Benzo[2,1‐b;3,4‐b′]dithiophene‐based low‐bandgap polymers for photovoltaic applications

The synthesis of four alternating copolymers using benzo[2,1‐b;3,4‐b′]dithiophene (BDP) as the common donor unit is presented. Before the synthesis, theoretical calculations that we performed predicted that the incorporation of BDP, which consists of fused dithiophene units with a benzene ring, into these polymers would produce a low‐lying highest occupied molecular orbital (HOMO) energy level. Low‐lying HOMO levels are desirable to produce high open circuit voltages (V_OC) in organic bulk heterojunction (BHJ) photovoltaic devices. The polymers' structural characterization, as well as the preliminary results of their performance in BHJ devices, using (6,6)‐phenyl C₆₁‐butyric acid methyl ester as the electron acceptor, is presented. The V_OC values follow the expected trend: increasing with decreasing HOMO level of the polymer. High V_OC values of 0.81 and 0.82 V have been obtained from two polymers: PBDPBT and PBDPDPP. The initial power conversion efficiency achieved in these unoptimized devices was 1.11% because of relatively low J_SC values. The variation observed in the J_SC values between the four polymers is discussed. Device performance is expected to increase with optimization of processing conditions for the devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and photovoltaic properties of conjugated copolymers based on benzimidazole and various thiophene

A new accepter unit, dimethyl‐2H‐benzimidazole, was prepared and used for the synthesis of the conjugated polymers containing electron donor–acceptor pair for organic photovoltaics (OPVs). Dimethyl‐2H‐benzimidazole unit was designed to substitute the BT unit of poly(N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)) (PCDTBT). A series of new semiconducting polymers with 2,2‐dimethyl‐2H‐benzimidazole, 9‐heptadecanyl‐9H‐carbazole, and thiophene (or bithiophene) units was synthesized using Stille polymerization to generate PCDTMBIs (or PCBBTMBIs). In dimethyl‐2H‐benzimidazole, the sulfur at 2‐position of BT unit was replaced with dialkyl substituted carbon, while keeping the 1,2‐quinoid form, to improve the solubility of the polymers. The absorption spectra of PCDTMBIs with thiophene units exhibit two maximum peaks at about 430 and 613–645 nm in solution. The solutions of PCBBTMBIs show two absorption peaks at about 445–456 and 630–645 nm which is red‐shifted about 20 nm when compared with PCDTMBIs caused by the introduction of bithiophene units. In most efficient polymer PCBBTMBI3, the device annealed at 100 °C for 10 min demonstrated a V_OC value of 0.60 V, a J_SC value of 4.31 mA/cm², and a FF of 0.35, leading to the power conversion efficiency (PCE) of 0.91%, under white light illumination (AM 1.5 G and 100 mW/cm²). © 2011 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     

A Photoelectrochemical Solar Cell Consisting of a Cadmium Sulfide Photoanode and a Ruthenium–2,2′‐Bipyridine Redox Shuttle in a Non‐aqueous Electrolyte

A photoelectrochemical (PEC) cell consisting of an n‐type CdS single‐crystal electrode and a Pt counter electrode with the ruthenium–2,2′‐bipyridine complex [Ru(bpy)₃]^2+/3+ as the redox shuttle in a non‐aqueous electrolyte was studied to obtain a higher open‐circuit voltage (V_OC) than the onset voltage for water splitting. A V_OC of 1.48 V and a short‐circuit current (I_SC) of 3.88 mA cm^?2 were obtained under irradiation by a 300 W Xe lamp with 420–800 nm visible light. This relatively high voltage was presumably due to the difference between the Fermi level of photo‐irradiated n‐type CdS and the redox potential of the Ru complex at the Pt electrode. The smooth redox reaction of the Ru complex with one‐electron transfer was thought to have contributed to the high V_OC and I_SC. The obtained V_OC was more than the onset voltage of water electrolysis for hydrogen and oxygen generation, suggesting prospects for application in water electrolysis.     

