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A pentacyclic indacenodiselenophene (IDS) arene was synthesized via intramolecular Friedel-Craft cyclization of the selenophene moieties. This IDS framework was used as a model system to investigate the alkyl/alkoxy side-chain effect by preparing IDS-OCH8 and IDS-C6, where the side chains on the sp3 carbon in the cyclopentadienyl ring are 4-octyloxyphenyl groups and 4-hexylphenyl groups, respectively. The Sn-IDS-OCH8 and Sn-IDS-C6 monomers were copolymerized with 4,7-dibromo-2,1,3-benzothiadiazole (BT), 4,7-diiodo-5,6-difluoro-2,1,3-benzothiadiazole (FBT) and 1,3-dibromothieno[3,4-c]pyrrole-4,6-dione (TPD) acceptor monomers by Stille polycondensation to afford five new IDS-based donor–acceptor alternating copolymers, PIDSBT-OCH8, PIDSBT-C6, PIDSFBT-OCH8, PIDSFBT-C6, and PIDSTPD-C6. Despite the fact that the octyloxy and hexyl side chains play a negligible role in the optical and electrochemical properties of the resulting polymers, the solar cell performance is highly associated with the side chains of th...

The versatility of a fl uoro-containing low band-gap polymer, poly[2,6-(4,4bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b’]dithiophene)-alt-4,7-(5-fl uoro2,1,3-benzothia-diazole)] (PCPDTFBT) in organic photovoltaics (OPVs) applications is demonstrated. High boiling point 1,3,5-trichlorobenzene (TCB) is used as a solvent to manipulate PCPDTFBT:[6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) active layer morphology to obtain high-performance single-junction devices. It promotes the crystallization of PCPDTFBT polymer, thus improving the charge-transport properties of the active layer. By combining the morphological manipulation with interfacial optimization and device engineering, the single-junction device exhibits both good air stability and high power-conversion effi ciency (PCE, of 6.6%). This represents one of the highest PCE values for cyclopenta[2,1-b;3,4-b’]dithiophene (CPDT)-based OPVs. This polymer is also utilized for constructing semitransparent solar cells and double-junction tandem solar cells to demonstrate high PCEs of 5.0% and 8.2%, respectively.

Indolo[3,2-b]indole, containing two fused indole units, is an unexplored but promising electron-rich molecule for constructing donor–acceptor materials due to its planar, symmetric, and extended conjugated structure. We have successfully developed a new synthetic pathway to prepare 2,7-diboronic ester-indolo[3,2-b]indole, which was then reacted with dithienodiketopyrrolo-pyrrole acceptor to afford a new acceptor–donor–acceptor (A–D–A) conjugated molecule, 2,7-bis(dithienodiketopyrrolo-pyrrole)indolo[3,2-b]indole (2,7-DPPIIDPP). II is used to stand for indolo[3,2-b]indole in order to emphasize that this compound is constructed from two indole units. The A–D–A linkage through the 2,7-positions of II not only preserves the phenylene units in the para-conjugation but also renders stronger electron-donating strength. This material exhibited good thermal stability, high crystallinity, and broad UV/Vis absorption. The solution-processed bulk heterojunction device using the configuration of ITO/PEDOT:PSS/2,7-DPPIIDPP:PC71BM/Ca/Al exhibited a Voc of 0.72 V, a Jsc of 6.88 mA/cm2, and an FF of 49.6 %, leading to a power conversion efficiency (PCE) of 2.45 %.

A new cross-linkable fullerene material, bis(2-(trichlorosilyl)propyl)-malonate C60 (TSMC), functionalized with two trichlorosilane groups, was easily synthesized by Pt-catalyzed olefin hydrosilylation. By making use of facile hydrolysis of the trichlorosilyl moieties, TSMC can be spontaneously self-assembled and cross-linked on the TiOx surface by a simple spin-coating processing without the aid of photoirradiation or post-thermal treatments. The rapid formation of self-assembled and cross-linked TSMC (SA-C-TSMC) effectively passivates the residual hydroxyl groups on the TiOx surface. More significantly, the solvent-resistant TSMC network features a nanostructured surface to provide extra charge-generating interfacial area and straight electron transport pathways. The device (ITO/TiOx/SA-C-TSMC/P3HT:PC61BM (1:1, w/w)/PEDOT:PSS/Ag) with this C60 interlayer exhibited an efficiency of 3.9% which greatly outperformed the device without this layer. Furthermore, the strategy can also be effectively applied to ...

A new polymer PDTFDPP20 based on dithieno[3,2-b:6,7-b′]fluorene (DTF) unit was developed. This polymer with a face-on orientation has achieved a high field-effect mobility up to 5 cm2 V–1 s–1., A ladder-type dithieno[3,2-b:6,7-b′]fluorene (DTF), where the central fluorene is fused with two outer thiophene rings at its 2,3- and 6,7-junctions, is developed. The pentacyclic DTF monomers were polymerized with dithienodiketopyrrolopyrrole (DPP) acceptors to afford three alternating donor–acceptor copolymers PDTFDPP16, PDTFDPP20, and PDTFDPP32 incorporating different aliphatic side chains (R1 group at DTF; R2 group at the DPP moieties). The side-chain variations in the polymers play a significant role in determining not only the intrinsic molecular properties but also the intermolecular packing. As evidenced by the 2-dimensional GIXS measurements, PDTFDPP16 with octyl (R1) and 2-ethylhexyl (R2) side chains tends to align in an edge-on π-stacking orientation, whereas PDTFDPP20 using 2-butyloctyl (R1) and 2-ethylhexyl (R2) adopts a predominately face-on orientation. PDTFDPP32 with the bulkiest 2-butyloctyl (R1) and 2-octyldodecyl (R2) side chains shows a less ordered amorphous character. The OFET device using PDTFDPP20 with a face-on orientation determined by GIXS measurements achieved a high hole-mobility of up to 5 cm2 V–1 s–1. The high rigidity and coplanarity of the DTF motifs play an important role in facilitating intramolecular 1-dimensional charge transport within the polymer backbones. The implementation of main-chain coplanarity and side-chain engineering strategies in this research provides in-depth insights into structure–property relationships for guiding development of high-mobility OFET polymers.

