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A high VOC (0.936 V) was obtained in P(TBDPDI-TT)-based all-PSCs. This study demonstrates that the fusing of PDI units to form a large coplanar aromatic system is an effective strategy for improving the VOC of all-PSCs based on PDI acceptor polymers.

Layer-by-layer (LBL) sequential solution processing of the active layer has been proven as an effective strategy to improve the performance of organic solar cells (OSCs), which could adjust vertical phase separation and improve device performance. Although perylene diimide (PDI) derivatives are typical acceptors with excellent photoelectric properties, there are few studies on PDI-based LBL OSCs. Herein, three PDI acceptors (TBDPDI-C5, TBDPDI-C11, and SdiPDI) were used to fabricate LBL and bulk heterojunction (BHJ) OSCs, respectively. A series of studies including device optimization, photoluminescence (PL) quenching, dependence of light intensity, carrier mobility, atomic force microscopy (AFM), transmission electron microscopy (TEM), grazing-incidence wide-angle X-ray scattering (GIWAXS), and depth analysis X-ray photoelectron spectroscopy (DXPS) were carried out to make clear the difference of the PDI-based LBL and BHJ OSCs. The results show that LBL OSCs possess better charge transport, higher and more balanced carrier mobility, less exciton recombination loss, more favorable film morphology, and proper vertical component distribution. Therefore, all the three PDI acceptor-based LBL OSCs exhibit higher performance than their BHJ counterparts. Among them, TBDPDI-C5 performs best with a power conversion efficiency of 6.11% for LBL OSCs, higher than its BHJ OSC (5.14%). It is the first time for PDI small molecular acceptors to fabricate high-efficiency OSCs by using an LBL solution-processed method.

In this study, wide bandgap (WBG) two-dimensional (2D) copolymer donors (DZ1, DZ2, and DZ3) based on benzodithiophene (BDT) on alkoxyphenyl conjugated side chains without and with different amounts of chlorine atoms and difluorobenzotriazole (FBTZ) are designed and synthesized successfully for efficient non-fullerene polymer solar cells (PSCs). Three polymer donors DZ1, DZ2, and DZ3 display similar absorption spectra at 300–700 nm range with optional band-gap (Egopt) of 1.84, 1.92, and 1.97 eV, respectively. Compared with reported DZ1 without chlorine substitution, it is found that introducing chlorine atoms into the meta-position of the alkoxyphenyl group affords polymer possessing a deeper the highest occupied molecular orbital (HOMO) energy level, which can increase open circuit voltage (VOC) of PSCs, as well as improve hole mobility. Non-fullerene bulk heterojunction PSCs based on DZ2:MeIC demonstrate a relatively high power conversion efficiency (PCE) of 10.22% with a VOC of 0.88 V, a short-circuit current density (JSC) of 17.62 mA/cm2, and a fill factor (FF) of 68%, compared with PSCs based on DZ1:MeIC (a PCE of 8.26%) and DZ3:MeIC (a PCE of 6.28%). The results imply that adjusting chlorine atom amount on alkoxyphenyl side chains based on BDT polymer donors is a promising approach of synthesizing electron-rich building block for high performance of PSCs.

In this contribution, readily available 5-methyl furfural (MF) derived from biomass was used as an excellent substitute of the chemically unstable 5-hydroxymethylfurfural (HMF) for preparing the commercial precursor 2,5-furandicarboxylic acid (FDCA). MF was catalytically oxidized by air into FDCA in acetic acid over homogeneous Co/Mn/Br catalysts at 130–170 °C. It was found that both the substitute reactivity and the ring chemical stability have a remarkable impact on the yield of aromatic dicarboxylic acids. The effects of reaction temperature, pressure, catalyst composition and concentration, water concentration in the solvent, and substrate/solvent mass ratio on both the main reaction and the side reaction were investigated systematically and thoroughly using HPLC and an online tail gas monitoring system. Under optimized conditions, the oxidation of MF gave 100% conversion of MF and 75.8% yield of FDCA with 99.6% purity. It was also proven that the addition of 200 ppm cerium could work well at low temperatures (130–140 °C) for enhancing FDCA selectivity via suppressing the side reactions.

