술대회 Tutorial

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3 3 Organic Semiconductors OLED Nano(Bio) Sensor Solar Cell OTFT Flexible Display Organic? vs. Inorganic?

4 4 진공학회 2011 하계학술대회 Tutorial Humanity’s Top 10 Problems for Next 50 year 1.Energy 2.Water 3.Food 4.Environment 5.Poverty 6.Terrorism & War 7.Disease 8.Education 9.Democracy 10.Population Why Solar Cells? 150,000,000 km 1.5 x 10 22 J/day

5 5 진공학회 2011 하계학술대회 Tutorial Classification of Solar Cells

6 6 진공학회 2011 하계학술대회 Tutorial Why Organic Thin-Film Solar Cells? 1. Low Cost Room temp. processing Cheap materials Mass production : roll-to-roll, ink-jet printing, etc. 2. Flexibility Flexible substrate Unbreakable devices 3. Variety of Property Various materials : fine tuning available Unlimited possibility

7 7 진공학회 2011 하계학술대회 Tutorial Solar Cell Efficiencies

8 8 진공학회 2011 하계학술대회 Tutorial Energy Conversion Process of Si Solar Cell

9 9 진공학회 2011 하계학술대회 Tutorial Small Molecule Organic Photovoltaic (OPV) Cell Basic Device Structure Energy Conversion Process (Exciton Blocking Layer)

10 10 진공학회 2011 하계학술대회 Tutorial Materials C 60 PTCDA Phthalocyanine (Pc) SubPc Electron Donor Materials Electron Acceptor Materials PTCBI EBL Materials BCPBPhen

11 11 진공학회 2011 하계학술대회 Tutorial History of Small Molecule OPV Cells C.W. Tang, Appl. Phys. Lett, 48(1986)183 ITO/CuPc(30nm)/PV(50nm)/Ag  p = 0.95% @ AM2.0  First Organic Solar Cell  Bulk Heterojunction  Tandem Cell ITO/CuPc(15nm)/CuPc:C60 (1:1,10nm)/C60(35nm)/BCP/Ag  p = 5.0% @ AM1.5  p = 5.7% @ AM1.5 J. Xue et al, Appl. Phys. Lett, 85 (2004)5757 J. Xue et al, Adv. Mater., 17(2005)66

12 12 진공학회 2011 하계학술대회 Tutorial Timeline of Power Conversion Efficiency (PCE) of Small Molecule OPV cells B. P. Rand et al, Prog. Photovolt.: Res. Appl., 15 (2007) 659.

13 13 진공학회 2011 하계학술대회 Tutorial Efficiency Measurement  EQE ( ) = A f ( ) ·  CG ( ) ·  CC (  )  IQE ( ) =  CG ( ) ·  CC (  ) J max · V max J SC · V OC · FF  PCE (%) = --------- X100 = ----------- X100 P in ( ) A · I AM1.5G

14 14 진공학회 2011 하계학술대회 Tutorial Org. vs. Inorg. : Fundamental Difference S. E. Gledhill et al, J. Mater. Res., 20 (2005) 3167

15 15 진공학회 2011 하계학술대회 Tutorial Excitons (a) Frenkel, (b) Wannier and (c) Charge-Transfer exciton

16 16 진공학회 2011 하계학술대회 Tutorial Energy Level Diagram of Organic Heterojunction between a Donor(D) and an Acceptor(A) Layer B. P. Rand et al, Prog. Photovolt.: Res. Appl., 15 (2007) 659. 0 vacuum level ITO ITO/PEDOT:PSS CuPc C 60 BCP Al 4.8 5.3 3.5 5.2 4.5 6.2 3.5 7.0 4.2 Energy / eV

17 17 진공학회 2011 하계학술대회 Tutorial HOMO-LUMO Energy Levels of Representative Organic Materials

18 18 진공학회 2011 하계학술대회 Tutorial Possible Reasons for Low PCE of Small Molecule OPV cells 1. Narrow absorption band 2. Low charge carrier mobility 3. Lack of ways of controlling morphology  Material selection  Material growth technique  Device architecture

19 19 진공학회 2011 하계학술대회 Tutorial Device Fabrication

20 20 진공학회 2011 하계학술대회 Tutorial Schematic of Device Fabrication System

21 21 진공학회 2011 하계학술대회 Tutorial Transparent Electrode & HTL  Indium tin oxide (ITO)  Hole transport layer (HTL)  PEDOT:PSS  Spin coating  E-beam evaporation  Thickness ~ 147 nm  Sheet resistance ~18Ω/cm 2

22 22 진공학회 2011 하계학술대회 Tutorial Purification of Materials S. R. Forrest, Chem. Rev., 97 (1997) 1793.  Temperature gradient sublimation

23 23 진공학회 2011 하계학술대회 Tutorial Organic Molecular Beam Deposition (OMBD) Substrate Solid source Knudsen Effusion Cell

24 24 진공학회 2011 하계학술대회 Tutorial Film Thickness Estimation  Quartz crystal microbalance (QCM)  Ex-situ calibrations SEMAFMCalibration

25 25 진공학회 2011 하계학술대회 Tutorial Molecular Thin Film Growth Techniques 1. Organic molecular beam deposition (OMBD) 2. Vacuum thermal evaporation (VTE) 3. Organic vapor phase deposition (OVPD) F. Yang et al, Nat. Mater., 4 (2005) 37.