A new class of heptacyclic ladder-type terbenzodithiophene (TBDT) structures merging three fused benzodithophenes was developed. Two TBDT conjugated isomers, named as syn-TBDT and anti-TBDT, where the two thienyl rings in the outmost BDT units are in the syn- and anti-fashion, are designed. Two decyl groups are introduced to their 6,13 and 7,14-positions to form four isomeric 6,13-syn-TBDT, 7,14-syn-TBDT, 6,13-anti-TBDT, and 7,14-anti-TBDT structures which are constructed by the DBU-induced 6-benzannulation involving propargyl-allenyl isomerization of the dieneyne moieties in the corresponding precursors followed by 6π-electrocyclization/aromatization, while isomeric TD-syn-TBDT and TD-anti-TBDT with four decyl groups substituted at 6,7,13,14-positions are synthesized via palladium-catalyzed dialkylacetylene insertion/C-H arylation of the corresponding iodobiaryl precursors. The intrinsic properties can be modulated by molecular manipulation of the main-chain and side-chain isomeric structures. anti-TBDT derivatives exhibit higher melting points, larger bandgaps, stronger intermolecular interactions, and higher mobility than the corresponding syn-TBDT analogues. These molecules can be further utilized as building blocks to make various TBDT-based materials for optoelectronic applications.

We have developed a new multifused indacenodithieno[3,2-b]thiophene arene (IDTT) unit where the central phenylene is covalently fastened with the two outer thieno[3,2-b]thiophene (TT) rings, forming two cyclopentadiene rings embedded in a heptacyclic structure. This rigid and coplanar IDTT building block was copolymerized with electron-deficient acceptors, 4,7-dibromo-2,1,3-benzothiadiazole (BT), 4,7-dibromo-5,6-difluoro-2,1,3-benzothiadiazole (FBT) and 1,3-dibromo-thieno[3,4-c]pyrrole-4,6-dione (TPD) via Stille polymerization, respectively. Because the higher content of the thienothiophene moieties in the fully coplanar IDTT structure facilitates π-electron delocalization, these new polymers show much improved light-harvesting abilities and enhanced charge mobilities compared to PDITTBT copolymer using hexacyclic diindenothieno[3,2-b]thiophene (DITT) as the donor moieties. The device using PIDTTBT:PC71BM (1:4, w/w) exhibited a decent power conversion efficiency (PCE) of 3.8%. Meanwhile, the solar cell us...

We have developed a new heptacyclic benzodi(cyclopentadithiophene) (BDCPDT) unit, where 3,7-positions of the central benzo[1,2-b:4,5-b′]dithiophenes (BDT) subunit are covalently rigidified with 3-positons of the two external thiophenes by two carbon bridges, forming two external CPDT rings that share two thiophene rings with the central BDT core. The distannyl-BDCPDT building block was copolymerized with 1,3-dibromo-thieno[3,4-c]pyrrole-4,6-dione (TPD) by Stille polymerization to afford a new alternating donor–acceptor copolymer PBDCPDT-TPD. The implementation of forced planarization greatly suppresses the interannular twisting to extend the effective conjugated length and preserve the interactions between the donor and acceptor segments. The device using the PBDCPDT-TPD/PC71BM (1:3 in wt%) blend processed with dimethyl sulfoxide as an additive delivered a marked PCE of 6.6% which represents a significant enhancement compared to the device using the corresponding nonfused polymer analogue with a PCE of 0.2%.

An isomerically pure anti-anthradithiophene (aADT) arranged in an angular shape is developed. Formation of the framework of aADT incorporating four lateral alkyl substituents was accomplished by a one-pot benzannulation via multiple Suzuki coupling. This newly designed 2,8-stannylated aADT monomer was copolymerized with a ditheniodiketopyrrolopyrrole (DPP) unit and a bithiophene unit, respectively, to furnish an alternating donor–acceptor copolymer poly(anthradithiophene-alt-dithienyldiketopyrrolopyrrole) (PaADTDPP) and a thiophene-rich poly(anthradithiophene-alt-bithiophene) (PaADTT). PaADTT with crystalline nature achieved a high FET mobility of 7.9 × 10–2 cm2 V–1 s–1 with an on–off ratio of 1.1 × 107. The photovoltaic device based on the PaADTDPP:PC71BM (1:2.5, w/w) blend exhibited a Voc of 0.66 V, a Jsc of 9.49 mA/cm2, and a FF of 58.4%, delivering a power conversion efficiency (PCE) of 3.66%. By adding 1.5 vol % 1-chloronaphthalene (CN) as a processing additive, the PCE can be improved to 4.24%. We d...

We have developed two nitrogen-bridged pentacyclic donor–acceptor dithienopyrrolobenzothiadiazole (DTPBT) and dithienopyrroloquinoxaline (DTPQX) arenes where the two outer electron-rich thiophene moieties are covalently fastened with the central electron-deficient benzothiadiazole and quinoxaline cores by two nitrogen bridges. These rigid and coplanar DTPBT and DTPQX building blocks were copolymerized with fluorene (F), carbazole (C) and cyclopentadithiophene (CPDT) units via Suzuki or Stille coupling polymerization to afford six new alternating copolymers PFDTPBT, PCDTPBT, PCPDTDTPBT, PFDTPQX, PCDTPQX and PCPDTDTPQX, respectively. The nitrogen bridges not only planarize the structure to induce stronger intermolecular π–π interaction but also play an important role in determining the electronic and photophysical properties of the polymers. The device based on PFDTPQX/PC71BM (1:4, w/w) exhibited a open-circuit voltage (Voc) of 0.72 V, a short-circuit current (Jsc) of 8.62 mA/cm2 and a FF of 0.55 leading to...