Subnaphthalocyanine triimides (SubNcTIs) as solution processable electron acceptors were designed and synthesized by introducing three electron-withdrawing imide groups to subnaphthalocyanines. Their solubility and crystallinity could be adjusted conveniently by substituents at imide terminals or boron atoms. Their absorption, electrochemistry, thermal properties, and applications as electron acceptors in bulk heterojunction organic solar cells (BHJOSCs) were investigated. SubNcTIs with strong absorption at 300–750 nm, maximum extinction coefficient of up to 16.8 × 104 M−1 cm−1, and deep lowest unoccupied molecular orbital energy levels (−3.79 to −3.90 eV) are expected to be excellent electron acceptors. The four SubNcTIs exhibit good thermal stability, with 5% weight loss at a temperature higher than 350 °C. Blending with the donor polymer of PTQ10, BHJOSCs based on acceptor 9b gave the highest power conversion efficiency (PCE) of 6.25%, which is the highest value among the solution processable cyanine family. Space-charge-limited current (SCLC), charge recombination, and charge collection ability measurements showed that PTQ10:9b devices have a high and balanced carrier mobility, less charge recombination, and better charge transport, which lead to high photovoltaic performance. Grazing incidence wide-angle X-ray scattering (GIWAXS) measurements revealed that relatively strong π–π stacking and large correlation lengths of PTQ10:9b films are favorable for charge transfer, which caused a high Jsc of corresponding solar cells. This study demonstrates that SubNcTIs as a promising chromophore could be used to construct potential electron acceptors.

Controlling the morphological stability of non-fullerene polymer solar cells (NF-PSCs) is a critical process for improving photovoltaic performances. In many systems, liquid additives have been widely used to produce favorable morphological features; however, liquid additives frequently leave residues after thermal treatment owing to their high boiling points, which has detrimental effects on the reproducibility of NF-PSCs. In this study, commercially available and volatilizable solid additives, 9,10-anthracenedione (BDT-1) and benzo[1,2-b:4,5-b′]dithiophene-4,8-dione (BDT-2), are selected to coordinate the molecular arrangement to enhance absorption intensity, charge transfer, and molecular crystallinity. Suppressed bimolecular recombination and a favorable balance between the domain size and relative domain purity were observed with the introduction of both solid additives, which improved the photovoltaic parameters of NF-PSCs. PM6:TPT10-based devices with BDT-1 and BDT-2 additives achieved the best power conversion efficiencies (PCEs) of 16.26% and 15.18%, respectively, which were better than the 13.55% achieved with a 1,8-diiodooctane (DIO) additive. Other NF-PSC systems of PBDB-T:TPT10 and PTQ10:TPT10 blends also showed that the photovoltaic performance with the solid additives is superior to that with liquid additives. These results imply that the use of solid additives is a promising strategy to improve the PCEs of NF-PSCs.

2,5-Furandicarboxylic acid (FDCA), a versatile platform chemical, can be widely used for synthesizing various polymers and has the potential to replace terephthalic acid in the green polymer indust...

The conventional bulk heterojunction (BHJ) structure is widely used for fabricating high-performance organic solar cells (OSCs) due to the nanometer-scale phase separation of the donor/acceptor component. However, the elaborate control of the BHJ morphology is difficult to carry out because the morphology evolution is such a complicated process. The compatibility requirement of materials in the same solvent restricts the structural diversity of the molecules to some extent. Meanwhile, the nanoscopic interpenetrating donor/acceptor domains reduce their crystallinity. The bilayer planar heterojunction (PHJ), by contrast, possesses complementary advantages that can make it an alternative candidate to achieve device fabrication and produce different vertical stratification in heterojunction films. However, the flat contact area limits the charge separation and transmission efficiency. The sequential solution processed approach was used to facilitate material diffusion in layers. Also, solvent additives were employed to further enhance the diffusion and thus the device performance. Nevertheless, the morphology of the formed pseudo-bilayer planar heterojunction (PPHJ) has not been fully revealed yet. Here, we carefully study the morphology of the nonfullerene-based PPHJ device in three dimensions. High hole mobility of 2.09 × 10-4 cm2 V-1 s-1 and electron mobility of 7.91 × 10-5 cm2 V-1 s-1 were obtained in the solution-processed PPHJ device. Meanwhile, a distinct phase separation size with a vertical rearrangement of donor and acceptor was observed, which enable the pseudo-bilayer devices to be equipped with a comparable spectral response to the BHJ devices. We demonstrate that a unique device architecture (ITO/ZnO/PBDB-T/ITIC/MoO3/Ag) with a power conversion efficiency of 7% can be obtained from a larger molecular weight of PBDB-T without using extra additives. The solution-processed PPHJ films have much in common with the BHJ films. The results proposed that with appropriate molecular design and vertical phase separation optimization, the performance of the solution-processed PPHJ-based OSCs can be further improved.

