Enhancement of photocurrent of polymer‐gelled dye‐sensitized solar cell by incorporation of exfoliated montmorillonite nanoplatelets

Poly(n‐isopropylacrylamide) (PNIPAAm) and its nanocomposite with exfoliated montmorillonite (MMT) were prepared by soap‐free emulsion polymerization and individually applied to gel the electrolyte systems for the dye‐sensitized solar cells (DSSCs). Each exfoliated MMT nanoplatelet had a thickness of ～ 1 nm, carried ～ 1.8 cation/nm², and acted like a two‐dimensional electrolyte. The DSSC with the LiI/I₂/tertiary butylpyridine electrolyte system gelled by this polymer nanocomposite had higher short‐circuit current density (J_sc) compared to that gelled by the neat PNIPAAm. The former has a J_sc of 12.6 mA/cm², an open circuit voltage (V_oc) of 0.73 V, and a fill factor (FF) of 0.59, which harvested 5.4% electricity conversion efficiency (η) under AM 1.5 irradiation at 100 mW/cm², whereas the latter has J_sc = 7.28 mA/cm², V_oc = 0.72 V, FF = 0.60, and η = 3.17%. IPCE of the nanocomposite‐gelled DSSC were also improved. Electrochemical impedance spectroscopy of the DSSCs revealed that the nanocomposite‐gelled electrolytes significantly decreased the impedances in three major electric current paths of DSSCs, that is, the resistance of electrolytes and electric contacts, impedance across the electrolytes/dye‐coated TiO₂ interface, and Nernstian diffusion within the electrolytes. The results were also consistent with the increased molar conductivity of nanocomposite‐gelled electrolytes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 47–53, 2008     

Preparation and characterization of solution processable phthalocyanine‐containing polymers via a combination of RAFT polymerization and post‐polymerization modification techniques

In this work, a benzenedinitrile functionalized monomer, 2‐methyl‐acrylic acid 6‐(3,4‐dicyano‐phenoxy)‐hexyl ester, was successfully polymerized via the reversible addition‐fragmentation chain transfer method. The polymerization behavior conveyed the characteristics of “living”/controlled radical polymerization: the first‐order kinetics, linear increase of number‐average molecular weight with monomer conversion, narrow molecular weight distribution, and successful chain‐extension experiment. The soluble Zn(II) phthalocyanine (Pc)‐containing (ZnPc) polymers were achieved by post‐polymerization modification of the obtained polymers. The Zn(II) phthalocyanine‐functionalized polymer was characterized by FTIR, UV–vis, fluorescence, atomic absorption spectroscopy, and thermogravimetric analysis. The potential application of above ZnPc‐functionalized polymer as electron donor material in bulk heterojunction organic solar cell was studied. The device with ITO/PEDOT:PSS/ZnPc‐Polymer/PC₆₁BM/LiF/Al structure provided a power conversion efficiency of 0.014%, fill factor of 0.24, open circuit voltage (V_oc) of 0.21 V, and short‐circuit current (J_sc) of 0.28 mA/cm². © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 691–698     

Poly(4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene vinylene): Synthesis,optical and photovoltaic properties

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 V_oc = 0.71 V, I_sc = 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     

Synthesis and properties of mono‐ and di‐fluoro‐substituted 2,3‐didodecylquinoxaline‐based polymers for polymer solar cells

