Search

Charge carrier nonradiative recombination (NRR) caused by interface defects and nonoptimal energy level alignment is the primary factor restricting the performance improvement of perovskite solar cells (PSCs). Interfacial modification is a vital strategy to restrain NRR and enable high-performance PSCs. We report here two interfacial materials, PhI-TPA and BTZI-TPA, consisting of phthalimide and a 2,1,3-benzothiadiazole-5,6-dicarboxylicimide core, respectively. The difunctionalized BTZI-TPA with imide and thiadiazole shows higher hole mobility, better aligned energy levels, and stronger interaction with uncoordinated Pb

Self-assembled molecules (SAMs) have shown great potential in replacing bulk charge selective contact layers in high-performance perovskite solar cells (PSCs) due to their low material consumption and simple processing. Herein, we design and synthesize a series of donor-acceptor (D-A) type SAMs (MPA-BT-CA, MPA-BT-BA, and MPA-BT-RA, where MPA is 4-methoxy-N-(4-methoxyphenyl)-N-phenylaniline; BT is benzo[c][1,2,5]-thiadiazole; CA is 2-cyanoacrylic acid, BA is benzoic acid, RA is rhodanine-3-propionic acid) with distinct anchoring groups, which show dramatically different properties. MPA-BT-CA with CA anchoring groups exhibited stronger dipole moments and formed a homogeneous monolayer on the indium tin oxide (ITO) surface by adopting an upstanding self-assembling mode. However, the MPA-BT-RA molecules tend to aggregate severely in solid state due to the sp3 hybridization of the carbon atom on the RA group, which is not favorable for achieving a long-range ordered self-assembled layer. Consequently, benefiting from high dipole moment, as well as dense and uniform self-assembled film, the device based on MPA-BT-CA yielded a remarkable power conversion efficiency (PCE) of 21.81%. Encouragingly, an impressive PCE approaching 20% can still be obtained for the MPA-BT-CA-based PSCs as the device area is increased to 0.80 cm2. Our work sheds light on the design principles for developing hole selecting SAMs, which will pave a way for realizing highly efficient, flexible, and large-area PSCs.

Solution-processed hole contact materials, as an indispensable component in perovskite solar cells (PSCs), have been widely studied with consistent progress achieved. One bottleneck for the commercialization of PSCs is the lack of hole contact materials with high performance, cost-effective preparation, and green-solvent processability. Therefore, the development of versatile hole contact materials is of great significance. Herein, we report two novel donor-acceptor (D-A)-type hole contact molecules (FMPA-BT-CA and 2FMPA-BT-CA) with low cost and alcohol-based processability by utilizing a fluorination strategy. We showed that the fluorine atoms lead to the lowered highest occupied molecular orbital (HOMO) energy levels and larger dipole moments for FMPA-BT-CA and 2FMPA-BT-CA. Moreover, fluorination also improves the buried interfacial interaction between hole contacts and perovskite. As a result, a remarkable power conversion efficiency (PCE) of 22.37% along with good light stability could be achieved for green-solvent-processed FMPA-BT-CA-based inverted PSC devices, demonstrating the great potential of environmentally compatible hole contacts for highly efficient PSCs.

Low-cost and eco-friendly hole-transport materials (HTMs) are exceedingly desirable for the practical application of perovskite solar cells (PVSCs). Here, a traditional bidentate ligand (1,10-phenanthroline), widely used as a chelating agent for bioorganic reagents and probes, is incorporated into an HTM to afford M1. Such a planar bidentate ligand at the central core of the HTM can facilitate π–π stacking and enable chelation to Pb2+ ion defects and thus achieve efficient passivation at the M1/perovskite interface, contributing to reduced recombination loss. When employed as an HTM in inverted PVSCs without dopants, bidentate-ligand-based M1 yields a high power conversion efficiency (PCE) of 20.14%, which is significantly higher than that (18.32%) of the M0 analogue that contains phenanthrene. More importantly, green solvent processing (ethyl acetate) of M1 achieves a PCE of 19.21%, which is among the highest values reported in PVSCs with a green-solvent-processable HTM. Besides, the facile one-step synthesis route reduces the cost to 45 $ gram−1 for M1, which is cheaper than the most reported HTMs for high-efficiency PVSCs without dopants. These findings demonstrate the potential of bidentate ligands in developing cost-effective and eco-friendly HTMs toward highly efficient PVSCs.

