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A new angular-shaped naphthodithiophene diimide (aNDTI) is designed and synthesized. The aNDTI-containing polymers are used as non-volatile additives to improve the efficiency of organic solar cells.

We discovered a unique synthetic route to construct 2H-pyran-containing tetracyclic dithienocyclopentapyran (DTCP) and dibenzocyclopentapyran (DBCP) architectures. The synthesis involves an acid-induced dehydration cyclization followed by a [1,5] hydride-shift isomerization to form a cyclopentanone moiety which was converted to the pyran-embedded tetracyclic products by a CuI-catalyzed intramolecular C-O bond formation in good yield. DTCP was used as a building block to prepare an acceptor-donor-acceptor (A-D-A) type n-type material DTCP-BC leading to a solar cell efficiency of 9.32%.

Two-dimensional alkylated αβ-TTN and βα-TTN were designed and synthesized. The cross-shaped αβ-TTN and βα-TTN moieties were polymerized to afford two isomeric polymers, Pαβ-TTNFBT40 and Pβα-TTNFBT4...

Pd(II)-catalyzed dehydrogenative Heck olefination of selenophenes with a broad olefinic substrate scope and high functional group tolerance is demonstrated. Carbonyl-substituted and phenyl-substituted olefins with electron-donating (D) and electron-accepting (A) groups can be regioselectively installed at C2 of the selenophene. The 2-olefinated selenophenes can subsequently undergo a second oxidative olefination to rapidly produce a new class of symmetrical D-π-D or unsymmetrical D-π

Three unsymmetrical diiodobichalcogenophenes SSeI2, STeI2, and SeTeI2 and a diiodoterchalcogenophene SSeTeI2 were prepared. Grignard metathesis of SSeI2, STeI2, SeTeI2, and SSeTeI2 occurred regioselectively at the lighter chalcogenophene site because of its relatively lower electron density and less steric bulk. Nickel-catalyzed Kumada catalyst-transfer polycondensation of these Mg species provided a new class of side-chain regioregular and main-chain AB-type alternating poly(bichalcogenophene)s—PSSe, PSTe, and PSeTe—through a chain-growth mechanism. The ring-walking of the Ni catalyst from the lighter to the heavier chalcogenophene facilitated subsequent oxidative addition, thereby suppressing the possibility of chain-transfer or chain-termination. More significantly, the Ni catalyst could walk over the distance of three rings (ca. 1 nm)—from a thiophene unit via a selenophene unit to a tellurophene unit—to form PSSeTe, the first ABC-type regioregular and periodic poly(terchalcogenophene) comprising three different types of 3-hexylchalcogenophenes., Three unsymmetrical diiodobichalcogenophenes SSeI2, STeI2, and SeTeI2 and a diiodoterchalcogenophene SSeTeI2 were prepared to synthesize a new class of polychalcogenophenes with precisely controlled sequences by catalyst-transfer polycondensation.

Acceptor–donor–acceptor (A–D–A) non-fullerene electron acceptors (NFEAs) using ladder-type donor structures have become the dominant n-type materials for achieving high-efficiency OSCs. In this work, two isomeric fluorene-based ladder-type structures FCTT (TT-C-F-C-TT) and FTCT (T-C-TFT-C-T) have been designed and synthesized. These two isomeric donors with the different fused-ring arrangement, molecular geometry, and side-chain placement were end-capped with the FIC acceptors to form two NFEAs FCTT-FIC and FTCT-FIC isomeric materials. Compared to FTCT-FIC using the thiophene (T)-terminal donor, FCTT-FIC with the thienothiophene (TT)-terminal donor has more evenly distributed side chains on both sides of the backbone and less steric hindrance near the FIC acceptors, which enables stronger antiparallel π–π packing among the end-groups to create a channel for efficient electron transport, as evidenced by the thin-film GIWAXS measurements. FCTT-FIC displayed a larger optical bandgap and deeper-lying energy levels than its FTCT-FIC isomer. Compared to the PBDB-T:FTCT-FIC device, the PBDB-T:FCTT-FIC device showed a higher PCE of 10.32% with an enhanced Jsc of 19.63 mA cm−2 and an FF of 69.14%. A PM6:FCTT-FIC device using PM6 as a p-type polymer achieved the highest PCE of 12.23%. By introducing PC71BM as the second acceptor to enhance the absorption at shorter wavelengths, optimize the morphology and facilitate electron transport, the ternary-blend PM6:FCTT-FIC:PC71BM (1 : 1 : 0.5 in wt%) device yielded the highest PCE of 13.37% with a Voc of 0.92 V, a higher Jsc of 19.86 mA cm−2, and an FF of 73.2%. This result demonstrated that the TT-terminal ladder-type donor is generally a better molecular design than the corresponding T-terminal ladder-type isomer for the development of new A–D–A NFEAs.