We synthesized two new alternating polymers, namely P(Tt‐FQx) and P(Tt‐DFQx) , incorporating electron rich tri‐thiophene and electron deficient 6‐fluoroquinoxaline or 6,7‐difluoroquinoxaline derivatives. Both polymers P(Tt‐FQx) and P(Tt‐DFQx) exhibited high thermal stabilities and the estimated 5% weight loss temperatures are 425 and 460 °C, respectively. Polymers P(Tt‐FQx) and P(Tt‐DFQx) displayed intense absorption band between 450 and 700 nm with an optical band gap (E_g) of 1.78 and 1.80 eV, respectively. The determined highest occupied/lowest unoccupied molecular orbital's (HOMO/LUMO) of P(Tt‐DFQx) (?5.48 eV/?3.68 eV) are slightly deeper than those of P(Tt‐FQx) ( ?5.32 eV/?3.54 eV). The polymer solar cells fabricated with a device structure of ITO/PEDOT:PSS/ P(Tt‐FQx) or P(Tt‐DFQx) :PC₇₀BM (1:1.5 wt %) + 3 vol % DIO/Al offered a maximum power conversion efficiency (PCE) of 3.65% with an open‐circuit voltage (V_oc) of 0.59 V, a short‐circuit current (J_sc) of 10.65 mA/cm² and fill factor (FF) of 59% for P(Tt‐FQx) ‐based device and a PCE of 4.36% with an V_oc of 0.69 V, a J_sc of 9.92 mA/cm², and FF of 63% for P(Tt‐DFQx) ‐based device. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 545–552     

Hole‐buffer polymer composed of alternating p‐terphenyl and tetraethylene glycol ether moieties: Synthesis and application in polymer light‐emitting diodes

Carrier balance is essential to obtain efficient emission in polymer light‐emitting diodes (PLEDs). A new polymer 3P5O composed of alternating p‐terphenyl and tetraethylene glycol ether segments is designed and synthesized by the Suzuki coupling reaction and successfully employed as hole‐buffer layer to improve carrier balance. Multilayer PLEDs [ITO/PEDOT:PSS/ 3P5O /SY/LiF/Al], with Super Yellow (SY) as the emitting layer and 3P5O as the hole‐buffer layer, reveal maximum luminance (17,050 cd/m²) and maximum current efficiency (6.6 cd/A) superior to that without the hole‐buffer layer (10,017 cd/m², 3.0 cd/A). Moreover, it also shows better performance than that using conventional BCP as hole‐blocking layer [ITO/PEDOT:PSS/SY/BCP/LiF/Al (80 nm): 13,639 cd/m², 4.1 cd/A]. The performance enhancement has been attributed to hole‐buffering characteristics of 3P5O that results in improved carrier recombination ratio and wider carrier recombination region. Current results indicate that the 3P5O is a promising hole‐buffer polymer to enhance the performance of optoelectronic devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 785–794     

Poly((2‐alkylbenzo[1,2,3]triazole‐4,7‐diyl)vinylene)s for organic solar cells

Poly((2‐Alkylbenzo[1,2,3]triazole‐4,7‐diyl)vinylene)s (pBTzVs) synthesized by Stille coupling show different absorption spectra, solid‐state morphology, and photovoltaic performance, depending on straight‐chain versus branched‐chain (pBTzV12 and pBTzV20) pendant substitution. Periodic boundary condition density functional computations show limited alkyl pendant effects on isolated chain electronic properties; however, pendants could influence polymer backbone conjugative planarity and polymer solid film packing. The polymers are electronically ambipolar, with best performance by pBTzV12 with hole and electron transport mobilities of 4.86 × 10^?6 and 1.96 × 10^?6 cm² V^?1 s^?1, respectively. pBTzV12 gives a smooth film morphology, whereas pBTzV20 gives a very different fibrillar morphology. For ITO/PEDOT:PSS/(1:1 w/w polymer:PC₇₁BM)/LiF/Al devices, pBTzV12 gives power conversion efficiency (PCE) up to 2.87%, and pBTzV20 gives up to PCE = 1.40%; both have open‐circuit voltages of V_OC = 0.6–0.7 V. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1539–1545     

Synthesis and characterization of indenofluorene‐based copolymers containing 2,5‐bis(2‐thienyl)‐N‐arylpyrrole for bulk heterojunction solar cells and polymer light‐emitting diodes

