Synthesis and characterization of naphtho[2,1‐b:3,4‐b′]dithiophene‐based polymers with extended π‐conjugation systems for use in bulk heterojunction polymer solar cells

Two novel polymeric semiconductor materials based on naphtho[2,1‐b:3,4‐b']dithiophene (NDT), PNDT‐TTT and PNDT‐TET , were designed and synthesized. These synthesized polymers were tested in bulk heterojunction solar cells as blends with the acceptor [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₁BM). PNDT‐TTT contained tri‐thiophene units, and PNDT‐TET contained bi‐thiophene units coupled by ethylenic linkages. Comparison to the properties of PNDT‐T , which contained single thiophene units, these polymers exhibit red‐shifted absorption spectra as a result of the enhanced conjugation lengths. These effects resulted in high short circuit currents (J_SC) in the organic solar cells. The PNDT‐TET ‐ and PNDT‐TTT ‐based devices exhibited considerably better photovoltaic performances, with power conversion efficiencies of 3.5 and 3.3%, respectively, compared to the PNDT‐T ‐based device (1.3%). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4742–4751     

New alternating D–A1–D–A2 copolymer containing two electron‐deficient moieties based on benzothiadiazole and 9‐(2‐Octyldodecyl)‐8H‐pyrrolo[3,4‐b]bisthieno[2,3‐f:3',2'‐h]quinoxaline‐8,10(9H)‐dione for efficient polymer solar cells

A novel D–A₁–D–A₂ copolymer denoted as P1 containing two electron withdrawing units based on benzothiadiazole (BT) and 9‐(2‐octyldodecyl)?8H‐pyrrolo[3,4‐b] bisthieno[2,3‐f:3′,2′‐h]quinoxaline‐8,10(9H)–dione (PTQD) units was synthesized and characterized. The resulting copolymer exhibits a broad‐absorption spectrum, relatively deep lying HOMO energy level (?5.44 eV) and narrow optical bandgap (1.50 eV). Bulk heterojunction (BHJ) polymer solar cells (PSCs) based on P1 as donor and PC₇₁BM as acceptor with optimized donor to acceptor weight ratio of 1:2 and processed with DIO/CB solvent showed good photovoltaic performance with power conversion efficiency of 6.21% which is higher than that of the device processed without solvent additive (4.40%). The absorption and morphology investigations of the active layers indicated that structural and morphological changes were induced by the solvent additive. This higher power conversion efficiency could be mainly attributed to the absorption enhancement and improved charge transported in the active layer induced by the better nanoscale morphology of the active layer. This study demonstrated that a copolymer with two different acceptor moieties in the backbone may be promising candidate as donor copolymer for solution processed BHJ PSCs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 155–168     

Chitosan/Ce(IV) redox polymerization‐based amplification for detection of DNA point mutation

Polymerization‐based signal amplification, a technique developed for use in rapid diagnostic tests, hinges on the ability to localize initiators as a function of interfacial binding events. We report here a new DNA detection method in which polymer growth in redox‐polymerization is used as a means to amplify detection signals. The introduction of biotin‐labeled chitosan (biotin‐CS) with highly dense amino groups into the polymerization amplification as macromolecular reducing agent, beneficially simplifies amplification operation, as well as, provides a large amount of initiation points to improve the sensitivity of detection. DNA hybridization, SA and biotin binding reactions led to the attachment of CS on a solid surface where specific DNA sequences were located. With the addition of the mixture containing monomer AM, crosslinker PEGDA and oxidant CAN onto the CS location, the growth of polymer films was triggered to render the corresponding spots readily distinguishable to the naked eye. Direct visualization of 0.21 fmol target DNA molecules of interest was demonstrated. Non‐small cell lung cancer p53 sequence was further selected as a proof‐of‐principle to detect DNA point mutation. The proposed method exhibited an efficient amplification performance for molecule detection, and paved a new way for visual diagnosis of biomolecules. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1929–1937     

Dithienosilole–phenylquinoxaline‐based copolymers with A‐D‐A‐D and A‐D structures for polymer solar cells

