Bulk heterojunction devices

Fig. 5.6. Schematic drawing of a bulk heterojunction device. Charge generation occurs throughout the bulk, but the quality of the two transport networks (p-and n-type channels) is essential for the functionality of the blend as an intrinsic, ambipolar semiconductor. Light emission occurs at the semi-transparent ITO electrode. Electron transport on the fullerenes is marked by full arrows and hole transport along the polymer by dotted arrows...

Fig. 5.12. Temperature dependent I/V characteristics of a bulk heterojunction device (ITO/PEDOT/MDMO-PPV PCBM/LiF-Al) in the dark (top) and under illumination (bottom)...

The previous section gave an overview of the transport and junction properties of conjugated materials regarding their importance for photovoltaic devices. In this chapter, the bulk heterojunction device itself will be in the spotlight. Device properties will be discussed and evaluated as for classical inorganic solar cells, concentrating on the short-circuit current /sc, the open-circuit voltage Foc, the fill factor FF, and the spectral sensitivity. 

Table 5.3. Solar cell characteristics (PF and Voc) of MDMO-PPV/PCBM bulk heterojunction devices for various interfacial layers (LiF, SiO ) with different thicknesses compared to a solar cell with a pristine A1 electrode, and also calculated diode characteristics Rs and Rp found using (5.39) for the various interfacial layers...

Table 5.4. PV performance parameters of various bulk heterojunction devices comprising a low bandagap p-type polymer PTPTB under AM 1.5 conditions...

Progress with polymer fullerene bulk heterojunction devices... 

Bulk heterojunction device performance has improved by strides since the first reports of charge separation in bulk heterojunctions, with power conversion efficiencies that now approach 5% (Li et al., 2005 Reyes-Reyes et al, 2005 Kim et al, 2006a). Smdies have focused on varying the donor and acceptor materials, optimising the... 

Fig. 11 In bulk heterojunction devices, charge carriers can be dissociated throughout the volume of the active layer. Thus every absorbed photon in the active layer can potentially contribute to the photocurrent...

Waldauf C, Scharber MC, Schilinsky P, Hauch JA, Brabec CJ (2006) Physics of organic bulk heterojunction devices for photovoltaic applications. J Appl Phys 99 104503... 

It should be noted that this ratio is significantly lower than that usually applied in polymcr/C tll bulk heterojunction devices, where the Copolymer ratio is typically 4 1 to allow the formation of C50 percolation paths for electron collection [59]. 

FIGURE 8.13 Schematic diagram of (a) a bulk heterojunction device and (b) an MEH-PPV/ Ti02 hilayer device, as a typical bilayer device. 

A polymer based on EDOT containing a perylenetetracarboxylic diimide unit has been prepared by electropolymerization of 250 [443]. The related absorption spectrum covers the visible range and extends up to 850 nm. Similarly, PV devices based on dyads 251 in which oligo(3-hexylthiophene)s are covalently linked to perylenemonoimide have been recently reported [444]. Preliminary results based on bulk heterojunction devices consisting of ITO/PEDOT-PSS/251 PCBM (l 4)/LiF/Al showed an open circuit voltage of 0.94 V and efficiencies of 0.33% (251, n=l) and 0.48% (251, =3) under standard test conditions (AM 1.5G, 1000 W m ). 

Bilker Heterojunction Devices Bulk Heterojunction Devices... 

The P3HT/PCBM bulk heterojunction device remained stable for 1000 h with less than 20% change in the device parameters tested at elevated temperatures, which indicates that both the chemical stability of the materials and the stability of the phase-separated network are promising for long-term operation [63]. Using encapsulation techniques, the stability of the devices can be improved to beyond 3000 h [64]. 

At the final stage (step V in Figure 6) of the photocurrent generation process charges have to be collected at the electrodes. In bulk heterojunction devices, the lower work... 

A special type of solar cells as a hybrid combination of planar bilayer and bulk heterojunction devices has been... 

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