OPV Tandems with CNTS: Why Are Parallel Connections Better Than Series Connections

Conference paper
Part of the NATO Science for Peace and Security Series B: Physics and Biophysics book series (NAPSB)


The efficiency of organic photovoltaic cells can be increased in tandem OPV structures with complementary light absorption in top and bottom sub-cells. We demonstrate that strong transparent CNT sheets can be used as an effective charge collector interlayer in OPV and hybrid tandem solar cells. Most importantly we show that CNT sheets can be used in monolithic parallel tandems (P-T) as common a electrode interconnect between top and bottom sub-cells. For achieving good performance one of these subcells in P-T should be of inverted type. We achieved good inversion in OPV, using ZnO nanoparticles, which act as hole barrier layers and invert a typical anode ITO into a cathode. With this inverted bottom cell the efficiency of P-T is significantly improved, as compared to our earlier results. We briefly discuss the modeling analysis of OPV tandems and derive an optimal set of parameters, for highest efficiency P-T. Our simple model shows that for tandems with unbalanced photocurrents but similar open circuit voltages the optimized P-T architecture is always better than conventional series tandem (S-T) geometry. Indeed the experimental comparison of P-T with S-T for hybrids of OPV and dye sensitized solar cells demonstrate the imporved efficiency of the former.


High Occupied Molecular Orbital Open Circuit Voltage Short Circuit Current Parallel Connection Bulk Heterojunction 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The authors gratefully acknowledge funding from DOE STTR grant #DE-FG02-10ER86425 on “Parallel Tandem Organic Solar Cells with Carbon Nanotube Sheet Interlayers”.