Two novel alternating π‐conjugated copolymers, poly[2,8‐(6,6′,12,12′‐tetraoctyl‐6,12‐dihydroindeno‐[1,2b]fluorene‐ alt‐5(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole) ( P1 ) and poly[2,8‐(6,6′,12,12′‐tetraoctyl‐6,12‐dihydroindeno‐[1,2b]fluorene‐ alt‐5(1‐(p‐octylphenyl)‐2,5‐di(2‐thienyl)pyrrole) ( P2 ), were synthesized via the Suzuki coupling method and their optoelectronic properties were investigated. The resulting polymers P1 and P2 were completely soluble in various common organic solvents and their weight‐average molecular weights (M_w) were 5.66 × 10⁴ (polydispersity: 1.97) and 2.13× 10⁴ (polydispersity: 1.54), respectively. Bulk heterojunction (BHJ) solar cells were fabricated in ITO/PEDOT:PSS/polymer:PC₇₀BM(1:5)/TiO_x/Al configurations. The BHJ solar cell with P1 :PC₇₀BM (1:5) has a power conversion efficiency (PCE) of 1.12% (J_sc= 3.39 mA/cm², V_oc= 0.67 V, FF = 49.31%), measured using AM 1.5 G solar simulator at 100 mW/cm² light illumination. We fabricated polymer light‐emitting diodes (PLEDs) in ITO/PEDOT:PSS/emitting polymer:polyethylene glycol (PEG)/Ba/Al configurations. The electroluminescence (EL) maxima of the fabricated PLEDs varied from 526 nm to 556 nm depending on the ratio of the polymer to PEG. The turn‐on voltages of the PLEDs were in the range of 3–8 V depending on the ratio of the polymer to PEG, and the maximum brightness and luminance efficiency were 2103 cd/m² and 0.37 cd/A at 12 V, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3169–3177, 2010     

Development of naphthalene and quinoxaline‐based donor–acceptor conjugated copolymers for delivering high open‐circuit voltage in photovoltaic devices

Two new quinoxaline‐based polymers, poly[1,5‐didecyloxynaphthalene‐alt‐5,5′‐(5,8‐dithiophen‐2‐yl)‐2,3‐bis(4‐octyloxyphenyl)quinoxaline (PNQx‐p) and poly[1,5‐didecyloxynaphthalene‐alt‐5,5′‐(5,8‐dithiophen‐2‐yl)‐2,3‐bis(3‐octyloxyphenyl)quinoxaline (PNQx‐m), were synthesized by Suzuki coupling reaction and characterized. Thermogravimetric analysis revealed that these polymers are thermally stable with degradation temperature up to 320 °C. As evident from the electrochemical and optical studies, the copolymers have comparable optical band gap (～2 eV) and nearly similar deep highest occupied molecular orbital (HOMO) energy levels of ?5.59 (PNQx‐p) and ?5.61 eV (PNQx‐p). The resulting copolymers possessed relatively low HOMO energy levels promising good air stability and high open circuit voltage (V_oc) for photovoltaic applications. The optimized photovoltaic device with a structure of ITO/PEDOT:PSS/PNQx‐m:PC₇₁BM (1:2, w/w)/LiF/Al shows a power conversion efficiency up to 2.29% with a short circuit current density of 5.61 mA/cm², an V_oc of 0.93 V and a fill factor of 43.73% under an illumination of AM 1.5, 100 mW/cm². The efficiency of the PNQx‐m polymer improved from 2.29 to 2.95% using 1,8‐diiodoocane as an additive (0.25%). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Solution‐processable and thermally cross‐linkable fluorene‐cored triple‐triphenylamines with terminal vinyl groups to enhance electroluminescence of MEH‐PPV: Synthesis,curing, and optoelectronic properties

This study reports the synthesis, curing, and optoelectronic properties of a solution‐processable, thermally cross‐linkable electron‐ and hole‐blocking material containing fluorene‐core and three periphery N‐phenyl‐N‐(4‐vinylphenyl)benzeneamine ( FTV ). The FTV exhibited good thermal stability with T_d above 478 °C in nitrogen atmosphere. The FTV is readily cross‐linked via terminal vinyl groups by heating at 160 °C for 30 min to obtain homogeneous film with excellent solvent resistance. Multilayer PLED device [ITO/PEDOT:PSS/cured‐ FTV /MEH‐PPV/Ca (50 nm)/Al (100 nm)] was successfully fabricated using solution processed. Inserting cured‐ FTV is between PEDOT:PSS and MEH‐PPV results in simultaneous reduction in hole injection from PEDOT:PSS to MEH‐PPV and blocking in electron transport from MEH‐PPV to anode. The maximum luminance and maximum current efficiency were enhanced from 1810 and 0.27 to 4640 cd/m² and 1.08 cd/A, respectively, after inserting cured‐ FTV layer. Current results demonstrate that the thermally cross‐linkable FTV enhances not only device efficiency but also film homogeneity after thermal curing. FTV is a promising electron‐ and hole‐blocking material applicable for the fabrication of multilayer PLEDs based on PPV derivatives. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000–000, 2012     

