Polymer solar cells based on quinoxaline and dialkylthienyl substituted benzodithiophene with enhanced open circuit voltage

A poly[benzodithiophene‐alt‐di‐2‐thienyl‐quinoxaline] series (PBDTDPQ‐EH, PBDTDPQ‐OD, and PBDTDPQ‐HDT) was synthesized via Stille coupling. Deep highest occupied molecular orbital (HOMO) levels were achieved by the introduction of 2‐decyl‐4‐hexyl‐thiophen‐yl (HDT) side chains. The introduction of the various side chains increased the molecular weight of the polymers, and the polymers dissolved well in common organic solvents at room temperature. The HOMO energy level (?5.20 to ?5.49 eV) decreased because of the 2D conjugated structure. X‐ray diffraction analysis showed that PBDTDPQ‐OD had a slightly edge‐on structure. In the case of PBDTDPQ‐HDT, however, the structure was amorphous due to the thiophene side chain, and the extent of π stacking increased. After fabricating bulk‐heterojunction‐type polymer solar cells, the OPV characteristics were evaluated. The values of open‐circuit voltage (V_oc), short‐circuit current (J_sc), fill factor, and power conversion efficiency (PCE) were 0.88 V, 7.9 mA cm^?2, 45.4%, and 3.2%, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1028–1036     

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.

     

Fused structures in the polymer backbone to investigate the photovoltaic and electrochromic properties of donor–acceptor‐type conjugated polymers

In this study, two new benzotriazole (BTz) and dithienothiophene (DTT) containing conjugated polymers were synthesized. After successful characterizations of the monomers by proton‐nuclear magnetic resonance (¹H NMR) and carbon‐NMR (¹³C NMR) techniques, poly(4‐(dithieno[3, 2‐b:2′,3′‐d]thiophen‐2‐yl)‐2‐(2‐octyldodecyl)‐2H‐benzo[d][1,2,3] triazole) P1 and poly(4‐(5‐(dithieno[3,2‐b:2′,3′‐d]thiophen‐2‐yl)thiophen‐2‐yl)‐2‐(2‐octyldodecyl)‐7‐(thiophen‐2‐yl)‐2H‐benzo[d][1,2,3]triazole) P2 were synthesized via a typical Stille coupling. Electrochemical and spectroelectrochemical studies showed that both polymers can be multipurpose materials and used in electrochromic and photovoltaic applications. Reported study indicated that incorporation of DTT into the structure leads to fast switching times compared with BTz‐based polymers and competent percentage transmittance in the near‐infrared region. Multichromism is important in the context of low‐cost flexible display device technology and both polymers are ambipolar and processable as well as multichromic. Throughout the preliminary photovoltaic studies, the best performances of photovoltaic devices were found as V_oc = 0.49 V, J_sc = 0.83 mA/cm², fill factor (FF) = 34.4%, and power conversion efficiency (PCE) = 0.14% for P1 , and as V_oc = 0.35 V, J_sc = 1.57 mA/cm², FF = 38.2%, and PCE = 0.21% for P2 . © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

The influence of electron deficient unit and interdigitated packing shape of new polythiophene derivatives on organic thin‐film transistors and photovoltaic cells

A series of new polythiophene derivatives containing a thiazole ring as an electron deficient unit were successfully synthesized via Stille coupling reactions. Synthesized polymers were classified into two types (H‐shape packing and A‐shape packing) based on their interdigitated packing structure induced by different side chain configurations. The thiophene derivatives that contained a thiazole unit ( PT50Tz50 , PTz100 , and PTTz ) exhibited much better thermal stability than did the full thiophene polymers ( PT100 and PTT ). The polymers containing the thiazole unit ( PTz100 and PTTz ) showed a red‐shifted absorption spectrum with clear vibronic structure. In addition, the XRD and AFM results showed that the polymers containing the thiazole unit and interdigitated H‐shape exhibited much better ordered and connected intermolecular structures than did other polymers. The improved intermolecular ordering and surface morphologies directly facilitated charge carrier transport in thin film transistor (TFT) devices, without introducing charge traps, and yielded higher solar cell performance. Among these polymers, the PTTz copolymer exhibited the best TFT performance (μ = 0.050 cm² V^?1 s^?1, on/off ratio = 10⁶, and V_th = ?2 V) and solar cell performance (PCE = 1.39%, J_sc = 6.58 mA cm^?2, and V_oc = 0.58 V). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A New D–A conjugated polymer P(PTQD‐BDT) with PTQD acceptor and BDT donor units for BHJ polymer solar cells application

