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ABSTRACT: Polymer or ''plastics'' solar cells have been an intensively studied area since the discovery of efficient electron transfer between polymers and fullerenes and the introduction of the bulk-heterojunction concept. The last few years have seen significant improvement in plastic solar cell performance through aggressive research on the regioregular poly(3-hexylthiophene) (RR-P3HT) : [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) system. The morphology of the system is controlled through two major strategies which have proven effective in improving the device efficiency—thermal annealing and solvent annealing (slow growth). In this Feature Article, we review the recent progress on this material system. A detailed discussion on thermal annealing and solvent annealing approaches to improve device performance is presented, including a comparison between the two strategies. The effects of these two approaches on improving polymer crystallinity, light absorption in the polymer, carrier transport, blend film nano-morphology, etc. are summarized. We also include a brief discussion on accurate measurement and characterization techniques for polymer solar cells to correctly determine the efficiency by applying spectral mismatch factors. Future directions and challenges on polymer solar cell development are also discussed.
03/2007;
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ABSTRACT: Efficient polymer solar cells based on a low band gap copolymer poly{(9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-decyloxythien-2-yl)-2,1,3-benzothiadiazole]- 5<sup>′</sup>,5<sup>″</sup> -diyl} and (6,6)-phenyl- C <sub>71</sub> -butyric acid methyl ester ( C <sub>70</sub> -PCBM) were demonstrated with 2.4% power conversion efficiency under air mass 1.5 G , 100 mW / cm <sup>2</sup> illumination. The broad absorption peak of C <sub>70</sub>- PCBM in 440–530 nm complements the absorption valley (regions between two absorption peaks at 416 and 584 nm ) of the polymer. The external quantum efficiency measurement further demonstrates that this increased absorption contributes significantly to the generation of photocurrent. Morphology studies on the blend films indicated that excellent miscibility between polymer and C <sub>70</sub>- PCBM favors exciton separation. The linear relationship between light intensity and short circuit current density shows efficient and balanced charge transport resulting in increased photocurrent and fill factor.
Applied Physics Letters 11/2006; · 3.84 Impact Factor
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ABSTRACT: The authors investigate the effect of self-organization by controlling the growth rate on the performance of polymer/fullerene bulk-heterojunction solar cells. The effect of growth rate on the morphology of the active layer is studied by atomic force microscopy technique. The electrical characterization by dark current and photocurrent measurements is performed. The hole mobility in the polymer increases by about two orders in magnitude and the carrier transport becomes highly balanced. Increased exciton generation rate, more efficient electron-hole pair dissociation, higher carrier mobility, and balanced carrier transport in the active layer explain the enhancement in the short-circuit current and fill factor.
Applied Physics Letters 09/2006; · 3.84 Impact Factor
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Applied Physics Letters. 01/2006; 88(6):064104.
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ABSTRACT: Regioregular poly3-hexylthiophene RR-P3HT is a promising candidate for polymer photovoltaic research due to its stability and absorption in the red region. In this manuscript, we report polymer photovoltaic devices based on RR-P3HT:methanofullerene 6,6-phenyl-C 61 -butyric acid methyl ester PCBM 1:1 weight-ratio blend. We studied the effects of annealing temperature and time on the device performance for devices annealed before and after cathode deposition. Thermal annealing shows significant improvement in the performance for both types of annealing conditions, with postproduction annealing being slightly better. For devices with a 43-nm-thick active layer, maximum power conversion efficiency PCE of 3.2% and fill factor up to 67% is achieved under Air Mass 1.5, 100-mW/ cm 2 illumination. We performed atomic force microscopy and ultraviolet-visible absorption spectroscopy on the P3HT:PCBM films to explain the effect of thermal annealing. By keeping the optimized thermal annealing condition and by varying the active layer thickness, we fabricated devices with PCE up to 4.0%, which is the highest efficiency reported so far for this system. © 2005 American Institute of Physics.
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ABSTRACT: The absorption spectra and the photovoltaic effect in thin films consisting of a blend of p-type poly(3-hexylthiophene) and n-type acceptor [6,6]-phenyl C60 butyric acid methyl ester have been studied and a decrease in inter-band absorption in the wavelength range of 450–600 nm is observed. This absorption quenching is attributed to the disordering of the poly(3-hexylthiophene) chains and a charge transfer between poly(3-hexylthiophene) and [6,6]-phenyl C60 butyric acid methyl ester, as evidenced by FTIR and X-ray photoelectron spectra. Finally, photovoltaic cells were fabricated utilizing the blend as the active layer and the device characteristics were studied.
Chemical Physics Letters.
