The preparation of 27 different derivatives of C60 and C70 fullerenes possessing various aryl (heteroaryl) and/or alkyl groups that are appended to the fullerene cage via a cyclopropane moiety and their use in bulk heterojunction polymer solar cells is reported. It is shown that even slight variations in the molecular structure of a compound can cause a significant change in its physical properties, in particular its solubility in organic solvents. Furthermore, the solubility of a fullerene derivative strongly affects the morphology of its composite with poly(3‐hexylthiophene), which is commonly used as active material in bulk heterojunction organic solar cells. As a consequence, the solar cell parameters strongly depend on the structure and the properties of the fullerene‐based material. The power conversion efficiencies for solar cells comprising these fullerene derivatives range from negligibly low (0.02%) to considerably high (4.1%) values. The analysis of extensive sets of experimental data reveals a general dependence of all solar cell parameters on the solubility of the fullerene derivative used as acceptor component in the photoactive layer of an organic solar cell. It is concluded that the best material combinations are those where donor and acceptor components are of similar and sufficiently high solubility in the solvent used for the deposition of the active layer.

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In order to realize enhanced spectral coverage in organic photovoltaic devices, the authors have stacked a zinc phthalocyanine:C60 based cell on the top of a poly-3-hexyl-thiophene:[6,6]-phenyl C61-butyric acid methyl ester layer using a 1nm thick Au intermediate recombination layer. Such tandem devices comprising active materials with complementary absorption spectra exhibit a short circuit current (Isc) of 4.8mAcm−2, an open circuit voltage (Voc) of 1020mV, and a fill factor of 0.45. Measurements of the photocurrent versus wavelength of the incident light show that photons are converted into charge carriers from 400 to more than 800nm. Further optimization of the respective layer thicknesses may lead to high efficiency devices.

Ionic impurities in gate dielectrics are outlined as a possible source for threshold voltage shifts in organic field effect transistors. Using poly(vinyl alcohol) containing sodium acetate impurities we show how transistors can be designed for memory elements or polymer integrated circuits.

We investigated donor−acceptor bilayer heterojunctions formed by deposition of solution-processed pyrrolidinofullerenes bearing chelating pyridyl groups (PyFs) on vacuum-evaporated films of zinc phthalocyanine (ZnPc). It is shown that coordination complexes are formed at the interface between these donor and acceptor components; such association facilitates photoinduced charge separation and results in improved performance of the photovoltaic devices. Thus, the bilayer photovoltaic cells fabricated from different pyrrolidinofullerenes and ZnPc exhibit short circuit current (I sc) densities in the range of 3−5 mA/cm2, open circuit voltages (V oc) of 400−600 mV, and fill factors (FF) of 40−50% that correspond to power conversion efficiencies (η) of up to 1.5% under 100 mW/cm2 simulated AM1.5 illumination. The reference cells based on the nonchelating fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) as acceptor component yield lower power conversion efficiencies (0.4−0.6%); the performance of such devices can be increased significantly by mixing PCBM with a small amount (4% w/w) of PyF in the acceptor layer. A novel multicomponent organic solar cell architecture is suggested in order to expand the active layer absorption by formal combination of the solution-processed bulk heterojunction polymer/fullerene cells with evaporated bilayer ZnPc/fullerene devices. For this purpose, a blend of the fullerene derivatives (PCBM and PyF mixed in different ratios) with the polyconjugated polymer poly((2-methoxy-5-(3,7-dimethyloctyloxy)-p-phenylene) vinylene (MDMO−PPV) is spin-coated on the ZnPc film sublimed on an indium tin oxide (ITO) substrate. Evaporation of the top aluminum electrodes yields photovoltaic devices that demonstrate power conversion efficiencies of up to 2% and efficient photocurrent generation in the full range from 350 to 820 nm.