Improved Performance of Polymer:Polymer Solar Cells by Doping Electron-Accepting Polymers with an Organosulfonic Acid
(4527–4534)Advanced Functional Materials 21  #23 (2011)
Nam et al, South Korea, improved the performance of polymer:polymer solar cells that are made using blend films of poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-co- benzothiadiazole (F8BT) by doping the F8BT polymer with an organosulfonic acid [4-ethylbezenesulfonic acid (EBSA)].  The F8BT-EBSA films exhibit huge photoluminescence quenching, ionization potential shift toward lower energy, and greatly enhanced electron mobility. The short-circuit current density of solar cells is improved by ca. twofold (10 wt.% EBSA doping), while the open-circuit voltage increases by ca. 0.4 V. Consequently, the power conversion efficiency was improved by ca. threefold, even though the optical density of the P3HT:F8BT-EBSA blend film is reduced by 10 wt.% EBSA doping due to the nanostructure and surface morphology change.  (RDC 12/6/2011)

Synthesis and Characterization of a Thiophene Copolymer for Photovoltaic Application
(1044-1048) Journal of Macromolecular Science Part A - Pure and Applied Chemistry 48 #12 (2011)
Abstract
Satapahti, Anandakathir and Kumar of the University of Massachusetts, Massachusetts, synthesized a soluble thiophene copolymer having polar and non polar side groups.  Dye sensitized solar cells were fabricated using this copolymer as sensitizer. An open-circuit voltage of 0.50V, a short-circuit current density of 1.195 mA/cm2 and an overall power conversion efficiency of 0.3% were measured.  (RDC 11/2/2011)

Degradation and stabilization of poly(3-hexylthiophene) thin films for photovoltaic applications
(211-222) Polymer Bulletin 66 #2 (2011)
Griffini, Turri and Levi, Italy studied the degradation of poly(3-hexylthiophene) (P3HT) by irradiating polymer films by means of simulated sunlight.  The results of this study highlighted a remarkable instability of P3HT. The addition of MWCNT appeared to significantly reduce the rate of degradation.  (RDC 1/28/2011)

Low bandgap polymers with benzo [1,2-b:4,5-b′] dithiophene and bisthiophene-dioxopyrrolothiophene units for photovoltaic applications  
(415-421) Polymer 52 #2 (2011)
Zhang et al of the Shanghai Jiao Tong University, China synthesized new donor/acceptor polymers PBDTTPT1 and PBDTTPT2 with alternating benzodithiophene (BDT) and bisthiophene-dioxopyrrolothiophene (TPT) units by the Stille coupling reaction. The polymers had optical bandgaps of 1.78 and 1.82 eV, and HOMO energy levels of −5.30 and −5.35 eV for PBDTTPT1 and PBDTTPT2, respectively. Polymeric solar cell devices based on these copolymers as donors and PC71BM as acceptor showed the highest open circuit voltage of 0.95 V and power conversion efficiency of 2.68% under the illumination of AM 1.5, 100 mW/cm2.  (RDC 1/27/2011)

Synthesis and application of H-Bonded cross-linking polymers containing a conjugated pyridyl H-Acceptor side-chain polymer and various carbazole-based H-Donor dyes bearing symmetrical cyanoacrylic acids for organic solar cells  
(6182-6192) Polymer 51 #26 (2010)
Sahu et al of the National Chiao Tung University and Academia Sinica, Taiwan prepared a series of hydrogen-bonded (H-bonded) cross-linking polymers were generated by complexing various proton-donor (H-donor) solar cell dyes containing 3,6- and 2,7-functionalized electron-donating carbazole cores bearing symmetrical thiophene linkers and cyanoacrylic acid termini with a proton-acceptor (H-acceptor) side-chain homopolymer carrying pyridyl pendants (with 1/2 M ratio of H-donor/H-acceptor).  From DFT (density functional theory) calculations, the optimized geometries of organic dyes reflected that the carbazole cores of H-donor dyes were coplanar with the conjugated thiophenes and cyanoacrylic acids, which is essential for strong conjugations across the donor-acceptor units in D1–D4 dyes. (RDC 1/27/2011)

1/21/2011
Thieno[3,4-c]pyrrole-4,6-dione-Based Donor−Acceptor Conjugated Polymers for Solar Cells
(269–277) Macromolecules 44 #2 (2011)
Guo et al  of the University of Kentucky and University of Washington synthesized three new donor−acceptor conjugated polymers incorporating thieno[3,4-c]pyrrole-4,6-dione (TPD) acceptor and dialkoxybithiophene or cyclopentadithiophene units as donors in bulk heterojunction (BHJ) solar cells and organic field-effect transistors (OFETs).  These results demonstrate the tuning of the open circuit voltage and thus the photovoltaic efficiency of BHJ solar cells based on copolymers containing thieno[3,4-c]pyrrole-4,6-dione acceptor.  (RDC 1/19/2011)

A Tale of Current and Voltage: Interplay of Band Gap and Energy Levels of Conjugated Polymers in Bulk Heterojunction Solar Cells
(10390–10396) Macromolecules 43 #24 (2010)
Zhou et al of the University of North Carolina at Chapel Hill, North Carolina have proposed a strategy of “weak donor−strong acceptor” copolymer to approach ideal polymers with both a low HOMO energy level and a small band gap for bulk heterojunction (BHJ) polymer solar cells in order to achieve both a high open circuit voltage (Voc) and a high short circuit current (Jsc)  Two such “weak donors”, naphtho[2,1-b:3,4-b′]dithiophene (NDT) and dithieno[3,2-f:2′,3′-h]quinoxaline (QDT), which differ only by two atoms, were copolymerized with a common acceptor, 4,7-di(2-thienyl)-2,1,3-benzothiadiazole (DTBT).  Through these two structurally related polymers, we demonstrate that incorporating electron-withdrawing atoms in the donor unit would lead to a lower HOMO energy level. This lower HOMO energy level translates into a higher open circuit voltage (Voc) of 0.83 V in PQDT−4DTBT-based BHJ devices. In contrast, the slightly higher HOMO energy level (− 5.34 eV) of PNDT−4DTBT limits the Voc to 0.67 V.  (RDC 1/19/2011)