Polythiophenes bearing electron‐withdrawing groups in the side chain and their application to bulk heterojunction solar cells

Soluble polythiophenes bearing strong electron withdrawing groups, dicyanoethenyl [? CH?C(CN)₂] (PTDCN) and cyano‐methoxycarbonylethenyl [? CH?C(CO₂Me)CN] (PTCNME), in the side chains have been prepared. Optical band gaps calculated from onset absorption were 1.70 eV and 1.73 eV for PTDCN and PTCNME, respectively. Highest occupied molecular orbital energy levels measured with a surface analyzer (AC‐2) were ?5.53 eV and ?5.29 eV for PTDCN and PTCNME, respectively, which were much lower than that of poly(3‐hexylthiophene) (?4.81 eV). To investigate photovoltaic properties, bulk heterojunction polymer solar cells based on PTDCN and PTCNME were fabricated with a structure of ITO/PEDOT:PSS/active layer/LiF/Al, where the active layer was a blend film of polymer and [6,6]‐phenyl C₆₁ butyric acid hexyl ester (PC₆₁BH). Solar cell parameters were estimated from current density–voltage (J–V) characteristics under the illumination of AM1.5 at 100 mW/cm². The solar cell based on the blend film of PTCNME:PC₆₁BH (1:1) showed power conversion efficiency (PCE) of 0.72% together with the open current voltage (V_oc) of 0.61 V, the short current density (J_sc) of 3.90 mA/cm², and the fill factor of 30.3%. The PCE of a solar cell fabricated from PTDCN in a similar way was 0.56%. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Thermally crosslinkable hole‐transporting poly(fluorene‐co‐triphenylamine) for multilayer polymer light‐emitting diodes

This article reports the synthesis and characterization of a novel thermally crosslinkable hole‐transporting poly (fluorene‐co‐triphenylamine) (PFO‐TPA) by Suzuki coupling reaction, followed with its application in the fabrication of multilayer light‐emitting diodes by wet processes. The thermal, photophysical, and electrochemical properties of PFO‐TPA were investigated by differential scanning calorimeter, thermogravimetric analysis, optical spectroscopy, and cyclic voltammetry, respectively. Thermally crosslinked PFO‐TPA, through pendant styryl groups, demonstrates excellent thermal stability (T_d > 400 °C, T_g = 152 °C), solvent resistance, and film homogeneity. Its highest occupied molecular orbital level (?5.30 eV) lies between those of PEDOT:PSS (?5.0 ～ ?5.2 eV) and poly(9,9‐dioctylfluorene) (PFO: ?5.70 eV), forming a stepwise energy ladder to facilitate hole injection. Multilayer device with crosslinked PFO‐TPA as hole‐injection layer (HIL) (ITO/PEDOT:PSS/HIL/PFO/LiF/Ca/Al) was readily fabricated by successive spin‐coating processes, its maximum luminance efficiency (3.16 cd/A) were about six times higher than those without PFO‐TPA layer (0.50 cd/A). The result of hole‐only device also confirmed hole‐injection and hole‐transport abilities of crosslinked PFO‐TPA layer. Consequently, the device performance enhancement is attributed to more balanced charges injection in the presence of crosslinked PFO‐TPA layer. The thermally crosslinkable PFO‐TPA is a promising material for the fabrication of efficient multilayer polymer light‐emitting diodes because it is not only a hole‐transporting polymer but also thermally crosslinkable. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and applications of 2,7‐carbazole‐based conjugated main‐chain copolymers containing electron deficient bithiazole units for organic solar cells

