A number of copolymers based on 4H-cyclopenta[2,1-b:3,4-b']dithiophene and 4H-dithieno[3,2-b:2',3'-d]silol are synthesized via direct С–Н arylation and Suzuki cross-coupling, and their properties are compared. The chemical structure of the copolymers is investigated by 1Н and 13С NMR spectroscopy, and their molecular-mass characteristics are determined by GPC. The study of absorption spectra of the copolymers in dilute solutions and thin films shows that they absorb light in a wide visible spectral range (300–800 nm). On the basis of the cyclic voltammetry data, the levels of boundary molecular orbitals—the highest occupied and the lowest unoccupied—are estimated and the width of the energy gap is shown to be in the range of 1.4–1.9 eV. Using the copolymers as donor components of the active layer, the samples of solar photocells are manufactured and their photovoltaic properties are investigated.

The performance of three different star-shaped oligomers (SSOs) as electron donor materials for organic solar cells is investigated. These promising donor components are blended with [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) fullerene acceptor and solution-processed normal and inverted organic solar cells are fabricated. These SSOs are based on a triphenylamine core and differ in the solubilizing groups and the oligothiophene arm length. We have found that the power conversion efficiency (PCE) is by 10-60% higher in the normal structure, mainly due to an enhanced open-circuit voltage and fill factor. The observed difference in device performance can be assigned partly to the lower leakage currents. By using contact angle measurements and atomic-force microscopy studies, we estimate the degree of vertical phase separation in bulk heterojunctions. The latter has a good correlation to the corresponding photocurrent differences obtained in the normal and inverted structure devices. (C) 2016 Elsevier B.V. All rights reserved.

Incorporation of the CF2 bridge into fullerene cages allows fine tuning of the boundary levels and endows bridgehead sites with enhanced reactivity in the anionic state. Further functionalization at those sites provides additional level tuning capabilities, which can give rise to promising acceptor-type building blocks for organic electronics. Here we report the regioselective synthesis, spectral and structural characterization of novel C-60(CF2)R-2 dialkyl derivatives (R = CH3, allyl, benzyl, CH2C6F5, CH2CO2Et), as well as their electrochemical behavior. The reported compounds can be reversibly reduced up to the trianionic state. Experimental electrochemical and DFT estimation of the HOMO and LUMO levels revealed that the energy of the frontier orbitals is increased as compared to C-60 making these compounds prospective for application as acceptor materials in polymer solar cells (PSCs). Testing the corresponding prototypical PSCs demonstrated that among the C-60(CF2)R-2 derivatives the highest power conversion efficiency was observed for C-60(CF2)(CH2CO2Et)(2) which exhibits better solubility and photoactive layer morphology. (C) 2016 Elsevier Ltd. All rights reserved.

Синтезированы четыре новых чередующихся узкозонных сополимера на основе бензодитиофена в условиях реакции Стилле. Все сополимеры обнаруживают хорошую растворимость в обычных органических растворителях и широкую абсорбцию в видимой области солнечного света по сравнению с гомополимерами бензодитиофена. Ширина запрещенной зоны полимерных пленок, полученная из вольтамперометрических данных, варьируется в пределах 1.34–2.28 эВ, а положение высшей занятой молекулярной орбитали в интервале 4.99–5.72 эВ. Напряжение холостого хода и эффективность полимерных солнечных фотоэлементов на основе синтезированных сополимеров лежат в интервале 0.22–0.65 В и 0.02–0.48% соответственно.

Solar cells based on organic semiconductor molecules are a promising alternative to conventional silicon photocells owing to their low cost, simple production, and good mechanical properties. Effective organic photocells are based on a heterojunction using an active layer consisting of two different organic semiconductors, one of which is an electron donor, while the other is an acceptor. Progress in organic photovoltaics is related to the development of new donor materials, while fullerene derivatives are commonly used as acceptors. The advantages and disadvantages of fullerene compounds for organic solar cells are discussed in this review, the principles of their operation are briefly considered, and the most successful new non-fullerene acceptors are described. The application of latter acceptors has made it possible to fabricate organic solar cells with an efficiency of about 2–4%.