Two copolymers having D‐A‐D‐A ( P1 ) and D‐A ( P2 ) structures with quinoxaline acceptor unit and dithienosilole donor unit were synthesized and their optical and electrochemical (both experimental and theoretical) properties were investigated. The optical properties showed that these copolymers P1 and P2 exhibit optical bandgaps of 1.54 and 1.62 eV, respectively, with broader absorption profiles extending up to 800 nm and 770 nm, respectively. The electrochemical investigation of these two copolymers indicates that they exhibit suitable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels for efficient exciton dissociation and high open circuit voltage in the resultant polymer solar cells (PSCs). These copolymers were used as donors along with the PC₇₁BM as acceptor for the fabrication of solution processed bulk heterojunction PSCs. The optimized P1 :PC₇₁BM and P2 :PC₇₁BM active layers treated with solvent vapor treatment showed overall power conversion efficiency (PCE) of 7.16% and 6.57%, respectively. The higher PCE of P1 ‐based device as compared to P2 might be attributed to higher crystallinity of P1 and good hole mobility resulting more balanced charge transport. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 376–386     

Porphyrin–diindenothieno[2,3‐b]thiophene alternating copolymer—a blue‐light harvester in ternary‐blend polymer solar cells

Porphyrin, despite chosen by Nature as light harvesting units, hasn't revealed its full potentials as a structural unit in porphyrin‐incorporated polymers (PPors). A novel PPor was synthesized to investigate the origins of the low performances of PPor‐based polymer solar cells (PSCs). The polymer features broad absorption in the blue‐light region, because the diindenothieno[2,3‐b]thiophene (DITT) unit extended the conjugation in the polymer backbone. PPor‐DITT/PC₇₁BM based PSCs have a high V_oc (0.79 V). Their low J_sc and fill factor (FF) were attributed to the un‐optimized morphology, as indicated by the photoluminescence quenching and atomic force microscopy (AFM) experiments. Using PPor‐DITT as a blue‐light harvesting dopant in an amorphous host leverage the strong 400–550 nm absorption of PPor‐DITT and circumvent the difficulties in reaching optimized morphology in the PPor/PCBM thin films. An addition of 2 wt % of PPor‐DITT in ternary‐blend PSCs resulted in a 10 % increase of external quantum efficiency (EQE) in the blue‐light region. However, in a crystalline host, the dopant decreased the crystallinity of the host and led to large drops in FF and power conversion efficiencies (PCEs). The study provides an alternative route and expands the application of PPors in PSCs as a blue‐light harvester in ternary‐blend PSCs using amorphous polymers as host. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

2,3‐bis(5‐Hexylthiophen‐2‐yl)‐6,7‐bis(octyloxy)‐5,8‐di(thiophen‐2‐yl) quinoxaline: A good construction block with adjustable role in the donor‐π‐acceptor system for bulk‐heterojunction solar cells

Three 2,3‐bis(5‐hexylthiophen‐2‐yl)‐6,7‐bis(octyloxy)‐5,8‐di(thiophen‐2‐yl)‐quinoxaline ( BTTQ )‐based conjugated polymers, namely, PF‐BTTQ ( P1 ), PP‐BTTQ ( P2 ), and PDCP‐BTTQ ( P3 ), were successfully synthesized for efficient polymer solar cells (PSCs) with electron‐rich units of fluorene and dialkoxybenzene and electron‐deficient unit dicyanobenzene, respectively. All the polymers exhibited good solubility in common organic solvents and good thermal stability. Their deep‐lying HOMO energy levels enabled them good stability in the air and the relatively low HOMO energy level assured a higher open circuit potential when used in PSCs. Bulk‐heterojunction solar cells were fabricated using these copolymers blended with a fullerene derivative as an acceptor. All of them exhibited promising performance, and the best device performance with power conversion efficiency up to 3.30% was achieved under one sun of AM 1.5 solar simulator illumination (100 mW/cm²). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A–π–D–π–A Electron‐Donating Small Molecules for Solution‐Processed Organic Solar Cells: A Review

Organic solar cells based on semiconducting polymers and small molecules have attracted considerable attention in the last two decades. Moreover, the power conversion efficiencies for solution‐processed solar cells containing A–π–D–π–A‐type small molecules and fullerenes have reached 11%. However, the method for designing high‐performance, photovoltaic small molecules still remains unclear. In this review, recent studies on A–π–D–π–A electron‐donating small molecules for organic solar cells are introduced. Moreover, the relationships between molecular properties and device performances are summarized, from which inspiration for the future design of high performance organic solar cells may be obtained.     