  1. 1.
    Tanaka S, Mielczarek K, Ovalle-Robles R, Wang B, Hsu D, Zakhidov AA (2009) Monolithic parallel tandem organic photovoltaic cell with transparent carbon nanotube interlayer. Appl Phys Lett 94(11):113506. doi:10.1063/1.3095594. Google Scholar
  2. 2.
    Zakhidov A, Papadimitratos A, Mielczarek K (2010) Multijunction monolithic solar cells with transparent interlayers for inverted parallel-connection.
  3. 3.
    GmbH H (2010) Heliatek achieves new world record for organic solar cells with certified 9.8 cell efficiency.
  4. 4.
    Yang Y, Mielczarek K, Aryal M, Zakhidov A, Hu W, ACS Nano 0(0), null (0). doi:10.1021/nn3001388.
  5. 5.
    Mielczarek K, Zakhidov A, Tanaka S (2012) Organic photovoltaics with carbon nanotube charge collectors: inverted structures for parallel tandems. Jpn J Electron Mater 12:47Google Scholar
  6. 6.
    Kim YH, Sachse C, Zakhidov AA, Meiss J, Zakhidov AA, Müller-Meskamp L, Leo K (2012) Combined alternative electrodes for semi-transparent and ITO-free small molecule organic solar cells. Org Electron 13(11):2422–2428. doi:10.1016/j.orgel.2012.06.034.
  7. 7.
    Kim YH, Müller-Meskamp L, Zakhidov AA, Sachse C, Meiss J, Bikova J, Cook A, Zakhidov AA, Leo K (2012) Semi-transparent small molecule organic solar cells with laminated free-standing carbon nanotube top electrodes. Sol Energ Mater Sol Cells 96(0):244–250. doi:10.1016/j.solmat.2011.10.001.
  8. 8.
    Tang CW (1986) Two-layer organic photovoltaic cell. Appl Phys Lett 48(2):183–185. doi:10.1063/1.96937. Google Scholar
  9. 9.
    Lögdlund M, Greczynski G, Crispin A, Fahlman M, Salaneck W, Kugler T (2001) Conjugated polymer and molecular interfaces. CRC Press, Boca Raton. doi:10.1201/9780203910870.ch4.
  10. 10.
    Coropceanu V, Cornil J, da Silva Filho DA, Olivier Y, Silbey R, Brédas JL (2007) Charge transport in organic semiconductors. Chem Rev 107(4):926–952. doi:10.1021/cr050140x. Google Scholar
  11. 11.
    Lunt RR, Giebink NC, Belak AA, Benziger JB, Forrest SR (2009) Exciton diffusion lengths of organic semiconductor thin films measured by spectrally resolved photoluminescence quenching. J Appl Phys 105(5):053711. doi:10.1063/1.3079797. Google Scholar
  12. 12.
    Shaw PE, Ruseckas A, Samuel IDW (2008) Exciton diffusion measurements in poly(3-hexylthiophene). Adv Mater 20(18):3516–3520. doi:10.1002/adma.200800982. Google Scholar
  13. 13.
    Brédas JL, Cornil J, Heeger AJ (1996) The exciton binding energy in luminescent conjugated polymers. Adv Mater 8(5):447–452. doi:10.1002/adma.19960080517.
  14. 14.
    Alvarado SF, Seidler PF, Lidzey DG, Bradley DDC (1998) Direct determination of the exciton binding energy of conjugated polymers using a scanning tunneling microscope. Phys Rev Lett 81:1082–1085. doi:10.1103/PhysRevLett.81.1082.
  15. 15.
    Campbell IH, Hagler TW, Smith DL, Ferraris JP (1996) Direct measurement of conjugated polymer electronic excitation energies using metal/polymer/metal structures. Phys Rev Lett 76:1900–1903. doi:10.1103/PhysRevLett.76.1900.
  16. 16.
    Halls JJM, Walsh CA, Greenham NC, Marseglia EA, Friend RH, Moratti SC, Holmes AB (1995) Efficient photodiodes from interpenetrating polymer networks. Nature 376(6540):498–500. doi:10.1038/376498a0. Google Scholar
  17. 17.
    Yu G, Gao J, Hummelen JC, Wudl F, Heeger AJ (1995) Polymer photovoltaic cells: enhanced efficiencies via a network of internal donor-acceptor heterojunctions. Science 270(5243):1789–1791. doi:10.1126/science.270.5243.1789. Google Scholar
  18. 18.
    Peumans P, Uchida S, Forrest SR (2003) Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin films. Nature 425(6954):158–162. Google Scholar
  19. 19.
    Hiramoto M, Fujiwara H, Yokoyama M (1991) Three-layered organic solar cell with a photoactive interlayer of codeposited pigments. Appl Phys Lett 58(10):1062–1064. doi:10.1063/1.104423. Google Scholar
  20. 20.
    Yu G, Gao J, Hummelen JC, Wudl F, Heeger AJ (1995) Polymer photovoltaic cells: enhanced efficiencies via a network of internal donor-acceptor heterojunctions. Science 270(5243):1789–1791. doi:10.1126/science.270.5243.1789. Google Scholar
  21. 21.
    Halls JJM, Walsh CA, Greenham NC, Marseglia EA, Friend RH, Moratti SC, Holmes AB (1995) Efficient photodiodes from interpenetrating polymer networks. Nature 376(6540):498–500. Google Scholar
  22. 22.
    Padinger F, Rittberger R, Sariciftci N (2003) Effects of postproduction treatment on plastic solar cells. Adv Funct Mater 13(1):85–88. doi:10.1002/adfm.200390011. Google Scholar
