Influences of the electron donor groups on the properties of thiophene-(N-aryl)pyrrole-thiophene-based organic sensitizers

In this study, 1-(2,6-diisopropylphenyl)-2,5-di(2-thienyl)pyrrole-based metal-free organic dyes containing three different non planar electron donor groups such as methoxy or hexyloxy substituted triphenylamine and difluorenephenylamine were prepared in order to see the effect of electron donor groups on the opto-electrical properties and applied in dye-sensitized solar cells (DSSC). All three dyes showed broad absorption band in visible part of the solar spectrum (∼300 nm–600 nm). The dye (TPTDYE-3) containing sterically less hindered methoxy substituted triphenylamine was found to show relatively red shifted absorption compared to that of the dye (TPTDYE-4) containing hexyloxy substituted triphenylamine or the dye (TPTDYE-5) containing difluorenephenylamine. The optical band gaps of the three dyes were calculated to be 2.19 eV, 2.22 eV and 2.24 eV, respectively, and the highest occupied molecular orbital (HOMO) energy levels of the three dyes were found to be located at 0.65 V, 0.68 V and 0.75 V, respectively. The DSSC performance of each dye was investigated with and without coadsorbent. The maximum solar to electrical energy conversion efficiencies (η) of the DSSCs made from only sensitizer were 4.18%, 5.28% and 5.42% while those of the DSSCs made from sensitizer with coadsorbent were 5.47%, 5.58% and 5.63%, respectively.     

Synthesis and photovoltaic properties of donor–acceptor polymers incorporating a structurally-novel pyrrole-based imide-functionalized electron acceptor moiety

A structurally-novel pyrrole-based imide-functionalized electron accepting monomer unit, 4,6-dibromo-2,5-dioctylpyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (DPPD), was prepared. The new DPPD unit was copolymerized with pyrrole-based electron rich monomers, such as thiophene-(N-alkyl)pyrrole-thiophene (TPT) and fused thiophene-(N-alkyl)pyrrole-thiophene (DTP) derivatives, to afford two new polymers, namely P(TPT-DPPD) and P(DTP-DPPD), respectively. The two polymers showed a strong absorption band at 300–600 nm and 300–650 nm, respectively, and their calculated optical band gaps were 2.09 eV and 1.89 eV, respectively. The electrochemical analysis reveals that the highest occupied molecular orbital (HOMO) energy levels of P(TPT-DPPD) and P(DTP-DPPD) were positioned at −5.55 eV and −5.24 eV, respectively, whereas their lowest unoccupied molecular orbital (LUMO) energy levels were positioned at −3.46 eV and −3.35 eV, respectively. The preliminary photovoltaic properties of the polymers, P(TPT-DPPD) and P(DTP-DPPD), were examined by fabricating polymer solar cells (PSCs) with each polymer as an electron donor and PC₇₁BM as an electron acceptor. The PSCs fabricated with the configuration of ITO/PEDOT:PSS/P(TPT-DPPD) or P(DTP-DPPD):PC₇₁BM/LiF/Al showed maximum power conversion efficiency (PCE) of 0.73% and 1.64%, respectively.     

Synthesis of conjugated polymers with broad absorption bands and photovoltaic properties as bulk heterojuction solar cells

Two new broad absorbing alternating copolymers, poly[1-(2,6-diisopropylphenyl)-2,5-bis(2-thienyl)pyrrole-alt-4,7-bis(3-octyl-2-thienyl)benzothiadiazole] (PTPTTBT-P1) and poly[1-(p-octylphenyl)-2,5-bis(2-thienyl)pyrrole-alt-4,7-bis(3-octyl-2-thienyl)benzothiadiazole] (PTPTTBT-P2), were prepared via Suzuki polycondensation with high yields. The two polymers were found to show characteristic absorption in the visible region of the solar spectrum. Interestingly the absorption of PTPTTBT-P1 was found to cover the visible region from 350 to 650 nm with the broad and flat absorption maximum from 440 to 510 nm in film and the absorption of PTPTTBT-P2 was found to cover the visible region from 350 to 950 nm with the relatively distinct absorption maxima at 425 and 522 nm and very weak absorption maximum at 832 nm in film. The electrochemical band gaps of the polymers were calculated to be 1.88 eV and 1.87 eV, respectively, while the optical band gaps of the polymers were calculated to be 1.94 eV and 1.87 eV, respectively. The photovoltaic properties of polymers were investigated with bulk heterojunction (BHJ) solar cells fabricated in ITO/PEDOT:PSS/polymer:PC₇₀BM(1:5 wt%)/TiOx/Al configurations. The maximum power conversion efficiency (PCE) of the solar cell composed of PTPTTBT-P1:PC₇₀BM as an active layer was 1.57% with current density (J_sc) of 8.17 mA/cm², open circuit voltage (V_oc) of 0.52 V and fill factor (FF) of 36%.     

