Abstract
Control of blend morphology at multi-scale is critical for optimizing the power conversion efficiency (PCE) of plastic solar cells. To better understand the physics of photoactive layer in the organic photovoltaic devices, it is necessary to gain understanding of morphology and the corresponding electronic property. Herein we report the correlation between nanoscale structural, electric properties of bulk heterojunction (BHJ) solar cells and the annealing-induced PCE change. We demonstrate that the PCE of BHJ solar cells are dramatically improved (from 1.3 % to 4.6 %) by thermal annealing, which results from P3HT crystalline stacking and the PCBM aggregation for interpenetrated network. The similar trend for annealing-induced photovoltage and PCE evolution present as an initial increase followed by a decrease with the annealing time and temperature. The surface roughness increase slowly and then abruptly after the same inflection points observed for photovoltage and PCE. The phase images in electric force microscopy indicate the optimized P3HT and PCBM crystallization for interpenetrating network formation considering the spectroscopic results as well. From the correlation between surface photovoltage, blend morphology, and PCE, we propose a model to illustrate the film structure and its evolution under different annealing conditions. This work would benefit the better design and optimization of the morphology and local electric properties of solar cell active layers for improved PCE.
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References
Yu G, Gao J, Hummelen JC et al (1995) Polymer photovoltaic cells: enhanced efficiencies via a network of internal donor–acceptor heterojunctions. Science 270:1789–1791
Günes S, Neugebauer H, Sariciftci NS (2007) Conjugated polymer-based organic solar cells. Chem Rev 107:1324–1338
Thompson BC, Fréchet JMJ (2008) Polymer-fullerene composite solar cells. Angew Chem Int Ed Engl 47:58–77
Dennler G, Scharber MC, Brabec CJ (2009) Polymer-fullerene bulk- heterojunction solar cells. Adv Mater 21:1323–1338
Chen LM, Hong Z, Li G et al (2009) Recent progress in polymer solar cells: manipulation of polymer:fullerene morphology and the formation of efficient inverted polymer solar cells. Adv Mater 21:1434–1449
Halls JJM, Walsh CA, Greenham NC et al (1995) Efficient photodiodes from interpenetrating networks. Nature 376:498–500
Yang X, Loos J, Veenstra SC et al (2005) Nanoscale morphology of high performance polymer solar cells. Nano Lett 5:579–583
Li G, Shrotriya V, Huang J et al (2005) High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends. Nat Mater 4:864–868
Park SH, Roy A, Beaupré S et al (2009) Bulk heterojunction solar cells with internal quantum efficiency approaching 100 %. Nat Photon 3:297–303
Chen HY, Hou J, Zhang S et al (2009) Polymer solar cells with enhanced open-circuit voltage and efficiency. Nat Photon 3:649–653
Piliego C, Holcombe TW, Douglas JD et al (2010) Synthetic control of structural order in N-alkylthieno[3,4-c]pyrrole-4,6-dione-based polymers for efficient solar cells. J Am Chem Soc 132:7595–7597
Liang Y, Xu Z, Xia J et al (2010) For the bright future—bulk heterojunction polymer solar cells with power conversion efficiency of 7.4 %. Adv Mater 22:E135–E138
He Z, Zhong C, Huang X et al (2011) Simultaneous enhancement of open-circuit voltage, short-circuit current density, and fill factor in polymer solar cells. Adv Mater 23:4636–4643
You J, Dou L, Yoshimura K et al (2013) A polymer tandem solar cell with 10.6 % power conversion efficiency. Nat Commun 4:1446. doi:10.1038/ncomms2411
Krebs FC, Gevorgyan SA, Alstrup J (2009) A roll-to-roll process to flexible polymer solar cells: model studies, manufacture and operational stability studies. J Mater Chem 19:5442–5451
Hoppe H, Sariciftci NS (2006) Morphology of polymer/fullerene bulk heterojunction solar cells. J Mater Chem 16:45–61
Ma W, Yang C, Gong X et al (2005) Thermal stable, efficient ploymer solar cells with nanoscale control of the interpenetrating network morphology. Adv Funct Mater 15:1617–1622
Peet J, Kim JY, Coates NE et al (2007) Efficiency enhancement in low-bandgap polymer solar cells by processing with alkane dithiols. Nat Mater 6:497–500
Peet J, Senatore ML, Heeger AJ et al (2009) The role of processing in the fabrication and optimization of plastic solar cells. Adv Mater 21:1521–1527
Kim Y, Cook S, Tuladhar SM et al (2006) A strong regioregularity effect in self-organizing conjugated polymer films and high-efficiency polythiophene:fullerene solar cells. Nat Mater 5:197–203
Walker B, Tamayo AB, Dang XD et al (2009) Nanoscale phase separation and high photovoltaic efficiency in solution-processed, small-molecule bulk heterojunction solar cells. Adv Funct Mater 19:3063–3069
Li HC, Rao KK, Jeng JY et al (2011) Nano-scale mechanical properties of polymer/fullerene bulk hetero-junction films and their influence on photovoltaic cells. Sol Energy Mater Sol C 95:2976–2980