A novel donor–acceptor ( D–A ) copolymer comprising of weak electron donating BDT moiety and strong 9‐(2‐octyldodecyl)?8H‐pyrrolo[3,4‐b] bisthieno[2,3‐f:3',2'‐h] quinoxaline‐8,10(9H)‐dione (PTQD) unit denoted as P(PTQD‐BDT) was synthesized as donor material for polymer solar cells. P(PTQD‐BDT) shows a broad visible‐near‐infrared absorption band with an optical bandgap of 1.74 eV and possesses a relatively low‐lying HOMO level at ?5.28 eV. Bulk‐heterojunction polymer solar cell with the optimized blend of 1:2 (weight ratio) P(PTQD‐BDT):PC₇₁BM (processed with chloroform) shows an open circuit voltage of 0.92 V, a short circuit current density of 7.84 mA/cm², and a fill factor of 0.50, achieving a power conversion efficiency (PCE) of 3.61%. The PCE has been further improved to 5.55 % (J_sc = 10.34 mA/cm², V_oc = 0.88V and FF = 0.61), when 3% v ol 1,8‐diio‐dooctane (DIO) was used as solvent additive for the processing of P(PTQD‐BDT):PC₇₁BM blended film. The enhancement in J_sc is as a result of the appropriate morphology and efficient exciton dissociation into free charge carrier. The increase in PCE has been attributed to the favorable nanoscale morphology for efficient exciton dissociation and charge transport (reduction in the electron to hole mobility ratio). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2390–2398     

Unidirectional Sidechain Engineering to Construct Dual-Asymmetric Acceptors for 19.23 % Efficiency Organic Solar Cells with Low Energy Loss and Efficient Charge Transfer

Achieving both high open-circuit voltage (V_oc) and short-circuit current density (J_sc) to boost power-conversion efficiency (PCE) is a major challenge for organic solar cells (OSCs), wherein high energy loss (E_loss) and inefficient charge transfer usually take place. Here, three new Y-series acceptors of mono-asymmetric asy-YC11 and dual-asymmetric bi-asy-YC9 and bi-asy-YC12 are developed. They share the same asymmetric D₁AD₂ (D₁=thieno[3,2-b]thiophene and D₂=selenopheno[3,2-b]thiophene) fused-core but have different unidirectional sidechain on D₁ side, allowing fine-tuned molecular properties, such as intermolecular interaction, packing pattern, and crystallinity. Among the binary blends, the PM6 : bi-asy-YC12 one has better morphology with appropriate phase separation and higher order packing than the PM6 : asy-YC9 and PM6 : bi-asy-YC11 ones. Therefore, the PM6 : bi-asy-YC12-based OSCs offer a higher PCE of 17.16 % with both high V_oc and J_sc, due to the reduced E_loss and efficient charge transfer properties. Inspired by the high V_oc and strong NIR-absorption, bi-asy-YC12 is introduced into efficient binary PM6 : L8-BO to construct ternary OSCs. Thanks to the broadened absorption, optimized morphology, and furtherly minimized E_loss, the PM6 : L8-BO : bi-asy-YC12-based OSCs achieve a champion PCE of 19.23 %, which is one of the highest efficiencies among these annealing-free devices. Our developed unidirectional sidechain engineering for constructing bi-asymmetric Y-series acceptors provides an approach to boost PCE of OSCs.     

