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Developing dopant-free hole-transporting materials (HTMs) for high-performance perovskite solar cells (PVSCs) has been a very active research topic in recent years since HTMs play a critical role in optimizing interfacial charge carrier kinetics and in turn determining device performance. Here, a novel dendritic engineering strategy is first utilized to design HTMs with a D-A type molecular framework, and diphenylamine and/or carbazole is selected as the building block for constructing dendrons. All HTMs show good thermal stability and excellent film morphology, and the key optoelectronic properties could be fine-tuned by varying the dendron structure. Among them, MPA-Cz-BTI and MCz-Cz-BTI exhibit an improved interfacial contact with the perovskite active layer, and non-radiative recombination loss and charge transport loss can be effectively suppressed. Consequently, high power conversion efficiencies (PCEs) of 20.8% and 21.35% are achieved for MPA-Cz-BTI and MCz-Cz-BTI based devices, respectively, accompanied by excellent long-term storage stability. More encouragingly, ultrahigh fill factors of 85.2% and 83.5% are recorded for both devices, which are among the highest values reported to date. This work demonstrates the great potential of dendritic materials as a new type of dopant-free HTMs for high-performance PVSCs with excellent FF.

As a key component in perovskite solar cells (PVSCs), hole-transporting materials (HTMs) have been extensively explored and studied. Aiming to meet the requirements for future commercialization of PVSCs, HTMs which can enable excellent device performance with low cost and eco-friendly processability are urgently needed but rarely reported. In this work, a traditional anchoring group (2-cyanoacrylic acid) widely used in molecules for dye-sensitized solar cells is incorporated into donor-acceptor-type HTMs to afford MPA-BT-CA, which enables effective regulation of the frontier molecular orbital energy levels, interfacial modification of an ITO electrode, efficient defect passivation toward the perovskite layer, and more importantly alcohol solubility. Consequently, inverted PVSCs with this low-cost HTM exhibit excellent device performance with a remarkable power conversion efficiency (PCE) of 21.24% and good long-term stability in ambient conditions. More encouragingly, when processing MPA-BT-CA films with the green solvent ethanol, the corresponding PVSCs also deliver a substantial PCE as high as 20.52% with negligible hysteresis. Such molecular design of anchoring group-based materials represents great progress for developing efficient HTMs which combine the advantages of low cost, eco-friendly processability, and high performance. We believe that such design strategy will pave a new path for the exploration of highly efficient HTMs applicable to commercialization of PVSCs.

Compared with p-type terpolymers, less effort has been devoted to n-type analogs. Herein, we synthesized a series of n-type terpolymers via incorporating three electron-deficient third components including thienopyrroledione (TPD), phthalimide, and benzothiadiazole into an imide-functionalized parent n-type copolymer to tune optoelectronic properties without sacrificing the n-type characteristics. Due to effects of the third components with different electron-accepting ability and solubility, the resulting three polymers feature distinct energy levels and crystallinity. In addition, heteroatoms (S, O, and N) attached on the third components trigger intramolecular noncovalent interactions, which can increase molecule planarity and have a significant effect on the packing structures of the polymer films. As a result, the best power conversion efficiency of 8.28% was achieved from all-polymer solar cells (all-PSCs) based on n-type terpolymer containing TPD. This is contributed by promoted electron mobility and face-on polymer packing, showing the pronounced advantages of the TPD used as a third component for thriving efficient n-type terpolymers. The generality is also successfully validated in a benchmark polymer donor/acceptor system by introducing TPD into the benchmark n-type polymer N2200. The results demonstrate the feasibility of introducing suitable electron-deficient building blocks as the third components for high-performance n-type terpolymers toward efficient all-PSCs.