Synthesis and characterization of thieno[3,2‐b]thiophene‐isoindigo‐based copolymers as electron donor and hole transport materials for bulk‐heterojunction polymer solar cells

A novel class of thieno[3,2‐b]thiophene (TT) and isoindigo based copolymers were synthesized and evaluated as electron donor and hole transport materials in bulk‐heterojunction polymer solar cells (BHJ PSCs). These π‐conjugated donor‐acceptor polymers were derived from fused TT and isoindigo structures bridged by thiophene units. The band‐gaps and the highest occupied molecular orbital (HOMO) levels of the polymers were tuned using different conjugating lengths of thiophene units on the main chains, providing band‐gaps from 1.55 to 1.91 eV and HOMO levels from ?5.34 to ?5.71 eV, respectively. The corresponding lowest unoccupied molecular orbital (LUMO) levels were appropriately adjusted with the isoindigo units. Conventional BHJ PSCs (ITO/PEDOT:PSS/active layer/interlayer/Al) with an active layer composed of the polymer and PC₇₁BM were fabricated for evaluation. Power conversion efficiency from a low of 1.25% to a high of 4.69% were achieved with the best performing device provided by the D?π?A polymer with a relatively board absorption spectrum, high absorption coefficient, and more uniform blend morphology. These results demonstrate the potential of this class of thieno[3,2‐b]thiophene‐isoindigo‐based polymers as efficient electron donor and hole transport polymers for BHJ PSCs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

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     

Synthesis and characterization of porphyrin‐based D‐π‐A conjugated polymers for polymer solar cells

Two novel porphyrin‐based D‐A conjugated copolymers, PFTTQP and PBDTTTQP , consisting of accepting quinoxalino[2,3‐b′]porphyrin unit and donating fluorene or benzo[1,2‐b:4,5‐b′]dithiophene unit, were synthesized, respectively via a Pd‐catalyzed Stille‐coupling method. The quinoxalino[2,3‐b′]porphyrin, an edge‐fused porphyrin monomer, was used as a building block of D‐A copolymers, rather than the simple porphyrin unit in conventional porphyrin‐based photovoltaic polymers reported in literature, to enhance the coplanarity and to extend the π‐conjugated system of polymer main chains, and consequently to facilitate the intramolecular charge transfer (ICT). The thermal stability, optical, and electrochemical properties as well as the photovoltaic characteristics of the two polymers were systematically investigated. Both the polymers showed high hole mobility, reaching 4.3 × 10^?4 cm² V^?1 s^?1 for PFTTQP and 2.0 × 10^?4 cm² V^?1 s^?1 for PBDTTTQP . Polymer solar cells (PSCs) made from PFTTQP and PBDTTTQP demonstrated power conversion efficiencies (PCEs) of 2.39% and 1.53%, both of which are among the highest PCE values in the PSCs based on porphyrin‐based conjugated polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013     

Synthesis and Characterization of a Soluble A–D–A Molecule Containing a 2D Conjugated Selenophene‐Based Side Group for Organic Solar Cells

A new acceptor–donor–acceptor (A–D–A) small molecule based on benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) is synthesized via a Stille cross‐coupling reaction. A highly conjugated selenophene‐based side group is incorporated into each BDT unit to generate a 2D soluble small molecule (SeBDT‐DPP). SeBDT‐DPP thin films produce two distinct absorption peaks. The shorter wavelength absorption (400 nm) is attributed to the BDT units containing conjugated selenophene‐based side groups, and the longer wavelength band is due to the intramolecular charge transfer between the BDT donor and the DPP acceptor. SeBDT‐DPP thin films can harvest a broad solar spectrum covering the range 350–750 nm and have a low bandgap energy of 1.63 eV. Solution‐processed field‐effect transistors fabricated with this small molecule exhibit p‐type organic thin film transistor characteristics, and the field‐effect mobility of a SeBDT‐DPP device is measured to be 2.3 × 10⁻³ cm² V⁻¹ s⁻¹. A small molecule solar cell device is prepared by using SeBDT‐DPP as the active layer is found to exhibit a power conversion efficiency of 5.04% under AM 1.5 G (100 mW cm⁻²) conditions.