A new class of ladder-type dithienosilolo-carbazole (DTSC), dithienopyrrolo-carbazole (DTPC), and dithienocyclopenta-carbazole (DTCC) units is developed in which two outer thiophene subunits are covalently fastened to the central 2,7-carbazole cores by silicon, nitrogen, and carbon bridges, respectively. The heptacyclic multifused monomers are polymerized with the benzothiadiazole (BT) acceptor by palladium-catalyzed cross-coupling to afford three alternating donor-acceptor copolymers poly(dithienosilolo-carbazole-alt-benzothiadiazole) (PDTSCBT), poly(dithienocyclopenta-carbazole-alt-benzothiadiazole) (PDTCCBT), and poly(dithienopyrrolo-carbazole-alt-benzothiadiazole) (PDTPCBT). The silole units in DTSC possess electron-accepting ability that lowers the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PDTSCBT, whereas stronger electron-donating ability of the pyrrole moiety in DTPC increases the HOMO and LUMO energy levels of PDTPCBT. The optical bandgaps (Egopt) deduced from the absorption edges of thin film spectra are in the following order: PDTSCBT (1.83 eV) > PDTCCBT (1.64 eV) > PDTPCBT (1.50 eV). This result indicated that the donor strength of the heptacyclic arenes is in the order: DTPC > DTCC > DTSC. The devices based on PDTSCBT and PDTCCBT exhibited high hole mobilities of 0.073 and 0.110 cm2 V−1 s−1, respectively, which are among the highest performance from the OFET devices based on the amorphous donor-acceptor copolymers. The bulk heterojunction photovoltaic device using PDTSCBT as the p-type material delivered a promising efficiency of 5.2% with an enhanced open circuit voltage, Voc, of 0.82 V.

A ladder-type nonacyclic thienyl-phenylene-thienylene-phenylene-thienyl TPTPT unit, consisting of alternate interfused thiophene and benzene units, is designed and synthesized. This multifused distannyl-TPTPT monomer was polymerized with two electron-deficient acceptors, 4,7-dibromo-2,1,3-benzothiadiazole BT and 5,8-dibromo-2,3-diphenylquinoxaline QX monomers, by Stille coupling reaction to afford two alternating donor–acceptor copolymers, PTPTPTBT and PTPTPTQX, respectively. Because of the covalent planarization of the conjugated framework, PTPTPTBT simultaneously possess excellent solubilities for solution-processability, low bandgaps with suitable position of HOMO/LUMO energy levels, and high hole mobilities. The devices based on the PTPTPTBT/PC71BM blend not only showed a promising PCE of 5.3% with conventional configuration but also achieved a high PCE of 5.9% with inverted configuration. This value is among the highest performance from the inverted solar cells incorporating a donor–acceptor low band...

We have developed a ladder-type multifused thienyl–phenylene–thienylene–phenylene–thienyl (TPTPT) unit where each thiophene ring is covalently fastened with the adjacent benzene rings by a carbon b...

Research on polymer solar cells (PSC) using organic p-type (donor) and n-type (acceptor) semiconductors has attracted tremendous scientific and industrial interest in recent years. The charge generation and charge transport play equally important roles in determining the device efficiency. To dramatically increase the area of the donor–acceptor interface for efficient charge separation, a bulk heterojunction (BHJ) is adopted to form an interpenetrating network of donor and acceptor materials. This configuration decreases the distance that excitons need to travel to reach the heterojunction interface, thus reducing exciton recombination. However, the donor and acceptor are randomly interspersed; pathways for charges to reach the electrodes through the active layer are disordered. Free charges are likely to encounter an opposite charge, resulting in charge recombination and reduced current. 4] Moreover, space charge may be built up if charges are locally trapped on isolated domains. Furthermore, an increase in the thickness of the BHJ layer to enhance absorption is usually accompanied by deteriorated charge collection. Consequently, controlling phase separation toward optimal morphology in BHJ by external treatments, such as thermal or solvent annealing, is an important but challenging task. To provide a direct path for charge transport while maintaining a large interfacial area, the ideal architecture of the donor and acceptor is the periodic, vertically aligned, and interpenetrating ordered bulk heterojunction (OBHJ). The electrons and holes have straight and independent pathways to the electrodes to shorten the carrier transport length and reduce the probability of charge recombination. Several elegant studies have attempted to demonstrate this conceptual architecture, for example by a template-assisted strategy or self-assembly of block copolymer. However, realization of high-performance OBHJ devices has not been successful. We envision that designing a system that combines a BHJ for efficient charge generation with an OBHJ for efficient charge transport and collection would be a more practical strategy. Such a configuration is specifically suitable for solar cells with inverted architecture, because an electron-selective layer is required at the bottom of the active layer for electron extraction and hole blocking. For instance, the upper BHJ active layer of an inverted solar cell is infiltrated into vertically aligned nanorods extending from a bottom layer of an inorganic semiconductor (e.g. ZnO or TiO2). [18–20] However, owing to the poor electrical coherence at the organic/inorganic interface, the improvement in efficiency is moderate (PCE ranges from 2.1 to 2.7%). Recently, we reported a cross-linkable fullerene material, [6,6]-phenyl-C61-butyric styryl dendron ester (PCBSD). The formation of a cross-linked PCBSD (C-PCBSD, Figure 1a) planar layer allows realization of a multilayer inverted device by all-solution processing. By using indene–C60 bisadduct (ICBA, Figure 1a) with a higher-lying lowest unoccupied molecular orbital (LUMO) energy level to serve as the acceptor in the blend, an inverted solar cell device based on the ITO/ZnO/C-PCBSD/ICBA:P3HT/PEDOT:PSS/Ag configuration achieved an enhanced power conversion efficiency