An NC-FIC nonfullerene acceptor, using a didodecylnaphthodithiophene (NDT) embedded octacyclic ladder-type donor NC, had been described previously. In this work, a new cross-shaped TC-FIC nonfullerene acceptor is designed by substitution of the NDT unit in the NC skeleton with a 2-dimensional didodecyltetrathienonaphthalene (TTN) unit. The 2-dimensional TC π-system with two vertically fused thiophenes strengthens the electron-donating ability, promotes π-electron delocalization and enhances intramolecular donor–acceptor charge transfer and intermolecular π–π interactions. As a result, TC-FIC shows more red-shifted and widened absorption compared to the NC-FIC counterpart. The PBDB-T:TC-FIC device exhibits a higher efficiency of 11.6% which greatly outperformed the corresponding PBDB-T:NC-FIC device with an efficiency of 7.52%. The dramatic 54% enhancement in efficiency is ascribed to the improved light-harvesting ability and enhanced charge mobilities which are benefited from the central 2-dimensional TTN moiety. By incorporating PC71BM to improve absorption and electron transport, the ternary-blend PBDB-T : TC-FIC : PC71BM device (1 : 1 : 1 in wt%) achieves a highest PCE of 13.49% with an enhanced Jsc of 23.80 mA cm−2, an FF of 64.4%, and a Voc of 0.88 V.

We performed frequency-modulated (AC) and steady-state (DC) surface photovoltage spectroscopy (SPS) measurements on a bilayer structure consisting of an organic semiconductor (P3HT, P3HT:PC61BM, or...

Ladder-type structures have been the key element for high performance non-fullerene acceptors (NFAs). In this work, two dithieno[3,2-b:6,7-b′]fluorine (DTF)-based nonfullerene acceptors, non-bridged DTFT5-FIC and carbon-bridged DTFT9-FIC, with an identical conjugated backbone were designed and synthesized for investigation of the planarization effect. The chemical rigidification with forced coplanarity indeed plays a pivotal role in determining the molecular properties. Compared to the non-bridged open-chain DTFT5-FIC counterpart, the nonacyclic ladder-type DTFT9-FIC with a fully planarized backbone exhibits higher thermal stability, bathochromic absorption and higher electron mobility. The devices using PBDB-T as the p-type polymer and fully planar DTFT9-FIC as the acceptor showed a high efficiency of 9.58%, which is superior to that of the device using the partially planar DTFT5-FIC material (5.45%). By incorporating PC71BM as the second acceptor to enhance the absorption at shorter wavelengths, optimize the morphology and facilitate electron transport, the ternary-blend device using PBDB-T:DTFT9-FIC:PC71BM achieved the highest PCE of 11.82% with a Voc of 0.88 V, a higher Jsc of 20.59 mA cm−2, and an FF of 65.27%.

A new zwitterionic small molecule 4-(dimethyl(pyridin-2-yl)ammonio)butane-1-sulfonate (PAS), synthesized from 2-dimethylaminopyrindine (2-DMAP), was developed for the ITO cathode modifier. PAS and 2-DMAP dissolved in methanol can form a thin layer on ITO cathode by a simple spin-coating process. The heteroatom moieties in 2-DMAP (sp2 and sp3 nitrogen) and PAS (sp2 nitrogen and sulfonate ion) can coordinate to the ITO surface and decrease the ITO work function by the induced surface dipoles. The fullerene-based (PBDTT-FTTE:PC71BM) inverted OSCs using PAS and 2-DMAP interlayer can achieve PCEs of 8.95 and 8.26%, respectively, which are superior to the devices without a modifier (PCE = 3.25%) and comparable to the corresponding ZnO-based device (PCE = 8.57%). Nevertheless, 2-DMAP, like other nitrogen-containing polymer interlayer materials, turns out to be not applicable to inverted organic solar cells (I-OSCs) with IT-4F as the n-type electron acceptor because the amino group of 2-DMAP can act as a nucleophile to attack the end-group of IT-4F at the interface. The decomposition of IT-4F by 2-DMAP was carefully proved to be via retro-aldol condensation. As a result, the device (PBDBT-F:IT-4F) modified with 2-DMAP displayed a low PCE of 7.34%. The zwitterionic PAS with reduced nucleophilicity and basicity can modify the ITO surface without decomposing IT-4F. The PBDBT-F:IT-4F-based device modified with PAS maintained a high PCE of 11.41%. Most importantly, the PAS-based device using the well-known Y6 acceptor (PBDBT-F:Y6) can achieve a PCE of 13.82%. This new interfacial material can be universally applied to I-OSCs employing various A-D-A-type acceptors installed with the electrophilic 1,1-dicyanamethylene-5,6-difluoro-3-indanone (FIC) end-group.

2-Alkyl(1)alkyl(2)-type aliphatic side chains with a branching point position at the C2-position (such as 2-ethylhexyl or 2-octayldodecyl) have been widely implanted into numerous donor–acceptor conjugated copolymers for solution processable transistors or organic solar cells. However, the tertiary branching site located at the second carbon inevitably imposes steric hindrance that twists the main-chain coplanarity and attenuates interchain interactions. In this research, we developed a new two-dimensonal thiophene–vinylene–thiophene (TVT) derivative where a carbon–carbon triple bond is inserted between the thiophene unit and the 2-octyldodecyl group. This acetylene-incorporated TVT (aTVT) was copolymerized with 5,10-di(thiophen-2-yl)naphtho[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (DTNT) and 5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTFBT) to form the polymers PaTVT-NT and PaTVT-FBT, respectively. PTVT-FBT, without the triple bond, was also prepared for comparison. The insertion of a line...