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.

A bithiophene donor unit, 3-alkoxy-3′-alkyl-bithiophene (TRTOR), was copolymerized with difluorobenzochalcogenadiazole (ffBZ) containing different heteroatoms on its diazole structure to afford a series of PffBZ copolymers (where Z = X, T, Se) with narrow optical bandgaps in the range of 1.34–1.47 eV. The effects of the ffBZ heteroatoms (O, S, and Se) on the optical properties, electrochemical characteristics and film morphologies of the polymers as well as the device performance were fully investigated. The results revealed that the highest occupied molecular orbitals (HOMOs) of the polymers gradually elevated accompanied by their increased materials solubility in common organic solvents as the size of the heteroatoms increased. The PffBZ copolymers exhibited a substantial hole mobility of 0.08–1.6 cm2 V−1 s−1 in organic thin-film transistors (OTFTs). The PffBX, PffBT, and PffBSe-based polymers exhibited maximum power conversion efficiencies (PCEs) of 5.47%, 10.12%, and 3.65%, respectively, in polymer solar cells (PSCs). For the PffBZ copolymers, the alkyl chain exerts a great influence on the morphology of the polymer:PC71BM blend films and hence affect the PCEs in PSCs. It was found that the performance of the polymers with branching on the 2nd position of the alkyl chain and the 3rd position of the alkoxy chain were the best among the PffBT and PffBSe-based polymers, different from the tetrathiophene-based benchmark polymer with branching on the 2nd position of the alkyl chain. X-ray diffraction revealed that all of the PffBZ-based polymers showed obvious face-on dominant orientation, and that chalcogen atoms and branched positions on the alkoxy chain have a great influence on the morphologies of the neat and blend films. The above results indicated that the branching positions and chalcogen atoms should be carefully optimized to maximize performance.

Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) represents the state-of-the-art hole transport material (HTM) in inverted perovskite solar cells (PSCs), however, unsatisfied surface properties of PTAA as well as high energy disorder in the bulk film hinder the further enhancement of device performance. Herein, we strategically develop a simple small molecule 10-(4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)-3,7-bis(4-vinylphenyl)-10H-phenoxazine (MCz-VPOZ) for in-situ crosslinking of polymer hole conductor (CL-MCz) via a facile and low-temperature cross-linking technology. The resulting polymer CL-MCz offers high energy ordering, improved electrical conductivity as well as appropriate energy-level alignment, enabling efficient charge carrier collection in the devices. Meanwhile, CL-MCz synchronously provides satisfied surface wettability and interfacial functionalization, facilitating the formation of high-quality perovskite films with fewer bulk iodine vacancies and suppressed carrier recombination. Significantly, the device with CL-MCz yields a champion power conversion efficiency of 23.9% along with an extremely low energy loss down to 0.41 eV, which represents the highest reported efficiency for non-PTAA based polymer HTMs in inverted PSCs. Furthermore, the corresponding unencapsulated devices exhibited competitive shelf-life stability under various operational stressors up to 2500 hours, reflecting high promises of CL-MCz in the scalable PSC application. This work underscores the promising potential of the cross-linking approach in preparing low-cost, stable and efficient polymer HTMs toward reliable PSCs. This article is protected by copyright. All rights reserved.

Intramolecular noncovalent interactions (INIs) have served as a powerful strategy for accessing organic semiconductors with enhanced charge transport properties. Herein, we apply the INI strategy for developing dopant-free hole-transporting materials (HTMs) by constructing two small-molecular HTMs featuring an INI-integrated backbone for high-performance perovskite solar cells (PVSCs). Upon incorporating noncovalent S⋅⋅⋅O interaction into their simple-structured backbones, the resulting HTMs, BTORA and BTORCNA, showed self-planarized backbones, tuned energy levels, enhanced thermal properties, appropriate film morphology, and effective defect passivation. More importantly, the high film crystallinity enables the materials with substantial hole mobilities, thus rendering them as promising dopant-free HTMs. Consequently, the BTORCNA-based inverted PVSCs delivered a power conversion efficiency of 21.10 % with encouraging long-term device stability, outperforming the devices based on BTRA without S⋅⋅⋅O interaction (18.40 %). This work offers a practical approach to designing charge transporting layers with high intrinsic mobilities for high-performance PVSCs.