Electron transport layers (ETLs) are critical for improving device performance and stability of perovskite solar cells (PVSCs). Herein, a distannylated electron-deficient bithiophene imide (BTI-Tin) is synthesized, which enables us to access structurally novel acceptor–acceptor (A–A) type polymers. Polymerizing BTI-Tin with dibrominated naphthalene diimide (NDI-Br) and perylene diimide (PDI-Br) affords two A–A copolymers P(BTI-NDI) and P(BTI-PDI). The all-acceptor backbone yields both low-lying highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels for the polymers, which combined with their high electron mobility render P(BTI-NDI) and P(BTI-PDI) as promising ETLs for perovskite solar cells (PVSCs). When applied as ETLs to replace the conventional [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) in planar p–i–n PVSCs, the PC61BM-free devices based on P(BTI-NDI) and P(BTI-PDI) achieve remarkable power conversion efficiencies (PCEs) of 19.5% and 20.8%, respectively, with negligible hysteresis. Such performance is attributed to efficient electron extraction and reduced charge recombination. Moreover, the devices based on P(BTI-NDI) and P(BTI-PDI) ETLs show improved stability compared to the PC61BM based ones due to the higher hydrophobicity of the new ETLs. This work provides important guidelines for designing n-type polymers to replace PC61BM as efficient ETLs for high-performance PVSCs with improved stability.

A novel nanomaterial, bismuth oxychloride nanoplates (BiOCl NPs), was first applied in organic solar cells (OSCs) as hole transporting layers (HTLs). It is worth noting that the BiOCl NPs can be facilely synthesized at ∼1/200 of the cost of the commercial PEDOT:PSS and well dissolved in green solvents. Different from the PEDOT:PSS interlayer, the deposition of BiOCl HTL is free of post-treatment at elevated temperature, which reduces device fabrication complexity. To demonstrate the universality of BiOCl in improving photovoltaic performance, OSCs containing various representative active layers were investigated. The power conversion efficiencies (PCEs) of the P3HT:PC

High-performance polymer semiconductors generally should have wide absorption, good solution process-ability, and fine-tuned physicochemical properties in order to achieve satisfying photovoltaic performance. Herein, two new alkynyl-functionalized electron donor units, 3-alkyl-3′-alkynyl-2,2′-bithiophene (TRTRy) and 3-alkoxy-3′-alkynyl-2,2′-bithiophene (TORTRy), were invented through the combination of the alkynyl side chain with the alkyl or alkoxy side chain, respectively. Copolymerization of these bithiophenes with difluorobenzothiadiazole (ffBT) afforded polymers ffBT-TRTRy and ffBT-TORTRy, respectively. When applied into polymer solar cells (PSCs), devices using ffBT-TRTRy donor polymer display a maximum power conversion efficiency (PCE) of 2.34% with a short-circuit current (Jsc) of 7.46 mA cm−2, an open circuit voltage (Voc) of 0.93 V, and a fill factor (FF) of 34.0%. The TORTRy containing polymer ffBT-TORTRy affords PSCs with a much improved PCE of 6.60% with a higher Jsc of 15.09 mA cm−2, a larger FF of 58.3%, and a Voc of 0.75 V. The performance improvement of PSC devices using ffBT-TORTRy donor is mainly attributed to the simultaneous realization of higher Jsc and FF, while maintaining a good Voc. The results demonstrate that alkynyl-functionalized H-H bithiophenes are promising building blocks for efficient PSCs.

Perovskite quantum dots (QDs) have gained significant attention for both fundamental research and commercial applications because of their outstanding optoelectronic properties and tremendous appli...

In this paper we report the rationale and implementation of a new building block for organic electronics based on 4,8-di(2-thienyl)-benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole) (iso-BBT-T2) and realization of two alkyl-functionalized iso-BBT-tetrathiophene (T4) alternating copolymers (P1 with alkyl = 2DT and P2 with alkyl = 2DH). Compared to the previously investigated small molecules/polymers based on the conventional 4,8-di(2-thienyl)-benzo[l,2-c:4,5-c′]bis[ l,2,5]thiadiazole (BBT-T2), the use of the iso-BBT heterocycle widens the polymer band gap to a region (∼1.4 eV) compatible for use in single junction solar cells. The influence of iso-BBT vs BBT structural variation on the molecular structure, electronic characteristics, and optical properties was accessed by DFT computations, single-crystal determination, optical absorption, and electrochemical measurements. In-plane charge transport for P1 and P2 was investigated in an organic thin-film transistor (OTFT) structure demonstrating hole mobilities appr...