A new class of fullerene bis-adducts—di(4-methylphenyl)methano-C60 bis-adduct (DMPCBA), di(4-fluorophenyl)methano-C60 bis-adduct (DFPCBA), and diphenylmethano-C60 bis-adduct (DPCBA)—were rationally designed and easily synthesized. Compared to the lowest unoccupied molecular orbital (LUMO) energy level of PC61BM (−3.95 eV), the double functionalization effectively raises the LUMO energy levels of these fullerene materials to ca. −3.85 eV, regardless of the substituent groups (CH3–, F–, and H−) at the para-position of the phenyl rings. This phenomenon suggests that the plane of the phenyl groups is preferentially parallel to the fullerene surface, leading to poor orbital interactions with C60 and negligible electronic effect. Importantly, such geometry sterically protects and shields the core C60 structure from severe intermolecular aggregation, rendering it intrinsically soluble, morphologically amorphous, and thermally stable. The device based on the P3HT:DMPCBA blend exhibited an open-circuit voltage (Vo...

A new class of cross-linkable N,N,N′,N′-tetraphenyl-1,1′-biphenyl-4,4′-diamine (TPD)-based hole-transporting materials (HTMs), DV-OMe-TPD, DV-Me-TPD, and DV-F-TPD, were designed and synthesized. Two vinyl groups in the TPD units are used for thermal cross-linking, whereas methoxy, methyl and fluoro groups are introduced to modulate the HOMO energy levels of the HTMs. These HTMs are thermally cross-linked to overcome interfacial mixing, realizing solution-processed polyfluorene (PFO)-based devices (ITO/cross-linked HTMs/PFO/CsF/Al). Besides the characteristic blue emission of PFO, the devices exhibited a red emission whose energy is highly dependent on the HOMO energy of the cross-linked HTM used in the device. This result suggests that the red electroluminescence is derived from the exciplex generated by the adjacent hole and electron at the cross-linked HTM/fluorenone heterojunction interface. By doping small amount of 4,7-bis(9,9-dihexylfluoren-2-yl)-2,1,3-benzothiadiazole (BFBT) into the emissive layer...

By utilizing Friedel−Crafts cyclization, we have successfully designed and synthesized a ladder-type heptacyclic carbazole-dicyclopentathiophene (CDCT-C8) unit in which two outer thiophene subunits are covalently fastened to the central 2,7-carbazole core. The nitrogen-directing effect of the carbazole unit facilitates the intramolecular cyclization and thereby suppresses the acid-induced dehydration, allowing us to incorporate two octyl side chains on the cyclopentadiene rings in good chemical yield. The distannyl-CDCT-C8 building block was copolymerized with benzothiadiazole (BT), dithienylbenzothiadiazole (DTBT), dithienyldiketopyrrolopyrrole (DTDPP) and quinoxaline (QX) units by Stille polymerization to afford four alternating donor−acceptor copolymers, PCDCTBT-C8, PCDCTDTBT-C8, PCDCTDTDPP-C8 and PCDCTQX-C8, respectively. The device based on the PCDCTBT-C8:PC71BM (1:3 in wt%) blend exhibited a Voc of 0.74 V, a Jsc of 10.3 mA/cm2, a FF of 60%, delivering an impressive PCE of 4.6%. This value represents...

The successful design and synthesis of two styryl-functionalized fullerene derivatives, [6,6]-phenyl-C61-butyric acid styryl dendron ester (PCBSD) and [6,6]-phenyl-C61-butyric acid styryl ester (PCBS) is presented. The polymerizable PCBS or PCBSD materials are incorporated into a poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend to form an active layer of ternary blend. The blending systems are first thermally annealed at 110 C for 10 min to induce optimal morphology, followed by heating at 150 C for 10 min to trigger the in situ polymerization of styrene groups. Through chemical crosslinking of PCBSD, the initial morphology of the blend (P3HT:PCBM:PCBSD = 6:5:1 in weight) can be effectively fixed and stably preserved. The device based on this blend shows extremely stable device characteristics, delivering an average power conversion efficiency (PCE) of 3.7% during long-term thermal treatment. By molecular engineering to reduce the insulating portion, PCBS with higher C60 content (71 wt%) possesses better electron-transport properties than PCBSD (58 wt%). Encouragingly, at a low doping concentration of PCBS in the blend (P3HT:PCBM:PCBS = 6:5:1 in weight), linear-polymerized PCBS can stabilize the morphology against thermal heating. This device exhibits more balanced charge mobility to achieve an average PCE of 3.8% over 25 h heating at 150 °C.

We have synthesized six p-type copolymers, CPDT-co-TPADCN, CPDT-co-TPADTA, CPDT-co-TPATCN, CPDT-co-DFADCN, CPDT-co-DFADTA, and CPDT-co-DFATCN, consisting of a cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) unit and an organic dye in an alternating arrangement. Triphenylamine (TPA) or difluorenylphenyl amine (DFA) units serve as the electron donors, whereas dicyanovinyl (DCN), 1,3-diethyl-2-thiobarbituric acid, or tricyanovinyl (TCN) units act as the electron acceptors in the dyes. The target polymers were prepared via Stille coupling, followed by postfunctionalization to introduce the electron acceptors to the side chains. Because of the strongest withdrawing ability of TCN acceptor to induce efficient intramolecular charge transfer, CPDT-co-TPATCN and CPDT-co-DFATCN exhibit the broader absorption spectra covering from 400 to 900 nm and the narrower optical band gaps of 1.34 eV. However, the CPDT-co-TPATCN:PC 71 BM and CPDT-co-DFATCN:PC 71 BM based solar cells showed the power conversion efficiencies (PCEs) of 0.22 and 0.31%, respectively, due to the inefficient exciton dissociation. The DFA-based polymers possess deeper-lying HOMO energy levels than the TPA-based polymer analogues, leading to the higher V oc values and better efficiencies. The device based on CPDT-co-DFADTA:PC 71 BM blend achieved the best PCE of 1.38% with a V oc of 0.7 V, a J sc of 4.57 mA/cm 2 , and a fill factor of 0.43.