In this study, a series of random conjugated polymers (PBDB-TBTn) as donors were designed and synthesized. In these polymers, benzodithiophene unit with thiophene conjugated side chains (BDT) are donor part, and two different content of benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) and difluorobenzothiadizole (BT) linked alkylthiophene are acceptor unit. Polymer solar cells (PSCs) were fabricated with ITIC as an acceptor, and over the power conversion efficiency (PCE) of 9% was obtained, with open circuit voltage (Voc) of 0.86 V, short-circuit current density (Jsc) of 16.84 mA/cm2, and fill factor (FF) of 62.5%. These random conjugated polymers based solar cells are insensitive to solvent additives and thermal annealing. The performance of the device decreases gradually with the increasing of the proportion of fluorinated acceptor unit. The declining efficiency is due to the excessive fluorinated acceptor unit, which leads to over aggregated topography, destroys the effective charge transport pathways, and affects phase separation domain size between the donor and the acceptor. The phenomena are explained by the charge carrier recombination, atomic force microscope (AFM), and transmission electron microscope (TEM). These results indicate that proper addition of fluorinated acceptor units to build random copolymers can enhance the efficiency of organic photovoltaics toward additive-free and thermal annealing-free PSCs.

Ten subphthalocyanine triimides (SubPcTI) with different substituents at imide sites and B atoms were designed and synthesized. These compounds with low-lying lowest unoccupied molecular orbital energy levels (from -3.91 to -3.98 eV), strong absorption in the range of 450-650 nm, and adjustable solubility are expected to be excellent electron acceptors. Non-fullerene bulk heterojunction organic solar cells based on acceptor 8c showed power conversion efficiency of 4.92%, which is the highest value among subphthalocyanine derivatives.

Naphthalocyanine derivatives (SiNcTI-N and SiNcTI-Br) were firstly used as excellent cathode interlayer materials (CIMs) in organic solar cells, via introducing four electron-withdrawing imide groups and two hydrophilic alkyls. Both of them showed deep LUMO energy levels (below -3.90 eV), good thermal stability (Td >210 °C), and strong self-doping property. The SiNcTI-Br CIM displayed high conductivity (4.5×10-5 S cm-1 ) and electron mobility (7.81×10-5 cm2 V-1 s-1 ), which could boost the efficiencies of the PM6:Y6-based OSCs over a wide range of CIM layer thicknesses (4-25 nm), with maximum efficiency of 16.71 %.

Correction for ‘Non-halogenated-solvent-processed highly efficient organic solar cells with a record open circuit voltage enabled by noncovalently locked novel polymer donors’ by Hui Guo et al., J. Mater. Chem. A, 2019, 7, 27394–27402.

The side-chain conjugation strategy is adopted in the synthesis of heptacyclic non-fullerene electron acceptors, ITIC2, ITIC-S, and ITIC-SF, for application in organic solar cells (OSCs). The new ITIC-SF molecule features a BDT-SF building block which is the electron-donating component in the widely used donor PBDB-T-SF. Compared with ITIC-S without fluorine substituents, fluorination weakens the crystallinity of ITIC-SF, while the intermolecular interaction between the PBDB-T-SF donor and ITIC-SF acceptor, containing the same BDT-SF building block, results in the increased crystallinity of the corresponding blend films. The OSC based on PBDB-T-SF:ITIC-SF exhibits a champion power conversion efficiency (PCE) of 12.1%, higher than the PCE of 10.1% for the device based on PBDB-T-SF:ITIC2 and the PCE of 11.6% for the device based on PBDB-T-SF:ITIC-S. The better photovoltaic performance of the OSC based on PBDB-T-SF:ITIC-SF is benefitted from the weaker bimolecular recombination and more efficient charge transfer and extraction of the device. The structure–property relationship of the non-fullerene acceptors revealed in this work will play an important role in instructing the molecular structure design of high performance photovoltaic materials for the development of OSCs.