A series of low‐band‐gap (LBG) donor–accepor conjugated main‐chain copolymers ( P1 – P4 ) containing planar 2,7‐carbazole as electron donors and bithiazole units (4,4′‐dihexyl‐2,2′‐bithiazole and 4,4′‐dihexyl‐5,5′‐di(thiophen‐2‐yl)‐2,2′‐bithiazole) as electron acceptors were synthesized and studied for the applications in bulk heterojunction (BHJ) solar cells. The effects of electron deficient bithiazole units on the thermal, optical, electrochemical, and photovoltaic (PV) properties of these LBG copolymers were investigated. Absorption spectra revealed that polymers P1 – P4 exhibited broad absorption bands in UV and visible regions from 300 to 600 nm with optical band gaps in the range of 1.93–1.99 eV, which overlapped with the major region of the solar emission spectrum. Moreover, carbazole‐based polymers P1 – P4 showed low values of the highest occupied molecular orbital (HOMO) levels, which provided good air stability and high open circuit voltages (V_oc) in the PV applications. The BHJ PV devices were fabricated using polymers P1 – P4 as electron donors and (6,6)‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) or (6,6)‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as electron acceptors in different weight ratios. The PV device bearing an active layer of polymer blend P4:PC₇₁BM (1:1.5 w/w) showed the best power conversion efficiency value of 1.01% with a short circuit current density (J_sc) of 4.83 mA/cm², a fill factor (FF) of 35%, and V_oc = 0.60 V under 100 mW/cm² of AM 1.5 white‐light illumination. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Side Chain Influence on Electrochemical and Photovoltaic Properties of Yne‐Containing Poly(phenylene vinylene)s

Summary: The electrochemical behaviour of four types of (phenylene ethynylene)‐alt‐(phenylene vinylene) hybrid polymers, 1 , 2 , 3 , and 4 have been investigated with respect to the influence of the grafted alkoxy side chains. In the case of the fully substituted polymers 2 , 3 , and 4 , the strong insulating nature of longer linear octadecyl or bulky branched 2‐ethylhexyl side chains lowers the HOMO levels of the polymers thereby increasing the discrepancy, ΔE_g, between the electrochemical, Eequation/tex2gif-stack-1.gif, and the optical, Eequation/tex2gif-stack-2.gif, bandgap energies. Thus it is not possible to establish a direct correlation between the open circuit voltage, V_OC, of bulk heterojunction solar cell devices of the configuration glass substrate/ITO/PEDOT:PSS/polymer 3 :PCBM(1:3, w/w)/LiF/Al and the HOMO energy levels of polymer 3 solely, as postulated in the literature. The photovoltaic (PV) parameters greatly depend on the grafted side chains.

Linear I–V curves of solar cell devices from polymers 3a – d , measured in the dark and under 100 mW · cm⁻² solar simulator illumination.     

Synthesis of three new 1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl) pyrrole‐based donor polymers and their bulk heterojunction solar cell applications

A series of three new 1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole‐based polymers such as poly[1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole] ( PTPT ), poly[1,4‐(2,5‐bis(octyloxy)phenylene)‐alt‐5,5'‐(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole)] ( PPTPT ), and poly[2,5‐(3‐octylthiophene)‐alt‐5,5'‐(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole)] ( PTTPT ) were synthesized and characterized. The new polymers were readily soluble in common organic solvents and the thermogravimetric analysis showed that the three polymers are thermally stable with the 5% degradation temperature >379 °C. The absorption maxima of the polymers were 478, 483, and 485 nm in thin film and the optical band gaps calculated from the onset wavelength of the optical absorption were 2.15, 2.20, and 2.13 eV, respectively. Each of the polymers was investigated as an electron donor blending with PC₇₀BM as an electron acceptor in bulk heterojunction (BHJ) solar cells. BHJ solar cells were fabricated in ITO/PEDOT:PSS/polymer:PC₇₀BM/TiO_x/Al configurations. The BHJ solar cell with PPTPT :PC₇₀BM (1:5 wt %) showed the power conversion efficiency (PCE) of 1.35% (J_sc = 7.41 mA/cm², V_oc = 0.56 V, FF = 33%), measured using AM 1.5G solar simulator at 100 mW/cm² light illumination. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Deep‐red light‐emitting phosphorescent dendrimer encapsulated tris‐[2‐benzo[b]thiophen‐2‐yl‐pyridyl] iridium (III) core for light‐emitting device applications