26 26 진공학회 2011 하계학술대회 Tutorial EBL, Metal Electrode & Encapsulation  Exciton blocking layer (EBL)  Metal electrode  Al, Ag  Thermal evaporation  BCP  OMBD  Encapsulation  UV-curable polymer  in glove box

27 27 진공학회 2011 하계학술대회 Tutorial Challenge for Improving PCE  Materials selection SubPcZnPcCuPc J sc 5.277.764.54 V oc 0.810.410.45 FF0.490.420.53 PCE2.081.311.09  Electron donor materials AlClPcSnPc ZnPc CuPc SubPc D. Y. Kim et al, Sol. Energy Mater. Sol. Cells, 93 (2009) 1452.

28 28 진공학회 2011 하계학술대회 Tutorial Challenge for Improving PCE  Materials selection  Electron acceptor materials F16CuPcDBP J. L. Yang et al, Org. Electron., 11 (2010) 1399. D. Fujishima et al, Sol. Energy Mater. Sol. Cells, 93 (2009) 1029. C 70 S. Pfuetzner et al, Appl. Phys. Lett., 94 (2009) 223307.

29 29 진공학회 2011 하계학술대회 Tutorial Challenge for Improving PCE  Tandem structure J. Xue et al, Appl.Phys. Lett., 85 (2004) 5757. M. Riede et al, Nanotechnology., 19 (2008) 424001. Narrow absorption band

30 30 진공학회 2011 하계학술대회 Tutorial Challenge for Improving PCE  Tandem structure J. Drechsel et al, Appl.Phys. Lett., 86 (2005) 244102.

31 31 진공학회 2011 하계학술대회 Tutorial Challenge for Improving PCE  Bulk heterojunction (BHJ)  OVPD (organic vapor phase deposition) F. Yang et al Nature Mater., 4 (2005) 37.

32 32 진공학회 2011 하계학술대회 Tutorial Challenge for Improving PCE  Bulk heterojunction (BHJ)  Gradient cell MixedGradient J sc 5.065.00 V oc 0.470.50 FF0.440.54 PCE1.051.36

33 33 진공학회 2011 하계학술대회 Tutorial Challenge for Improving PCE  Bulk heterojunction (BHJ) B, P. Rand et al, J. Appl.Phys., 98 (2005) 124902. Low hole mobility

34 34 진공학회 2011 하계학술대회 Tutorial Challenge for Improving PCE  Templating effect P. Sullivan et al, Appl.Phys. Lett., 91 (2007) 233114.

35 35 진공학회 2011 하계학술대회 Tutorial Challenge for Improving PCE  Substrate temperature 30ºC90ºC150ºC J sc 7.68.810.0 V oc 0.560.520.50 FF0.380.450.49 PCE1.612.052.44 M. Deisenroth et al, J. Appl.Phys., 101 (2008)

36 36 진공학회 2011 하계학술대회 Tutorial Theoretical Maximum of PCE M. Riede et al, Nanotechnology., 19 (2008) 424001.

37 37 진공학회 2011 하계학술대회 Tutorial Long Term Stability  Need to standardize measurements for OSCs.  Only few data on OSCs based on small molecules R. Franke et al, Sol. Energy Mater. Sol. Cells, 92 (2008) 732. ZnPc:C 60 tandem solar cellpentacene:C 60 solar cell W. J. Potscavage et al, Appl. Phys. Lett., 90 (2007) 253511.

38 38 진공학회 2011 하계학술대회 Tutorial Current Challenge  Surface nanostructuring – solvent vapor treatment

39 39 진공학회 2011 하계학술대회 Tutorial Current Challenge  Surface nanostructuring – NIL (nanoimprint lithography)

40 40 진공학회 2011 하계학술대회 Tutorial Current Challenge  Organic photonic crystal (PC) layer

41 41 진공학회 2011 하계학술대회 Tutorial Summary  There has been large progress in small-molecular weight based organic solar cells.  Yet, the power conversion efficiency is relatively low, but various efforts to improve the device performance have been made.  To improve the device performance, exploit of new materials having broad absorption band and high charge carrier mobility, and optimization of interfacial structure are needed.  Investigation on the better device architecture such as high- efficiency tandem cells and optimization of open-circuit voltage and short-circuit current are also necessary.