Molecular Engineering of Simple Phenothiazine‐Based Dyes To Modulate Dye Aggregation,Charge Recombination,and Dye Regeneration in Highly Efficient Dye‐Sensitized Solar Cells

A series of simple phenothiazine‐based dyes, namely, TP , EP , TTP , ETP , and EEP have been developed, in which the thiophene (T), ethylenedioxythiophene (E), their dimers, and mixtures are present to modulate dye aggregation, charge recombination, and dye regeneration for highly efficient dye‐sensitized solar cell (DSSC) applications. Devices sensitized by the dyes TP and TTP display high power conversion efficiencies (PCEs) of 8.07 (J_sc=15.2 mA cm^?2, V_oc=0.783 V, fill factor (FF)=0.679) and 7.87 % (J_sc=16.1 mA cm^?2, V_oc=0.717 V, FF=0.681), respectively; these were measured under simulated AM 1.5 sunlight in conjunction with the I^?/I₃^? redox couple. By replacing the T group with the E unit, EP ‐based DSSCs had a slightly lower PCE of 7.98 % with a higher short‐circuit photocurrent (J_sc) of 16.7 mA cm^?2. The dye ETP , with a mixture of E and T, had an even lower PCE of 5.62 %. Specifically, the cell based on the dye EEP , with a dimer of E, had inferior J_sc and V_oc values and corresponded to the lowest PCE of 2.24 %. The results indicate that the photovoltaic performance can be finely modulated through structural engineering of the dyes. The selection of T analogues as donors can not only modulate light absorption and energy levels, but also have an impact on dye aggregation and interfacial charge recombination of electrons at the interface of titania, electrolytes, and/or oxidized dye molecules; this was demonstrated through DFT calculations, electrochemical impedance analysis, and transient photovoltage studies.     

Random poly(3‐hexylthiophene‐co‐3‐cyanothiophene‐co‐3‐(2‐ethylhexyl)thiophene) copolymers with high open‐circuit voltage in polymer solar cells

For the purpose of developing poly(3‐hexylthiophene) (P3HT) based copolymers with deep‐lying highest occupied molecular orbital (HOMO) levels for polymer solar cells with high open‐circuit voltage (V_oc), we report a combined approach of random incorporation of 3‐cyanothiophene (CNT) and 3‐(2‐ethylhexyl)thiophene (EHT) units into the P3HT backbone. This strategy is designed to overcome CNT content limitations in recently reported P3HT‐CNT copolymers, where incorporation of more than 15% of CNT into the polymer backbone leads to impaired polymer solubility and raises the HOMO level. This new approach allows incorporation of a larger CNT content, reaching even lower‐lying HOMO levels. Importantly, a very low HOMO level of ?5.78 eV was obtained, representing one of the lowest HOMO values for exclusively thiophene‐based polymers. Lower HOMO levels result in higher V_oc and higher power conversion efficiencies (PCE) compared to the previously reported P3HT‐CNT copolymers containing only 3‐hexylthiophene and CNT units. As a result, solar cells based on P3HT‐CNT‐EHT(15:15) , which contains 70% of P3HT, 15% of CNT and 15% of EHT, yield a V_oc of 0.83 V in blends with PC₆₁BM while preserving high fill factor (FF) and high short‐circuit current density (J_sc), resulting in 3.6% PCE. Additionally, we explored the effect of polymer number‐average molecular weight (M_n) on the optoelectronic properties and solar cell performance for the example of P3HT‐CNT‐EHT(15:15). The organic photovoltaic (OPV) performance improves with polymer M_n increasing from 3.4 to 6.7 to 9.6 kDa and then it declines as M_n further increases to 9.9 and to 16.2 kDa. The molecular weight study highlights the importance of not only the solar cell optimization, but also the significance of individual polymer properties optimization, in order to fully explore the potential of any given polymer in OPVs. The broader ramification of this study lies in potential application of these high band gap copolymers with low‐lying HOMO level in the development of ternary blend photovoltaics as well as tandem OPV. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1526–1536     

Synthesis and applications of cyano‐vinylene‐based polymers containing cyclopentadithiophene and dithienosilole units for photovoltaic cells