     

Pyrrolo[3,4‐c]pyrrole‐1,3‐dione‐based large band gap polymers containing benzodithiophene derivatives for highly efficient simple structured polymer solar cells

Pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione (DPPD)‐based large band gap polymers, P(BDT‐TDPPDT) and P(BDTT‐TDPPDT), are prepared by copolymerizing electron‐rich 4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene (BDT) or 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) unit with novel electron deficient 2,5‐dioctyl‐4,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione (TDPPDT) unit. The absorption bands of polymers P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) cover the region from 300 to 600 nm with an optical band gap of 2.11 eV and 2.04 eV, respectively. The electrochemical study illustrates that the highest occupied/lowest unoccupied molecular orbital energy levels of P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) are ?5.39 eV/?3.28 eV and ?5.44 eV/?3.40 eV, respectively. The single layer polymer solar cell (PSC) fabricated with a device structure of ITO/PEDOT:PSS/P(BDT‐TDPPDT) or P(BDTT‐TDPPDT):PC70BM+DIO/Al offers a maximum power conversion efficiency (PCE) of 6.74% and 6.57%, respectively. The high photovoltaic parameters such as fill factor (～72%), open circuit voltage (V_oc, ～0.90 V), incident photon to collected electron efficiency (～76%), and PCE obtained for the PSCs made from polymers P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) make them as promising large band gap polymeric candidates for PSC application. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3564–3574     

Thieno[3,4‐c]pyrrole‐4,6‐dione‐Based Small Molecules for Highly Efficient Solution‐Processed Organic Solar Cells

Two small molecules named BT‐TPD and TBDT‐TTPD with a thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) unit were designed and synthesized for solution‐processed bulk‐heterojunction solar cells. Their thermal, electrochemical, optical, charge‐transport, and photovoltaic characteristics were investigated. These compounds exhibit strong absorption at 460–560 nm and low highest occupied molecular orbital levels (?5.36 eV). Field‐effect hole mobilities of these compounds are 1.7–7.7×10^?3 cm² V^?1 s^?1. Small‐molecule organic solar cells based on blends of these donor molecules and a acceptor display power conversion efficiencies as high as 4.62 % under the illumination of AM 1.5G, 100 mW cm^?2.     

Regioisomeric Effects on the Electronic Features of Indenothiophene‐Bridged D–π‐A′–A DSSC Sensitizers

Two D–π‐A′–A regioisomers (A‐IDT‐D and D‐IDT‐A) featuring 4,4′‐di‐p‐tolyl‐4 H‐indeno[1,2‐b]‐thiophene as a π linker (π) between the diarylamino donor (D) and the pyrimidine–cyanoacrylic acid acceptor (A′–A) have been successfully synthesized and characterized as efficient sensitizers for the dye‐sensitized solar cells (DSSCs). The different arrangements of the D and A′–A blocks on the unsymmetrical indenothiophene (IDT) core render the dipole of IDT being along (A‐IDT‐D) or opposite (D‐IDT‐A) to the direction of intramolecular (donor‐to‐acceptor) charge transfer, and thus induce variations in the physical properties. The experimental observations correlated well with the theoretical analyses, clearly revealing the trade‐off between the molar extinction coefficient (ε) and the S₀→S₁ transition energy. As a result, a superior ε value was observed for D‐IDT‐A, whereas a bathochromic shift in the absorption occurred in A‐IDT‐D. The larger ε value of D‐IDT‐A together with its more favorable energy level relative to TiO₂ led to a higher power conversion efficiency of 7.41 % for the D‐IDT‐A‐based DSSC, retaining approximately 95 % of the N719‐based DSSC efficiency. This work manifests the clear structure–property relationship for the case of donor and acceptor components being connected by an unsymmetrical π linker and provides insights for molecular engineering of organic sensitizers.     