Highly Efficient Dye‐Sensitized Solar Cells Based on Panchromatic Ruthenium Sensitizers with Quinolinylbipyridine Anchors

Panchromatic Ru^II sensitizers TF‐30–TF‐33 bearing a new class of 6‐quinolin‐8‐yl‐2,2′‐bipyridine anchor were synthesized and tested under AM1.5 G simulated solar irradiation. Their increased π conjugation relative to that of the traditional 2,2′:6′,2′′‐terpyridine‐based anchor led to a remarkable improvement in absorptivity across the whole UV–Vis–NIR spectral regime. Furthermore, the introduction of a bulky tert‐butyl substituent on the quinolinyl fragment not only led to an increase in the J_SC value owing to the suppression of dye aggregation, but remarkably also resulted in no loss in V_OC in comparison with the reference sensitizer containing a tricarboxyterpyridine anchor. The champion sensitizer in DSC devices was found to be TF‐32 with a performance of J_SC=19.2 mA cm^?2, V_OC=740 mV, FF=0.72, and η=10.19 %. This 6‐quinolin‐8‐yl‐2,2′‐bipyridine anchor thus serves as a prototype for the next generation of Ru^II sensitizers with any tridentate ancillary.     

Dithieno[2,3‐d:2',3'‐d']benzo[1,2‐b:4,5‐b']dithiophene (DTBDAT)‐based copolymers for high‐performance organic solar cells

P(BDT‐TCNT) and P(DTBDAT‐TCNT) , which has an extended conjugation length, were designed and synthesized for applications in organic solar cell (OSCs). The solution absorption maxima of P(DTBDAT‐TCNT) with the extended conjugation were red‐shifted by 5–15 nm compared with those of P(BDT‐TCNT) . The optical band gaps and highest occupied molecular orbital (HOMO) energy levels of both P(BDT‐TCNT) and P(DTBDAT‐TCNT) were similar. The structure properties of thin films of these materials were characterized using grazing‐incidence wide‐angle X‐ray scattering and tapping‐mode atomic force microscopy, and charge carrier mobilities were characterized using the space‐charge limited current method. OSCs were formed using [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as the electron acceptor and 3% diphenylether as additive suppress aggregation. OSCs with P(BDT‐TCNT) as the electron donor exhibited a power conversion efficiency (PCE) of 4.10% with a short‐circuit current density of J_SC = 9.06 mA/cm², an open‐circuit voltage of V_OC = 0.77 V, and a fill factor of FF = 0.58. OSCs formed using P(DTBDAT‐TCNT) as the electron donor layer exhibited a PCE of 5.83% with J_SC = 12.2 mA/cm², V_OC = 0.77 V, and FF = 0.62. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3182–3192     

Synthesis and characterization of new selenophene‐based conjugated polymers for organic photovoltaic cells

Three new polymers poly(3,4′′′‐didodecyl) hexaselenophene) (P6S), poly(5,5′‐bis(4,4′‐didodecyl‐2,2′‐biselenophene‐5‐yl)‐2,2′‐biselenophene) (HHP6S), and poly(5,5′‐bis(3′,4‐didodecyl‐2,2′‐biselenophene‐5‐yl)‐2,2′‐biselenophene) (TTP6S) that have the same selenophene‐based polymer backbone but different side chain patterns were designed and synthesized. The weight‐averaged molecular weights (M_w) of P6S, HHP6S, and TTP6S were found to be 19,100, 24,100, and 19,700 with polydispersity indices of 2.77, 1.48, and 1.41, respectively. The UV–visible absorption maxima of P6S, HHP6S, and TTP6S are at 524, 489, and 513 nm, respectively, in solution and at 569, 517, and 606 nm, respectively, in the film state. The polymers P6S, HHP6S, and TTP6S exhibit low band gaps of 1.74, 1.95, and 1.58 eV, respectively. The field‐effect mobilities of P6S, HHP6S, and TTP6S were measured to be 1.3 × 10^?4, 3.9 × 10^?6, and 3.2 × 10^?4 cm² V^?1 s^?1, respectively. A photovoltaic device with a TTP6S/[6,6]‐phenyl C₇₁‐butyric acid methyl ester (1:3, w/w) blend film active layer was found to exhibit an open circuit voltage (V_OC) of 0.71 V, a short circuit current (J_SC) of 5.72 mA cm^?2, a fill factor of 0.41, and a power conversion efficiency (PCE) of 1.67% under AM 1.5 G (100 mW cm^?2) illumination. TTP6S has the most planar backbone of the tested polymers, which results in strong π–π interchain interactions and strong aggregation, leading to broad absorption, high mobility, a low band gap, and the highest PCE. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Side‐chain effects on phenothiazine‐based donor–acceptor copolymer properties in organic photovoltaic devices