An angular-shaped 4,9-didodecylnaphthodithiophene-based octacyclic ladder-type structure was developed. This new ladder-type donor (LD) was coupled with electron-withdrawing IC and FIC units to form two A-LD-A type non-fullerene acceptor materials, NCIC and NCFIC. NCIC and NCFIC as the n-type acceptors are blended with a p-type donor PBDB-T to form the complementary absorption and suitable energy level alignments. The binary-blend PBDB-T:NCIC and PBDB-T:NCFIC devices achieved an efficiency of 7.3% and 7.5%, respectively. PC71BM was incorporated to form D1:A1:A2 ternary blends which further strengthen the absorption at shorter wavelengths. Introduction of PC71BM not only efficiently improves the absorption but also provides multiple channels for exciton dissociation and electron transport to dramatically improve Jsc. It is interesting to find that the Voc of the ternary-blend devices is reversely in proportional to the added amount of PC71BM. The device using the PBDB-T:NCIC:PC71BM (1:1:1 in wt %) showed a...

A new thieno[3,2-b]thiophene-incorporated acceptor TTC has been developed. The TTC acceptor was installed in a haptacyclic ladder-type core (BDCPDT) to furnish an n-type BDCPDT-TTC. The standard PBDB-T:BDCPDT-IC device showed a PCE of 9.33% with a Voc of 0.86 V and a Jsc of 16.56 mA/cm2. By molecular engineering of the acceptor unit, the BDCPDT-TTC:PBDB-T-based device delivered an enhanced efficiency of 10.29% with a simultaneously enhanced Voc of 0.94 V and Jsc of 17.72 mA/cm2. Incorporation of the electron-donating thieno[3,2-b]thiophene unit into the acceptor moiety decreases the electron-accepting strength, thereby upshifting the HOMO/LUMO energy levels to decrease the ΔEHOMO and Eloss, achieving a larger Voc. Second, the extended conjugated bicyclic thieno[3,2-b]thiophene ring beneficially induces an additional optical transition at short wavelengths, leading to improvement of Jsc. Alternatively, BDCPDT-FIC installed with the fluorinated acceptor shows more red-shifted absorption to achieve a high Js...

A new class of additive materials bis(pentafluorophenyl) diesters (BFEs) where the two pentafluorophenyl (C6F5) moieties are attached at the both ends of a linear aliphatic chain with tunable tether lengths (BF5, BF7, and BF13) were designed and synthesized. In the presence of the BF7 to restrict the migration of fullerene by hand-grabbing-like supramolecular interactions induced between the C6F5 groups and the surface of fullerene, the P3HT:PC61BM:BF7 device showed stable device characteristics after thermal heating at 150 oC for 25 h. The morphologies of the active layers were systematically investigated by OM, GISAXS, and AFM. The tether length between the two C6F5 groups plays a pivotal role in controlling the intermolecular attractions. BF13 with long and flexible tether might form a BF13-fullerene sandwich complex that fails to prevent fullerene’s movement and aggregation, while BF5 with too short tether length decreases the possibility of interactions between the C6F5 groups and the fullerenes. BF7...

Three selenophene-incorporated quaterchalcogenophene-based donor–acceptor copolymers PFBT2Th2Se, PFBT2Se2Th, and PFBT4Se are designed and synthesized. To systematically fine-tune the molecular properties and investigate the chalcogen effect, PFBT2Th2Se and PFBT2Se2Th hybridize two thiophenes and two selenophenes as the donor with different isomeric main-chain placement while thiophene-free PFBT4Se uses quaterselenophene as the donor. On account of the selenophene’s advantageous features such as higher quinoidal population and higher molecular polarizability, the three polymers show good light-harvesting ability, strong intermolecular interactions, high crystallinity, and high charge mobilities. Bulk-heterojunction solar cells incorporating these selenophene-containing polymers have exhibited promising photovoltaic performance with impressive current densities over 20 mA/cm2. The device with the PFBT2Se2Th:PC71BM blend showed a PCE of 9.02% with a Jsc of 21.02 mA/cm2. In addition, the device using quaterse...

In this research, a haptacyclic carbazole-based dithienocyclopentacarbazole (DTCC) ladder-type structure was formylated to couple with two 1,1-dicyanomethylene-3-indanone (IC) moieties, forming a new nonfullerene acceptor DTCCIC-C17 using a bulky branched 1-octylnonayl side chain at the nitrogen of the embedded carbazole and four 4-octylphenyl groups at the sp3-carbon bridges. The rigid and coplanar main-chain backbone of the DTCC core provides a broad light-absorbing window and a higher-lying LUMO energy level, whereas the bulky flanked side chains reduce intermolecular interactions, making DTCCIC-C17 amorphous with excellent solution processability. The DTCCIC-C17 as an acceptor is combined with a medium band gap polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))] (PBDB-T) as the donor in the active layer to obtain suitable highest occupied molecular orbital/lowest u...