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

A new indacenodithiophene-based acceptor–donor–acceptor (A–D–A) type nonfullerene acceptor material ITBTC, featuring a conjugation-extended benzo[b]thiophene-fused end group, was designed and synthesized. Compared to the well known phenyl-fused ITIC acceptor containing a 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) end group, incorporation of an additional electron-rich thiophene into the IC moiety decreased the electron-accepting strength of the end group and increased the intermolecular interactions of ITBTC molecules. As a result, ITBTC exhibited an elevated lowest unoccupied molecular orbital, an improved electron mobility, and a more favorable blend film morphology. Despite its slightly blue-shifted absorption, the photocurrent of ITBTC-based devices was well-maintained due to the extra absorption band in the short wavelength range, which is induced by its conjugation-extended end group. Benefitting from these characteristics, the ITBTC-based solar cells achieved an enhanced power conversion efficiency (PCE) of 10.99% with a simultaneously improved open-circuit voltage (Voc, 0.94 V) and fill factor (FF, 71.3%) and well-maintained short-circuit current density (Jsc, 16.37 mA cm−2), compared to those of the ITIC-based devices (PCE of 9.53%). These results suggest that extending the π-conjugation of end group through thiophene incorporation is an efficient approach for optimizing both the energy level alignment and intermolecular interaction of the acceptor materials while maintaining their efficient light-harvesting ability. Our study also demonstrates the great potential of the new benzo[b]thiophene-fused end group for constructing high-performance nonfullerene acceptors and provided insight into overcoming the trade-off between Jsc and Voc to realize simultaneously enhanced photovoltaic parameters.

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...

Conductive polyelectrolytes such as P3CT-Na have been widely used as efficient hole-transporting layers (HTLs) in inverted perovskite solar cells (PSCs) due to their high hole mobility. However, the acid-base neutralization reaction is indispensable for preparing such polyelectrolytes and the varied content of cations usually leads to poor reproducibility of the device performance in PSCs. In this work, a commercially available polymer poly[3-(4-carboxybutyl)thiophene-2,5-diyl] (P3CT) was directly applied as an HTL in PSCs for the first time. Encouragingly, it was found that due to the dual functionality of carboxyl groups on side chains, a thin layer of P3CT can not only strongly anchor on ITO electrode and optimize its work function but also show an effective passivation effect toward perovskite active layer. Benefiting from such dual functionality, a uniform perovskite film with better quality was obtained on P3CT. As a result, the P3CT-based PSCs show much lower nonradiative recombination and achieve a champion power conversion efficiency (PCE) of 21.33% with a high fill factor (FF) of 83.6%. Impressively, as the device area is increased to 0.80 cm2, a PCE of 19.65% can still be obtained for the PSCs based on P3CT HTL. Our work provides important strategy for developing HTLs for high-performance PSCs.

A new polymer acceptor poly{(N,N'-bis(2-ethylhexyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl)-alt-5,5-(3,3'-didodecyl-2,2'-bifuran)} (NDI-BFR) made from naphthalenediimide (NDI) and furan-derived head-to-head-linked 3,3'-dialkyl-2,2'-bifuran (BFR) units is reported in this study. Compared to the benchmark polymer poly(naphthalenediimide-alt-bithiophene) (N2200), NDI-BFR exhibits a larger bathochromic shift of absorption maxima (842 nm) with a much higher absorption coefficient (7.2 × 104 m-1 cm-1 ), leading to an ultranarrow optical bandgap of 1.26 eV. Such properties ensure good harvesting of solar light from visible to the near-infrared region in solar cells. Density functional theory calculation reveals that the polymer acceptor NDI-BFR possesses a higher degree of backbone planarity versus the polymer N2200. The polymer NDI-BFR exhibits a decent electron mobility of 0.45 cm2 V-1 s-1 in organic thin-film transistors (OTFTs), and NDI-BFR-based all-polymer solar cells (all-PSCs) achieve a power conversion efficiency (PCE) of 4.39% with a very small energy loss of 0.45 eV by using the environmentally friendly solvent 1,2,4-trimethylbenzene. These results demonstrate that incorporating head-to-head-linked BFR units in the polymer backbone can lead to increased planarity of the polymer backbone, reduced optical bandgap, and improved light absorbing. The study offers useful guidelines for constructing n-type polymers with narrow optical bandgaps.

