Controlled nanomorphology of PCDTBT–fullerene blends via polymer end-group functionalization for high efficiency organic solar cells

We propose a novel method for the control of nanoscale morphologies of the photoactive layers of organic solar cells by using end group functionalization of p-type polymers. The devices based on the end-fluorinated PCDTBT exhibit a remarkably enhanced efficiency as high as 6.0% without applying any post-treatments, additives or optical spacers.open114139sciescopu

Microwave Photonic Mixer Utilizing an InGaAs Photoconductor for Radio over Fiber Applications

A microwave photonic mixer utilizing an InGaAs photoconductor for radio over fiber applications is proposed and fabricated. Static and dynamic characteristics of the fabricated microwave photonic mixer were investigated. The microwave photonic mixer showed an optical bandwidth of approximately 300 MHz and a uniform conversion loss characteristic for the electrical input frequency up to 20 GHz.1145sciescopu

High performance organic photovoltaic cells using polymer-hybridized ZnO nanocrystals as a cathode interlayer

Solution-processed zinc oxide nanocrystals (ZnO NCs) hybridized with insulating poly(ethylene glycol) (PEG) are introduced as a cathode interlayer in bulk heterojunction organic photovoltaic cells based on poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C61 butyric acid methyl ester (PC61BM) blends. The performance of devices with ZnO-PEG interlayers exhibit an excellent maximum power conversion efficiency (PCE) of 4.4% with a fill factor (FF) of 0.69 under optimized conditions. This enhanced device performance is attributed to decreased series resistance from the hole blocking properties of ZnO, as well as the facilitated electron transport due to the reduced area of ZnO domain boundaries upon addition of PEG. The addition of PEG also lowers the electron affinity of ZnO, which leads to a nearly Ohmic contact at the polymer/metal interface. Moreover, the ZnO-PEG interlayer serves as an optical spacer that enhances light absorption and thereby increases the photocurrent. The addition of PEG permits control over layer thickness and refractive indices. Improved photon energy absorption is supported by optical simulations. Devices with highly stable metals such as Ag and Au also show dramatically enhanced performance comparable to conventional devices with Al cathode. Due to its simplicity and excellent characteristics, this multifunctional interlayer is suitable for high performance printed photovoltaic cells.X1186Nsciescopu

Synthesis and photovoltaic properties of benzo[1,2-b:4,5-b′]dithiophene derivative-based polymers with deep HOMO levels

Two benzo[1,2-b:4,5-b']dithiophene (BDT) derivatives with conjugated substituents, triisopropylsilylethynyl (TIPS) and 4-octylphenylethynyl groups, were synthesized as donor units (D) and copolymerized with two acceptor units (A), 4,7-bis(4-octylthiophen-2-yl)-2,1,3-benzothiadiazole (BT) and 4,4'-diundecyl-2,2'-bithiazole (BTZ), respectively, using Stille coupling reaction to afford four new copolymers, PTBDT-BT, PTBDT-BTZ, POPEBDT-BT, POPEBDT-BTZ. All polymers exhibited highest occupied molecular orbital (HOMO) energy levels that were deeper than -5.4 eV due to the conjugated substituents. Small band gaps were successfully achieved for PTBDT-BT (1.67 eV) and POPEBDT-BT (1.67 eV) and were attributable to the strong intramolecular charge transfer within the D-A alternating structure. The resultant photovoltaic performances showed high open-circuit voltages (V-oc) ranging from 0.73 V to 0.92 V, whereas the power conversion efficiencies (PCEs) depended strongly on the blend morphologies. The polymer solar cell based on the blend of PTBDT-BT and PC71BM gave the best photovoltaic performance among the series, with a high V-oc of 0.81 V and a PCE of 4.61%.open112828sciescopu

Enhanced Performance in Polymer Solar Cells by Surface Energy Control

Enhanced performance of an inverted-type polymer solar cell is reported by controlling the surface energy of a zinc oxide (ZnO) buffer layer, on which a photoactive layer composed of a polymer: fullerene-derivative bulk heterojunction is formed. With the approach based on a mixed self-assembled monolayer, the surface energy of the ZnO buffer layer can be controlled between 40 mN m(-1) and 70 mN m(-1) with negligible changes in its work function. For the given range of surface energy the power conversion efficiency increases from 3.27% to 3.70% through enhanced photocurrents. The optimized morphology obtained by surface energy control results in the enhanced photocurrent and transmission electron microscopy analysis verifies the correlation between the surface energy and the phase morphology of the bulk heterojunction. These results demonstrate that surface energy control is an effective method for further improving the performance of polymer solar cells, with potentially important implications for other organic devices containing an interface between a blended organic active layer and a buffer or an electrode layer.X11188179sciescopu

ITO-free inverted polymer solar cells using a GZO cathode modified by ZnO

A gallium-doped ZnO (GZO) layer was investigated and compared with a conventional indium-tin-oxide (ITO) layer for use as a cathode in an inverted polymer solar cell based on poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C-61 butyric acid methyl ester (PCBM) bulk heterojunctions (BHJ). By modifying the GZO cathode with a ZnO thin layer, a high power conversion efficiency (3.4%) comparable to that of an inverted solar cell employing the same P3HT:PCBM BHJ photoactive layer with a conventional ITO/ZnO cathode was achieved. This result indicates that GZO is a transparent electrode material that can potentially be used to replace high-cost ITO. (C) 2011 Elsevier B.V. All rights reserved.X114849sciescopu