We have successfully designed and synthesized two oxetane-functionalized fullerene derivatives, [6,6]-phenyl-C61-butyric oxetane ester (PCBO) and [6,6]-phenyl-C61-butyric oxetane dendron ester (PCBOD). We demonstrated that the oxetane functionality with neutral nature can anchor onto the TiOx surface via cationic ring-opening reaction under thermal and UV treatment, as evidenced by contact angle measurement and X-ray photoelectron spectroscopy. The self-assembly of PCBO, functionalized with one oxetane group, on the TiOx surface forms an adhesive monolayer with intimate contact. Inverted bulk-heterojunction device B [ITO/TiOx/SA-PCBO/P3HT:PCBM (1:1 w/w)/MoO3/Ag, where ITO is indium tin oxide, SA is self-assembled, P3HT is poly(3-hexylthiophene), and PCBM is [6,6]-phenyl-C61-butyric acid methyl ester] with this self-assembled PCBO (SA-PCBO) modifier showed an impressive power conversion efficiency (PCE) of 4.1%, which outperforms the reference device A (PCE = 3.6%) without this monolayer [ITO/TiOx/P3HT:PCB...

Pentacyclic diindeno[1,2-b:2',1'-d]thiophene (DIDT) unit is a rigid and coplanar conjugated molecule. To the best of our knowledge, this attractive molecule has never been incorporated into a polymer and thus its application in polymer solar cells has never been explored. For the first time, we report the detailed synthesis of the tetra-alkylated DIDT molecule leading to its dibromo- and diboronic ester derivatives, which are the key monomers for preparation of DIDT-based polymers. Two donor-acceptor alternating polymers, poly(diindenothiophene-alt-benzothiadiazole) PDIDTBT and poly(diindenothiophene-alt-dithienylbenzothiadiazole) PDIDTDTBT, were synthesized by using Suzuki polymerization. Copolymer PTDIDTTBT was also prepared by using Stille polymerization. Although PTDIDTTBT is prepared through a manner of random polymerization, we found that the different reactivities of the dibromo-monomers lead to the resulting polymer having a block copolymer arrangement. With the higher structural regularity, PTDIDTTBT, symbolized as (thiophene-alt-DIDT)(0.5)-block-(thiophene-alt-BT)(0.5), shows the higher degree of crystallization, stronger π-π stacking, and broader absorption spectrum in the solid state, as compared to its alternating PDIDTDTBT analogue. Bulk heterojunction photovoltaic cells based on ITO/PEDOT:PSS/polymer:PC(71)BM/Ca/Al configuration were fabricated and characterized. PDIDTDTBT/PC(71)BM and PTDIDTTBT/PC(71)BM systems exhibited promising power-conversion efficiencies (PCEs) of 1.65 % and 2.00 %, respectively. Owing to the complementary absorption spectra, as well as the compatible structures of PDIDTDTBT and PTDIDTTBT, the PCE of the device based on the ternary blend PDIDTDTBT/PTDIDTTBT/PC(71)BM was further improved to 2.40 %.

Six of three-component donor−acceptor random copolymers P1−P6, symbolized as (thiophene donor)m−(thiophene acceptor)n, were rationally designed and successfully synthesized by the palladium-catalyzed Stille coupling. The 4H-cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT) unit serves as the donor for P1−P4, while the benzothiadiazole (BT), quinoxaline (QU), dithienoquinoxaline, and thienopyrazine (TP) units are used as the acceptor for P1, P2, P3, and P4, respectively. P5 and P6 are structurally analogous to P1 and P2 except for using the dithieno[3,2-b:2′,3′-d]silole (DTS) unit as the donor. Because the band gap lowering ability of the acceptor units in the polymer is in the order TP > BT > QU presumably due to the quinoid form population in the polymers, the optical band gaps can be well adjusted to be 1.2, 1.6, and 1.8 eV for P4, P1, and P2, respectively. It is found that the two bridged bithiophene units, CPDT and DTS, have similar steric and electronic effects on the P1 and P5 as well as P2 and P6, respect...

phenylenevinylene)s L4. Fluorene-Based Conjugated Polymers L4.1. Fluorene-Based Copolymers ContainingElectron-Rich MoietiesM4.2. Fluorene-Based Copolymers ContainingElectron-Deficient MoietiesN4.3. Fluorene-Based Copolymers ContainingPhosphorescent ComplexesQ5. Carbazole-Based Conjugated Polymers R5.1. Poly(2,7-carbazole)-Based Polymers R5.2. Indolo[3,2

Using an in situ Diels−Alder (DA) “click chemistry” strategy for reactions between anthracene and maleimide functional groups, two prototypes of novel nonlinear optical (NLO) side-chain polymers (PMI-A7 and PMI-B7) containing highly hyperpolarizable but chemically sensitive phenyltetraene-based chromophores were synthesized and their nonlinear optical and thermal properties were characterized. Through rational material design, these NLO side-chain polymers exhibited good processibility, large electro-optic (E-O) coefficients (r33, of up to 263 and 287 pm/V at 1.31 μm wavelength respectively), and excellent temporal stability. These combined properties make them promising materials for E-O device applications. Compared to PMI-B7, PMI-A7 exhibited significantly enhanced temporal stability (87% of the initial r33 values was retained after 550 h at 85 °C) and solvent resistance, which was attributed to slight cross-linking from the side reaction between maleimide and phenyltetraenic chromophore moieties. This...