Two new wide bandgap copolymers PTzTIBDTT and PTzTIBDTT-S based on thiazolothienyl imide (TzTI) and benzodithiophene with a distinct side chain were synthesized and characterized for applications in polymer solar cells (PSCs). The single crystal of the TzTI model compound showed a highly planar backbone with a close π-stacking distance of 3.65 A, a desired structural feature for efficient charge transport. Moreover, the TzTI incorporation can trigger intramolecular noncovalent N⋯S interactions to yield a self-planarized polymer backbone, which should be beneficial for achieving ordered molecular packing and efficient charge transport. Due to its strong electron-withdrawing effect, the incorporation of the TzTI unit largely lowers the polymer HOMO levels to −5.65 and −5.69 eV for PTzTIBDTT and PTzTIBDTT-S, respectively. The PSCs containing the PTzTIBDTT:PC71BM active layer exhibited a promising power conversion efficiency (PCE) of 8.00% with a large Voc of 0.90 V. To the best of our knowledge, the PCE is among the highest values for fullerene PSCs based on an imide-containing polymer donor. This work not only demonstrates that thiazolothienyl imide is a promising building block for constructing high-performance wide bandgap photovoltaic polymer semiconductors, but also reveals that a noncovalent N⋯S conformational lock is an effective molecular design approach for enabling polymer semiconductors with a planar backbone for efficient PSCs.

Thiophene and its derivatives have been extensively used in organic electronics, particularly in the field of polymer solar cells (PSCs). Significant research efforts have been dedicated to modifying thiophene-based units by attaching electron-donating or withdrawing groups to tune the energy levels of conjugated materials. Herein, we report the design and synthesis of a novel thiophene derivative, FE-T, featuring a monothiophene functionalized with both an electron-withdrawing fluorine atom (F) and an ester group (E). The FE-T unit possesses distinctive advantages of both F and E groups, the synergistic effects of which enable significant downshifting of the energy levels and enhanced aggregation/crystallinity of the resulting organic materials. Shown in this work are a series of polymers obtained by incorporating the FE-T unit into a PM6 polymer to fine-tune the energetics and morphology of this high-performance PSC material. The optimal polymer in the series shows a downshifted HOMO and an improved morphology, leading to a high PCE of 16.4% with a small energy loss (0.53 eV) enabled by the reduced non-radiative energy loss (0.23 eV), which are among the best values reported for non-fullerene PSCs to date. This work shows that the FE-T unit is a promising building block to construct donor polymers for high-performance organic photovoltaic cells.

Two carboxylate-functionalized wide band gap polymers, 2TC-TT-BDTFT and 2T-TTC-BDTFT, which feature a fluorinated benzodithiophene (BDTFT)-alt-2,5-di(thiophen-2-yl)thieno[3,2-b]thiophene (2T-TT) ba...

A new building block, 1,4-di(3-alkoxy-2-thienyl)-2,5-difluorophenylene (DOTFP) with several desirable features such as high backbone planarity, suitably lying highest occupied molecular orbital (HOMO), and good solubility, was developed by inserting an electron-deficient difluorophenylene into the 3,3′-dialkoxy-2,2′-bithiophene (BTOR) unit. Three regioregular D-A1-D-A2 type polymers based on DOTFP and benzothiadiazole (BT) derivatives were synthesized and characterized by comparing with a D–A type BTOR-based polymer. The content of highly electron-rich alkoxythiophene is reduced by half in the DOTFP-based polymers versus that of the BTOR-based polymer analogue, which results in a deeper HOMO level and benefits high open-circuit voltage (Voc) in polymer solar cells (PSCs). Consequently, the DOTFP-ffBT-based solar cells exhibited a significantly improved power conversion efficiency (PCE) of 8.7% and an increased Voc of 0.84 V compared to the BTOR-ffBT-based solar cells with a PCE of 2.6% and a Voc of 0.49 V...