Chemical doping is a key process for investigating charge transport in organic semiconductors and improving certain (opto)electronic devices

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...

Building blocks having a high degree of backbone planarity, good solubilizing characteristics, and well-tailored physicochemical properties are highly desirable for constructing high-performance polymer semiconductors. Due to the detrimental steric hindrance created by alkyl chain substituents at the 3- and 3′-positions of bithiophene, “head-to-head” linkage containing 3,3′-dialkyl-2,2′-bithiophenes (BTR) are typically avoided in materials design. Replacing alkyl chains with less steric demanding alkynyl chains should greatly reduce steric hindrance by eliminating two H atoms at the sp-hybridized carbon center. Here we report the synthesis of a novel electron donor unit, 3,3′-dialkynyl-2,2′-bithiophene (BTRy), and its incorporation into conjugated polymer backbones. The alkynyl-functionalized head-to-head bithiophene linkage yields polymers with good solubility without sacrificing backbone planarity; the BTRy-based polymers show a high degree of conjugation with a narrow bandgap of ∼1.6 eV. When incorpora...

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 (

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.

Currently, n-type acceptors in high-performance all-polymer solar cells (all-PSCs) are dominated by imide-functionalized polymers, which typically show medium bandgap. Herein, a novel narrow-bandgap polymer, poly(5,6-dicyano-2,1,3-benzothiadiazole-alt-indacenodithiophene) (DCNBT-IDT), based on dicyanobenzothiadiazole without an imide group is reported. The strong electron-withdrawing cyano functionality enables DCNBT-IDT with n-type character and, more importantly, alleviates the steric hindrance associated with typical imide groups. Compared to the benchmark poly(naphthalene diimide-alt-bithiophene) (N2200), DCNBT-IDT shows a narrower bandgap (1.43 eV) with a much higher absorption coefficient (6.15 × 104 cm-1 ). Such properties are elusive for polymer acceptors to date, eradicating the drawbacks inherited in N2200 and other high-performance polymer acceptors. When blended with a wide-bandgap polymer donor, the DCNBT-IDT-based all-PSCs achieve a remarkable power conversion efficiency of 8.32% with a small energy loss of 0.53 eV and a photoresponse of up to 870 nm. Such efficiency greatly outperforms those of N2200 (6.13%) and the naphthalene diimide (NDI)-based analog NDI-IDT (2.19%). This work breaks the long-standing bottlenecks limiting materials innovation of n-type polymers, which paves a new avenue for developing polymer acceptors with improved optoelectronic properties and heralds a brighter future of all-PSCs.

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.

In article number 1801743, Xugang Guo and co‐workers develop two phthalimide‐based polymers featuring a D‐A1‐D‐A2 backbone motif. Eliminating benzodithiophene leads to polymers with substantial mobility. Nonfullerene polymer solar cells utilizing these high‐mobility polymers achieve a remarkable power conversion efficiency >13%. The results demonstrate that phthalimides are excellent building blocks for enabling polymer semiconductors with outstanding solar cell performances and benzodithiophenes are not necessary for constructing such polymers.

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%.

We report the design, synthesis, and implemention in semiconducting polymers of a novel head-to-head linkage containing the TRTOR (3-alkyl-3′-alkoxy-2,2′-bithiophene) donor subunit having a single strategically optimized, planarizing noncovalent S···O interaction. Diverse complementary thermal, optical, electrochemical, X-ray scattering, electrical, photovoltaic, and electron microscopic characterization techniques are applied to establish structure–property correlations in a TRTOR-based polymer series. In comparison to monomers having double S···O interactions, replacing one alkoxy substituent with a less electron-donating alkyl one yields TRTOR-based polymers with significantly depressed (0.2–0.3 eV) HOMOs. Furthermore, the weaker single S···O interaction and greater TRTOR steric encumberance enhances materials processability without sacrificing backbone planarity. From another perspective, TRTOR has comparable electronic properties to ring-fused 5H-dithieno[3,2-b:2′,3′-d]pyran (DTP) subunits, but a cen...

