Blend donor-acceptor

Fig. 15 Charge-transfer state electroluminescence (EL) for several polymer fullerene blends used in donor/acceptor organic solar cells. Adapted with permission from [184]. Copyright 2009 American Chemical Society...

A bulk heteroj unction is by definition a blend of p-type and n-type semiconductors (donor/acceptor). As a prototype bulk heteroj unction, we shall discuss the properties of polymer/fullerene blends. Apart from the poly-... 

A different combination of blend and bilayer structures can also be quite efficient. Having a mixture of polymers in the donor layer and using Ceo as the acceptor provides a way of increasing the spectrai range of absorption of photovoltaic cells while retaining good collection efficiency [23]. A blend donor layer can also be used to mimic the process of photosynthesis where many... 

Schneider HA, Cantow HJ, Percec V. (1982) Donor-acceptor complexation in macromolecu-lar systems. 1. Viscoelastic properties of polydonor-polyacceptor blends and of corresponding copolymers. Polym. Bull. (Berlin, Germany) 6 617-621. 

The stracture formed by donor acceptor BHJ blends is dependent on the solvent used. Studies of polyfluorene PCBM blends show that choice of solvent controls the segregation of materials within the blend film so that a vertical multilayer structure forms spontaneously in some cases (Bjorstrom and Moons, 2007). Similarly, the choice of solvent in a polymer-polymer blend controls the vertical arrangement of materials and the device performance (Arias et al, 2002). Exploitation of these effects may open new avenues for materials-processing procedures in the organic photovoltaic field. 

Structural instability due to phase segregation in donor-acceptor blends over time is a function of materials and temperature. At moderate temperatures of 50-80 C, the problem is more severe in MDMO-PPV PCBM than P3HT PCBM blend films. This... 

Frost J. M., Cheyitis F., Tuladhar S. M. and Nelson J. (2006), Influence of polymer-blend morphology on charge transport and photocurrent generation in donor-acceptor polymer blends , Lett. 6, 1674-1681. 

In Figure 6, PL spectra and images of blended films with different relative donor/acceptor concentrations, spin-coated on quartz substrates, are reported. It is seen that enhancing the concentration of STO a broad red-shifted emission due to exciplex states appears, in addition to the blue emission due to TPD, which is responsible for the white emission within a concentration range 17-53% of STO in TPD. The normalized EL spectra were similar to the PL spectra for the concentration used (20%), showing that the shape of the low-energy exciplex spectrum is almost independent of the applied voltage. The CIE coordinates of the EL spectra indicated a balanced white emission (0.39, 0.40) (Mazzeo et al., 2003 b). 

Charge-transfer or donor-acceptor interactions. The development of polymers for non-linear optics has been concerned with substituents such as nitro groups that are electron acceptors. When these are blended with polymers containing... 

Recently, geminate polaron pairs have been proposed for polymer-polymer [35,56,57] and polymer-fullerene [58,59] blends as photoinduced intermediates. Here the hole and electron remain coulombically bound across the interface of the donor-acceptor heterojunction. Only via an electric field and/or a temperature-assisted secondary process, these geminate polaron pairs are dissociated, leading to free charge carriers. This can have a considerable effect on the achievable charge separation efficiencies, since the geminate... 

This limitation was finally overcome by the concept of the bulk heterojunction, where the donor and acceptor materials are intimately blended throughout the bulk [28-30]. In this way, excitons do not need to travel long distances to reach the donor/acceptor interface, and charge separation can take place throughout the whole depth of the photoactive layer. Thus the active zone extends throughout the volume, as illustrated in Fig. 11. Conse-... 

Ridoffi G, Camainoni N, Samori P, Gazzano M, Accorsi G, Armaroli N, Favaretto L, BarbareUa G (2005) All-thiophene donor-acceptor blends photophysics, morphology and photoresponse. J Mater Chem 15 895... 

Abstract. Copper phthalocyanine (CuPc)-fullerene (C60) photovoltaic cells are produced by organic vapour phase deposition reaching efficiencies of 3%. The electronic transport properties of the devices are investigated as a function of the CuPc C60 absorber blend layer composition and its preparation temperature. The analysis of the transport properties of the devices employs the one-diode model. It is shown that the dominant recombination process takes place at the donor-acceptor interfaces of the CuPc and C60 absorber domains. The activation energy of recombination is related to the effective band gap of the blend layer. 

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