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A non‐conjugated polymer acceptor PF1‐TS4 was firstly synthesized by embedding a thioalkyl segment in the mainchain, which shows excellent photophysical properties on par with a fully conjugated polymer, with a low optical band gap of 1.58 eV and a high absorption coefficient >105 cm−1, a high LUMO level of −3.89 eV, and suitable crystallinity. Matched with the polymer donor PM6, the PF1‐TS4‐based all‐PSC achieved a power conversion efficiency (PCE) of 8.63 %, which is ≈45 % higher than that of a device based on the small molecule acceptor counterpart IDIC16. Moreover, the PF1‐TS4‐based all‐PSC has good thermal stability with ≈70 % of its initial PCE retained after being stored at 85 °C for 180 h, while the IDIC16‐based device only retained ≈50 % of its initial PCE when stored at 85 °C for only 18 h. Our work provides a new strategy to develop efficient polymer acceptor materials by linkage of conjugated units with non‐conjugated thioalkyl segments. [ABSTRACT FROM AUTHOR]

Two wide‐bandgap (WBG) conjugated polymers (PBPD‐p and PBPD‐m) based on phenyl‐substituted benzodithiophene (BDT) with the different substitution position of the alkyl side chain and benzodithiophene‐4,8‐dione (BDD) units are designed and synthesized to investigate the influence of alkyl substitution position on the photovoltaic performance of polymers in polymer solar cells (PSCs). The thermogravimetric analysis, absorption spectroscopy, molecular energy level, X‐ray diffraction, charge transport and photovoltaic performance of the polymers are systematically studied. Compared with PBPD‐p, PBPD‐m exhibits a slight blue‐shift but a deeper highest occupied molecular orbital (HOMO) energy level, a tighter alkyl chain packing and a higher hole mobility. The PBPD‐m‐based PSCs blended with acceptor IT‐4F shows a higher power conversion efficiency (PCE) of 11.95% with a high open‐circuit voltage (Voc) of 0.88 V, a short‐circuit current density (Jsc) of 19.76 mA cm−2 and a fill factor (FF) of 68.7% when compared with the PCE of 6.97% with a Voc of 0.81 V, a Jsc of 15.97 mA cm−2 and an FF of 53.9% for PBPD‐p. These results suggest that it is a feasible and effective strategy to optimize photovoltaic properties of WBG polymers by changing the substitution position of alkyl side chain in PSCs. [ABSTRACT FROM AUTHOR]

Abstract: Two D–A copolymers containing dithienosilole (DTS) donor unit and phthalimide (Ph) acceptor unit, PDTSPh and PDTSBTPh, were synthesized by the Pd-catalyzed Stille-coupling method. The copolymers have a strong absorption ranging from 350 to 650nm, exhibit good solubility and thermal stability. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the copolymers determined by cyclic voltammetry were about −5.2 and −3.0eV, respectively. The power conversion efficiency of the polymer solar cells based on PDTSBTPh:PC70BM (1:2, w/w) reached 2.1% with open-circuit voltage of 0.83V and a short-circuit current of 6.27mA/cm2, under the illumination of AM1.5, 100mW/cm2. [Copyright &y& Elsevier]

A new benzodithiophene (BDT)‐based polymer, poly(4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene vinylene) (PBDTV), was synthesized by Pd‐catalyzed Stille‐coupling method. The polymer is soluble in common organic solvents and possesses high thermal stability. PBDTV film shows a broad absorption band covering from 350 nm to 618 nm, strong photoluminescence peaked at 545 nm and high hole mobility of 4.84 × 10−3 cm2/Vs. Photovoltaic properties of PBDTV were studied by fabricating the polymer solar cells based on PBDTV as donor and PC70BM as acceptor. With the weight ratio of PBDTV: PC70BM of 1:4 and the active layer thickness of 65 nm, the power conversion efficiency of the device reached 2.63% with Voc = 0.71 V, Isc = 6.46 mA/cm2, and FF = 0.57 under the illumination of AM1.5, 100 mW/cm2. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1822–1829, 2010 [ABSTRACT FROM AUTHOR]