Highly efficient nonfullerene polymer solar cells (PSCs) are developed based on two new phthalimide‐based polymers phthalimide‐difluorobenzothiadiazole (PhI‐ffBT) and fluorinated phthalimide‐ffBT (ffPhI‐ffBT). Compared to all high‐performance polymers reported, which are exclusively based on benzo[1,2‐b:4,5‐b′]dithiophene (BDT), both PhI‐ffBT and ffPhI‐ffBT are BDT‐free and feature a D‐A1‐D‐A2 type backbone. Incorporating a second acceptor unit difluorobenzothiadiazole leads to polymers with low‐lying highest occupied molecular orbital levels (≈−5.6 eV) and a complementary absorption with the narrow bandgap nonfullerene acceptor IT‐4F. Moreover, these BDT‐free polymers show substantially higher hole mobilities than BDT‐based polymers, which are beneficial to charge transport and extraction in solar cells. The PSCs containing difluorinated phthalimide‐based polymer ffPhI‐ffBT achieve a substantial PCE of 12.74% and a large V oc of 0.94 V, and the PSCs containing phthalimide‐based polymer PhI‐ffBT show a further increased PCE of 13.31% with a higher J sc of 19.41 mA cm−2 and a larger fill factor of 0.76. The 13.31% PCE is the highest value except the widely studied BDT‐based polymers and is also the highest among all benzothiadiazole‐based polymers. The results demonstrate that phthalimides are excellent building blocks for enabling donor polymers with the state‐of‐the‐art performance in nonfullerene PSCs and the BDT is not necessary for constructing such donor polymers.

A series of difluorobenzoxadiazole-based copolymers are synthesized for applications in high-performance organic thin-film transistors. Four π-spacers with distinct electrical properties, bithiophene, difluorobithiophene, 2-thiophene-2′-thiazole, and bithiazole, are inserted between head-to-head linkage containing bithiophene to promote polymer chain packing. Among the series, polymer containing bithiophene exhibits a unipolar p-channel performance with a substantial hole mobility of 2.92 cm2 V−1 s−1, and minor structural modification leads to polymer containing bithiazole showing a remarkable unipolar n-channel performance with an electron mobility of 0.83 cm2 V−1 s−1. Through a simple structural modification, such a drastic charge carrier polarity change without sacrificing mobility is elusive in organic thin-film transistor field. Polymer containing hybrid 2-thiophene-2′-thiazole spacer exhibits ambipolarity with encouraging hole/electron mobility of 0.27/0.35 cm2 V−1 s−1, and polymer containing difluorobithiophene shows an average hole mobility of 0.53 cm2 V−1 s−1. Among the results, p-channel transistors exhibit encouraging device stability. The results demonstrate that difluorobenzoxadiazole is a versatile building block for enabling high-mobility semiconductors with variable charge carrier polarity. X-ray diffraction reveals that all difluorobenzoxadiazole-based polymers have substantial film crystallinity with close π-stacking and varied polymer chain orientation. The structure–property–device performance correlations from this study offer useful insights for materials innovation in organic thin-film transistors.

A series of donor–acceptor (D–A) conjugated polymers P1–P4 was synthesized by copolymerization of a novel pentacyclic aromatic lactam acceptor unit, thieno[20,30:5,6]pyrido[3,4-g]thieno[3,2-c]-isoquinoline-5,11(4H,10H)-dione (TPTI), with a donor unit, benzo-[1,2-b:4,5-b0]dithiophene (BDT) or dithieno[3,2-b:20,30-d]silole (DTS). The effect of the donor units and the side chains on TPTI on polymer properties and solar cell performance was investigated. Bulk heterojunction solar cells based on P1 and PC71BM afforded the highest power conversion efficiency (PCE) of 5.30%.