Head-to-head (HH) bithiophenes are typically avoided in polymer semiconductors since they engender undesirable steric repulsions, leading to a twisted backbone. While introducing electron-donating alkoxy chains can lead to intramolecular noncovalent S···O interactions, this comes at the cost of elevating the HOMOs and compromising polymer solar cell (PSC) performance. To address the limitation, a novel HH bithiophene featuring an electron-withdrawing ester functionality, 3-alkoxycarbonyl-3′-alkoxy-2,2′-bithiophene (TETOR), is synthesized. Single crystal diffraction reveals a planar TETOR conformation (versus highly twisted diester bithiophene), showing distinctive advantages of incorporating alkoxy on promoting backbone planarity. Compared to first-generation 3-alkyl-3′-alkoxy-2,2′-bithiophene (TRTOR), TETOR contains an additional planarizing (thienyl)S···O(carbonyl) interaction. Consequently, TETOR-based polymer (TffBT-TETOR) has greatly lower-lying FMOs, stronger aggregation, closer π-stacking, and bett...

Due to their high-lying lowest unoccupied molecular orbitals (LUMOs), π-conjugated polymers based on benzothiadiazole and its derivatives typically are p-type. We report here the successful development of two narrow bandgap, ambipolar donor–acceptor copolymers, PDCNBT2T and PDCNBSe2T, which are based on new cyano-substituted strong electron acceptors, 4,7-dibromo-5,6-dicyano-2,1,3-benzothiadiazole (DCNBT) and 4,7-dibromo-5,6-dicyano-2,1,3-benzoselenadiazole (DCNBSe), respectively. Compared to their polymer analogues with fluorine substituents, the LUMO was lowered by a big margin of ca. 0.6 eV and the bandgap was reduced by 0.2–0.3 eV for the cyano-substituted polymers. Therefore, the cyano-substituted benzothiadiazole polymers showed very low-lying LUMO levels of ca. 4.3 eV. Benefiting from their narrow bandgaps of 1.1–1.2 eV and appropriately positioned LUMO levels, both polymers exhibit well balanced ambipolar transport characteristics in organic thin-film transistors, which differ from the p-type dominating transport properties of their fluorinated polymer analogues. A balanced hole/electron mobility of 0.59/0.47 cm2 V−1 s−1 was achieved for polymer PDCNBT2T, and a reduced hole/electron mobility of 0.018/0.014 cm2 V−1 s−1 was observed for the benzoselenadiazole-based PDCNBSe2T due to its lower crystallinity. These results show that the electron mobility can be enhanced by approximately two orders versus the electron mobility of the previously reported 4,7-di(thiophen-2-yl)-5,6-dicyano-2,1,3-benzothiadiazole-based polymer. This improvement was achieved by using the new acceptor units without additional electron-rich thiophene flanks, which allow a higher degree of freedom in selecting the donor co-unit and more effective tuning of energy levels of frontier molecular orbitals.

Two novel polymeric acceptors based on naphthalene diimide (NDI) and 2.2′-bithiophene, named as P(NDI2THD-T2) and P(NDI2TOD-T2), were designed and synthesized for all polymer solar cells application. The structural and electronic properties of the two acceptors were modulated through side-chain engineering of the NDI units. The optoelectronic properties of the polymers and the morphologies of the blend films composed of the polymer acceptors and a donor polymer PTB7-Th were systemically investigated. With thiophene groups introduced into the side chains of the NDI units, both polymers showed wider absorption from 350 nm to 900 nm, compared with the reference polymer acceptor of N2200. No redshift of absorption spectra from solutions to films indicated reduced aggregation of the polymers due to the steric hindrance effect of thiophene rings in the side chains. The photovoltaic performance were characterized for devices in a configuration of ITO/PEDOT:PSS/PTB7-Th:acceptors/2,9-bis(3-(dimethylamino)propyl)anthra[2,1,9-def:6,5,10-def]diisoquinoline-1,3,8,10(2H,9H)-tetraone (PDIN)/Al. With the addition of diphenyl ether as an additive, the power conversion efficiencies (PCEs) of 2.73% and 4.75% for P(NDI2THD-T2) and P(NDI2TOD-T2) based devices were achieved, respectively. The latter showed improved Jsc, Fill Factor (FF), and PCE compared with N2200 based devices. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3679–3689