Two β‐cyano‐thiophenevinylene‐based polymers containing cyclopentadithiophene ( CPDT‐CN ) and dithienosilole ( DTS‐CN ) units were synthesized via Stille coupling reaction with Pd(PPh₃)₄ as a catalyst. The effects of the bridged atoms (C and Si) and cyano‐vinylene groups on their thermal, optical, electrochemical, charge transporting, and photovoltaic properties were investigated. Both polymers possessed the highest occupied molecular orbital (HOMO) levels of about ?5.30 eV and the lowest unoccupied molecular orbital (LUMO) levels of about ?3.60 eV, and covered broad absorption ranges with narrow optical band gaps (ca. 1.6 eV). The bulk heterojunction polymer solar cell (PSC) devices containing an active layer of electron‐donor polymers ( CPDT‐CN and DTS‐CN ) blended with an electron‐acceptor, that is, [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) or [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM), in different weight ratios were explored under 100 mW/cm² of AM 1.5 white‐light illumination. The PSC device based on DTS‐CN: PC₇₁BM (1:2 w/w) exhibited a best power conversion efficiency (PCE) value of 2.25% with V_oc = 0.74 V, J_sc = 8.39 mA/cm², and FF = 0.36. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Novel alkoxyanthracene donor and benzothiadiazole acceptor for organic thin film transistor and bulk heterojunction organic photovoltaic cells

Novel alkoxy anthracene (ODA)‐based polymeric semiconductors were designed for polymer solar cell applications. Alkoxyanthracene, which contains many π electrons and electron donating group, was easily synthesized. The copolymers, poly(alkoxy anthracene‐alt‐thiophene benzothiadiazole thiophene) poly(ODA‐TBT) and poly(alkoxy anthracene‐alt‐benzothiadiazole) poly(ODA‐BT), have been obtained by Suzuki coupling polymerization. Both polymers have ODA unit as a donor and benzothiadiazole as an acceptor. ODA‐TBT has thiophene linkages between ODA and benzothiadiazole. The optical, thermal, and electrochemical properties have been investigated by UV–visible absorption, thermal gravimetric analysis, differential scanning calorimetry, and CV. Organic thin‐film transistor using polymers showed that the hole mobility of poly(ODA‐alt‐TBT) was around 3.6 × 10^?3 cm²/Vs with on/off ratio of 9.91 × 10⁵ while that of poly(ODA‐alt‐BT) was around 1.21 × 10^?2 cm²/Vs with on/off ratio of 2.64 × 10⁶. Organic photovoltaic performance based on polymers were evaluated with a configuration of ITO/PEDOT:PSS/active layer/LiF/Al. Poly(ODA‐TBT) exhibits a short circuit current (J_sc) of 3.9 mA/cm² and power conversion efficiency (PCE) of 1.4%, and poly(ODA‐BT) exhibits the J_sc of 6.4 mA/cm² and PCE of 2.2%. The better device performance of poly(ODA‐BT) is attributed to its charge transfer ability and enhanced mobility and crystallinity although poly(ODA‐BT) does not have extended π‐conjugation due to twisted structure compared with poly(ODA‐TBT). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1306–1314     

A Pentacyclic Nitrogen‐Bridged Thienyl–Phenylene–Thienyl Arene for Donor–Acceptor Copolymers: Synthesis,Characterization, and Applications in Field‐Effect Transistors and Polymer Solar Cells

A pentacyclic benzodipyrrolothiophene ( BDPT ) unit, in which two outer thiophene rings are covalently fastened with the central phenylene ring by nitrogen bridges, was synthesized. The two pyrrole units embedded in BDPT were constructed by using one‐pot palladium‐catalyzed amination. The coplanar stannylated Sn‐BDPT building block was copolymerized with electron‐deficient thieno[3,4‐c]pyrrole‐4,6‐dione ( TPD ), benzothiadiazole ( BT ), and dithienyl‐diketopyrrolopyrrole ( DPP ) acceptors by Stille polymerization. The bridging nitrogen atoms make the BDPT motif highly electron‐abundant and structurally coplanar, which allows for tailoring the optical and electronic properties of the resultant polymers. Strong photoinduced charge‐transfer with significant band‐broadening in the solid state and relatively higher oxidation potential are characteristic of the BDPT‐based polymers. Poly(benzodipyrrolothiophene‐alt‐benzothiadiazole) ( PBDPTBT ) achieved the highest field‐effect hole mobility of up to 0.02 cm² V^?1 s^?1. The photovoltaic device using the PBDPTBT /PC₇₁BM blend (1:3, w/w) exhibited a V_oc of 0.6 V, a J_sc of 10.34 mA cm^?2, and a FF of 50 %, leading to a decent PCE of 3.08 %. Encouragingly, the device incorporating poly(benzodipyrrolothiophene‐alt‐thienopyrrolodione) ( PBDPTTPD )/PC₇₁BM (1:3, w/w) composite delivered a highest PCE of 3.72 %. The enhanced performance arises from the lower‐lying HOMO value of PBDPTTPD to yield a higher V_oc of 0.72 V.     