In order to fulfill the promise of organic electronic devices, performance-limiting factors, such as the energetic discontinuity of the material interfaces, must be overcome. Here, improved performance of polymer light-emitting diodes (PLEDs) is demonstrated using self-assembled monolayers (SAMs) of triarylamine-based hole-transporting molecules with phosphonic acid-binding groups to modify the surface of the indium tin oxide (ITO) anode. The modified ITO surfaces are used in multilayer PLEDs, in which a green-emitting polymer, poly[2,7-(9,9-dihexylfluorene)-co-4,7-(2,1,3-benzothiadiazole)] (PFBT5), is sandwiched between a thermally crosslinked hole-transporting layer (HTL) and an electron-transporting layer (ETL). All tetraphenyl-diamine (TPD)-based SAMs show significantly improved hole-injection between ITO and the HTL compared to oxygen plasma-treated ITO and simple aromatic SAMs on ITO. The device performance is consistent with the hole-transporting properties of triarylamine groups (measured by electrochemical measurements) and improved surface energy matching with the HTL. The turn-on voltage of the devices using SAM-modified anodes can be lowered by up to 3 V compared to bare ITO, yielding up to 18-fold increases in current density and up to 17-fold increases in brightness at 10 V. Variations in hole-injection and turn-on voltage between the different TPD-based molecules are attributed to the position of alkyl-spacers within the molecules.

A series of cross-linkable electro-optic (E-O) dendrimers have been developed with anthracene- and acrylate-containing dendrons functionalized on the periphery of chromophores that can form thermally stable Diels−Alder adducts. These new E-O dendrimers with a high density of standardized AJL8-type chromophore are originally prone to thermo-decomposition in their thermoplastic form but can be converted into thermally stable networks to provide excellent site isolation for these chromophores. After poling, large E-O coefficients (up to 84 pm/V at 1310 nm) can be obtained in these dendrimers. These poled E-O dendrimers can maintain their alignment stability at 200 °C for 30 min and also possess impressive long-term stability at 150 °C for more than 200 h. This result provides a very effective molecular engineering approach to systematically increase the thermal stability of highly polarizable dipolar chromophores for high temperature on-chip applications.

We have successfully utilized epoxyisophorone ring-opening chemistry to efficiently incorporate the butylthio group to the phenyltetraene bridge of highly efficient nonlinear optical chromophores in high overall yield. By following the guidance of Dewar’s rules, the sulfur atom functions as a moderate π-accepting group at a starred position of the conjugated bridge. Several of very critical material parameters of the phenyltetraenic chromophores for device applications have been intrinsically and simultaneously improved through such a simple and straightforward engineering of molecular structures. Compared with the nonsubstituted analogue 2, thiolated chromophore 1 achieves higher molecular hyperpolarizability (34%), enhanced E-O coefficient (38%), significantly improved photochemical stability against 1O2 (by an order of magnitude), and better optical transparency (17 nm blue-shifted λmax absorption spectrum).

Recent developments of molecular architectural control and solid-state engineering have led to exceptionally large electro-optic (EO) activities in organic and polymeric nonlinear optical (NLO) materials. A new generation of NLO dendrimers has been developed to generate well-defined nano-objects, minimize strong intermolecular electrostatic interactions, and improve poling efficiency and stability. A facile and reliable Diels−Alder “click” reaction was applied for lattice hardening to improve physical properties of cross-linkable EO polymers. The “click” chemistry also provides means to study the relationship between EO activity, chromophore shape, and number density of the chromophore, systematically. The NLO dendrimers or polymers were used as hosts for guest chromophores to increase chromophore concentration and improve poling efficiency. A variety of nanostructured organic and polymeric materials with ultrahigh r33 values (>350 pm/V at the wavelength of 1310 nm, more than 10 times that of LiNbO3) and ...

A series of novel hole-transporting materials (HTMs) bearing thermally cross-linkable styryl groups have been synthesized and characterized. These HTMs could be in situ cross-linked under mild thermal polymerization without any initiator. The cross-linking temperatures (150–180 °C) for these HTMs are substantially lower than that typically used for curing perfluorocyclobutane (PFCB)-based HTMs (230 °C). After cross-linking, the resultant HTMs form robust, smooth, and solvent-resistant networks, which enables the subsequent spin-coating of emissive layer (EML). The HTMs based on an ether linkage connecting triarylamine dimers exhibited better hole-transporting ability compared to their corresponding monotriarylamine compounds due to higher content and closer distance of the hole-transporting units. Most importantly, the milder cross-linking condition for these HTMs allows the commonly used conducting polymer, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), to be incorporated as the b...

Novel fluorene-based blue-light-emitting copolymers with an ultraviolet-blue-light (UV-blue-light) emitting host and a blue-light emitting component, 4-N,N-diphenylaminostilbene (DPS) have been designed and synthesized by using the palladium-catalyzed Suzuki coupling reaction. It was found that both copolymers poly [2,7-(9,9-dioctylfluorene)-alt-1,3-(5-carbazol-phenylene)] (PFCz) DPS1 and PFCz-DPS1-OXD show pure blue-light emission even with only 1 % DPS units because of the efficient energy transfer from the UV-blue-light emitting PFCz segments to the blue-light-emitting DPS units. Moreover, because of the efficient energy transfer/charge trapping in these copolymers, PFCz-DPS1 and PFCz-DPS1-OXD show excellent device performance with a very stable pure blue-light emission. By using a neutral surfactant poly[9,9-bis(6'-(diethanolamino)-hexyl)-fluorene] (PFN-OH) as the electron injection layer, the device based on PFCz-DPS1-OXD5 with the configuration of ITO/PEDOT:PSS/PVK/polymer/PFN-OH/Al showed a maximum quantum efficiency of 2.83 % and a maximum luminous efficiency of 2.50 cd A -1 . Its CIE 1931 chromaticity coordinates of (0.156, 0.080) match very well with the NTSC standard blue pixel coordinates of (0.14, 0.08). These results indicate that this kind of dopant/host copolymer could be a promising candidate for blue-light-emitting polymers with high efficiency, good color purity, and excellent color stability.