A series of new phenothiazine‐based donor–acceptor copolymers, P1 and P2, were synthesized via a Suzuki coupling reaction. The weight‐averaged molecular weights (M_w) of P1 and P2 were found to be 16,700 and 16,100, with polydispersity indices of 1.74 and 1.39, respectively. The UV–visible absorption spectra of the polymer thin films contained three strong absorption bands in the ranges 318–320 nm, 430–436 nm, and 527–568 nm. The absorption peaks at 320 and 430 nm originated mainly from the phenothiazine‐based monomer units, and the longer wavelength absorption band at 527–568 nm was attributed to the increased effective conjugation length of the polymer backbones. Solution‐processed field‐effect transistors fabricated with these polymers exhibited p‐type organic thin film transistor characteristics. The field‐effect mobilities of P1 and P2 were measured to be 1.0 × 10^?4 and 7.5 × 10^?5 cm² V^?1 s^?1, respectively, with on/off ratios in the order of 10⁴ for all polymers. A photovoltaic device in which a P2/PC₇₁BM (1/3) blend film was used as the active layer exhibited an open‐circuit voltage (V_OC) of 0.70 V, a short‐circuit current (J_SC) of 6.79 mA cm⁽², a fill factor of 0.39, and a power conversion efficiency of 1.86% under AM 1.5 G (100 mW cm^?2) illumination. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Enhanced Performance of Organic Photovoltaic Cells Fabricated with a Methyl Thiophene‐3‐Carboxylate‐Containing Alternating Conjugated Copolymer

A new donor‐acceptor copolymer, containing benzodithiophene (BDT) and methyl thiophene‐3‐carboxylate (3MT) units, is designed and synthesized for polymer solar cells (PSCs). The 3MT unit is used as an electron acceptor unit in this copolymer to provide a lower highest occupied molecular orbital (HOMO) level for obtaining polymer solar cells with a higher open‐circuit voltage (V_OC). The resulting bulk heterojunction PSC made of the copolymer and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) exhibits a power conversion efficiency (PCE) up to 4.52%, a short circuit current (J_SC) of 10.5 mA·cm‐², and a V_OC of 0.86 V.     

Synthesis and electronic energy‐level regulation of imide‐fused poly(thienylene vinylene) derivatives

A series of novel poly(thienylene vinylene) derivatives (PTVs), P20‐P24 , with imide substituents were designed and synthesized by palladium‐catalyzed Stille coupling polymerization, wherein the imide substituent density was decreased gradually, which allowed us to explicitly study the effect of electron‐deficient substituent on the optical, electrochemical, and photovoltaic properties of the PTVs. All of the four polymers showed broad absorption bands with optical bandgaps between1.66 and 1.78 eV. By reducing density of electron‐deficient imide group, the LUMO energy levels of the polymers could be tuned gradually from ?3.75 to ?3.43 eV, with HOMO levels upshifted from ?5.64 to ?5.16 eV. Bulk heterojunction solar cells with the polymers as donor and PC₇₁BM as acceptor demonstrated very different excitons dissociation behavior. With decreasing the imide‐fused unit density, the open‐circuit voltage (V_OC) values in the devices decreased from 0.78 to 0.62 V, whereas the short‐circuit currents (J_SC) increased from 0 to 2.26 mA cm^?2 and then decreased to 1.01 mA cm^?2. By adjusting the electron‐withdrawing imide substituent density, power conversion efficiency of the PTVs‐based solar cells can be increased to four times, reached 0.86%. To the best of our knowledge, this is the first systematic study of the relationship between molecular energy level and photovoltaic properties of PTVs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4975–4982     