  23. 23.
    Li G, Shrotriya V, Huang J, Yao Y, Moriarty T, Emery K, Yang Y (2005) High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends. Nat Mater 4(11):864–868. Google Scholar
  24. 24.
    Shaheen SE, Brabec CJ, Sariciftci NS, Padinger F, Fromherz T, Hummelen JC (2001) 2.5 % efficient organic plastic solar cells. Appl Phys Lett 78(6):841–843. doi:10.1063/1.1345834. Google Scholar
  25. 25.
    Al-Ibrahim M, Ambacher O, Sensfuss S, Gobsch G (2005) Effects of solvent and annealing on the improved performance of solar cells based on poly(3-hexylthiophene): fullerene. Appl Phys Lett 86(20):201120. doi:10.1063/1.1929875. Google Scholar
  26. 26.
    Peet J, Kim JY, Coates NE, Ma WL, Moses D, Heeger AJ, Bazan GC (2007) Efficiency enhancement in low-bandgap polymer solar cells by processing with alkane dithiols. Nat Mater 6(7):497–500. Google Scholar
  27. 27.
    Chen JT, Hsu CS (2011) Conjugated polymer nanostructures for organic solar cell applications. Polym Chem 2(2):2707–2722. doi:10.1039/C1PY00275A. Google Scholar
  28. 28.
    Weickert J, Dunbar RB, Hesse HC, Wiedemann W, Schmidt-Mende L (2011) Nanostructured organic and hybrid solar cells. Adv Mater 23(16):1810–1828. doi:10.1002/adma.201003991. Google Scholar
  29. 29.
    Wang Q, Moser JE, Grätzel M (2005) Electrochemical impedance spectroscopic analysis of dye-sensitized solar cells. J Phys Chem B 109(31):14945–14953. doi:10.1021/jp052768h. Google Scholar
  30. 30.
    Masahiro H, Minoru S, Masaaki Y (1990) Effect of thin gold interstitial-layer on the photovoltaic properties of tandem organic solar cell. Chem Lett 19(3):327–330Google Scholar
  31. 31.
    Yakimov A, Forrest SR (2002) High photovoltage multiple-heterojunction organic solar cells incorporating interfacial metallic nanoclusters. Appl Phys Lett 80(9):1667–1669. do:10.1063/1.1457531. Google Scholar
  32. 32.
    Guo X, Liu F, Yue W, Xie Z, Geng Y, Wang L (2009) Efficient tandem polymer photovoltaic cells with two subcells in parallel connection. Organ Electron 10(6):1174–1177. doi:10.1016/j.orgel.2009.06.010. Scholar
  33. 33.
    O’Regan B, Grätzel M (1991) A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature 353(6346):737–740. doi:10.1038/353737a0. Google Scholar
  34. 34.
    Barbé CJ, Arendse F, Comte P, Jirousek M, Lenzmann F, Shklover V, Grätzel M (1997) Nanocrystalline titanium oxide electrodes for photovoltaic applications. J Am Ceram Soc 80(12):3157–3171. doi:10.1111/j.1151-2916.1997.tb03245.x. Google Scholar
  35. 35.
    Beek W, Wienk M, Janssen R (2004) Efficient hybrid solar cells from zinc oxide nanoparticles and a conjugated polymer. Adv Mater 16(12):1009–1013. doi:10.1002/adma.200306659. Google Scholar
  36. 36.
    Beek WJE, Wienk MM, Kemerink M, Yang X, Janssen RAJ (2005) Hybrid zinc oxide conjugated polymer bulk heterojunction solar cells. J Phys Chem B 109(19):9505–9516. doi:10.1021/jp050745x. Google Scholar
  37. 37.
    Kumar A, Sista S, Yang Y (2009) Dipole induced anomalous S-shape I-V curves in polymer solar cells. J Appl Phys 105(9):094512. doi:10.1063/1.3117513. Google Scholar
  38. 38.
    Rowell MW, Topinka MA, McGehee MD, Prall HJ, Dennler G, Sariciftci NS, Hu L, Gruner G (2006) Organic solar cells with carbon nanotube network electrodes. Appl Phys Lett 88(23):233506. doi:10.1063/1.2209887. Google Scholar
  39. 39.
    van de Lagemaat J, Barnes TM, Rumbles G, Shaheen SE, Coutts TJ, Weeks C, Levitsky I, Peltola J, Glatkowski P (2006) Organic solar cells with carbon nanotubes replacing In[sub 2]O[sub 3]:Sn as the transparent electrode. Appl Phys Lett 88(23):233503. doi:10.1063/1.2210081. Google Scholar
  40. 40.
    Pasquier AD, Unalan HE, Kanwal A, Miller S, Chhowalla M (2005) Conducting and transparent single-wall carbon nanotube electrodes for polymer-fullerene solar cells. Appl Phys Lett 87(20):203511. doi:10.1063/1.2132065. Google Scholar
  41. 41.
    Kaskela A, Nasibulin AG, Timmermans MY, Aitchison B, Papadimitratos A,Tian Y, Zhu Z, Jiang H, Brown DP, Zakhidov A, Kauppinen EI (2010) Aerosol-synthesized SWCNT networks with tunable conductivity and transparency by a dry transfer technique. Nano Lett 10(11):4349–4355. doi:10.1021/nl101680s. Google Scholar
  42. 42.
    Kuznetsov A, Zakhidov A (2013) To Be Submitted (in press)Google Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  1. 1.Department of Physics and Alan G. MacDiarmid Nanotech InstituteUniversity of Texas at DallasRichardsonUSA

Personalised recommendations