Synthesis and photovoltaic performances of benzo[1,2‐b:4,5‐b']dithiophene‐alt‐2,3‐diphenylquinoxaline copolymers pending functional groups in phenyl rings

Two donor/acceptor (D/A)‐based benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐2,3‐biphenyl quinoxaline copolymers of P 1 and P 2 were synthesized pending different functional groups (thiophene or triphenylamine) in the 4‐positions of phenyl rings. Their thermal, photophysical, electrochemical, and photovoltaic properties, as well as morphology of their blending films were investigated. The poly(4,8‐bis((2‐ethyl‐hexyl)oxy)benzo[1,2‐b:4,5‐b'] dithiophene)‐alt‐(2,3‐bis(4′‐bis(N,N‐bis(4‐(octyloxy) phenylamino)‐ 1,1′‐biphen‐4‐yl)quinoxaline) ( P 2) exhibited better photovoltaic performance than poly(4,8‐bis((2‐ethylhexyl)oxy)benzo[1,2‐b:4,5‐b'] dithiophene)‐alt‐(2,3‐bis(4‐(5‐octylthiophen‐2‐yl)phenyl)quinoxaline) ( P 1) in the bulk‐heterojunction polymer solar cells with a configuration of ITO/PEDOT:PSS/polymers: [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM)/LiF/Al. A power conversion efficiency of 3.43%, an open‐circuit voltage of 0.80 V, and a short‐circuit current of 9.20 mA cm^?2 were achieved in the P 2‐based cell under the illumination of AM 1.5, 100 mW cm^?2. Importantly, this power conversion efficiency level is 2.29 times higher than that in the P 1‐based cell. Our work indicated that incorporating triphenylamine pendant in the D/A‐based polymers can greatly improved the photovoltaic properties for its resulting polymers.     

D–π–A polysulfones for blue electroluminescence

Donor–π–acceptor type fluorene‐based copolymers with a sulfone unit were designed and synthesized for application in efficient pure‐blue light emitting. The electroluminescence behaviors of these copolymers were investigated by fabricating light‐emitting diodes and electrochemical cell devices. The former device little functioned but the latter worked well. The electrochemical cell devices having a configuration of ITO/PEDOT:PSS/copolymer:ionic liquid/Al exhibited purplish blue electroluminescence with an emission maximum at 434 nm (CIE coordinates (x, y) = (0.17, 0.10)) measured at 7 V. The initial positive scan of the D–π–A polysulfone based light emitting electrochemical cell with a sweep rate of 0.1 V s^?1 afforded a maximum luminance of 1080 cd m^?2 with a current efficiency of 1.96 cd A^?1 at an operating voltage of 12.5 V. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3454–3461     

Naphtho[2,1‐b:3,4‐b′]dithiophene‐based Bulk Heterojunction Solar Cells: How Molecular Structure Influences Nanoscale Morphology and Photovoltaic Properties

Organic bulk heterojunction photovoltaic devices based on a series of three naphtho[2,1‐b:3,4‐b′]dithiophene (NDT) derivatives blended with phenyl‐C₇₁‐butyric acid methyl ester were studied. These three derivatives, which have NDT units with various thiophene‐chain lengths, were employed as the donor polymers. The influence of their molecular structures on the correlation between their solar‐cell performances and their degree of crystallization was assessed. The grazing‐incidence angle X‐ray diffraction and atomic force microscopy results showed that the three derivatives exhibit three distinct nanoscale morphologies. We correlated these morphologies with the device physics by determining the J–V characteristics and the hole and electron mobilities of the devices. On the basis of our results, we propose new rules for the design of future generations of NDT‐based polymers for use in bulk heterojunction solar cells.     