Synthesis and characterization of isoindigo‐based polymers using CH‐arylation polycondensation reactions for organic photovoltaics

A series of three new low bandgap donor–acceptor–donor–acceptor^/ (D–A–D–A^/) polymers have been successfully synthesized based on the combination of isoindigo as the electron‐deficient acceptor and 3,4‐ethylenedioxythiophene as the electron‐rich donor, followed by CH‐arylation with different acceptors (4,7‐dibromo[c][1,2,5]‐(oxa, thia, and/or selena)diazole ( 4a‐c )). These polymers were used as donor materials for photovoltaic applications. All of the polymers are highly stable and show good solubility in chlorinated solvents. The highest power conversion efficiency of 1.6% was achieved in the bulk heterojunction photovoltaic device that consisted of poly ((E)?6‐(7‐(benzo‐[c][1,2,5]‐thiadiazol‐4‐yl)?2,3‐dihydrothieno‐[3,4‐b][1,4]dioxin‐5‐yl)?6′‐(2,3‐dihydrothieno‐[3,4‐b][1,4]‐dioxin‐5‐yl)?1,1′‐bis‐(2‐octyldodecyl)‐[3,3′‐biindolinylidene]‐2,2′‐dione) as the donor and PC₆₁BM as the acceptor, with a short‐circuit current density (J_sc) of 8.10 mA/cm², an open circuit voltage (V_oc) of 0.56 V and a fill factor of 35%, which indicates that these polymers are promising donors for polymer solar cell applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2926–2933     

Effect of long alkyl chains of aniline donor on the photovoltaic performance of D‐π‐A zinc porphyrin for dye‐sensitized solar cells

Three novel dyes of JJ1 , JJ2 , and JJ6 featured zinc porphyrin as a basic core structure; N, N‐alkyl‐4‐(prop‐1‐yn‐1‐yl)aniline as an electron donor linked to meso‐10‐position; 4‐(prop‐1‐yn‐1‐yl)benzoic acid as an electron acceptor linked to meso‐20‐position; and 2,6‐bis(dodecyloxy)phenyl or 2,6‐bis(octyloxy)phenyl respectively linked to meso‐5 and meso‐15‐positions of zinc porphyrin have been synthesized and used for dye‐sensitized solar cells. Porphyrin JJ6 featured the shortest alkyl group (─C₄H₉) on the donor, whereas JJ2 contained the longest alkyl groups (─C₁₂H₂₅), and JJ1 has a medium length of octyl groups. With these new porphyrin sensitizers, we observed that JJ6 has 7.55% power conversion efficiency under simulated one‐sun illumination (AM 1.5 G, 100 mW/cm²) with J_SC = 18.64 mA/cm², V_OC = 0.66 V, and fill factor (FF) = 0.61, which was higher than the other two; JJ1 (7.35%) with J_SC = 18.83 mA/cm², V_OC = 0.68 V, and FF = 0.60; and JJ2 (6.33%) with J_SC = 15.69 mA/cm², V_OC = 0.62 V, and FF = 0.65. The power conversion efficiency of JJ6 and JJ1 were higher than JJ2 , demonstrating that the lengthy alkyl groups on the aniline cause a decrease in efficiency of the devices.     

