Bulk heterojunction cells polymer:PCBM blends

One of the most promising uses of C60 involves its potential application, when mixed with 7r-conjligated polymers, in polymer solar cells. Most often the so-called bulk heterojunction configuration is used, in which the active layer consists of a blend of electron-donating materials, for example, p-type conjugated polymers, and an electron-accepting material (n-type), such as (6,6)-phenyl-Cgi -butyric acid methyl ester (PCBM, Scheme 9.6).38... 

Figure 7.10 Tandem solar cell structure for polymer blend solar cells, based on the design demonstrated by Hadipour et al. (2006). In this all-solution-processed device, the top cell consists of a polymer PCBM bulk heterojunction with an absorption maximum of 550 nm and preferentially absorbs short-wavelength light, while the bottom cell is made from a bulk heterojunction of PCBM with a red-absortring polymer and absorbs longer-wavelength light. The composite gold-PEDOT PSS internal layer connects the two cells in...

Andersson and coworkers have prepared solar cells based on blends of poly(2,7-(9-(2 -ethylhexyl)-9-hexyl-fluorene)-fl/t-5,5-(4, 7 -di-2-thienyl-2, l, 3 -benzothiadiazole) (223) and PCBM [416]. The polymer shows a Amax (545 nm) with a broad optical absorption in the visible spectrum and an efficiency of 2.2% has been measured under simulated solar light. The same group has also reported the synthesis of low bandgap polymers 200 (1 = 1.25 eV) and 224 (1 = 1.46 eV) which have been blended with a soluble pyrazolino[70]fiillerene and PCBM, respectively, to form bulk heterojunction solar cells of PCE of 0.7% [417] and 0.9% [418]. Incorporation of an electron-delident silole moiety in a polyfluorene chain affords an alternating conjugated copolymer (225) with an optical bandgap of 2.08 eV. A solar cell based on a mixture 1 4 of 225 and PCBM exhibits 2.01% of PCE [419]. 

Vanderzande et al. reported the facile synthesis to 5,6-disubstituted-l,3-dithienylbenzo[c]thiophenes 3.10 via Pd°-catalyzed coupling reaction of 5,6-dichloroterthiophenes 3.9 with an alkyl Grignard reagent (Scheme 1.30) [309, 321]. Chemical polymerization of the 5,6-modified monomers with FcCIb yielded polymers with bandgaps of 1.4-1.8 eV, which are similar to that of poly(dithienylbenzo[c]thiophene) P3.3 [309]. Application of these polymers as donors and fullerene PCBM as acceptor in bulk heterojunction solar cells (BHJSC) was also investigated and reported. An overall power conversion efficiency of 0.3 % and an internal power conversion efficiency of 24% were obtained for PMMA-poly-P3.9c-PCBM (1 2 6) blended devices [321]. 

Nevertheless, it was recently demonstrated that introduction of thin (5 nm) interlayer of PF-PO(Et)2 (Figure 74) improves the performance of the conventional P3HT/ [60JPCBM blend from 2.0 to 3.4% mainly due to increase in the open-circuit voltage and FF from 450 to 640 mV and from 51 to 59%, respectively.Another polymer abbreviated as PFNBr-PFMEE in Figure 74 improved the power conversion efficiency of P3HT/[60]PCBM bulk heterojunction solar cells from 3.0 to 3.8%. The open-circuit... 

The improvement in power conversion efficiency (PCE) of plasmonic solar cells is always an urgent problem and short circuit current density is one of the key factors for the PCE. The improvement in the Jsc of plasmonic solar cells is mainly achieved by the introduction of metallic nanoparticles, such as blending Au nanoparticles into the anodic buffer layer or the interconnecting layer that connects two subcells of the tandem plasmonic solar cells [86]. Compared with the metallic NPs, nanowires (NWs) are superior in terms of improving photocurrent, while most of the metallic NWs introducing in cells reported previously were used for the anodic contact of the cells [87]. The improvement of PCE in bulk heterojunction polymer solar cells with active layer P3HT PCBM by introducing 40 nm Au nanoparticles between ITO and PEDOT PSS layer with various concentrations is also observed by Gao et al. [88]. It has been found that both short-circuit current density and PCE increase from 3.50% to 3.81% with 0.9 wt. % Au NPs due to the localized surface plasmon excitation of Au NPs. 

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