Cyclometalated Ruthenium(II) Complexes Featuring Tridentate Click‐Derived Ligands for Dye‐Sensitized Solar Cell Applications

A series of heteroleptic bis(tridentate) Ru^II complexes featuring N^C^N‐cyclometalating ligands is presented. The 1,2,3‐triazole‐containing tridentate ligands are readily functionalized with hydrophobic side chains by means of click chemistry and the corresponding cyclometalated Ru^II complexes are easily synthesized. The performance of these thiocyanate‐free complexes in a dye‐sensitized solar cell was tested and a power conversion efficiency (PCE) of up to 4.0 % (J_sc=8.1 mA cm^?2, V_oc=0.66 V, FF=0.70) was achieved, while the black dye ((NBu₄)₃[Ru(Htctpy)(NCS)₃]; Htctpy=2,2′:6′,2′′‐terpyridine‐4′‐carboxylic acid‐4,4′′‐dicarboxylate) showed 5.2 % (J_sc=10.7 mA cm^?2, V_oc=0.69 V, FF=0.69) under comparable conditions. When co‐adsorbed with chenodeoxycholic acid, the PCE of the best cyclometalated dye could be improved to 4.5 % (J_sc=9.4 mA cm^?2, V_oc=0.65 V, FF=0.70). The PCEs correlate well with the light‐harvesting capabilities of the dyes, while a comparable incident photon‐to‐current efficiency was achieved with the cyclometalated dye and the black dye. Regeneration appeared to be efficient in the parent dye, despite the high energy of the highest occupied molecular orbital. The device performance was investigated in more detail by electrochemical impedance spectroscopy. Ultimately, a promising Ru^II sensitizer platform is presented that features a highly functionalizable “click”‐derived cyclometalating ligand.     

Significantly improved photovoltaic performances of the dithiophene‐benzothiadiazole‐alt‐fluorene copolymers by incorporating carbazole units in fluorene moiety

To exploit an effective way to improve polymeric photovoltaic performance, a series of dithiophene‐benzothiadiazole‐alt‐fluorene copolymers containing carbazole groups at C‐9 positions of the alternating fluorene units (PFO‐FCz‐DBT) were synthesized and characterized. The effect of the carbazole groups on the optophysical, electrochemical, and photovoltaic properties of these copolymers was investigated. By comparison, this type of copolymers with carbazole units exhibited significantly improved photovoltaic properties than poly(2,7‐(9,9‐dioctyl‐fluorene)‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole) (PFO‐DBT) in the bulk heterojunction solar cells. A maximum power‐conversion efficiency (PCE) of 2.41% and a highest short‐circuit current density (J_sc) of 9.68 mA cm^?2 were obtained for the PFO‐FCz‐DBT30, which are about two times higher than the corresponding levels for the PFO‐DBT30. This work demonstrated that introducing a hole‐transporting carbazole unit into copolymer is a simple and effective method to improve the J_sc and PCE. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

The side chain effects on TPD-based copolymers: the linear chain leads to a higher jsc