Thiophene π bridge effect on bulky side‐chained benzodithiophene‐based photovoltaic polymers

Recently, we have used terthiophene side chain to modify benzo[1,2‐b:4,5‐b′]dithiophene (BDT) to form novel building block for BDT polymers. In this paper, this building block is used to copolymerized with thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) and thieno[3,4‐b]thiophene (TT). This building block and TPD‐ or TT‐based polymers (P1 and P3) show high open circuit voltage (V_OC) (ca. 0.9–0.95 V) and low energy loss (E_g–eV_OC) in solar cells devices compared with similar polymers without bulky side chain. We further introduce thiophene π bridge into these polymers backbone to form two other polymers (P2 and P4). We find this thiophene π bridge does contribute to this bulky side chained benzodithiophene polymer photovoltaic performances, especially for power conversion efficiencies (PCEs). The polymer solar cells (PSCs) performances are moderate in this article due to the serious aggregation in the PSCs active layer. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1615–1622     

Synthesis and properties of phenothiazylene vinylene‐based polymers: New organic semiconductors for field‐effect transistors and solar cells

A series of new phenothiazylene vinylene‐based semiconducting polymers, poly[3,7‐(4′‐dodecyloxyphenyl)phenothiazylene vinylene] ( P1 ), poly[3,7‐(4′‐dodecyloxyphenyl)phenothiazylene vinylene‐alt‐1,4‐phenylene vinylene] ( P2 ), and poly[3,7‐(4′‐dodecyloxyphenyl)phenothiazylene vinylene‐alt‐2,5‐thienylene vinylene] ( P3 ), have been synthesized via a Horner‐Emmons reaction. FTIR and ¹H NMR spectroscopies confirmed that the configurations of the vinylene groups in the polymers were all‐trans (E). The weight‐averaged molecular weights (M_w) of P1 , P2 , and P3 were found to be 27,000, 22,000, and 29,000, with polydispersity indices of 1.91, 2.05, and 2.25, respectively. The thermograms for P1 , P2 , and P3 each contained only a broad glass transition, at 129, 167, and 155 °C, respectively, without the observation of melting features. UV–visible absorption spectra of the polymers showed two strong absorption bands in the ranges 315–370 nm and 450–500 nm, which arose from absorptions of the phenothiazine segments and the conjugated main chains. Solution‐processed field‐effect transistors fabricated from these polymers showed p‐type organic thin‐film transistor characteristics. The field‐effect mobilities of P1 , P2 , and P3 were measured to be 1.0 × 10^?4, 3.6 × 10^?5, and 1.0 × 10^?3 cm² V^?1 s^?1, respectively, and the on/off ratios were in the order of 10² for P1 and P2 , and 10³ for P3 . Atomic force microscopy and X‐ray diffraction analysis of thin films of the polymers show that they have amorphous structures. A photovoltaic device in which a P3 /PC₇₁BM (1/5) blend film was used as the active layer exhibited an open‐circuit voltage (V_OC) of 0.42 V, a short circuit current (J_SC) of 5.17 mA cm^?2, a fill factor of 0.35, and a power conversion efficiency of 0.76% under AM 1.5 G (100 mW cm^?2) illumination. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 635–646, 2010     

Phenanthrene‐Fused‐Quinoxaline as a Key Building Block for Highly Efficient and Stable Sensitizers in Copper‐Electrolyte‐Based Dye‐Sensitized Solar Cells

Dye‐sensitized solar cells (DSSCs) based on Cu^II/I bipyridyl or phenanthroline complexes as redox shuttles have achieved very high open‐circuit voltages (V_OC, more than 1 V). However, their short‐circuit photocurrent density (J_SC) has remained modest. Increasing the J_SC is expected to extend the spectral response of sensitizers to the red or NIR region while maintaining efficient electron injection in the mesoscopic TiO₂ film and fast regeneration by the Cu^I complex. Herein, we report two new D‐A‐π‐A‐featured sensitizers termed HY63 and HY64 , which employ benzothiadiazole (BT) or phenanthrene‐fused‐quinoxaline (PFQ), respectively, as the auxiliary electron‐withdrawing acceptor moiety. Despite their very similar energy levels and absorption onsets, HY64 ‐based DSSCs outperform their HY63 counterparts, achieving a power conversion efficiency (PCE) of 12.5 %. PFQ is superior to BT in reducing charge recombination resulting in the near‐quantitative collection of photogenerated charge carriers.     