"Push-pull" phenyltetraene-based chromophores are too sensitive to be incorporated into Diels-Alder-type cross-linkable polymers due to the reactivity of its diene segment with maleimides. A facile synthetic route has been explored to incorporate a methoxy group into the R position of such chromophores, which reduces their diene reactivity during the poling and lattice hardening process. The poled polymers with one of such chromophores doped in a cross-linked polymer lattice showed ultrahigh electro-optic activities, up to 306 pm/V at 1310 nm.

We examine the effects of surface ligand exchange on the performance of hybrid organic/inorganic light emitting diodes (LEDs) that use colloidal nanocrystal quantum dots as emissive centers. Using a series of primary alkylamines with different alkane chain lengths, we exchange the native surface ligands on a series of CdSe/CdZnS/ZnS core/shell/shell nanocrystal quantum dots and compare the differences in photoluminescence and electroluminescence efficiency of the emissive quantum dot layer. We fabricate LEDs made with octadecylamine-, octylamine-, and butylamine-exchanged quantum dots. We find that the differences in electroluminescence efficiency of the devices are not always proportional to the photoluminescence quantum efficiency of the quantum dots. We discuss this trend both in terms of the competing needs of high photoluminescence efficiency and good charge injection and energy transfer, and also in terms of the different processability and film morphology arising from the use of nanoparticles passivated with shorter ligands.

A series of new hydrophobic two-photon absorbing (2PA) chromophores with varied electron-donating groups in quasi-linear and multibranched structures are synthesized to correlate their structure/photophysical property relationships. The feasibility of using these large two-photon absorption cross-sectional (δ, expressed in GM = 1 × 10–50 cm4 s photon–1 molecule–1) materials in aqueous solution is also explored. All four hydrophobic 2PA materials can be encapsulated into micelles generated by dispersing an amphiphilic block copolymer, poly(methacrylic acid)-block-polystyrene (PMAA-b-PS), into water. The micellar nanostructures are characterized using dynamic light scattering, atomic force microscopy, and transmission electron microscopy. After these dyes are incorporated into micelles, they exhibit strong fluorescence in water. It is found that the quantum yield and δ values of these chromophores are strongly dependent on the diameters of the micelles, concentrations of the PMAA-b-PS, and molecular structures of the 2PA chromophores. One of the compounds that has a strong triarylamino donor and a multibranched structure exhibits a large δ value of 2790 GM and high quantum yield (0.56) in micelle-containing water. Although this value is smaller than the original value of 5300 GM in toluene, it is still substantially larger than the values of most water-soluble 2PA materials, which have δ values of less than 100 GM.

Silylene-spaced copolymers with alternating azacrown and anthracene moieties were synthesized for photoinduced electron transfer investigations. These polymers exhibited efficient intrachain photoinduced electron transfer with charge separation yield about 0.96-0.99 and corresponding charge-transfer rates around 10.8-32.2 ns -1 in different solvents. Metal cations have been shown to enhance the fluorescence intensity due to complexation. These results are comparable to those of small molecules having similar chromophores. The geminal dimethyl substituents on silicon in these copolymers may direct the relative conformation (or distance) of the remaining substituents on silicon. Intrachain interactions between these chromophores may readily take place leading to highly efficient electron transfer processes.

Two series of highly efficient and thermally stable nonlinear optical chromophores based on the (4-diarylamino)phenyl electron donors have been synthesized and systematically investigated. A modular approach has been employed to synthesize these electron donors with tunable size, shape, and electron-donating abilities. Efficient conjugated bridges were extended from these donors and coupled with very strong CF3−TCF electron acceptors to afford chromophores with very high β values (up to 7077 × 10-30 esu at 1.907 μm). These chromophores possess much higher thermal stability (with their onset decomposition temperatures all above 220 °C) than those substituted with (4-dialkylamino)phenyl donors. Most importantly, the high molecular hyperpolarizability of these chromophores can be effectively translated into very large electro-optic (E-O) coefficients (r33) in poled polymers through suitable shape engineering. Exemplified by the chromophore B4, which has a fluorinated aromatic substituent anchored at its dono...

Bulk-heterojunction (BHJ) polymer solar cells have achieved significant progress in the recent years, with the efficiency now over 10 %. The p-type polymer in the BHJ blend played a key role in the amazing technology advance. In this chapter, we will timely update over 80 conjugated polymers leading to high-performance solar cells. The principle of molecular design with structure-properties relationship with respect to device characteristics will also be discussed, as the materials and morphology are tightly interconnected.

A summary of recent advances on the chemistry and photophysics of silylene-spaced divinylarene copolymers is presented. The silicon moieties have been shown to serve as an insulating spacer in these copolymers. The photophysical studies have provided useful insights into how chromophores in polymers interact intramolecularly. Because different chromophores can be regioregularly introduced into the polymeric chain, these copolymers have been extensively used as models for studying energy transfer, light harvesting as well as chiroptical transfer.

Regioregular silylene-spaced copolymers 1 composed of an energy gradient with three different chromophores have been achieved by rhodium-catalyzed hydrosilylation of bis-vinylsilanes 3 and bis-alkynes 4. Monomeric reference compounds 2 were prepared for comparison. The ratio of three chromophores is 1:2:1, corresponding to D1, D2, and A chromophores, respectively. The dimethylsilylene (SiMe2) moiety serves as an insulating bridge between chromophores. Upon excitation of the donor chromophore (D1), only emission from the acceptor (A) was observed. Efficient and sequential energy transfer across three different chromophores along the polymeric backbone may proceed smoothly in these silylene-spaced copolymers.