Abstract

Alkyl substituents appended to polymers play the determining role on self-assembly and film-forming properties, and on device performance. In this work, we highlight the effects of the linear and branched flexible chains appended to the acceptor moiety (A) in D-A type copolymers. Two thieno[3,4-c]-pyrrole-4,6-dione (TPD) based copolymers PT1 and PT2 with different alkyl chains, were designed and synthesized. By comparison their UV-vis absorptions, HOMO/LUMO energy levels, as well as the characters in polymer solar cells, the influences of alkyl chains were investigated. Both copolymers showed molecular weights of 21?kDa and similar optical properties with a medium band gap of 1.93?eV, while PT2 with the branched chain exhibited a lower HOMO than that of PT1 (?5.43 vs???5.37?eV). In bulk heterojunction (BHJ) solar cells, PT1 with a linear chain presented a short circuit current (J_sc) of 6.76?mA cm^?2, open circuit voltage (V_oc) of 0.89?V and power conversion efficiency (PCE) of 2.92%. To the contrary, PT2 showed a J_sc of 3.53?mA cm^?2, V_oc of 0.99?V, delivering a relatively lower PCE of 2.05%. The result indicates that appending a linear alkyl chain to the TPD unit could sufficient enhance the J_sc value of the related polymer.     

Synthesis of macrocycles by the ring‐crossover reaction of a cyclic dithioester

The ring‐crossover polymerization of cyclic dithioester 1 was performed in the presence of quaternary onium salts as catalysts at 70–150 °C for 24 h in NMP. It was found that predictable cyclic polymers with the same repeating structures as 1 were obtained with M_ns in the range between 700 and 3,500, quantitatively. It was observed that intermolecular and intramolecular thioester‐exchange reactions proceeded between cyclic monomer 1 and resulting cyclic polymers under thermodynamic control to give a lower‐molecular‐weight cyclic polymer with a lower polydispersity ratio (M_n = 2,400, M_w/M_n = 1.70). © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 680–687, 2007     

Decreased domain size and improved crystallinity by adjusting solvent–polymer interaction parameters in all‐polymer solar cells

We have investigated the effect of solvent–polymer interaction on the morphology, crystallinity, and device performance of poly‐(3‐hexylthiophene) (P3HT) and poly{2,7‐(9,9‐didodecyl‐fluorene)‐alt‐5,5‐[4′,7′‐bis(2‐thienyl)‐2′,1′,3′‐benzothia‐diaole]} (PF12TBT) blend system. 3‐Hexylthiophene (3‐HT), which had the similar structural units with both donor and acceptor materials, was chosen as the solvent additive to be added into the main solvent chlorobenzene (CB), to adjust the solvent–polymer interaction. With the 3‐HT percentage increasing from 5 to 30% in CB solution, the solvent–polymer interaction between polymer and solvent molecules decreased slightly according to the calculated solubility parameters (δ) and interaction parameters (χ₁₂). As a result, nanoscale phase‐separated and interconnected morphology with decreased domain size of both donor and acceptor was formed. Meanwhile, the order of P3HT molecule was enhanced which resulted from the extended film drying time and increased molecular planarity after incorporation of 3‐HT. The power conversion efficiency (PCE) had a gradual improvement to 1.08% as the 3‐HT percentage reached 10%, which can be attributed to the enhanced short‐circuit current (J_sc) and fill factor (FF). However, when the 3‐HT percentage exceeded 20%, the decreased J_sc and FF ultimately decreased the PCE. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 288–296     

Synthesis of phenanthro[1,10,9,8‐cdefg]carbazole‐based conjugated polymers for organic solar cell applications

Low bandgap polymers with dithienylquinoxaline moieties based on 6H‐phenanthro[1,10,9,8‐cdefg]carbazole were synthesized via the Suzuki coupling reaction. Alkoxy groups were substituted at two different positions on the phenyl groups of the quinoxaline units of these polymers: in the para‐position (PPQP) and in the meta‐position (PPQM). The two polymers showed similar physical properties: broad absorption in the range of 400–700 nm, optical bandgaps of ～1.8 eV, and the appropriate frontier orbital energy levels for efficient charge transfer/separation at polymer/PC₇₁BM interfaces. However, the PPQM solar cell achieved a higher PCE due to its higher J_sc. Our investigation of the morphologies of the polymer:PC₇₁BM blend films and theoretical calculations of the molecular conformations of the polymer chains showed that the polymer with the meta‐positioned alkoxy group has better miscibility with PC₇₁BM than the polymer with the para‐positioned alkoxy group because the dihedral angle of its phenyl group with respect to the quinoxaline unit is higher. This higher miscibility resulted in a polymer:PC₇₁BM blend film with a better morphology and thus in a higher PCE. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 796–803     