Mihailetchi VD, Xie H, Boer BD et al (2006) Charge transport and photocurrent generation in poly(3-hexylthiophene):methanofullerene bulk-heterojunction solar cells. Adv Funct Mater 16:699–708
Quiles MC, Ferenczi T, Agostinelli T et al (2008) Morphology evolution via self-organization and lateral and vertical diffusion in polymer: fullerene solar cell blends. Nat Mater 7:158–164
Woo CH, Thompson BC, Kim BJ et al (2008) The influence of poly(3-hexylthiophene) regioregularity on fullerene-composite solar cell performance. J Am Chem Soc 130:16324–16329
Li G, Yao Y, Yang H et al (2007) “Solvent annealing” effect in polymer solar cells based on poly(3-hexylthiophene) and methanofullerenes. Adv Funct Mater 17:1636–1644
Watts B, Belcher WJ, Thomsen L et al (2009) A quantitative study of PCBM diffusion during annealing of P3HT:PCBM blend films. Macromolecules 42:8392–8397
Bavel SV, Sourty E, With GD et al (2009) Relation between photoactive layer thickness, 3D morphology, and device performance in P3HT/ PCBM bulk-heterojunction solar cells. Macromolecules 42:7396–7403
Andersson BV, Herland A, Masich S et al (2009) Imaging of the 3D nanostructure of a polymer solar cell by electron tomography. Nano Lett 9:853–855
Chiesa M, Bürgi L, Kim JS et al (2005) Correlation between surface photovoltage and blend morphology in polyfluorene-based photodiodes. Nano Lett 5:559–563
Hoppe H, Glatzel T, Niggemann M et al (2005) Kelvin probe force microscopy study on conjugated polymer/fullerene bulk heterojunction organic solar cells. Nano Lett 5:269–274
Palermo V, Ridolfi G, Talarico AM et al (2007) A Kelvin probe force microscopy study of the photogeneration of surface charges in all-thiophene photovoltaic blends. Adv Funct Mater 17:472–478
Maturová K, Kemerink M, Wienk MM et al (2009) Scanning Kelvin probe microscopy on bulk heterojunction polymer blends. Adv Funct Mater 19:1379–1386
Liscio A, Luca GD, Nolde F et al (2008) Photovoltaic charge generation visualized at the nanoscale: a proof of principle. J Am Chem Soc 130:780–781
Spadafora EJ, Demadrille R, Ratier B et al (2010) Imaging the carrier photogeneration in nanoscale phase segregated organic heterojunctions by Kelvin probe force microscopy. Nano Lett 10:3337–3342
Douheret O, Lutsen L, Swinnen A et al (2006) Nanoscale electrical characterization of organic photovoltaic blends by conductive atomic force microscopy. Appl Phys Lett 89:032107
Dante M, Peet J, Nguyen TQ (2008) Nanoscale charge transport and internal structure of bulk heterojunction conjugated polymer/fullerene solar cells by scanning probe microscopy. J Phys Chem C 112:7241–7249
Coffey DC, Reid OG, Rodovsky DB et al (2007) Mapping local photocurrents in polymer/fullerene solar cells with photoconductive atomic force microscopy. Nano Lett 7:738–744
Pingree LSC, Reid OG, Ginger DS (2009) Imaging the evolution of nanoscale photocurrent collection and transport networks during annealing of polythiophene/fullerene solar cells. Nano Lett 9:2946–2952
Coffey DC, Ginger DS (2006) Time-resolved electrostatic force microscopy of polymer solar cells. Nat Mater 5:735–740
Verploegen E, Mondal R, Bettinger CJ et al (2010) Effects of thermal annealing upon the morphology of polymer-fullerene blends. Adv Funct Mater 20:3519–3529
Chirvase D, Parisi J, Hummelen JC et al (2004) Influence of nanomorphology on the photovoltaic action of polymer-fullerene composites. Nanotechnology 15:1317–1323
Jaquith M, Muller EM, Marohn JA (2007) Time-resolved electric force microscopy of charge trapping in polycrystalline pentacene. J Phys Chem B 111:7711–7714
Muller EM, Marohn JA (2005) Microscopic evidence for spatially inhomogeneous charge trapping in pentacene. Adv Mater 17:1410–1414
Brown PJ, Thomas DS, Köhler A et al (2003) Effect of interchain interactions on the absorption and emission of poly(3-hexylthiophene). Phys Rev B 67:064203
Zhokhavets U, Erb T, Gobsch G et al (2006) Relation between absorption and crystallinity of poly(3-hexylthiophene)/fullerene films for plastic solar cells. Chem Phys Lett 418:347–350
Malik S, Nandi AK (2002) Crystallization mechanism of regioregular poly(3-alkyl thiophene)s. J Polym Sci B 40:2073–2085
Acknowledgments
This work was supported by the National Basic Research Program of China (2011CB932800 and 2013CB934200), Sino-British Collaboration Program (2010DFA64680), National Natural Science Foundation of China (20973043), and Chinese Academy of Sciences (KGCX2-YW-375-3).
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Denghua Li and Han Yan have contributed equally to this work.
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Li, D., Yan, H., Li, C. et al. Nanoscale structural and electronic evolution for increased efficiency in polymer solar cells monitored by electric scanning probe microscopy. Chin. Sci. Bull. 59, 360–368 (2014). https://doi.org/10.1007/s11434-013-0040-5
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DOI: https://doi.org/10.1007/s11434-013-0040-5