Bulk heterojunction cells device performance

Dye-Sensitized Cells Dye-sensitized solar cells (DSSCs) are slightly more complex than bilayer and bulk heterojunction cells, but as was the case for bilayer cells, the increase in device complexity reduces the number of functions that must be performed by each of the materials. A schematic drawing of a dye-sensitized solar cell is shown in Fig. 8.8. A layer of sintered, interconnected TiC>2 nanoparticles, which serves as the electron transport material (ETM), is coated by a thin layer of light absorbing dye. The remaining pores in the dye-coated TiC>2 layer are then filled with a... 

Figure 2.1 The key factors rJetermining the power conversion efficiency (17) of bulk heterojunction PSCs, together with parameters of solar cell device performance short-circuit current densityJ c, open-circuit voltage Voc. and fill factor FF. All three basic processes, light absorption (characterized by efficiency r/ ), exciton dissociation (j/ed). and transport and...

In a bulk-heterojunction photovoltaic cell with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as an electron acceptor, alternating copolymer 19 (Fig. 9), derived from 2,7-fluorene and 2,5-dithienylsilole, can show impressive performance as the electron donor.31 In a device configuration of ITO/PEDOT/active layer/Ba/Al, the dark current density—bias curve shows a small leakage current, suggesting a continuous, pinhole-free active layer in the device. Under illumination of an AM 1.5 solar simulator at 100 mW/cm2, a high short-circuit current of 5.4 mA/cm2, an open-circuit voltage of 0.7 V, and a fill factor of 31.5% are achieved. The calculated energy conversion efficiency is 2.01%. 

Further, the model allows us to estimate electrical losses in the device. Figures 5.18c and d show the local variations in the energy levels and the carrier densities for the bulk heterojunction solar cell for different mobilities. In Fig. 5.18c, balanced mobilities for electrons and holes are assumed, while Fig. 5.18d describes the situation for the case where the electron mobility is higher than the hole mobility. In the latter case recombination is enhanced as seen from the carrier densities, and the performance of the device (Jsc) is significantly lowered. 

Synthesis via the sulfinyl route led to a reduced number of defects on the MDMO-PPV donor polymer and showed some improved performances in MDMO-PPV PCBM bulk heterojunctions [ 167,168]. The lower defect density resulted in a more regioregular (head-to-taU) order within the MDMO-PPV, leading to charge carrier mobihty improvements and ultimately to an improved efficiency of 2.65% for MDMO-PPV PCBM based bulk heterojimc-tions [ 169]. This was accompanied by a fill factor of 71% [169], which to date has not been exceeded by any other polymer solar cell device. 

In this spirit, we will smdy the performance of structured PEDOT films in batteries and/or supercapacitors as well as the application of dedoped PT and P3MT in bulk heterojunction solar cells in the near future [12-15]. Furthermore, thenanostructured conjugated polymer films may find application in thermoelectric devices [47-50],... 

At the early development of polymer solar cells, a planar p-n junction structure represented the mainstream in mimicking conventional silicon-based solar cells. However, the obtained devices demonstrated poor photovoltaic performances due to the long distance between the exciton and junction interface and insufficient light absorption due to the thin light absorber. It was not until 1995 that the dilemma was overcome with the discovery of a novel bulk heterojunction in which donor and acceptor form interpenetrated phases. Poly[2-methoxy-5-(2 -ethylhexyloxy)-p-phenylene vinylene] was blended with Ceo or its derivatives to form the bulk heterojunction. A much improved power conversion efficiency of 2.9% was thus achieved under the illumination of 20 mW/cm. (Yu et al., 1995). The emergence of the donor/acceptor bulk-heterojunction structure had boosted the photovoltaic performances of polymer solar cells. Currently, a maximal power conversion efficiency of 10.6% had been reported on the basis of synthesizing appropriate polymer materials and designing a tandem structure (You et al., 2013). The detailed discussions are provided in Chapter 5. 

Chu, T.Y. et al. (2011) Morphology control in polycarbazole based bulk heterojunction solar cells and its impact on device performance. Appl. Phys. Lett., 98 (25), 253-301. 

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