Since dibromo perylene diimides (DBPDIs) contain two isomers that are difficult to separate, isomeric effect on properties and applications of PDI polymers has been rarely studied. Few ladder-type polymers have been used in organic solar cells. Herein, single-strand polymers (PrPDIT) were synthesized by the polymerization of regioisomerically-pure 1,7-dibromo-PDIs (1,7-DBPDIs) and 2,5-bis(trimethylstannyl)thiophene. Furthermore, ladder-type polymers (FPrPDIT) were obtained by the highly efficient photo-induced cyclization of polymers PrPDIT. The effects of isomers and molecular weight on the absorption, electrochemistry, thermal stability, and photovoltaic application of polymers were studied. Pure 1,7-DBPDIs lead to polymers with molecular weight distribution as low as 1.08. These polymers with strong absorption in 300–700 nm, low-lying lowest unoccupied molecular orbital (LUMO) energy levels around −4.0 eV and high thermal stability could be excellent electron acceptors. Regioisomerically-pure polymers demonstrate better photovoltaic performance than that of mixed ones. The highest power conversion efficiency (PCE) of all-polymer solar cells based on PrPDIT and FPrPDIT is up to 5.95% and 4.52% respectively.

With the development of non-fullerene organic solar cells, more and more conductive materials are available for bulk-heterojunction (BHJ) active layers. Matching of the two materials in all aspects, including energy alignment, absorption complementation, BHJ morphology etc., is very critical to obtain a high performance device. In this work, three analogues of ITIC, ITIC-F and ITIC-Th1 with different end-capping groups or side-chains were selected as non-fullerene acceptors (NFAs) for an alkylsilyl functionalized copolymer donor (PBDS-T), to reveal the basic matching principle of the donor and acceptor for optimizing the active layer morphology. We found that the interaction between the donor and acceptor, the crystallinity of each component and the difference in the surface tensions greatly impact the morphology of blend films and device performance. Such a significant change can be realized by a subtle variation of the NFA structure. As a result, the power conversion efficiency (PCE) is boosted from 10.72% to 12.04%, together with a dramatically improved fill factor (FF) of 60% for PBDS-T:ITIC, 66% for PBDS-T:ITIC-F and 70% for PBDS-T:ITIC-Th1, respectively. Note that the PCE of 12.04% is one of the best values for the devices based on alkylsilyl functionalized copolymers reported so far.

Random conjugated terpolymers (RCTs) not only promote great comprehension and realization for the state-of-the-art highly effective non-fullerene organic solar cells (OSCs) but also offer a simple and practical synthetic strategy. However, the photovoltaic properties of RCTs yet lagged behind that of the donor-acceptor (D-A) alternating copolymer, especially in additive-free devices. Hence, we developed two feasible "double-acceptor-type" random conjugated terpolymers, PBDB-TAZ20 and PBDB-TAZ40. The additive-free OSCs based on PBDB-TAZ20:ITIC and PBDB-TAZ40:ITIC exhibit decent efficiencies of 12.34 and 11.27%, respectively, which both surpass the PBDB-T:ITIC-based device. For RCTs, the reasonably weakened crystallinity and the reduced phase separation degree are demonstrated to help in improving charge transport, reducing bimolecular recombination, and thus enhancing the photovoltaic performance of additive-free OSCs. The results imply that adding a third moiety into the D-A polymer donors provides a simple but efficient synthetic approach for high-performance OSCs.