A vinylene‐linked benzo[1,2‐b:4,5‐b']dithiophene‐2,1,3‐benzothiadiazole low‐bandgap polymer

A new heteroarylene‐vinylene donor–acceptor polymer P(BDT‐V‐BTD) with reduced bandgap has been synthesized and its photophysical, electronic and photovoltaic properties investigated both experimentally and theoretically. The structure of the polymer comprises an unprecedented combination of a strong donor (4,8‐dialkoxy‐benzo[1,2‐b:4,5‐b']dithiophene, BDT), a strong acceptor (2,1,3‐benzothiadiazole, BTD) and a vinylene spacer. The new polymer was obtained by a metal‐catalyzed cross‐coupling Stille reaction and fully characterized by NMR, UV–vis absorption, GPC, TGA, DSC and electrochemistry. Detailed ab initio computations with solvation effects have been performed for the monomer and model oligomers. The electrochemical investigation has ascertained the ambipolar character of the polymer and energetic values of HOMO, LUMO and bandgap matching materials‐design rules for optimized organic photovoltaic devices. The HOMO and LUMO energies are consistently lower than those of previous heteroarylene‐vinylene polymer while the introduction of the vinylene spacer afforded lower bandgaps compared to the analogous system P(BDT‐BTD) with no spacer between the aromatic rings. These superior properties should allow for enhanced photovoltages and photocurrents in photovoltaic devices in combination with PCBM. Preliminary photovoltaic investigation afforded relatively modest power conversion efficiencies of 0.74% (AM 1.5G, 100 mW/cm²), albeit higher than that of previous heteroarylene‐vinylene polymers and comparable to that of P(BDT‐BTD). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Small D–π–A Systems with o‐Phenylene‐Bridged Accepting Units as Active Materials for Organic Photovoltaics

Donor–acceptor (D–π–A) systems that combine triarylamine donor blocks and dicyanovinyl (DCV) acceptor groups have been synthesized. Starting from the triphenylamine (TPA)? thiophene? DCV compound ( 1 ) as a reference system, various synthetic approaches have been developed for controlling the light‐harvesting properties and energy levels of the frontier orbitals in this molecule. Thus, the introduction of methoxy groups onto TPA, the replacement of one phenyl ring of TPA by a thiophene ring, or the extension of the π‐conjugating spacer group lead to the modulation of the HOMO level. On the other hand, the fusion of the DCV group onto the vicinal thiophene ring by an ortho‐phenylene bridge allows for a specific fine‐tuning of the LUMO level. The electronic properties of the molecules were analyzed by using UV/Vis spectroscopy and cyclic voltammetry and the compounds were evaluated as donor materials in basic bilayer planar heterojunction solar cells by using C₆₀ as acceptor material. The relationships between the electronic properties of the donors and the performance of the corresponding photovoltaic devices are discussed. Bilayer planar heterojunction solar cells that used reference compound 1 and C₇₀ afforded power‐conversion efficiencies of up to 3.7 %.     

Molecular Engineering of Pyrido[3,4‐b]pyrazine‐Based Donor–Acceptor–π‐Acceptor Organic Sensitizers: Effect of Auxiliary Acceptor in Cobalt‐ and Iodine‐Based Electrolytes

Due to the ease of tuning its redox potential, the cobalt‐based redox couple has been extensively applied for highly efficient dye‐sensitized solar cells (DSSCs) with extraordinarily high photovoltages. However, a cobalt electrolyte needs particular structural changes in the organic dye components to obtain such high photovoltages. To achieve high device performance, specific requirements in the molecular tailoring of organic sensitizers still need to be met. Besides the need for large electron donors, studies of the auxiliary acceptor segment of donor–acceptor–π‐acceptor (D‐A‐π‐A) organic sensitizers are still rare in molecular optimization in the context of cobalt electrolytes. In this work, two novel organic D‐A‐π‐A‐type sensitizers ( IQ13 and IQ17 ) have been developed and exploited in cobalt‐ and iodine‐based redox electrolyte DSSCs, specifically to provide insight into the effect of π‐bridge modification in different electrolytes. The investigation has been focused on the additional electron‐withdrawing acceptor capability with grafted long alkoxy chains. Optoelectronic transient measurements have indicated that IQ17 containing a pyrido[3,4‐b]pyrazine moiety bearing long alkoxyphenyl chains is more suitable for application in cobalt‐based DSSCs.