Inspired by the excellent device performance of imide-functionalized polymer semiconductors in organic electronics, a novel imide-based building block, dithienylbenzodiimide (TBDI), with fused backbone is designed and synthesized. Single-crystal structure analysis reveals that the TBDI unit features non-planar backbone conformation but with a tight π-stacking distance of 3.36 A. By copolymerizing with various electron-rich co-units, a series of TBDI-based polymer semiconductors is synthesized and the optoelectronic, thermal, electrochemical and charge transport properties of the semiconductors are characterized. Attributed to the non-planar backbone and intrinsic electrical property of TBDI, all polymers exhibit wide bandgaps (∼2.0 eV) with low-lying HOMOs (

High degree of polymer backbone planarity is achieved by incorporating intramolecular noncovalent sulfur···oxygen interaction, which also affords good solubility by attaching alkoxy chains at the 3,3′-positions of bithiophene. However, the applications of the resulting polymers are plagued by their high-lying HOMOs due to the strong electron-donating alkoxy chains, resulting in small open-circuit voltages (Vocs) in polymer solar cells. Herein, a novel head-to-head linkage containing 3,3′-dialkoxy-4,4′-dicyano-2,2′-bithiophene (BTCNOR) is invented. Single-crystal X-ray diffraction shows direct evidence of noncovalent sulfur···oxygen interaction and coplanar backbone of BTCNOR. Very low-lying HOMOs (−5.5 to −5.6 eV) of the corresponding polymers with high degree of backbone planarity and good solubility are achieved by introducing strong electron-withdrawing cyano group onto the dialkoxybithiophene. The cyano offsets the effect of the electron-donating alkoxy chain, rendering the new BTCNOR as a weak donor ...

An isomerization method was utilized to yield a novel near-infrared nonfullerene acceptor DTA-IC-M. By simply changing the linking fashion between the anthracene and neighboring thiophenes, a remarkable redshift (∼170 nm) of absorption was observed from DTA-IC-S to its isomer DTA-IC-M which shows a maximum absorption peak over 800 nm with a narrow bandgap of 1.35 eV. Due to the enhanced photo-to-current response in the near-infrared region, an improved short-circuit current of 12.96 mA cm−2 was achieved for the DTA-IC-M based OSCs.

Halogenated solvents are prevailingly used in the fabrication of nonfullerene organic solar cells (NF-OSCs) at the current stage, imposing significant restraints on their practical applications. By copolymerizing phthalimide or thieno[3,4

