The carrier collection efficiency (ηc) and energy conversion efficiency (ηe) of polymer photovoltaic cells were improved by blending of the semiconducting polymer with C60 or its functionalized derivatives. Composite films of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and fullerenes exhibit ηc of about 29 percent of electrons per photon and ηe of about 2.9 percent, efficiencies that are better by more than two orders of magnitude than those that have been achieved with devices made with pure MEH-PPV. The efficient charge separation results from photoinduced electron transfer from the MEH-PPV (as donor) to C60 (as acceptor); the high collection efficiency results from a bicontinuous network of internal donor-acceptor heterojunctions.

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Polymer photovoltaic cells : enhanced efficiencies via a network of internal donor-acceptor heterojunctions

2.2. Materials 929 2.3. Factors Influencing Charge Mobility 931 2.3.1. Molecular Packing 931 2.3.2. Disorder 932 2.3.3. Temperature 933 2.3.4. Electric Field 934 2.3.5. Impurities 934 2.3.6. Pressure 934 2.3.7. Charge-Carrier Density 934 2.3.8. Size/molecular Weight 935 3. The Charge-Transport Parameters 935 3.1. Electronic Coupling 936 3.1.1. The Energy-Splitting-in-Dimer Method 936 3.1.2. The Orthogonality Issue 937 3.1.3. Impact of the Site Energy 937 3.1.4. Electronic Coupling in Oligoacene Derivatives 938

Charge transport in organic semiconductors.

About Supramolecular Assemblies of π-Conjugated Systems

Organic solar cell research has developed during the past 30 years, but especially in the last decade it has attracted scientific and economic interest triggered by a rapid increase in power conversion efficiencies. This was achieved by the introduction of new materials, improved materials engineering, and more sophisticated device structures. Today, solar power conversion efficiencies in excess of 3% have been accomplished with several device concepts. Though efficiencies of these thin-film organicdevices have not yet reached those of their inorganic counterparts (η ≈ 10–20%); the perspective of cheap production (employing, e.g., roll-to-roll processes) drives the development of organic photovoltaic devices further in a dynamic way. The two competitive production techniques used today are either wet solution processing or dry thermal evaporation of the organic constituents. The field of organic solar cells profited well from the development of light-emitting diodes based on similar technologies, which have entered the market recently. We review here the current status of the field of organic solar cells and discuss different production technologies as well as study the important parameters to improve their performance.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400094498

Organic solar cells: An overview

Charge-Transfer and Energy-Transfer Processes in π-Conjugated Oligomers and Polymers: A Molecular Picture

THE search for organic materials suitable for electronic applica-tions dates back to the early 1950s. But the only organic systems known so far to show electronic charge-carrier mobilities comparable to the amorphous inorganic semiconductors that are the main-stay of the microelectronics industry are zone-refined organic single crystals1–4. Single crystals are difficult and costly to process, however, and are not suitable for device applications. Here we show that a highly ordered columnar (stacked) phase of disk-like organic molecules can exhibit high mobilities for photoinduced charge carriers, of the order of 0.1 cm2 V-1 s-1—higher than for any organic material other than single-crystal phases. Specifically, we study the helical columnar phase of 2,3,6,7,10,11-hexahexylthiotriphenylene, which can be prepared simply by cooling the isotropic liquid melt via the discotic liquid-crystal phase, in which the molecules are already stacked with a high degree of order.

Fast photoconduction in the highly ordered columnar phase of a discotic liquid crystal

The mobility of charge carriers in all four phases of the columnar discotic material hexakis(hexylthio)triphenylene: Combined TOF and PR‐TRMC results

Photoconductivity in the columnar phases of a glassy discotic twin

The novel conjugated polymer poly(9-hexyl-3,6-carbazoylyleneethylene) (16) was prepared by palladium-catalyzed polycondensation of 3,6-diiodo-9-hexylcarbazole and 3,6-diethynyl-9-hexylcarbazole. The polymer has a number-average molecular weight (Mn) of 3 100. By fractionation a polymer with Mn of 6 400 was obtained. Besides polycondensation, a palladium-catalyzed bond-opening polymerization of the triple bonds occurs as a side reaction which can be partially suppressed by lowering the reaction temperature to 60°C. Two well-defined model compounds of the title polymer, a dimer and a trimer, were synthesized by stepwise reaction. The mass spectra of both model compounds demonstrate the remarkably high stability of the radical cations of the dimer and trimer. Since the trimer forms a stable glass it is ideally suited for the investigation of its photoconductive properties. First experiments carried out by the Time-of-Flight technique showed remarkably high carrier mobilities up to 2 · 10−4 cm2/(V · s) for the trimer.

Jürgen Simmerer

Papers

Fast photoconduction in the highly ordered columnar phase of a discotic liquid crystal

The mobility of charge carriers in all four phases of the columnar discotic material hexakis(hexylthio)triphenylene: Combined TOF and PR‐TRMC results

Photoconductivity in the columnar phases of a glassy discotic twin

Synthesis of poly(9-hexyl-3,6-carbazolyleneethynylene) and its model compounds

Electroluminescent devices based on poly(methylphenylsilane)