Four new alternating narrow-band-gap copolymers based on benzodithiophene are synthesized under conditions of the Stille reaction. In comparison to benzodithiophene homopolymers, all these copolymers show good solubility in common organic solvents and broad absorption in the visible spectrum of sunlight. The band gaps of the polymer films, as estimated from the cyclic voltammetry data, vary within 1.34–2.28 eV, and the position of the highest occupied molecular orbital lies in the range 4.99–5.72 eV. The values of the open-circuit voltage and the efficiency of polymer solar cells based on the copolymers are within 0.22–0.65 V and 0.02–0.48%, respectively.

Four new alternating narrow band-gap copolymers containing benzodithiophene, 4,8-dithiophen-2-yl-benzo[1,2-c;4,5-c′-bis[1,2,5]thiadiazole, 4,9-bis(thiophen-2-yl)-6,7-di(2-ethylhexyl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline, 5,8-dibromo-2,3-bis(5-octylthiophen-2-yl)quinoxaline, and 4,7-bis(5-bromothiophen-2-yl)benzo[1,2,5] thiadiazole units are synthesized under Stille reaction conditions. The structures, molecular masses, and physical properties of the copolymers are studied via 1H NMR spectroscopy, GPC, cyclic voltammetry, and thermomechanical and thermogravimetric analyses. The polymers show solubility and a broad absorption region (with the band gap in the range from 0.81 to 1.53 eV). All of the polymers are photostable in air, and their levels of the highest occupied molecular orbital vary from −4.98 to −5.30 eV. Polymer solar cells based on these copolymers as donors and fullerene PC60BM as an acceptor show open-circuit voltages in the range 0.16–0.61 V, and the efficiencies of the devices are in the range 0.02–0.49%.

В условиях реакции Стиле синтезировано четыре новых чередующихся узкозонных сополимера, содержащих бензодитиофеновые, 4,8-дитиофен-2-ил-бензо[1,2-c;4,5-c]-бис-[1,2,5]тиадиазольные, 4,9-бис-(тиофен-2-ил)-6,7-ди(2-этилгексил)-[1,2,5]тиадиазоло[3,4-g]хиноксалиновые, 5,8-дибром-2,3-бис-(5-октилтиофен-2-ил)хиноксалиновые и 4,7-бис-(5-бромтиофен-2-ил)бензо[1,2,5]тиадиазольные структуры. Строение, молекулярная масса и физические свойства сополимеров исследованы с помощью спектроскопии ЯМР 1, ГПХ, циклической вольтамперометрии, термомеханического и термогравиметрического анализов. Полимеры обладают хорошей растворимостью, широкой абсорбцией (с шириной запрещенной зоны в пределах 0.81–1.53 эВ). Все полимеры фотостабильны на воздухе, уровень высшей занятой молекулярной орбитали находится в пределах от –4.98 до –5.30 эВ. Полимерные солнечные фотоэлементы на основе этих сополимеров в качестве доноров и фуллерена РС60 в роли акцептора показывают напряжение холостого хода в интервале 0.16–0.61 В и эффективность устройств в пределах 0.02–0.49%.

Conventional models of planar and bulk heterojunction organic solar cells have been extended by introducing doping in the active layer. We have studied the performance of organic solar cells as a function of dopant concentration. For bulk heterojunction cells, the modeling shows that for the most studied material pair (poly-3-hexylthiophene, P3HT, and phenyl-C61-butyric acid methyl ester, PCBM) doping decreases the short-circuit current density (JSC), fill factor (FF) and efficiency. However, if bulk heterojunction cells are not optimized, namely, at low charge carrier mobilities, unbalanced mobilities or non-ohmic contacts, the efficiency can be increased by doping. For planar heterojunction cells, the modeling shows that if the acceptor layer is n doped, and the donor layer is p doped, the open-circuit voltage, JSC, FF and hence the efficiency can be increased by doping. Inversely, when the acceptor is p doped, and the donor is n doped; FF decreases rapidly with increasing dopant concentrations so that the current-voltage curve becomes S shaped. We also show that the detrimental effect of nonohmic contacts on the performance of the planar heterojunction cell can be strongly weakened by doping.