Two silicon naphthalocyanine electron acceptors, CH3O-SiNcTI and 3BSO-SiNcTI, with four strong electron-withdrawing imide groups, were designed, synthesized, and applied in bulk heterojunction organic solar cells (BHJ OSCs). They exhibited strong near-infrared absorption in 300–1100 nm, maximum extinction coefficients of up to 5.2 × 105 M−1 cm−1, deep lowest unoccupied molecular orbital energy levels of −3.92 eV, and good photothermal stability. The power conversion efficiency of BHJ OSCs based on acceptor of 3BSO-SiNcTI reached 4.22%, which is the highest value among solution-processable phthalocyanine or naphthalocyanine derivatives. The measurements of space-charge-limited current, charge recombination, charge collection capability, atomic force microscopy (AFM), and transmission electron microscopy (TEM) were carried out. It is found that BHJ OSCs based on PTB7-Th:3BSO-SiNcTI, have higher and balanced carrier mobility, less charge recombination, better charge transport, and favorable film morphology, which lead to their higher photovoltaic performance. This study indicates the great potential of SiNcTIs as near-infrared chromophores for high-performance electron acceptors in BHJ OSCs.

Organic solar cells based on narrow bandgap small-molecule acceptors (SMAs) with highly crystalline characteristics have attracted great attentions for their superiority in obtaining high photovoltaic efficiency. Employing highly crystalline SMAs to enhance power conversion efficiencies (PCEs) by regulating and controlling morphology and compatibility of donor and acceptor materials has turned out to be an effective approach. In this study, we synthesized three different crystalline SMAs by using fluorine substitution on alkoxyphenyl conjugated side chains to modulate the relationship of crystallinity and morphologies, namely ZY1 (zero F atoms), ZY2 (two F atoms), and ZY3 (four F atoms). The three SMAs show the broad absorption edges and similar frontier orbital energy levels, generating the analogical (over 0.9 ​V) open circuit voltage (VOC) of the polymer solar cells (PSCs). As a result, the PM6:ZY2-based PSCs yield a PCE of 10.81% with a VOC of 0.95 ​V, a short-circuit current density (JSC) of 16.154 ​mA ​cm−2, and a fill factor (FF) of 0.71, which is higher than that of 9.17% (PM6:ZY1) and 6.37% (PM6:ZY3). And the PCE (17.23%) of the PM6:Y6:ZY2 based ternary PSCs is also higher than that of 16.32% PM6:Y6 based binary device. Obviously, the results demonstrate that adding fluorine atoms on the conjugated side chains to construct high crystalline materials is a positive strategy to effectively increase the efficiencies of binary and ternary PSCs.

1,4,8,9-Naphthalene diimides (NDIs) with strong electron accepting ability and high stability are excellent building blocks for semiconductor polymers. However, 1,8-naphthalene monoimide (NMI) with similar structure and energy levels as that of NDI has never been used to construct conjugated polymers because of synthetic difficulty. Herein, 3,6-dibromo-NMI (DBNMI) with bulky alkyl groups was obtained effectively in a four-step synthesis, and three donor-acceptor (D-A) type conjugated polymers based on NMI were firstly prepared. These polymers have strong absorption in the range of 300–600 nm, low LUMO level of 3.68 eV, and moderate bandgaps of 2.18 eV. Space charge limiting current measurements indicate these polymers are typical electron transporting materials, and the highest electron mobility is up to 5.8 × 10−3 cm2 V−1 s−1, which is close to the star acceptor based on NDI (N2200, 5.0 × 10−3 cm2 V−1 s−1). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

Perylene diimides (PDIs) and their derivatives are excellent semiconductors, while conjugated polymers based on PDIs have limited applications because of their low electron mobility (μe) derived from low molecular weight. The reported maximum number-average molecular weight (Mn) of related polymers is only 21 kDa because PDIs have very poor solubility due to strong π–π stacking of their big planar conjugated cores. Herein, it is found that suitable semi-perfluoroalkyl groups could enhance the solubility of PDIs significantly, and a series of semi-perfluoroalkyl modified conjugated polymers with high molecular weight and electron mobility were synthesized. The maximum Mn reaches 94.8 kDa [P(4CF8CH-PDI-T2)HW]. In their space-charge-limited current (SCLC) devices, all polymers exhibit typical characters of electron transporting semiconductors, and the highest μe is up to 8.40 × 10−3 cm2 V−1 s−1 [P(4CF8CH-PDI-T2)HW], which is similar as that of widely used electron transporting semiconductor PC61BM (6.41 × 10−3 cm2 V−1 s−1). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017.