Significant progress has been made in nonfullerene small molecule acceptors (NF‐SMAs) that leads to a consistent increase of power conversion efficiency (PCE) of nonfullerene organic solar cells (NF‐OSCs). To achieve better compatibility with high‐performance NF‐SMAs, the direction of molecular design for donor polymers is toward wide bandgap (WBG), tailored properties, and preferentially ecofriendly processability for device fabrication. Here, a weak acceptor unit, methyl 2,5‐dibromo‐4‐fluorothiophene‐3‐carboxylate (FE‐T), is synthesized and copolymerized with benzo[1,2‐b:4,5‐b′]dithiophene (BDT) to afford a series of nonhalogenated solvent processable WBG polymers P1‐P3 with a distinct side chain on FE‐T. The incorporation of FE‐T leads to polymers with a deep highest occupied molecular orbital (HOMO) level of −5.60−5.70 eV, a complementary absorption to NF‐SMAs, and a planar molecular conformation. When combined with the narrow bandgap acceptor ITIC‐Th, the solar cell based on P1 with the shortest methyl chain on FE‐T achieves a PCE of 11.39% with a large V oc of 1.01 V and a J sc of 17.89 mA cm−2. Moreover, a PCE of 12.11% is attained for ternary cells based on WBG P1, narrow bandgap PTB7‐Th, and acceptor IEICO‐4F. These results demonstrate that the new FE‐T is a highly promising acceptor unit to construct WBG polymers for efficient NF‐OSCs., A series of wide bandgap donor polymers are designed and synthesized by incorporating a monothiophene functionalized with both a fluorine atom and an ester group. Fabricated from nonhalogenated solvent, power conversion efficiencies of 11.39% and 12.11% are achieved for binary and ternary nonfullerene solar cells, respectively.

Polythiophenes, built on the electron-rich thiophene unit, typically possess high-lying energy levels of the lowest unoccupied molecular orbitals (LUMOs) and show hole-transporting properties. In this study, we develop a series of n-type polythiophenes, P1-P3, based on head-to-head-linked 3,3'-dialkoxy-4,4'-dicyano-2,2'-bithiophene (BTCNOR) with distinct side chains. The BTCNOR unit shows not only highly planar backbone conformation enabled by the intramolecular noncovalent sulfur-oxygen interaction but also significantly suppressed LUMO level attributed to the cyano-substitution. Hence, all BTCNOR-based polymer semiconductors exhibit low-lying LUMO levels, which are ∼1.0 eV lower than that of regioregular poly(3-hexylthiophene) (rr-P3HT), a benchmark p-type polymer semiconductor. Consequently, all of the three polymers can enable unipolar n-type transport characteristics in organic thin-film transistors (OTFTs) with low off-currents ( I

A novel imide-functionalized arene, di(fluorothienyl)thienothiophene diimide (f-FBTI2), featuring a fused backbone functionalized with electron-withdrawing F atoms, is designed, and the synthetic challenges associated with highly electron-deficient fluorinated imide are overcome. The incorporation of f-FBTI2 into polymer affords a high-performance n-type semiconductor f-FBTI2-T, which shows a reduced bandgap and lower-lying lowest unoccupied molecular orbital (LUMO) energy level than the polymer analog without F or with F-functionalization on the donor moiety. These optoelectronic properties reflect the distinctive advantages of fluorination of electron-deficient acceptors, yielding "stronger acceptors," which are desirable for n-type polymers. When used as a polymer acceptor in all-polymer solar cells, an excellent power conversion efficiency of 8.1% is achieved without any solvent additive or thermal treatment, which is the highest value reported for all-polymer solar cells except well-studied naphthalene diimide and perylene diimide-based n-type polymers. In addition, the solar cells show an energy loss of 0.53 eV, the smallest value reported to date for all-polymer solar cells with efficiency > 8%. These results demonstrate that fluorination of imide-functionalized arenes offers an effective approach for developing new electron-deficient building blocks with improved optoelectronic properties, and the emergence of f-FBTI2 will change the scenario in terms of developing n-type polymers for high-performance all-polymer solar cells.

In order to improve light absorption and promote n-type performance, random copolymerization strategy was employed to afford a series of random terpolymer acceptors with acceptor1-acceptor2-acceptor3 (A1-A2-A3) type backbone. The polymers were synthesized from distannylated electron-deficient bithiophene imide monomer with various electron-deficient dibrominated co-monomers using the typical palladium-catalyzed Stille coupling condensation polymerization. Compared with their parent polymers, these A1-A2-A3 type terpolymer acceptors, particularly the dihexylthieno[3,4-b]pyrazine based terpolymer PBTP, can exhibit good miscibility, appropriate polymer crystallinity, and improved absorption in the long-wavelength region due to the incorporation of a third strong electron-withdrawing acceptor moiety thieno[3,4-b]pyrazine. Benefitting from the noncovalent S⋯N interactions, PBTP possessed a planar skeleton and achieved the highest power conversion efficiency (PCE) of 7.35% in the polymer series when serving as the acceptor material in all-polymer solar cells. These results indicate that the A1-A2-A3 type terpolymer acceptors should be promising candidates for developing high-performance all-polymer solar cells.

