Donor–acceptor copolymers based on phenanthrene as electron‐donating unit: Synthesis and photovoltaic performances

Abstract

Using 9,10-bis(dodecyloxy)phenanthrene as electrondonating unit and 4,7-dithienyl-5,6-bis(dodecyloxy)benzothiadiazole, 4,7-dithienyl-5,6-bis(octyloxy)benzoxadiazole, 5,8-dithienyl-2,3-bis(para-octyloxyphenyl)quinoxaline, and 5,8-dithienyl-2,3-bis(meta-octyloxyphenyl)quinoxaline as electron-accepting unit, four D-A copolymers PPA-DTBT, PPA-DTBX, PPA-p-DTQ, and PPA-m-DTQ, respectively, were successfully synthesized as new polymeric donors for photovoltaic cells. All the alternating copolymers can show two absorption bands, both in solutions and thin films. The optical bandgaps of the polymers are quite close, which are between 1.93 and 2.00 eV. The HOMO and LUMO levels of the polymers are also comparable of 25.52 6 0.03 eV and 23.57 6 0.03 eV, respectively. Thus, using the dialkoxyphenanthrene as the D unit could afford D-A copolymers with deep-lying HOMO levels, which would be an important factor to achieve high open-circuit voltages (V oc ) in bulkheterojunction solar cells. With the copolymers as the donor and PC 71 BM as the acceptor, the resulting solar cells could display good V oc between 0.86 and 0.88 V. Among the four copolymers, PPA-DTBT containing the dialkoxybenzothiadiazole unit showed the best power conversion efficiency of 3.03% because of its relatively higher hole mobility and better phase separation. The results suggest that dialkoxyphenanthrene is a valuable electron-donating unit in the constructions of D-A copolymers for efficient solar cells with high V oc . V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4966-4974

Low band‐gap D–A conjugated copolymers based on anthradithiophene and diketopyrrolopyrrole for polymer solar cells and field‐effect transistors

“…The second band at the long‐wavelength range, with the absorptions peaks at 775 for PADT‐DPP and 745 nm for PADT‐FDPP, should be attributed to intramolecular charge transfer (ICT) of the D–A conjugated polymers . The extent of ICT transition is an indirect parameter to assess the electron‐donating ability of a donor unit . The ratio of the maximum absorbance of the first band to the second band in PADT‐DPP is 0.64, which is higher than that in PADT‐FDPP with a value of 0.45.…”

“…Bilayer cathode consisting of a hydrophilic conjugated polymer and a high work‐function metal electrode has shown great potential to improve the device performances, where open‐circuit voltage ( V oc ), short‐circuit current density ( J sc ), and fill factor (FF) could be increased simultaneously in some cases . 2,7‐Carbazole‐1,4‐phenylene‐based alternating copolymer (PCP‐EP) with phosphonate end groups as pendants has exhibited good modification effects as cathode interlayer in light‐emitting diodes and solar cells . Here, we also selected the PCP‐EP/Al as the bilayer cathode for the constructions of solar cells with a device configuration of ITO/PEDOT:PSS (40 nm)/(polymer:PC 71 BM = 1:2) (80 nm)/PCP‐EP (10 nm)/Al (100 nm).…”

Solubilized 5,6-bis(octyloxy)benzoxadiazole as a versatile acceptor block for designing novel (-X-DADAD-)n and (-X-DADADAD-)n electron donor copolymers for bulk heterojunction organic solar cells

“…Additionally, BO-based polymers usually are more crystalline and demonstrate higher charge carrier mobilities in comparison with the BT-based analogues [18,19]. However, a high crystallinity might also cause low solubility of the BO-containing polymers challenging their processing and leading to a non-optimal morphology of the polymer-fullerene blend films [20,21,22]. This problem was partially solved by application of soluble 5,6-bis(alkoxy)-substituted BO as an acceptor block [23,24].…”