4,9‐Dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐4,9‐dione functionalized copolymers for organic photovoltaic devices

The synthesis of conjugated polymers 1 – 5 functionalized with 4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐4,9‐dione in the backbone is reported and their use in the construction of organic solar cells is demonstrated. Increasing the molar ratio of 2,7‐dibromo‐3,8‐dihexyl‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐4,9‐dione, relative to 4,4′‐dihexyl‐5,5′‐dibromo‐2,2′‐bithiophene, in the copolymer synthesis significantly lowers the solubility of these polymers. The incorporation of highly conjugated 3,8‐dihexyl‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐4,9‐dione unit into the polymer backbone has been confirmed by UV–vis absorption. The observation of decreasing quantum yield for the emission in the order of 1 , 2 , 3 is consistent with copolymers with different comonomer content. The power conversion efficiencies of solar cells using blends of these polymers with PCBM ([6,6]‐phenyl C₆₁‐butyric acid methyl ester) were determined to be 0.11% for polymer 1 , 0.33% for 2 , and 0.26% for 3 , respectively. Under identical white light illumination, the power conversion efficiency of the device based on polymer 2 /PCBM as the active layer was three times higher compared to that of device based on polymer 1 /PCBM. Owing to the limited solubility and poor film‐forming ability of polymer 3 , the power conversion efficiency of solar cell based on 3 /PCBM blend is lower than that of 2 /PCBM blend, but is still larger than that of 1 /PCBM blend. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2680–2688, 2008     

Tailor‐Made Hole‐Conducting Coadsorbents for Highly Efficient Organic Dye‐Sensitized Solar Cells

The Y‐shaped, low molecular mass, hole‐conductor (HC), acidic coadsorbents 4‐{3,7‐bis[4‐(2‐ethylhexyloxy)phenyl]‐10H‐phenothiazin‐10‐yl}benzoic acid ( PTZ1 ) and 4‐{3,7‐bis[4‐(2‐ethylhexyloxy)phenyl]‐10H‐phenothiazin‐10‐yl}biphenyl‐4‐carboxylic acid ( PTZ2 ) were developed. Owing to their tuned and negative‐shifted HOMO levels (vs. NHE), they were used as HC coadsorbents in dye‐sensitized solar cells (DSSCs) to improve cell performance through desired cascade‐type hole‐transfer processes. Their detailed functions as HC coadsorbents in DSSCs were investigated to obtain evidence for the desired cascade‐type hole‐transfer processes. They have multiple functions, such as preventing π–π stacking of dye molecules, harvesting light of shorter wavelengths, and faster dye regeneration. By using PTZ2 as the tailor‐made HC coadsorbent on the TiO₂ surface with the organic dye NKX2677, an extremely high conversion efficiency of 8.95 % was achieved under 100 mW cm^?2 AM 1.5G simulated light (short‐circuit current J_SC=16.56 mA cm^?2, open‐circuit voltage V_OC=740 mV, and fill factor of 73 %). Moreover, J_SC was increased by 13 %, V_OC by 27 % and power‐conversion efficiency by 49 % in comparison to an NKX2677‐based DSSC without an HC coadsorbent. This is due to the HC coadsorbent having a HOMO energy level well matched to that of the NKX‐2677 dye to induce the desired cascade‐type hole‐transfer processes, which are associated with a slower charge recombination, fast dye regeneration, effective screening of liquid electrolytes, and an induced negative shift of the quasi‐Fermi level of the electrode. Thus, this new class of Y‐shaped, low molecular weight, organic, HC coadsorbents based on phenothiazine carboxylic acid derivatives hold promise for highly efficient organic DSSCs.     

