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ABSTRACT: A significant increase in open circuit voltage (VOC) is obtained in the polymer-fullerene bulk heterojunction solar cell by using the e-beam deposited Al cathode. Compared with the device with the thermal evaporated Al cathode, an obvious enhancement of VOC from 596 to 664 mV is obtained, which makes the overall device power conversion efficiency improved by 12.4% (from 3.79% to 4.26%). Electrical characterizations suggest that the energetic particles in the e-beam deposition induce deep interface hole traps in the poly(3-hexylthiophene-2,5-diyl) (P3HT), while leaving the fullerene unaffected. The deep trapped holes near the P3HT/cathode interface can induce the image negative charges in the cathode and thus form “dipoles.” These dipoles lead to the lowering of the Al effective work function and cause the enhancement of VOC.
Applied Physics Letters 03/2009; 94(10):103305-103305-3. · 3.84 Impact Factor
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ABSTRACT: A multilayer structure of copper phthalocyanine/poly(3-hexylthiophene-2,5-diyl): [6,6]-phenyl- C <sub>61</sub> -butyric acid methyl ester (CuPc/P3HT:PCBM) is used to extend the light absorption spectrum covering almost the entire visible spectrum. To maximize the light absorption, the total number of excitons created in the multilayer structure as a function of layer thickness of both CuPc and P3HT:PCBM is simulated by using the optical transfer matrix formalism. The solar cells with a device structure of ITO/PEDOT:PSS/CuPc/P3HT:PCBM/Al are fabricated with different layers thicknesses. The optimized solar cell with a high short circuit current density of 12.54 mA / cm <sup>2</sup> and power conversion efficiency as high as 4.13% is achieved, owing to the utilization of the second optical interference peak in the multilayer structure for the enhanced light absorption.
Applied Physics Letters 08/2008; · 3.84 Impact Factor
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ABSTRACT: A simple method is developed to make an interpenetrating network of poly(3-hexylthiophene-2,5-diyl) (P3HT) and fullerene (C60) by mixing P3HT solution with a thermal initiator 2,2′-azobis(isobutyronitrile) (AIBN). After mild annealing, the release of nitrogen from AIBN increases the roughness of P3HT dramatically. Significant photoluminescence quenching between the roughened donor P3HT and overlaying acceptor C60 is related to the significant increment of donor-acceptor interfacial areas. Based on this interpenetrated network of P3HT/C60, more than threefold increase in the photovoltaic efficiency of devices is achieved compared with bilayer structure. Fill factor is also improved, implying good percolation path in this heterojunction structure.
Applied Physics Letters 07/2008; 93(4):043304-043304-3. · 3.84 Impact Factor
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ABSTRACT: We proposed and demonstrated a simple tandem structure of organic photovoltaic (PV) cell for efficient light harvesting. In this device structure, a soluble fullerene derivative of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is employed simultaneously to form a bilayer heterojunction PV subcell with the underlying copper phthalocyanine (CuPc) and a bulk heterojunction PV subcell with blended poly(3-hexylthiophene-2,5-diyl) (P3HT). In comparison with the conventional tandem structure, the omission of the semitransparent intercellular connection layer reduces the complexity of the device and the light loss. The enhanced short circuit current density (JSC = 8.63 mA/cm2) and power conversion efficiency (PCE) (2.79%) of the tandem structure are nearly the sum of those of the stand-alone cells of CuPc/PCBM (JSC = 2.09 mA/cm2, PCE = 0.43%) and P3HT:PCBM (JSC = 6.87 mA/cm2, PCE = 2.50%).
Applied Physics Letters 02/2008; 92(8):083310-083310-3. · 3.84 Impact Factor