A formylated benzodi(cyclopentadithiophene) (BDCPDT) ladder-type structure with forced coplanarity is coupled with two 1,1-dicyanomethylene-3-indanone (IC) moieties via olefination to form a non-fullerene acceptor, BDCPDT-IC. The BDCPDT-IC, as an acceptor (A1) with broad light-absorbing ability and excellent solution processability, is combined with a second PC71BM acceptor (A2) and a medium band gap polymer, PBDB-T, as the donor (D) to form a ternary blend with gradient HOMO/LUMO energy alignments and panchromatic absorption. The device with the inverted architecture using the D:A1:A2 ternary blend has achieved a highest efficiency of 9.79% with a superior Jsc of 16.84 mA cm–2.

A systematic methodology is developed to construct the angular-shaped β-form naphthodithiophene (β-aNDT) core with regiospecific substitution of two alkyl groups at its 4,9- or 5,10-positions via the base-induced double 6π-cyclization of dithienyldieneyne precursors, leading to the two isomeric 4,9-β-aNDT and 5,10-β-aNDT monomers. It is found that a more curved geometry of the β-aNDT units intrinsically increases the solubility and thus the solution-processability of the resultant polymers. Therefore, β-aNDT units are ideal for polymerization with an acceptor-containing monomer without the need for any solubilizing aliphatic side chains, which are considered the insulating portion that jeopardizes charge transport. Based on this consideration, the 4,9- and 5,10-dialkylated β-aNDT monomers are polymerized with the non-alkylated DTFBT acceptor to afford two P4,9-βNDTDTFBT and P5,10-βNDTDTFBT copolymers for head-to-head comparison of the 4,9-inner/5,10-outer isomeric alkylation effect. It is found that 4,9-β-aNDT adopts a twisted conjugated structure due to the intramolecular steric repulsion between the inner branched side chains and the β-hydrogens on the thiophene rings. The slightly twisted 4,9-β-aNDT moiety allows P4,9-βNDTDTFBT to have higher solubility upon polymerization and thus a higher molecular weight, which eventually induces a higher ordered packing structure in the thin film compared to P5,10-βNDTDTFBT. As a result, P4,9-βNDTDTFBT exhibits a higher OFET mobility of 0.18 cm2 V−1 s−1, and the P4,9-βNDTDTFBT:PC71BM-based solar cell device also achieves a higher PCE of 7.23%, which is even better than the corresponding P4,9-αNDTDTFBT-based device.

Benzene-based 1,1-dicyanomethylene-3-indanone (IC) derivatives have been widely utilized as the end-group to construct acceptor-donor-acceptor type nonfullerene acceptors (A-D-A type NFAs). The extension of the end-group conjugation of nonfullerene acceptors (NFAs) is a rational strategy to facilitate intermolecular stacking of the end-groups which are responsible for efficient electron transportation. A bicyclic benzothiophene-based end-group acceptor, 2-(3-oxo-2,3-dihydro-1

In this research, we developed six new selenophene-incorporated naphthobisthiadiazole-based donor-acceptor polymers PNT2Th2Se-OD, PNT2Se2Th-OD, PNT4Se-OD, PNT2Th2Se-DT, PNT2Se2Th-DT, and PNT4Se-DT. The structure-property relationships have been systematically established through the comparison of their structural variations: (1) isomeric biselenophene/bithiophene arrangement between PNT2Th2Se and PNT2Se2Th polymers, (2) biselenophene/bithiophene and quarterselenophene donor units between PNT2Th2Se/PNT2Se2Th and PNT4Se polymers, and (3) side-chain modification between the 2-octyldodecylthiophene (OD)- and 2-decyltetradecyl (DT)-series polymers. The incorporation of selenophene units in the copolymers induces stronger charge transfer to improve the light-harvesting capability while maintaining the strong intermolecular interactions to preserve the intrinsic crystallinity for high carrier mobility. The organic field-effect transistor device using PNT2Th2Se-OD achieved a high hole mobility of 0.36 cm2 V-1 s-1 with an on/off ratio of 1.9 × 105. The solar cells with PNT2Th2Se-OD:PC71BM exhibited a power conversion efficiency of 9.47% with a Voc of 0.68 V, an fill factor of 67%, and an impressive Jsc of 20.69 mA cm-2.

Electrochromic devices (ECDs) play an important role in smart window applications for blocking heat from sunlight. Tungsten trioxide (WO3) is one of the best candidates for making electrochromic films. Current manufacturing processes are, however, costly, have long processing time, and often use non-eco-friendly precursors. Here an alternative facile method integrating electro-exploding wire and spray coating techniques is demonstrated for applications in large size ECDs. The electro-exploding wire technique is used to synthesize WO3 nanomaterials (NMs) in deionized water. The varied size distribution of WO3 NMs is achieved by changing the exploding voltage. The NMs are characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The exploding voltage of 36 V is selected to generate WO3 NMs in a wide size distribution for making porous WO3 films. Subsequently, spray coating is used to disperse WO3 NM suspension on the ITO/glass substrate to form an electrochromic film. The films are characterized by scanning electron microscopy (SEM) and by cycle voltammetry, chronoamperometry, and chronocoulometry measurements in dilute sulfuric acid. The WO3 NM films prepared at a high exploding voltage and a high substrate temperature present a higher electrochemical stability. Considering porosity and electrochemical stability, WO3 NMs exploded at 36 V are used to prepare WO3 films on substrates heated at 300 °C. The electrochromic WO3 film can be operated for over 1000 cycles. We demonstrate an ECD with an area of 15 × 15 cm2 and propose a way to make large size ECDs with low cost and eco-friendly processes.