Fluorene‐based alternating polymers containing electron‐withdrawing bithiazole units: Preparation and device applications

We report here the synthesis via Suzuki polymerization of two novel alternating polymers containing 9,9‐dioctylfluorene and electron‐withdrawing 4,4′‐dihexyl‐2,2′‐bithiazole moieties, poly[(4,4′‐dihexyl‐2,2′‐bithiazole‐5,5′‐diyl)‐alt‐(9,9‐dioctylfluorene‐2,7‐diyl)] (PHBTzF) and poly[(5,5′‐bis(2″‐thienyl)‐4,4′‐dihexyl‐2,2′‐bithiazole‐5″,5″‐diyl)‐alt‐(9,9‐dioctylfluorene‐2,7‐diyl)] (PTHBTzTF), and their application to electronic devices. The ultraviolet–visible absorption maxima of films of PHBTzF and PTHBTzTF were 413 and 471 nm, respectively, and the photoluminescence maxima were 513 and 590 nm, respectively. Cyclic voltammetry experiment showed an improvement in the n‐doping stability of the polymers and a reduction of their lowest unoccupied molecular orbital energy levels as a result of bithiazole in the polymers' main chain. The highest occupied molecular orbital energy levels of the polymers were ?5.85 eV for PHBTzF and ?5.53 eV for PTHBTzTF. Conventional polymeric light‐emitting‐diode devices were fabricated in the ITO/PEDOT:PSS/polymer/Ca/Al configuration [where ITO is indium tin oxide and PEDOT:PSS is poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid)] with the two polymers as emitting layers. The PHBTzF device exhibited a maximum luminance of 210 cd/m² and a turn‐on voltage of 9.4 V, whereas the PTHBTzTF device exhibited a maximum luminance of 1840 cd/m² and a turn‐on voltage of 5.4 V. In addition, a preliminary organic solar‐cell device with the ITO/PEDOT:PSS/(PTHBTzTF + C₆₀)/Ca/Al configuration (where C₆₀ is fullerene) was also fabricated. Under 100 mW/cm² of air mass 1.5 white‐light illumination, the device produced an open‐circuit voltage of 0.76 V and a short‐circuit current of 1.70 mA/cm². The fill factor of the device was 0.40, and the power conversion efficiency was 0.52%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1845–1857, 2005     

First‐Generation Subporphyrinatoboron(III) Sensitizers Surpass the 10 % Power Conversion Efficiency Threshold

Subporphyrinatoboron(III) (SubB) sensitizers were synthesized for use in dye‐sensitized solar cells (DSSCs). The prototype, which comprises a sterically demanding 3,5‐di‐tert‐butylphenyl scaffold, a meso‐ethynylphenyl spacer, and a cyanoacrylic acid anchoring group, achieved an open‐circuit voltage V_OC of 836 mV, short‐circuit current density J_SC of 15.3 mA cm^?2, fill factor of 0.786, and a photon‐to‐current conversion efficiency of 10.1 %. Such astonishing figures suggest that a bright future lies ahead for SubB in the realm of DSSCs.     

Design and synthesis of dithieno[3,2‐b:2′3′‐d]pyrrole‐based conjugated polymers for photovoltaic applications: consensus between low bandgap and low HOMO energy level

A strategy of the fine‐tuning of the degree of intrachain charge transfer and aromaticity of polymer backbone was adopted to design and synthesize new polymers applicable in photovoltaics. Three conjugated polymers P1 , P2 , and P3 were synthesized by alternating the electron‐donating dithieno[3,2‐b:2′3′‐d]pyrrole (D) and three different electron‐accepting (A) segments ( P1 : N‐(2‐ethylhexyl)phthalimide; P2 : 1,4‐diketo‐3,6‐diphenylpyrrolo[3,4‐c]pyrrole; and P3 : thiophene‐3‐hexyl formate) in the polymer main chain. Among the three polymers, P2 possessed the broadest absorption band ranging from 300 to 760 nm, the lowest bandgap (1.63 eV), and enough low HOMO energy level (?5.27 eV) because of the strong intrachain charge transfer from D to A units and the appropriate extent of quinoid state in the main chain of P2 , which was convinced by the theoretical simulation of molecular geometry and front orbits. Photovoltaic study of solar cells based on the blends of P1 – P3 and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) demonstrated that P2 :PCBM exhibited the best performance: a power conversion efficiency of 1.22% with a high open‐circuit voltage (V_OC) of 0.70 V and a large short‐circuit current (I_SC) of 5.02 mA/cm² were achieved. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011