Abstract: Fluorination of conjugated polymers is one of the effective strategies to tune the molecular energy levels and morphology for high efficient polymer solar cells (PSCs). Herein, two novel donor‐acceptor conjugated polymers, PffBT and PBT, based on bis(3,5‐bis(hexyloxy)phenyl)benzo[1,2‐ b:4,5‐b']dithiophene and benzo[c][1,2,5]thiadiazole (BT) with or without fluorination, respectively, were synthesized, and their photovoltaic properties were compared. The polymer PffBT based on fluorinated BT showed lower frontier energy levels, improved polymer ordering, and a well‐developed fibril structure in the blend with PC71BM. As a result, the PSCs based on PffBT/PC71BM exhibit a superior power conversion efficiency (PCE) of 8.6% versus 4.4% for PBT‐based devices, due to a high space charge limit current (SCLC) hole mobility, mixed orientation of polymer crystals in the active layer, and low bimolecular recombination. [ABSTRACT FROM AUTHOR]

Abstract: Two low bandgap conjugated polymers containing vinylene unit on their main chains, poly(dithienosilole vinylene) derivatives P1 and P2, were synthesized by Pd-catalyzed Stille-coupling method. The two polymers show good solubility in common organic solvents, broad absorption bands from 500nm to 700nm and lower energy bandgap of 1.72eV for P1 and 1.77eV for P2. The electronic energy levels of the polymers were measured by electrochemical cyclic voltammetry. The HOMO and LUMO energy levels of P1 and P2 are at −5.03eV, −5.18eV and −3.39eV, −3.43eV, respectively. The polymers P1 and P2 containing dithienosilole units show lower HOMO and LUMO energy levels, in comparison with other poly(thienylene vinylene) derivatives. [Copyright &y& Elsevier]

Two new 2D-conjugated D-A copolymers, PBDTT-S-DPP and PBDTSe-S-DPP , based on benzodithiophene (BDT) donor unit with alkylthio-thiophene or alkylthio-selenophene conjugated side chains and 2,5-bis(2-butyloctyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione) (DPP) acceptor unit, were synthesized for the application as donor materials in polymer solar cells (PSCs). The two polymers were characterized by absorption spectroscopy, cyclic voltammetry, thermogravimetric analysis, theoretical calculation with density functional theory, X-ray diffraction and photovoltaic measurements. The results show that the alkylthio-thiophene/selenophene side groups on BDT unit and intramolecular hydrogen bonding interaction in DPP acceptor unit play important roles in affecting the absorption, HOMO energy levels, molecular planarity and the crystallinity of the polymers. The PSCs based on PBDTT-S-DPP or PBDTSe-S-DPP as donor and PC 71 BM as acceptor demonstrate power conversion efficiency (PCE) of 5.62% and 5.01%, with relatively higher V oc of 0.79 V and 0.76 V, respectively. [ABSTRACT FROM AUTHOR]

Two electron-donating sides chain (octylthio and methoxy) were strategically attached on BDTT unit to develop two new polymers ( PBDTT-OS-TT-EF and PBDTT-OS-TT-CF ) as donor materials for polymer solar cells. PBDTT-OS-TT-EF and PBDTT-OS-TT-CF show broad absorption spectra with narrow optical band-gap of 1.52 and 1.56 eV, and low-lying HOMO energy level of −5.34 and −5.46 eV, respectively. A high V oc of 0.92 V was obtained from the PSC devices based on PBDTT-OS-TT-EF . Particularly, the V oc of PSC device based on PBDTT-OS-TT-CF is as high as 1.00 V, which is the highest value for the devices based on TT-base polymers. The results indicate that the engineering two electron-donating side chains in BDTT unit is an effective strategy to narrow the band-gap and manipulate the energy levels of polymers, which can be potentially applied to design polymer donor materials with high V oc values. [ABSTRACT FROM AUTHOR]