Narrow bandgap (1.37-1.46 eV) polymers incorporating a head-to-head linkage containing 3-alkoxy-3'-alkyl-2,2'-bithiophene are synthesized. The head-to-head linkage enables polymers with sufficient solubility and the noncovalent sulfur-oxygen interaction affords polymers with high degree of backbone planarity and film ordering. When integrated into polymer solar cells, the polymers show a promising power conversion efficiency approaching 10%.

Head-to-head linked bithiophenes with planar backbones hold distinctive advantages for constructing organic semiconductors, such as good solubilizing capability, enabling narrow bandgap, and effective tuning of frontier molecular orbital (FMO) levels using minimal thiophene numbers. In order to realize planar backbone, alkoxy chains are typically installed on thiophene head positions, owing to the small van der Waals radius of oxygen atom and accompanying noncovalent S⋯O interaction. However, the strong electron donating alkoxy chains on the electron-rich thiophenes lead to elevated FMO levels, which are detrimental to material stability and device performance. Thus, a new design approach is needed to counterbalance the strong electron donating property of alkoxy chains to bring down the FMOs. In this study, we designed and synthesized a new head-to-head linked building block, 4-alkoxy-5-(3-alkylthiophen-2-yl)thiazole (TRTzOR), using an electron-deficient thiazole to replace the electron-rich thiophene. Compared to previously reported 3-alkoxy-3′-alkyl-2,2′-bithiophene (TRTOR), TRTzOR is a weaker electron donor, which considerably lowers FMOs and maintains planar backbone through the noncovalent S⋯O interaction. The new TRTzOR was copolymerized with benzothiadiazoles with distinct F numbers to yield a series of polymer semiconductors. Compared to TRTOR-based analogous polymers, these TRTzOR-based polymers have broader absorption up to 950 nm with lower-lying FMOs by 0.2–0.3 eV, and blending these polymers with PC71BM leads to polymer solar cells (PSCs) with improved open-circuit voltage (Voc) by ca. 0.1 V and a much smaller energy loss (Eloss) as low as 0.59 eV. These results demonstrate that thiazole substitution is an effective approach to tune FMO levels for realizing higher Vocs in PSCs and the small Eloss renders TRTzOR a promising building block for developing high-performance organic semiconductors.

Diketopyrrolopyrrole (DPP)-based copolymers have received considerable attention as promising semiconducting materials for high-performance organic thin-film transistors (OTFTs). However, these polymers typically exhibit p-type or ambipolar charge-transporting characteristics in OTFTs due to their high-lying highest occupied molecular orbital (HOMO) energy levels. In this work, a new series of DPP-based n-type polymers have been developed by incorporating fused bithiophene imide oligomers (BTIn) into DPP polymers. The resulting copolymers BTIn-DPP show narrow band gaps as low as 1.27 eV and gradually down-shifted frontier molecular orbital energy levels upon the increment of imide group number. Benefiting from the coplanar backbone conformation, well-delocalized π-system, and favorable polymer chain packing, the optimal polymer in the series shows promising n-type charge transport with an electron mobility up to 0.48 cm2 V-1 s-1 in OTFTs, which is among the highest values for the DPP-based n-type polymers reported to date. The results demonstrate that incorporating fused bithiophene imide oligomers into polymers can serve as a promising strategy for constructing high-performance n-type polymeric semiconductors.