A nonacylic building block TPTPT with the alternate thiophene and benzene subunits fastened by four bridging methylene groups was connected with various acceptors including diphenylquinoxaline ( QX ), thieno[3,4- c ]pyrrole-4,6(5H)-dione ( TPD ), thieno[3,4- b ]thiophene ( TT ) to afford donor-acceptor (D-A) alternating copolymers - PTPTPTQX , PTPTPTTPD , and PTPTPTTT and random copolymers - PTPTPTQX11 , PTPTPTQX12 , PTPTPTTPD11 , PTPTPTTPD12 , PTPTPTTT11 , and PTPTPTTT12 . The thermal, optical, and electrochemical properties of these copolymers were measured and compared. The random copolymers all have higher glass transition temperature ( T g ) than the corresponding alternating copolymers. ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) calculations suggest that the increase of planarity in the random copolymers arises from the introduction of thiophene units intercalating between donor and acceptor moieties. Bulk heterojunction (BHJ) polymer solar cells (PSCs) were fabricated on the basis of ITO/PEDOT:PSS/polymer:PC 71 BM/Ca/Al device configuration. When the acceptor is QX or TPD , the resultant alternating copolymers performed superior than the random counterparts. When the acceptor is TT , the high content of TT seems to be harmful to the device efficiency, which may relate with the strong quinoidal character of the TT unit. Overall, for the TPTPT core structure, in the used acceptors, the alternating-copolymer arrangement appears to be a better construction manner for the purpose of BHJ PSC applications.

A new tetracyclic 4,9-dialkyl angular-shaped naphthodiselenophene (4,9-α-aNDS) was designed and synthesized. The naphthalene core in 4,9-α-aNDS is formed by the DBU-induced 6π-cyclization of an (E)-1,2-bis(3-(tetradec-1-yn-1-yl)selenophen-2-yl)ethene intermediate followed by the second PtCl2-catalyzed benzannulation. This synthetic protocol allows for incorporating two dodecyl groups regiospecifically at 4,9-positions of the resulting α-aNDS. An ordered supramolecular self-assembly formed via noncovalent selenium–selenium interactions with a short contact of 3.5 A was observed in the single-crystal structure of 4,9-α-aNDS. The distannylated α-aNDS building block was copolymerized with Br-DTFBT and Br-DPP acceptors by Stille cross coupling to form two new donor–acceptor polymers PαNDSDTFBT and PαNDSDPP, respectively. The bottom-gate/top-contact organic field-effect devices using the PαNDSDTFBT and PαNDSDPP semiconductors accomplished superior hole mobility of 3.77 and 2.17 cm2 V–1 s–1, respectively, which ...

Isomeric 2,8-distannyl 5,11-didodecyl αβ-TTN (1, tetrathienonaphthalene = TTN) and 2,8-didodecyl 5,11-distannyl αβ-TTN (2) have been designed and successfully synthesized. The naphthalene core structures in αβ-TTNs were constructed by a systematic protocol using PtCl2-catalyzed cyclization followed by oxidative Scholl annulation in good yields. Compared to the one-dimensional naphthodithiophene derivatives, the two-dimensional αβ-TTN molecules showed good solubility, extended conjugation, strong absorptivity, and highly coplanar structures. Compounds 1 and 2 were polymerized with a 5,5'-dibromo-2,2'-bithiophene-based monomer to afford 2,8-αβ-PTTNTT and 5,11-αβ-PTTNTT copolymers. 2,8-αβ-PTTNTT with the α-aNDT moiety in the main chain exhibited a higher hole mobility of 1.26 × 10(-2) cm(2) V(-1) s(-1).

We have designed and synthesized a tricyclic diseleno[3,2-b:2′,3′-d]silole (DSS) wherein the 3,3′-position of a biselenophene is bridged by a dioctylsilyl moiety. The distannylated DSS was copolymerized with a diketopyrrolopyrrole (DPP) acceptor to form a donor–acceptor copolymer PDSSDPP. The thiophene-based dithieno[3,2-b:2′,3′-d]silole (DTS) monomer and its corresponding copolymer PDTSDPP are also prepared as references for investigation of the chalcogen effect. Compared to PDTSDPP, PDSSDPP exhibits a more red-shifted absorption spectrum, a higher-lying HOMO energy level, and closer interchain packing associated with the more polarizable Se atom to induce stronger intermolecular interactions. The selenophene-based PDSSDPP shows a mobility of 2.47 × 10−2 cm2 V−1 s−1, which is nearly one order magnitude higher than the thiophene-based PDTSDPP with a mobility of 3.89 × 10−3 cm2 V−1 s−1. This result suggests that the DSS unit and its polymers are promising for OFET applications.

