F. C. Chen

Synthesis of alternating D–A1–D–A2 terpolymers comprising two electron-deficient moieties, quinoxaline and benzothiadiazole units for photovoltaic applications

Two new regular (D–A1–D–A2) terpolymers P1 and P2 containing two electron-deficient moieties, quinoxaline and benzothiadiazole, were designed and synthesized. The resulting copolymers exhibit high thermal stability, broad absorption in the range of 300 to 950 nm, low Eg of both 1.36 and 1.57 eV, as well as deep HOMO energy levels of −5.24 and −5.62 eV. Such properties are useful in improving photovoltaic properties. Polymer solar cells (PSCs) based on optimized P1:PC71BM and P2:PC71BM (1u2006:u20062 by weight) active layers with a 3 v% DIO/CF additive displayed a power conversion efficiency (PCE) of 5.28% (Voc of 0.93 V, Jsc of 10.28 mA cm−2 and FF of 0.55) and 5.54% (Voc of 0.80 V, Jsc of 12.18 mA cm−2 and FF of 0.57), respectively, under illumination of AM1.5G (100 mW cm−2). In order to increase the PCE further, the DIO/CF processed active layer was subjected to methanol treatment that resulted in a PCE increase up to 7.13% and 7.59% for the P1:PC71BM and P2:PC71BM based devices, respectively. The methanol treatment increases all of the photovoltaic parameters, which is attributed to the lowering of series resistance, an increase of hole mobility, and reduction of charge recombination due to enlarged built-in potential.

Novel regular D–A-conjugated polymers based on 2,6-bis(6-fluoro-2-hexyl-2H-benzotriazol-4-yl)-4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene derivatives: Synthesis, optoelectronic, and electrochemical properties

Regioregular (P1) and random (P2) polymers were prepared by the reaction of equimolar amounts of dibromides M2 or M3 with bis(stannyl) monomer M1. The regioregularity of the conjugated chain in P1 was shown to affect considerably its optical properties. The HOMO/LUMO values and electrochemical band gap for polymers P1 or P2 found by cyclic voltammetry are–5.40/–3.40,–5.31/–3.33, and 2.00/1.96 eV, respectively. The LUMO levels for P1 and P2 are located higher than for PC71BM (–4.3 eV) by 0.84 and 0.97 eV, respectively. The low-lying HOMO levels of P1 and P2 are favorable for the high value of open-circuit voltage and make these polymers attractable candidates for polymer solar cells.

Conjugated poly(fluoroalkyl 3-thienylacetate)s synthesized in supercritical carbon dioxide

101 Conjugated polymers and supercritical carbon dioxide (sc CО2) in recent time have attracted a con siderable attention of researchers not only from scien tific but also from practical viewpoint on account of their use in different areas of science and technology. These polymers are intensely used as electroactive materials for light emitting diodes, field effect tran sistors, electrochromic devices, chemosensors, and solar photoelectric cells [1–7], whereas sc CО2 behaves as an environmentally friendly “green” solvent that becomes a real alternative to organic solvents for different chemical processes, including fine organic synthesis and polymer preparation [8, 9]. However, the practical application of sc CО2 for the synthesis of polymers is confined on account of poor solubility of the majority of polymers except for amorphous fluo rine containing polymers and silicones [10].

New Donor-Acceptor Benzotrithiophene-Containing Conjugated Polymers for Solar Cells

In the present study four new low band gap alternating donor-acceptor copolymers based on benzotrithiophene were synthesized under Stille reaction conditions. All polymers show good solubility in common organic solvents and a broad absorption in the visible region of the solar spectrum. The band gap of polymer films and HOMO levels of polymers were obtained from the voltammograms and vary in the range 1.4–2.4 eV and −5.0 – 5.4 eV, respectively. Open circuit voltage and efficiency of the developed polymer solar cells are in the range 0.33–0.57 V and 0.01–0.14 %, respectively.

New conjugated electroluminescent triphenylamine-containing polymers with side-chain pyridin-2-ylimidazo[1,5-a]pyridine groups for polymer light-emitting diodes

165 In recent years, light emitting diodes (LEDs) based on conjugated polymers have attracted considerable attention of researchers owing to their promising potential as new generation full color flat panel dis plays [1–6]. An important problem that still remains unsolved is improving of the external quantum effi ciency (EQE) of polymeric light emitting diodes. The principle of operation of thin layer LED structures is based on electroluminescence (EL) caused by radia tive decay of excitons arising upon recombination of the electrons and holes injected from opposite elec trodes into the polymer layer. Perfect conditions for producing intense EL and reaching high EQE values for a polymer are high electron–hole conductivity of the medium (that is, high mobility of charge carriers) and maintenance of the balance of injected charge carriers of different signs from the opposite electrodes into the material bulk. The mobilities of electrons and holes should not differ considerably. The main approach to the improvement of EQE for polymeric light emitting diodes is development of luminescent bipolar (donor–acceptor) polymers [7, 8] where charge transport and light emission functions are con centrated within the same macromolecule. However, in donor–acceptor polymers, rather strong intramo lecular charge transfer (ICT) occurs along the back bone, resulting in a decrease in the luminescence intensity despite better charge transport [7, 8]. An alternative strategy to overcome this issue is develop ment of p type polymers with n type electronegative side groups [9]. According to this approach, a number of conjugated polymers with oxadiazole and quinoxa line side groups exhibiting promising electrolumines cence properties were successfully developed [10–12]. However, the application of these materials was held up due to complexity of the synthesis.