We present here a series of wide-band-gap (Eg: >1.8 eV) polymer donors by incorporating thiophene-flanked phenylene as an electron-donating unit and quinoxaline as an electron-accepting co-unit to attain large open-circuit voltages (Vocs) and short-circuit currents (Jscs) in nonfullerene organic solar cells (OSCs). Fluorination was utilized to fine-tailor the energetics of polymer frontier molecular orbitals (FMOs) by replacing a variable number of H atoms on the phenylene moiety with F. It was found that fluorination can effectively modulate the polymer backbone planarity through intramolecular noncovalent S···F and/or H···F interactions. Polymers (P2–P4) show an improved molecular packing with a favorable face-on orientation compared to their nonfluorinated analogue (P1), which is critical to charge carrier transport and collection. When mixed with IDIC, a nonfullerene acceptor, P3 with two F atoms, achieves a remarkable Voc of 1.00 V and a large Jsc of 15.99 mA/cm2, simultaneously, yielding a power-con...

High-performance polymer solar cells (PSCs) with thick active layers are essential for large-scale production. Polymer semiconductors exhibiting a temperature-dependent aggregation property offer great advantages toward this purpose. In this study, three difluorobenzoxadiazole (ffBX)-based donor polymers, PffBX-T, PffBX-TT, and PffBX-DTT, were synthesized, which contain thiophene (T), thieno[3,2-b]thiophene (TT), and dithieno[3,2-b:2′,3′-d]thiophene (DTT) as the π-spacers, respectively. Temperature-dependent absorption spectra reveal that the aggregation strength increases in the order of PffBX-T, PffBX-TT, and PffBX-DTT as the π-spacer becomes larger. PffBX-TT with the intermediate aggregation strength enables well-controlled disorder–order transition in the casting process of blend film, thus leading to the best film morphology and the highest performance in PSCs. Thick-film PSCs with an average power conversion efficiency (PCE) of 8.91% and the maximum value of 9.10% are achieved using PffBX-TT:PC71BM ...

Development of high-performance unipolar n-type organic semiconductors still remains as a great challenge. In this work, all-acceptor bithiophene imide-based ladder-type small molecules BTIn and semiladder-type homopolymers PBTIn (n = 1–5) were synthesized, and their structure–property correlations were studied in depth. It was found that Pd-catalyzed Stille coupling is superior to Ni-mediated Yamamoto coupling to produce polymers with higher molecular weight and improved polymer quality, thus leading to greatly increased electron mobility (μe). Due to their all-acceptor backbone, these polymers all exhibit unipolar n-type transport in organic thin-film transistors, accompanied by low off-currents (10–10–10–9 A), large on/off current ratios (106), and small threshold voltages (∼15–25 V). The highest μe, up to 3.71 cm2 V–1 s–1, is attained from PBTI1 with the shortest monomer unit. As the monomer size is extended, the μe drops by 2 orders to 0.014 cm2 V–1 s–1 for PBTI5. This monotonic decrease of μe was al...

A series of polymer semiconductors incorporating 2,1,3-benzothiadiazole-5,6-dicarboxylicimide (BTZI) as strong electron-withdrawing unit and an alkoxy-functionalized head-to-head linkage containing bithiophene or bithiazole as highly electron-rich co-unit are designed and synthesized. Because of the strong intramolecular charge transfer characteristics, all three polymers BTZI-TRTOR (P1), BTZI-BTOR (P2), and BTZI-BTzOR (P3) exhibit narrow bandgaps of 1.13, 1.05, and 0.92 eV, respectively, resulting in a very broad absorption ranging from 350 to 1400 nm. The highly electron-deficient 2,1,3-benzothiadiazole-5,6-dicarboxylicimide and alkoxy-functionalized bithiophene (or thiazole) lead to polymers with low-lying lowest unoccupied molecular orbitals (−3.96 to −4.28 eV) and high-lying highest occupied molecular orbitals (−5.01 to −5.20 eV). Hence, P1 and P3 show substantial and balanced ambipolar transport with electron mobilities/hole mobilities of up to 0.86/0.51 and 0.95/0.50 cm2 V–1 s–1, respectively, and ...