We present a facile synthesis method to make a new ladder-type heptacyclic dithienobenzofluorene (DTBF) framework, where the central 2,7-fluorene unit is covalently fastened with two external thiophenes via two CC bridges. A dieneyne-containing precursor undergoes DBU-induced double benzannulation to regiospecifically introduce two solubilizing 2-octyldodecyl side chains at 5,10-positions of DTBF. The rigid and coplanar Br-DTBF monomer with sufficient solubility was copolymerized with 5,6-difluoro-4,7-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (Sn-DTFBT) and 5,10-bis(5-(trimethylstannyl)thiophen-2-yl)naphtho[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (Sn-DTNT) via Stille coupling to furnish two donor–acceptor copolymers, PDTBFFBT and PDTBFNT, respectively. Their thermal, optical, electrochemical, molecular stacking and photovoltaic properties are investigated. PDTBFNT has a higher molecular weight, smaller optical and electrochemical band gaps, and stronger solid-state packing than PDTBFFBT. DFT calculations were carried out to gain insight into the electronic and structural properties of DTBF and its derivatives. Bulk heterojunction solar devices with the ITO/ZnO/polymers:PC71BM/MoO3/Ag configuration were fabricated. By adding 5 vol% diphenyl ether (DPE) as an additive, PDTBFNT:PC71BM and PDTBFFBT:PC71BM devices achieved the power conversion efficiencies of 5.22% and 2.68%, respectively. The superior efficiency of PDTBFNT over PDTBFFBT is attributed to the better LUMO energy alignment between PDTBFNT and PC71BM and the face-on π-stacking of PDTBFNT in the active layer. Moreover, PDTBFNT exhibited a higher field-effect transistor hole mobility of 1.90 × 10−2 cm2 V−1 s−1 than PDTBFFBT with a value of 3.96 × 10−3 cm2 V−1 s−1.

Non-conjugated triethylene glycol (3-EG), tetraethylene glycol (4-EG) and pentaethylene glycol (5-EG) are presented as new cathode modification materials to achieve high-performance inverted-PCSs. By spin-coating from a non-chlorinated solvent, these small molecules can self-assemble on ITO via surface coordination and hydrogen bonding to form an ultra-thin layer. Theoretical simulations reveal that the coordination of oxygen atoms in the EG molecules to indium moieties on the ITO surface is the major mechanism in inducing interfacial dipoles, thereby reducing the work function (WF) of ITO for efficient electron collection. Based on the PBDTTT-EFT:PC71BM blend, the bulk heterojunction device using the 5-EG layer exhibited a higher short-circuit current density (Jsc) of 15.27 mA cm−2, fill factor (FF) of 0.69, and power conversion efficiency (PCE) of 8.46%, which are better than those of the corresponding devices using either inorganic ZnO or non-conjugated poly(ethylene oxide) (PEO) as the cathode buffer layer. More importantly, this simple and expedited strategy is also demonstrated to be universally applicable to various p-type conjugated polymers. The EG oligomers with well-defined chemical structures have the advantages of easy availability, simple processability and good device reproducibility, which are crucial keys for future commercialization using large-scale roll-to-roll production.

Angular-shaped dialkyltetracenedithiophenes (aTDTs) undergo [4+4] photodimerization in solution to form a butterfly-shaped skeleton. This reaction proceeds in a regio- and stereo-selective manner, forming only a single planosymmetric syn-[2,2]-daTDT out of six possible products. The photocycloaddition of aTDTs can take place topochemically in the thin-film state while maintaining regio- and stereo-selectivity. Stronger aliphatic dispersion forces and π–π interactions play important roles in forming the eclipsed dimeric complex that leads to the syn-[2,2]-daTDT isomer.

The device performance of inverted organic metallohalide perovskite solar cells (OMPSCs) is optimized via tailoring the electrode surfaces with electron- and hole-transporting materials. This work demonstrates the fabrication of PEDOT:PSS-free OMPSCs using a hole-transporting composite material consisting of bilayered vanadium oxide (VOx) and a thermally cross-linked triarylamine-based material X-DVTPD, which contributes to higher Voc and Jsc values. The hydrophobicity of X-DVTPD resulted in the formation of large perovskite crystals and enhanced the stability of OMPSCs. Integration of ionic fullerene derivative, fulleropyrrolidinium iodide, in OMPSCs as a hole-blocking interfacial layer at the interface with Ag proves effective to further boost the device efficiency to 18.08%.

An angular-shaped and isomerically pure 4,10-di(2-octyl)dodecylanthradiselenophene (aADS) was successfully developed. The expedient synthesis to form the framework of aADS with two lateral side chains regioselectively at its 4,10-positions is via a base-induced propargyl–allenyl isomerization/6π-electrocyclization/aromatization protocol. This pentacyclic distannylated aADS unit was then copolymerized with dithienyldiketopyrrolopyrrole (DPP) and dithienyl-5,6-difluoro-2,1,3-benzothiadiazole (DTFBT) acceptors with different alkyl side chains to afford four donor–acceptor copolymers: PaADSDPP, PaADSDTFBT-C4, PaADSDTFBT-C8, and PaADSDTFBT-C8C12. UV–vis spectroscopy and cyclic voltammetry revealed that PaADSDPP has the narrowest energy band gap, and PaADSDTFBT-C8C12 has larger band gap than PaADSDTFBT-C4 and PaADSDTFBT-C8. Two layer ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) calculations were implemented to investigate the disparity in optical, electrochemical, and device pr...

