MDMO-PPV Poly

Figure 7.1 Chemical stractures of some common organic photovoltaic materials poly(2-methoxy-5-(3,7-dimethyloctyloxy)-l,4 phenylenevinylene) (MDMO-PPV), poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl Cei-butyric acid methyl ester (PCBM).

Significant amount of research has been dedicated to two material systems MDMO-PPV PCBM (MDMO-PPV poly(2-methoxy-5-(3, 7 -dimethyl-octyloxy)-l,4-phenylenevinylene)) and RR-P3HT PCBM, which represent the state-of-the-art polymer solar cell technology. Because there are excellent review papers on the MDMO-PPV PCBM system in the literature, in this section we will only focus on the recent improvements in RR-P3HT PCBM system, especially the approaches to optimize the active blend layer for enhancing device efficiency. 

MDMO-PPV Poly(2-methoxy-5-(3, 7 -dimethyloctyloxy)-1,4-phenylene vinylene) 55... 

FIGURE 10.2 Chemical structures of materials commonly used in bulk heterojunction solar cells. MDMO-PPV, poly[2-methoxy-5-(3, 7 -dimethyloctyloxy)-p-phenylene vinylene] MEH-PPV] poly[2-methoxy-5(2-ethylhexoxy)-1, 4-phenylene vinylene] P3HT, poly(3-hexylthiophene) CeolPCBM], 3 -phenyl-3 H-cyclopropa[l,9] ]5,6]fullerene-Cgo-fh 3 -butanoic acid methyl ester C70]PCBM], 3 -phenyl-3 H-cyclopropa[8,25] ]5,6]fullerene-C7o-D5i,(6)-3 -butanoic acid methyl ester. 

PCBM [(6,6)-phenyl-C 61-butyric acid methyl ester] has been widely used as electron acceptor in polymer/fiiUerene solar cells due to its greater solubility than Ceo- The polymer MDMO-PPV [poly- 2-methoxy-5-(3,7-dimethyloctyloxy) -para-phenylenevinylene] has been used as electron donor polymer for better absorption of solar light. This heterojunction solar cell has 80 wt% of PCBM, which is supposed to be the main light absorber. The change of solvent from toluene to chlorobenzene increases the efficiency by a factor of 3 [13]. 

EDOT) coated CdSe nanorods as a function of the quantity of poly [2-methoxy-5-(3, 7 -dimethy locty loxy)-1,4-phenylenevinylene] (MDMO-PPV) added (solvent CHC13).151 (Reprinted with permission from D. Aldakov et al., Eur. Phys. J. Appl. Phys. 2006, 36, 261-265. Copyright the European Physical Journal.)... 

In order to learn about the true quantum efficiency of photogeneration one therefore has to study the photoinduced charge generation mechanism at faster time scales. Pump probe spectroscopy utilising a few optical-cycle laser pulses (5-6 fs) in the visible spectral range with broadband frequency conversion techniques [89] now makes it possible to study extremely fast optically-initiated events with unprecedented time resolution. Such a setup was used to time-resolve the kinetics of the charge transfer process from a polymer chain to a fullerene moiety in thin films of poly[2-methoxy, 5-(3, 7 -dimethyl-octyloxy)]-p-phenylene vinylene (MDMO-PPV) and [6,6]-phenyl C6i butyric acid methyl ester (PCBM). Solutions prepared from 1 wt% solutions of toluene on thin quartz substrates were studied. 

Exciplex formation and subsequent transfer to a lower lying triplet state of MDMO-PPV in blends with PCNEPV (poly[oxa-l,4-phenylene-(l-cyano-l,2-vinylene)-(2-methoxy-5-(3,7-dimethyloctyloxy)-l,4-phenylene)-l,l-(2-cyano-... 

In general, photovoltaic devices are sensitive to atmospheric oxygen and humidity, which reduces their service times. With MDMO-PPV based solar cells, it was demonstrated that the encapsulation with poly(ethylene naphthalate) (PEN) increases the service time from a few hours up to more than four months.In general, PEN is used as an ultra-high barrier material. 

Hybrid films of ZnO nanoparticles and poly[2-methoxy - 5 - (3, 7 -dimethyloctyloxyl) -1,4-phenylene vinylene] (MDMO-PPV) have been characterized as a model hybrid bulk heterojunction photovoltaic cell [145]. 

High absorption cross section for photon harvesting. Ideally, the electronic structure of conjugated polymers is that of a one-dimensional semiconductor in which the absorption coefficient increases steeply above the band gap absorption. The absorption coefficient of the frequently used poly(p-phenylene vinylene) polymer MDMO-PPV (Figure 10.2.) reaches 10 cm just... 

The influence of morphology formation on the performance of PSCs was first observed for systems where PCBM was blended with the electron-donor polymer poly[2-mefhoxy-5-(3, 7 -dimethyloctyloxy)-l,4-phenylene vinylene] (MDMO-PPV). A strong increase in power conversion efficiency was obtained by changing the solvent from toluene (0.9% efficiency) to chlorobenzene (2.5% efficiency) [13]. The better performance of MDMO-PPV/PCBM PSCs in case of using chlorobenzene (or o-dichlorobenzene) as a solvent rather than toluene was found to be due to smaller and thus more favorable scale of phase segregation (Figure 2.5). The higher... 

---