A range of silylene-spaced divinyloligoarene alternating copolymer 3 has been synthesized regioregularly by rhodium-catalyzed hydrosilylation of bis(alkynes) 5 with bis(silanes) 6. Monomeric reference compounds 4 having similar chromophore components were also prepared for comparison. The silylene moieties serve as insulating spacers between chromophores. Intrachain interaction appears to be negligible due to the localization of exciton in these conjugated chromophores, resulting in the emission that closely resembles that of the parent chromophore.

A range of silanylene-spaced divinylbenzene copolymers (1) and the corre- sponding monomers (2) have been synthesized by the rhodium-catalyzed hydrosilyla- tion of the corresponding bisalkynes with bissilyl hydrides, and the photophysical properties of 1 and 2 have been investigated. The silicon moiety in 1 serves as an insulating tetrahedral spacer that makes 1 highly folded. The two chromophores may be in close proximity such that a ground-state intrachain interaction between two conjugated moieties through space might occur. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2218 -2231, 2003

A new class of biselenophene-based materials including an sp(3)-silicon-bridged diselenosilole (DSS), an sp(3)-germanium-bridged diselenogermole (DSG), and an sp(3)-nitrogen-bridged diselenopyrrole (DSP) as well as an sp(2)-vinylidene-bridged dicyanodiselenofulvene (CDSF), a diacetylenediselenofulvene (ADSF), and a dioctylethylene-bridged benzodiselenophene (BDS) have been successfully synthesized and characterized. The bridging moieties play an important role in determining the optical and electrochemical properties. The six brominated derivatives are ready to construct various biselenophene-based conjugated materials with tunable properties for organic photovoltaics and field effect transistors.

Bis-adduct fullerenes surrounded by two insulating addends sterically attenuate intermolecular interaction and cause inferior electron transportation. In this research, we have designed and synthesized a new class of bis-adduct fullerene materials, methylphenylmethano-C60 bis-adduct (MPC60BA), methylthienylmethano-C60 bis-adduct (MTC60BA), methylphenylmethano-C70 bis-adduct (MPC70BA), and methylthienylmethano-C70 bis-adduct (MTC70BA), functionalized with two compact phenylmethylmethano and thienylmethylmethano addends via cyclopropyl linkages. These materials with much higher-lying lowest unoccupied molecular orbital (LUMO) energy levels successfully enhanced the Voc values of the P3HT-based solar cell devices. The compact phenylmethylmethano and thienylmethylmethano addends to promote fullerene intermolecular interactions result in aggregation-induced phase separation as observed by the atomic force microscopy (AFM) and transmission electron microscopy (TEM) images of the poly(3-hexylthiophene-2,5-diyl) (P3HT)/bis-adduct fullerene thin films. The device based on the P3HT/MTC60BA blend yielded a Voc of 0.72 V, a Jsc of 5.87 mA/cm(2), and a fill factor (FF) of 65.3%, resulting in a power conversion efficiency (PCE) of 2.76%. The unfavorable morphologies can be optimized by introducing a solvent additive to fine-tune the intermolecular interactions. 1-Chloronaphthalene (CN) having better ability to dissolve the bis-adduct fullerenes can homogeneously disperse the fullerene materials into the P3HT matrix. Consequently, the aggregated fullerene domains can be alleviated to reach a favorable morphology. With the assistance of CN additive, the P3HT/MTC60BA-based device exhibited enhanced characteristics (a Voc of 0.78 V, a Jsc of 9.04 mA/cm(2), and an FF of 69.8%), yielding a much higher PCE of 4.92%. More importantly, the additive-assisted morphological optimization is consistently effective to all four compact bis-adduct fullerenes regardless of the methylphenylmethano or methylthienylmethano scaffolds as well as C60 or C70 core structures. Through the extrinsic additive treatment, these bis-adduct fullerene materials with compact architectures show promise for high-performance polymer solar cells.

C60 bis-adduct containing a mixture of regio-isomers with different LUMO energy levels and steric geometries could greatly affect the morphological and bulk properties. To investigate the regio-isomer effect on solar cell performance, we have successfully designed and synthesized a regio-selective 4-acetatephenyl-4'-methylphenylmethano C60 bis-adduct (S-APM-CBA) by "tether-directed remote functionalization" strategy and a random 4-acetatephenyl-4'-methylphenylmethano C60 bis-adduct denoted as R-APM-CBA by traditional cyclopropanation. The dramatic reduction in the number of regio-isomers in S-APM-CBA is confirmed by the (1)H NMR and HPLC measurements and theoretical calculation. Compared to the R-APM-CBA-based device with a Jsc of 6.63 mA/cm(2), an FF of 44.3% and a PCE of 2.46%, the device using S-APM-CBA yielded a much lower Jsc of 1.48 mA/cm(2), an FF of 32.2%, and a PCE of 0.38%. Consistently, the electron-only device using S-AMP-CBA exhibited lower electron mobility than the R-AMP-CBA-based device. These results imply that the electronic shallow-trap effect ascribed to the LUMO energy variations turned out to be insignificant in the AMP-CBA system. The lower efficiency and mobility of S-AMP-CBA might due to the assumption that the most probable trans-4-III isomer in S-AMP-CBA prevents the intermolecular facial contact of fullerenes, thereby hindering the electron transporting. Furthermore, the nanomorphology of S-AMP-CBA and R-AMP-CBA active layers could be different because of their different three-dimensional structures. This research demonstrated that steric effect of regio-isomers in a given C60 bis-adduct is more crucial than electronic shallow-trap effect.