Direct C–H arylation polymerization of 2-bromo-3-hexylselenophene and 2-bromo-3-hexylthiophene catalyzed by N-heterocyclic carbene (NHC) palladium-based and Pd(OAc)2-based systems has been carried out and investigated. Under the optimized conditions, high molecular weight poly(3-hexylthiohphene) (P3HT) (Mn = 26.9K g/mol) with high head-to-tail regioregularity (94%) can be obtained by using [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]chloro[3-phenylallyl]palladium(II) (Pd-IPr) as the catalyst. Pd-IPr exhibits a wide range of working temperatures from 70 to 140 °C and good catalytic reproducibility as a result of its high thermal stability. It was found that the presence of additional phosphine ligand, such as tris(o-methoxyphenyl)phosphine, can increase the polymerization efficiency in the Pd(OAc)2 system. This improvement is linked to the stability enhancement for the active species during the course of catalysis. For the first time, poly(3-hexylselenophene) (P3HS) was also obtained by direct-arylat...

Although the tetracyclic angular-shaped naphthodithiophenes (aNDTs) derivatives are an emergent building block for constructing promising semiconductor conjugated polymers, the absence of aliphatic side chains as solubilizing groups on the aNDTs greatly restricted their further application toward polymer synthesis. To create a new class of aNDT-based polymers for widespread applications in solution-processable OFETs and PSCs, side-chain engineering of the aNDT-based structures plays a pivotal role in improving solubility and optimizing electronic/steric properties associated with the resultant solar cell characteristics. In this research, we developed an efficient and straightforward methodology to construct the angular naphthodithophene core with regiospecific introduction of two aliphatic chains at its 4,9-positions via a base-induced double 6π-cyclization. For the first time, the corresponding 2,7-distannylated-4,9-dialkylated aNDT monomers were polymerized with FBT and DPP acceptors to make two new Pa...

A triarylamine-based material DVTPD containing two styryl groups has been developed. Upon isothermal heating at 180 °C for 30 min, DVTPD can be thermally cross-linked to form a solvent-resistant layer to realize the fabrication of solution-processed multilayer devices. The crosslinked DVTPD (denoted as X-DVTPD) layer possesses not only hole-collecting ability (HOMO = −5.3 eV) but also electron-blocking capability (LUMO = −2.2 eV). By incorporation of an ionic dopant, 4-isopropyl-4′-methyldiphenyliodonium tetrakis(pentafluorophenylborate) (DPITPFB), into the X-DVTPD material (1 : 10 in wt%), a favourable morphology of the dopant/matrix layer was formed and the hole-mobility is significantly improved by three orders of magnitude compared to its non-doped state. This DPITPFB : X-DVTPD (1 : 10 in wt%) layer was employed as the hole-transporting layer to fabricate polymer solar cell devices (PSCs). The EHOMO of the polymer in the active layer relative to the EHOMO of the X-DVTPD (−5.3 eV) governs the hole transportation highly associated with the device performance. The higher-lying EHOMO (−5.0 eV) of P3HT causes a large energy barrier for the hole transportation at the interface, leading to an unsatisfactory efficiency. The EHOMO level of the PTB7 copolymer (−5.15 eV) is closer to −5.3 eV. As a result, the PTB7-based device can achieve 80% of the efficiency obtained from the corresponding PEDOT:PSS-based device. Furthermore, the PBDCPDTFBT copolymer has the same EHOMO (−5.3 eV) with X-DVTPD. Consequently, the PBDCPDTFBT-based device showed a comparable efficiency of 5.3% to the corresponding PEDOT:PSS-based device. More importantly, PNDTDTFBT having the lowest-lying EHOMO of −5.4 eV exhibits superior performance with a high PCE of 6.64%, outperforming its reference PEDOT:PSS-based device. This simple and useful hole-transporting system integrating the crosslinking and doping strategies to replace PEDOT:PSS can be widely used in solution-processed organic electronic devices.

Harvesting solar energy from sunlight to generate electricity is considered as one of the most important technologies to address the future sustainability of humans. Polymer solar cells (PSCs) have attracted tremendous interest and attention over the past two decades due to their potential advantage to be fabricated onto large area and light-weight flexible substrates by solution processing at a lower cost. PSCs based on the concept of bulk heterojunction (BHJ) configuration where an active layer comprises a composite of a p-type (donor) and an n-type (acceptor) material represents the most useful strategy to maximize the internal donor-acceptor interfacial area allowing for efficient charge separation. Fullerene derivatives such as [6,6]-phenyl-C61 or 71-butyric acid methyl ester (PCBM) are the ideal n-type materials ubiquitously used for BHJ solar cells. The major effort to develop photoactive materials is numerously focused on the p-type conjugated polymers which are generally synthesized by polymerization of electron-rich donor and electron-deficient acceptor monomers. Compared to the development of electron-deficient comonomers (acceptor segments), the development of electron-rich donor materials is considerably flourishing. Forced planarization by covalently fastening adjacent aromatic and heteroaromatic subunits leads to the formation of ladder-type conjugated structures which are capable of elongating effective conjugation, reducing the optical bandgap, promoting intermolecular π-π interactions and enhancing intrinsic charge mobility. In this review, we will summarize the recent progress on the development of various well-defined new ladder-type conjugated materials. These materials serve as the superb donor monomers to prepare a range of donor-acceptor semi-ladder copolymers with sufficient solution-processability for solar cell applications.