New deep‐red light‐emitting phosphorescent dendrimers with hole‐transporting carbazole dendrons were synthesized by reacting tris(2‐benzo[b]thiophen‐2‐yl‐pyridyl) iridium (III) complex with carbazolyl dendrons by DCC‐catalyzed esterification. The resulting first‐, second‐, and third‐generation dendrimers were found to be highly efficient as solution‐processable emitting materials and for use in host‐free electrophosphorescent light‐emitting diodes. We fabricated a host‐free dendrimer EL device with configuration ITO/PEDOT:PSS (40 nm)/dendrimer (55 nm)/BCP (10 nm)/Alq₃ (40 nm)/LiF (1 nm)/Al (100 nm) and characterized the device performance. The multilayered devices showed luminance of 561 cd/m² at 383.4 mA/cm² (12 V) for 15 , 1302 cd/m² at 321.3 mA/cm² (14 V) for 16 , and 422 cd/m² at 94.4 mA/cm² (18 V) for 17 . The third‐generation dendrimer, 17 (η_ext = 6.12% at 7.5 V), showed the highest external quantum efficiency (EQE) with an increase in the density of the light‐harvesting carbazole dendron. Three dendrimers exhibited considerably pure deep‐red emission with CIE 1931 (Commission International de L'Eclairage) chromaticity coordinates of x = 0.70, y = 0.30. The CIE coordinates remained very stable with the current density. The integration of rigid hole‐transporting dendrons and phosphorescent complexes provides a new route to design highly efficient solution‐processable materials for dendrimer light‐emitting diode (DLED) applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7517–7533, 2008     

Cascade hole transport in efficient green phosphorescent light‐emitting devices achieved by layer‐by‐layer solution deposition using photocrosslinkable‐conjugated polymers containing oxetane side‐chain moieties

A hole‐injection/transport bilayer structure on an indium tin oxide (ITO) layer was fabricated using two photocrosslinkable polymers with different molecular energy levels. Two photoreactive polymers were synthesized using 2,7‐(or 3,6‐)‐dibromo‐9‐(6‐((3‐methyloxetan‐3‐yl)methoxy)hexyl)‐9H‐carbazole) and 2,4‐dimethyl‐N,N‐bis(4‐ (4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)phenyl)aniline via a Suzuki coupling reaction. When the oxetane groups were photopolymerized in the presence of a cationic photoinitiator, the photocured film showed good solvent resistance and compatibility with a poly(N‐vinylcarbazole) (PVK)‐based emitting layer. Without the use of a conventional hole injection layer (HIL) of poly(3,4‐ethylenedioxythiophene)/(polystyrenesulfonate) (PEDOT:PSS), the resulting green light‐emitting device bearing PVK: 5‐4‐tert‐butylphenyl‐1,3,4‐oxadiazole (PBD):Ir(Cz‐ppy)3 exhibited a maximum external quantum efficiency of 9.69%; this corresponds to a luminous efficiency of 29.57 cd/A for the device K‐4 configuration ITO/POx‐I/POx‐II/PVK:PBD:Ir(Cz‐ppy)3/triazole/Alq3/LiF/Al. These values are much higher than those of PLEDs using conventional PEDOT:PSS as a single HIL. The significant improvement in device efficiency is the result of suppression of the hole injection/transport properties through double‐layered photocrosslinked‐conjugated polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Anthracene‐Containing Wide‐Band‐Gap Conjugated Polymers for High‐Open‐Circuit‐Voltage Polymer Solar Cells

