Millenniums-old natural dye indigo--a "new" ambipolar organic semiconductor. Indigo shows balanced electron and hole mobilities of 1 × 10(-2) cm(2) V(-1) s(-1) and good stability against degradation in air. Inverters with gains of 105 in the first and 110 in the third quadrant are demonstrated. Fabricated entirely from natural and biodegradable compounds, these devices show the large potential of such materials for green organic electronics.

achieve the highest performance so far in combination with the commonly used methanofullerene derivatives like phenyl-C 61 -butyric acid methyl ester ([60]PCBM) or [6,6]-phenyl-C 71 -butyric acid methyl ester ([70]PCBM). [11] Functional fullerenes, on the one hand, can preserve the properties of pristine fullerenes, such as superior electron-transporting ability and high electron affinity. On the other hand, by properly attaching suitable addends, one can manipulate a wide variety of chemical, physical, or thermo dynamic properties, such as better solubility in organic solvents, higher lowest unoccupied molecular orbital (LUMO) level, and improved compatibility with organic donors. [12] These advantages endow functional fullerenes with extraordinary capability, acting as unique electron-accepting components in OPV devices. [2,13] Although PCBM is the most prominent acceptor in OPV devices, [5,14] the energy levels of PCBM should be further optimized in order to achieve high open circuit voltage (V OC ) in combination with the state-of-theart organic donors. [15] Fullerene derivatives with more suitable electronic levels are expected to reduce the bandgap to V OC loss and approach the theoretical efficiency limit. [13,16] PCBM bisadduct [17] and indene-C 60 bisadduct [18] made their glory debut for being well compatible with poly(3-hexylthiophene-2,5-diyl) (P3HT) and for achieving promising high V OC and PCE compared to the PCBM-based counterparts. However, resulting from constitutional isomer impurities and inefficient charge generation, fullerene bisadducts failed to produce similarly satisfying performance with the latest outstanding organic donors. [19] Another effective way of increasing the LUMO level of fullerene derivatives is to add an electron-donating group to the fullerene cage. [20] A series of newly developed functional fullerenes have shown higher photovoltaic performance than PCBM resulting from their high-lying LUMO levels. Itoh and co-workers carried out a systematic study on a series of fulleropyrrolidine derivatives, some of which possess higher V OC and efficiency than PCBM when blended with P3HT. [21] Troshin and co-workers reported that solar cells based on the novel pyrrolidinofullerene acceptors exhibited impressively high V OC and promising efficiency in combination with Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and P3HT compared to the PCBM-based references. [22] As the PCE of OPV devices was improved to over 11%, currently, more research efforts are required to address the long-term stability issue. Many factors may cause degradation Extensive research efforts around the world have been devoted to organic photovoltaics (OPV) over the last decade due to their unique advantages for commercial application, such as low cost, light weight, flexibility, and easy manufacture on large-scale. [1][2][3] By introducing the bulk heterojunction (BHJ) [4,5] structure into OPV devices, tremendous progress has been achieved to boost the powe...

It was shown that ESR spectroscopy is a very useful technique for monitoring the photochemical and thermal degradation of conjugated polymers commonly used in organic solar cells. The relative stability of materials can be quantified by comparing the rates of trap accumulation (dC(R)/dt) estimated from their ESR profiles.

Optical memory elements based on photoswitchable organic field-effect transistors have been designed by using an interfacial layer of photochromic spirooxazine molecules sandwiched between semiconductor and dielectric layers. Optical and electrical programming of the designed devices leads to multiple discrete states demonstrating drastically different electrical characteristics (VTH, IDS) and advanced stability.

Here we report a systematic investigation of indigo thin films grown on different dielectric underlayers. It has been revealed that aliphatic hydrocarbon chains serve as templates inducing the formation of a new crystal modification of indigo which possesses advanced charge transport properties and affords a dramatic improvement in the electrical performance of organic field-effect transistors.

The problem of batch‐to‐batch variation of electronic properties and purity of conjugated polymers used as electron donor and photon harvesting materials in organic solar cells is addressed. A simple method is developed for rapid analysis of electronic quality of polymer‐based materials. It is shown that appearance of impurities capable of charge trapping changes electrophysical properties of conjugated polymers. In particular, a clear correlation between the effective relaxation time τeff and relative photovoltaic performance (η/ηmax) is revealed for samples of poly(3‐hexylthiophene) intentionally polluted with a palladium catalyst. This dependence is also valid for all other investigated samples of conjugated polymers. Therefore, fast impedance measurements at three different frequencies allow one to draw conclusions about the purity of the analyzed polymer sample and even estimate its photovoltaic performance. The developed method might find extensive applications as a simple tool for product quality control in the laboratory and industrial‐scale production of conjugated polymers for electronic applications.

Here we report the application of the Electron Spin Resonance (ESR) spectroscopy as a highly sensitive analytical technique for assessment of the electronic quality of organic semiconductor materials, particularly conjugated polymers. It has been shown that different batches of the same conjugated polymer might contain substantially different amounts of radical species which were attributed to structural defects and/or impurities behaving as traps for mobile charge carriers. Good correlations between the concentrations of radicals in various batches of conjugated polymers and their performances in organic solar cells have been revealed.

Photochemical degradation of fullerene derivatives producing persistent radical species represents one of the key failure mechanisms of organic solar cells.