In this study, we developed a new cathodic buffer layer consisting of a cross-linked [6,6]-phenyl-C61-butyric styryl dendron ester (C-PCBSD) matrix and an ionic FPI dopant. The incorporation of FPI can improve the electron mobility via an anion induced charge transfer (AIET) mechanism, while maintaining the solvent-resistant properties of the crosslinked layer. ZnO combined with the C-PCBSD/FPI layer can effectively and universally improve the performance of bulk-heterojunction polymer solar cells (BHJPSCs), planar heterojunction polymer solar cells (PHJPSCs), and organic metallohalide perovskite solar cells (OMPSCs). Furthermore, the insertion of the C-PCBSD/FPI layer can improve the thermal stability of the device by preventing the residual moisture in ZnO from diffusing into the CH3NH3PbI3 layer in OMPSCs.

We have developed a new germanium-bridged heptacyclic arene, dithienogermolocarbazole (DTGC), in which two outer thiophene subunits are covalently fastened to the central 2,7-carbazole core by two dibutylgermanium bridges. The germole moieties embedded in the DTGC structure were successfully constructed by one-pot nucleophilic cyclization in a high yield of 88%. Because of the relatively lower polarity of carbon–germanium bonds, the DTGC unit is chemically stable under basic conditions, rendering its more versatile functionalization. Comparison of germanium-bridged DTGC with the carbon-bridged DTCC (dithienocyclopentacarbazole) and silicon-bridged DTSC (dithienosilolocarbazole) analogues reveals that the HOMO energy level of DTGC lies between those of DTCC and DTSC and so does the LUMO energy level of DTGC. Density functional theory (DFT) calculations suggest that DTSC and DTGC have more bent structures than DTCC, which plays an important role in determining their frontier orbital energies. The structural...

The electrical and optical properties of the hole transport layer (HTL) are critical for organic and halide perovskite solar cell (OSC and PSC, respectively) performance. In this work, we studied the effect of Mg doping on CuCrO2 (CCO) nanoparticles and their performance as HTLs in OSCs and PSCs. CCO and Mg doped CCO (Mg:CCO) nanoparticles were hydrothermally synthesized. The nanoparticles were characterized by various experimental techniques to study the effect of Mg doping on structural, chemical, morphological, optical, and electronic properties of CCO. We found that Mg doping increases work function and decreases particle size. We demonstrate CCO and Mg:CCO as efficient HTLs in a variety of OSCs, including the first demonstration of a non-fullerene acceptor bulk heterojunction, and CH3NH3PbI3 PSCs. A small improvement of average short-circuit current density with Mg doping was found in all systems.

A new PC61BM-based fullerene, [6,6]-phenyl-C61 butyric acid pentafluorophenyl ester (PC61BPF) is designed and synthesized. This new n-type material can replace PC61BM to form a P3HT:PC61BPF binary blend or serve as an additive to form a P3HT:PC61BM:PC61BPF ternary blend. Supramolecular attraction between the pentafluorophenyl group of PC61BPF and the C60 cores of PC61BPF/PC61BM can effectively suppress the PC61BPF/PC61BM materials from severe aggregation. By doping only 8.3 wt% PC61BPF, device PC61BPF651 exhibits a PCE of 3.88% and decreases slightly to 3.68% after heating for 25 h, preserving 95% of its original value. When PC61BP with non-fluorinated phenyl group is used to substitute PC61BPF, the stabilizing ability disappears completely. The efficiencies of PC61BP651 and PC61BP321 devices significantly decay to 0.44% and 0.11%, respectively, after 25 h isothermal heating. Most significantly, this strategy is demonstrated to be effective for a blend system incorporating a low band-gap polymer. By adding only 10 wt% PC61BPF, the PDTBCDTB:PC71BM-based device exhibits thermally stable morphology and device characteristics. These findings demonstrate that smart utilization of supramolecular interactions is an effective and practical strategy to control morphological evolution.

A new strategy to synthesize 4,9- and 5,10-dialkylated α-aNDTs as well as 4,9- and 5,10-dialkylated β-aNDTs is described. Four isomeric precursors with different dithienyl-ene-diyne arrangements undergo base-induced double 6π-cyclization to construct the central naphthalene cores, leading to the formation of the regiospecific products. These 2,7-distannylated dialkylated aNDT-based monomers can be used for Stille cross-coupling to produce promising conjugated materials for various optoelectronic applications.