Optimization of phosphatase- and redox cycling-based immunosensors and its application to ultrasensitive detection of troponin I

The authors herein report optimized conditions for ultrasensitive phosphatase-based immunosensors (using redox cycling by a reducing agent) that can be simply prepared and readily applied to microfabricated electrodes. The optimized conditions were applied to the ultrasensitive detection of cardiac troponin I in human serum. The preparation of an immunosensing layer was based on passive adsorption of avidin (in carbonate buffer (pH 9.6)) onto indium-tin oxide (ITO) electrodes. The immunosensing layer allows very low levels of nonspecific binding of proteins. The optimum conditions for the enzymatic reaction were investigated in terms of the type of buffer solution, temperature, and concentration of MgCl(2), and the optimum conditions for antigen-antibody binding were determined in terms of incubation time, temperature, and concentration of phosphatase-conjugated IgG. Very importantly, the antigen-antibody binding at 4 °C is extremely important in obtaining reproducible results. Among the four phosphatase substrates (L-ascorbic acid 2-phosphate (AAP), 4-aminophenyl phosphate, 1-naphthyl phosphate, 4-amino-1-naphthyl phosphate) and four phosphatase products (L-ascorbic acid (AA), 4-aminophenol, 1-naphthol, 4-amino-1-naphthol), AAP and AA meet the requirements most for obtaining easy dissolution and high signal-to-background ratios. More importantly, fast AA electrooxidation at the ITO electrodes does not require modification with any electrocatalyst or electron mediator. Furthermore, tris(2-carboxyethyl)phosphine (TCEP) as a reducing agent allows fast redox cycling, along with very low anodic currents at the ITO electrodes. Under these optimized conditions, the detection limit of an immunosensor for troponin I obtained without redox cycling of AA by TCEP is ca. 100 fg/mL, and with redox cycling it is ca. 10 fg/mL. A detection limit of 10 fg/mL was also obtained even when an immunosensing layer was simply formed on a micropatterned ITO electrode. From a practical point of view, it is of great importance that ultralow detection limits can be obtained with simply prepared enzyme-based immunosensors.     

Synthesis and photovoltaic properties of heteroaromatic low-band gap oligomers for bulk heterojunction solar cells

Two new low band gap oligomers, TPyTDzQ-P1 and TPyTDzQ-P2, comprised of electron rich 1-(2,6-diisopropylphenyl)-2,5-di(2-thienyl)pyrrole or 1-(p-octylphenyl)-2,5-di(2-thienyl)pyrrole (TPyT) and electron deficient 6,7-di-2-methylpropane-4,9-bis-(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline (DzQ) units were synthesized using the Suzuki polycondensation reaction. The oligomers were found to harvest the solar flux from the ultraviolet (300 nm) to near infrared (1200 nm) regions. The optical bad gaps of the two oligomers were calculated to be 1.08 eV and 1.10 eV, respectively, while the electrochemical band gaps were calculated to be 1.17 eV and 1.19 eV, respectively. The two oligomers were used as electron donor materials in bulk heterojunction (BHJ) solar cells. The solution processable bulk heterojunction solar cells with ITO/PEDOT:PSS/TPyTDzQ-P1 or TPyTDzQ-P2:PC₇₀BM/TiOx/Al configuration showed a maximum power conversion efficiency (PCE) of 0.43% with a short-circuit current density (J_sc) of 3.41 mA/cm², open-circuit voltage (V_oc) of 0.39 V and fill factor (FF) of 32%.