The synthesis, characterization, and photophysical and photovoltaic properties of two anthracene‐containing wide‐band‐gap donor and acceptor (D–A) alternating conjugated polymers ( P1 and P2 ) are described. These two polymers absorb in the range of 300–600 nm with a band gap of about 2.12 eV. Polymer solar cells with P1 :PC₇₁BM as the active layer demonstrate a power conversion efficiency (PCE) of 2.23% with a high V_oc of 0.96 V, a J_sc of 4.4 mA cm⁻², and a comparable fill factor (FF) of 0.53 under simulated solar illumination of AM 1.5 G (100 mW cm⁻²). In addition, P2 :PC₇₁BM blend‐based solar cells exhibit a PCE of 1.42% with a comparable V_oc of 0.89 V, a J_sc of 3.0 mA cm⁻², and an FF of 0.53.

     

Synthesis of polymers containing 1,2,4‐oxadiazole as an electron‐acceptor moiety in their main chain and their solar cell applications

To explore the aptitude of 1,2,4‐oxadiazole‐based electron‐acceptor unit in polymer solar cell applications, we prepared four new polymers (P1–P4) containing 1,2,4‐oxadiazole moiety in their main chain and applied them to solar cell applications. Thermal, optical, and electrochemical properties of the polymers were studied using thermogravimetric, absorption, and cyclic voltammetry analysis, respectively. All four polymers showed high thermal stability (5% degradation temperature over 335 °C), and the optical band gaps were calculated to be 2.20, 1.72, 1.37, and 1.74 eV, respectively, from the onset wavelength of the film‐state absorption band. The energy levels of the polymers were found to be suitable for bulk heterojunction (BHJ) solar cell applications. The BHJ solar cells were prepared by using the synthesized polymers as a donor and PC₇₁BM as an electron acceptor with the configuration of ITO/PEDOT:PSS/polymer:PC₇₁BM (1:3 wt %)/LiF/Al. One of the polymers was found to show the maximum power conversion efficiency of 1.33% with a Jsc of 4.95 mA/cm², a V_oc of 0.68 V, and a FF of 40%, measured using AM 1.5 G solar simulator at 100 mW/cm₂ light illumination. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and photovoltaic properties of conjugated D–A copolymers based on thienyl substituted pyrene and diketopyrrolopyrrole for polymer solar cells

A new donor‐acceptor conjugated copolymer (PDTPyDPP), comprising 2,7‐di‐2‐thienyl‐4,5,9,10‐tetrakis(hexyloxy)pyrene as a donor and diketopyrrolopyrrole (DPP) as an acceptor, was synthesized. PDTPyDPP showed good solubility in common organic solvents, broad visible absorption from 300 to 900 nm, and a moderate hole mobility up to 6.3 × 10^?3 cm² V^?1 s^?1. The power conversion efficiency of the photovoltaic device based on the PDTPyDPP/PC₇₁BM photoactive layer reached 4.43% with 0.66 V of open‐circuit voltage (V_oc), 10.52 mA cm^?2 of short‐circuit current (J_sc) and 64.11% of fill factor. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3198–3204     

Synthesis of π‐conjugated copolymers composed of benzo[2,1,3]thiadiazole and thiophene units bearing various alkyl groups and their application to photovoltaic cells

π‐Conjugated polymers, PTOTBT , PTEHTBT , and PTt‐BTBT , composed of benzothiadiazole as an electron accepting unit and terthiophene as an electron donating unit in the backbone were prepared. PTOTBT , PTEHTBT , and PTt‐BTBT contained side chain groups of n‐octyl, 2‐ethylhexyl, and t‐butyl groups, respectively. Solubility, optical and thermal properties of the polymers showed strong dependences on their side chain groups. PTEHTBT having 2‐ethylhexyl groups in the side chain exhibited absorption maximum (λ_max) at longer wavelength (565 nm) than PTOTBT (534 nm) and PTt‐BTBT (495 nm). PTOTBT showed higher thermal stability than the others. The prepared polymers were employed to polymer solar cells (PSCs) with a configuration of ITO/PEDOT‐PSS/polymer: PC₆₁BH/LiF/Al. Power conversion efficiency of the PSC‐based on PTEHTBT was 1.32%. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011