Design and Synthesis of Conjugated Polymers towards Organic Solar by byk79441

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									    Design and Synthesis of
 Conjugated Polymers towards
Organic Photovoltaic Applications
 Ying Jiang, Toshihiro Okamoto, Zhenan Bao
           GCEP conference 2008



                                             1
   Organic Photovoltaics (OPV)

• Solar energy – abundant and renewable
• Organic active material
  – Low cost, high-throughput production
  – Mountable on flexible substrates
  – Flexibility for chemical engineering
  – Need material innovation to improve efficiency



                                                     2
    Photovoltaic energy conversion
E                                        1. Light absorption and
                                            exciton formation.
             LUMO    -
                           LUMO          2. Charge dissociation
                hν                          at heterojunction.

             HOMO                        3. Charge transport
                                            and collection at
                     +    HOMO
                                            electrodes.

    Anode       Donor    Acceptor   Cathode



            ηTOTAL = ηABS × ηDISS × ηCOLL
                                                            3
 Organic Heterojunction Solar Cells




Double-layer                    Bulk               Ordered bulk
heterojunction             heterojunction          heterojunction
     Type of Device        Record efficiency (%)    Design guidelines:
   Single-junction BHJ              5.5             1. Low bandgap
       Tandem BHJ                   6.3             2. High mobility
                                                    3. High absorptivity
    Inorganic solar cell           > 30
                                                    4. Good processibility
     Target for OPV               15 – 20                               4
          Promising classes of materials to-date
                                                                             Fluorene
         Material                     PPVs                PTs
                                                                            copolymers


      Structure

 HOMO-LUMO gap (eV)                  2.0 – 2.2       ~1.9 – 2.2[5]                1.6

   Mobility (cm2/V s)                ~10-7[3]          ~0.01-0.1             ~10-6 – 10-4

                     ISC
                                        5.4               12.5                    8.9
                  (mA/cm2)
    Best
performance         VOC (V)            0.80               0.65                   0.59
  reported             FF              0.56               0.65                   0.42
                    PCE (%)            3.0[1]            4.6[2]                  2.2[4]


    1. Chem. Commun., 2003, 2116–2118; 2. Solar Energy Materials & Solar Cells 91 (2007)
    1187–1193; 3. J. Phys. Chem. B 2004, 108, 5235-5242; 4. Adv Mater 2006, 18, 2169-2173;   5
    5. Adv. Funct. Mater. 2007, 17, 1071-1078
           Our approach:
acene-containing conjugated polymers




                                       6
            Why choose acenes?
Pentacene
  – Optical band gap 1.77 eV in thin film, mobility >1 cm2/Vs
  – Further reduction of band gap by extending conjugation



                             -0.24 eV
                              0.146 eV


LUMO

          -2.38 eV
          −1.626 eV
                                                   −1.772 eV
                                                   -2.52 eV

                             -0.02 eV
                             0.032 eV
HOMO



          -4.59 eV
           −7.612 eV                                −7.644 eV
                                                   -4.61 eV     7
    TIPSEP-diethynylbenzene copolymer




                                  HOMO      Eg
  Polymer         Mn×103   PDI
                                   (eV)    (eV)
                                                            Films                ODCB
     1a            11      2.21   5.28     1.68
     1b            24      2.41   5.24     1.76
  TIPSEP            -       -     5.20     1.86

                                                                                 1a
                                                                                 1b
                    Modest solubility in
                    common organic
                    solvents (< 5 mg/ml)
Dark Green Film
 (Polymer 1b)                                    Okamoto et al; JACS 2007, 129, 34, 10308
                                                                                      8
   Regioregular TIPSEP-
diethynylbenzene copolymer




      Films       CHCl3


                                                      HOMO     Eg
                          Polymer   Mn    103   PDI
                                                       (eV)   (eV)
                             2           15     2.6   5.23    1.74
                             3           13     1.6   5.14    1.67




                                                               9
   Anthradithiophene-containing copolymers




                                 HOMO          Eg
Polymer     Mn    103   PDI
                                  (eV)        (eV)
   6             28     1.2      5.22[1]      1.82
  5[2]           58     2.3      5.22[3]      1.98

[1] Film oxidation onset measured by PES             6 (oDCB)
[2] Okamoto et al; Macromolecules
                                                     6 (film)
[3] Solution oxidation onset measured by CV                     10
(x105cm-1)
                                                                  P3HT


                                                                    2,9-TP-DDT




                                                                    2,9-TP-EHCPDT




                                        Absorption
               Polymer
                                      Coefficient (cm-1)
                                                                    TIPSEAdT-CPDT
               P3HT                    307,000 (557nm)
               2,9-TP-DDT              27,000 (691nm)
               2,9-TP-EHCPDT           50,000 (711nm)
               TIPSEAdT-CPDT           202,000 (538nm)
                                                                            11
             6 shows too promising preliminary TFT performance.
   Summary and future work
• Synthesized TIPSEP- and TIPSEdTA-
  containing copolymers with promising
  properties (Eg between 1.6 – 2.0 eV)

• Will continue to build and characterize
  acene-containing copolymers and assess
  their performance


                                         12
        Acknowledgements
       Synthesis                    Solar Cell Device
Michelle Senatore (UG)               Dr. Alex Myer
     Fei Qu (UG)
                                      Jack Parmer
  Transistor Device             Professor Mike McGehee
  Dr. Hector Becerril


            The Air Force Office of Scientific Research, AFRL




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