Ethynylene‐containing donor–acceptor alternating conjugated polymers: Synthesis and photovoltaic properties

Four ethynylene‐containing donor‐acceptor alternating conjugated polymers P1 – P4 with 2,5‐bis(dodecyloxy) substituted phenylene or carbazole as the donor unit and benzothiadiazole (BTZ) as the acceptor unit were synthesized and used as donor polymers in bulk heterojunction polymer solar cells. The optical, electrochemical, and photovoltaic properties of these four polymers with the ethylene unit located at different positions of the polymer chains were systematically investigated. Our results demonstrated that absorption spectra and the HOMO and LUMO energy levels of polymers could be tuned by varying the position of the ethynylene unit in the polymer chains. Photovoltaic devices based on polymer/PC₇₁BM blend films spin coated from chloroform and dichlorobenzene solutions were investigated. For all four polymers, open circuit voltages (V_oc) higher than 0.8 V were obtained. P4 , with ethynylene unit between BTZ and thiophene, shows the best performance among these four polymers, with a V_oc of 0.94 V, a J_sc of 4.2 mA/cm², an FF of 0.40, and a PCE of 1.6%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Conjugated polymer consisting of dibenzosilole and quinoxaline as donor materials for organic photovoltaics

The new D–A type polymers poly(dibenzosilole-diphenylquinoxaline) (PSiPDTQ) and dibenzosilole-dibenzophenazine) (PSiFDTQ), both of which adopted benzosilole as a donor, were polymerized through a Suzuki coupling reaction. PSiPDTQ and PSiFDTQ were able to be dissolved in organic solvents and exhibited high thermal stability. Due to the appropriate LUMO energy levels, an effective charge transport was observed in PSiPDTQ and PSiFDTQ. According to X-ray diffraction measurements, a single broad diffraction peak was detected at approximately 20.5°. The π–π stacking distances (d_π) for PSiPDTQ and PSiFDTQ were 4.4 and 4.3 Å, respectively. When PSiPDTQ and PC₇₁BM were blended in a 1:3 ratio and used as the active layer in a solar cell, the resulting V_oc, J_sc, FF and PCE were 0.89 V, 5.1 mA/cm², 30.2% and 1.4%, respectively. For solar cells using a 1:6 ratio of PSiFDTQ to PC₇₁BM, the resulting V_oc, J_sc, FF and PCE were 0.98 V, 3 mA/cm², 52.8% and 1.6%, respectively. In addition, for a PSiPDTQ and PC₇₁BM blended film (1:3 ratio) with an additional layer of PFN, the PCE of the resulting solar cells was improved (relative to solar cells without PFN) to 2.1% due to the interfacial adhesion of PFN.     

Two novel branched chain polymeric metal complexes based on Cd(II), Zn(II) with fluorene,thiophene, 8‐hydroxyquinoline,and 1,10‐phenathroline ligand: synthesis,characterization, photovoltaic properties,and their application in DSSCs

Two novel side chain polymeric metal complexes (PFT‐Cd and PFT‐Zn) have been designed, synthesized, and characterized. These polymers were found to be good thermally stable and high glass transitions temperature, which indicate that these polymers could be applied as photovoltaic materials for dye‐sensitized solar cells (DSSCs). The obtained polymers exhibited good photovoltaic property. The DSSCs based on the PFT‐Cd and PFT‐Zn exhibited a maximum solar‐to‐electricity conversion efficiency (η) up to 3.37% (J_sc = 7.27 mA/cm², V_oc = 0.67 V, and FF = 0.69) and 3.01% (V_oc = 0.72 V, J_sc = 6.10 mA/cm², FF = 0.69) under simulated AM 1.5 G solar irradiation (90–95 mW/cm²). The result shows that these novel materials are suitable for the dye‐sensitized solar cells. Copyright © 2011 John Wiley & Sons, Ltd.