[Display omitted] • Derived from Y6, BTSi-4F has a novel bulky siloxane-terminated group as side-chains. • BTSi-4F exhibits a better solubility and up-shifted LUMO energy level. • BTSi-4F shows a more ordered molecular packing, and higher electron-mobility. • The PM6:BTSi-4F film shows a better blend miscibility than PM6:Y6 film. • The PCE of the OSCs was improved from 13.0% to 16.6% upon modification. As one of the simple but most effective molecular design strategies, side-chain engineering has been widely employed to modify the photoelectric properties of active layer materials for boosting the photovoltaic performance of organic solar cells (OSCs). Herein, a functionalized small molecule acceptor (SMA) named BTSi-4F with a bulky siloxane-terminated solubilizing group as side-chains, derived from a classical SMA of Y6, was designed and synthesized. The results demonstrate that the introduction of siloxane-functional terminated groups into SMA not only affects the optical absorption and molecular energy levels, but also regulates the miscibility between the polymer donor and SMA. Compared to the original Y6, BTSi-4F exhibits a better solubility, upshifted lowest unoccupied molecular orbital (LUMO) energy level, more ordered molecular packing, and higher electron-mobility. Matched with a wide bandgap polymer donor PM6, the chlorobenzene-processed OSCs based on PM6:BTSi-4F achieved a superior power conversion efficiency (PCE) of 16.6% with both high open-circuit voltage (V oc) of 0.90 V and high fill factor (FF) of 0.77, while the devices based on PM6:Y6 obtained a much lower PCE of 13.0% with a V oc of 0.81 V and FF of 0.69 under the same conditions. This work offers a promising molecular design strategy of siloxane-terminated side chain engineering to develop high-performance SMAs for efficient OSCs. [ABSTRACT FROM AUTHOR]

As researcherscontinue to develop new organic materials for solarcells, benzo[1,2-b:4,5-b']dithiophene(BDT)-based polymers have come to the fore. To improve the photovoltaicproperties of BDT-based polymers, researchers have developed and appliedvarious strategies leading to the successful molecular design of highlyefficient photovoltaic polymers. Novel polymer materials composedof two-dimensional conjugated BDT (2D-conjugated BDT) have boostedthe power conversion efficiency of polymer solar cells (PSCs) to levelsthat exceed 9%. [ABSTRACT FROM AUTHOR]

Abstract: A new conjugated polymer, poly(3,6-dihexyl-thieno[3,2-b]thiophenyl-2,5-diyl-alt-2,5-di(2-ethylhexyl)-3,6-bis(thien-2,5-diyl)-pyrrolo[3,4-c]-pyrrole-1,4-dione) (DH-PTTDPP) was synthesized by Pd-catalyzed Stille-coupling method. The thermal, absorption, electrochemical, photovoltaic properties, and field-effect charge transport of the polymer were examined. The polymer is soluble in common organic solvents and possesses a broad absorption band covering from 500nm to 900nm with an optical bandgap of 1.33eV. Field-effect transistors (FETs) based on DH-PTTDPP thin film showed a hole mobility of 2.5×10−3 cm2 V−1 s−1 with an on/off ratio of 105, which is among the high values for the conjugated polymers. Polymer solar cells (PSCs) based on DH-PTTDPP/PC70BM (1:1.5, w/w) demonstrated a power conversion efficiency of 1.90% under the illumination of AM 1.5, 100mWcm−2. These results indicate that DH-PTTDPP is an attractive polymer semiconductor for the applications in FETs and PSCs. [Copyright &y& Elsevier]

Abstract: Three alternative copolymers of carbazole (Cz) and triphenylamine (TPA) with substituent containing acceptor group of aldehyde (PCzTPA-CHO), mono-cyano (PCzTPA-CN) or di-cyano (PCzTPA-DCN), were designed and synthesized. Through manipulating the acceptor group attached to TPA unit, the electronic properties and energy levels of the copolymers were effectively tuned. The presence of pendant cyano groups leads to a decrease in the LUMO levels, but influences the HOMO levels very little, so that results in a lower bandgap and red-shift of its absorption spectrum. These results suggest a simple and effective approach for tuning the bandgap in a conjugated polymer through modification of the pendant acceptor groups. Their optoelectronic properties are largely determined by the nature of pendant substituent. Polymer solar cell based on PCzTPA-CN as donor and PC70BM as acceptor demonstrates a power conversion efficiency of 0.81% with a high V oc of 0.93V. [Copyright &y& Elsevier]