Twisted benzodiperylenediimides (TBDPDI) with large rigid conjugated core and strong absorption is regarded as an excellent acceptor in non-fullerene solar cells. Since side chains of semiconductors play a crucial role in the solar cells, TBDPDI acceptors with different side chains (1-ethylpropyl, C5; 2-ethylhexyl, C8; 1-pentylhexyl, C11; 2-octyldodecyl, C20; 1-undecyldodecyl, C23) were synthesized. In solution, TBDPDI compounds (C5, C11, and C23) with alkyl chains branched at 1-position show significantly different absorption profiles and fluorescence intensity with those (C8 and C20) branched at 2-position, due to stronger aggregation of the latter. Nevertheless, alkyl chains have little effect on the molecular orbital energy levels and optical band gaps, as verified by cyclic voltammetry and solid state absorption. Due to their complementary absorption and matchable energy levels with donor of PCE10, these acceptors and PCE10 were used together to fabricate bulk heterojunction (BHJ) solar cells. Because of inferior phase separation with large domain size around 100 nm and bulky insulated side chains, acceptors (C20 and C23) with long alkyl chains have the low electron mobility (μe) around 10−8 cm2 V−1 s−1 and the low power conversion efficiency (PCE) of solar cells. TBDPDI (C11) with 1-pentylhexyl gives the highest PCE of 5.0% under the optimized condition, which is attributed to proper phase separation with domain size around 20 nm and highest μe of 10−6 cm2 V−1 s−1.

Electron acceptors based on perylene monoimide (PMI) are rare due to the synthetic challenge. Herein, starting from commercially available perylene dianhydride, brominated perylene monoimide (PMI-Br) with short side chains and good solubility was efficiently synthesized in a high overall yield of 71%. With PMI-Br as the intermediate, acceptor-donor-acceptor type electron acceptors with low-lying LUMO energy levels and strong visible absorption were successfully obtained. The nonfullerene bulk heterojunction solar cells based on these acceptors were fabricated with the highest PCE of 1.3%.

Two n-type conjugated D-A copolymers with perylene diimide (PDI) as acceptor unit and benzodithiophene (BDT) as donor unit, P(PDI-BDT-Ph) and P(PDI-BDT-Th), were synthesized and applied as electron acceptor in all-polymer solar cells (all-PSCs). P(PDI-BDT-Ph) and P(PDI-BDT-Th) films exhibit similar absorption spectra in the visible region with optical bandgap (Eg) of 1.65 eV and 1.55 eV respectively, and the identical LUMO level of −3.89 eV. The all-PSCs based on P(PDI-BDT-Ph) as acceptor and PTB7-Th as donor demonstrated a power conversion efficiency (PCE) of 4.31% with a short-circuit current density (Jsc) of 11.94 mA cm−2, an open-circuit voltage (Voc) of 0.81 V, and a fill factor (FF) of 44.49%. By contrast, the corresponding all-PSCs with P(PDI-BDT-Th) as acceptor showed a relative lower PCE of 3.58% with a Jsc of 11.36 mA cm−2, Voc of 0.79 V, and FF of 40.00%.

A small-molecule nonfullerene acceptor, ITIC-S, bearing a fused heptacyclic benzodi(cyclopentadithiophene) core with a thioether-bond-substituted thiophene, is designed, synthesized, and compared with its alkyl-substituted analog, ITIC2. Compared with ITIC2, ITIC-S with a thioether bond exhibits higher electron mobility, a slightly larger optical band gap, and similar absorption. The active layer incorporating ITIC-S and the wide-bandgap polymeric donor PBDB-T-SF displays a smaller crystalline coherent length of π-π stacking, more balanced mobilities, weaker bimolecular recombination, and more effective charge collection than its PBDB-T-SF:ITIC2 counterpart. Accordingly, polymer solar cells incorporating ITIC-S and PBDB-T-SF demonstrate a fill factor (FF) of 66.8% and a champion power conversion efficiency (PCE) of 11.6%, exceeding those of the PBDB-T-SF:ITIC2 blend (PCE = 10.1%, FF = 59.7%), which shows that the thioether bond substitution strategy is an easy yet viable way for designing high-performance electron acceptors.

A series of perylene diimide derivatives (PDIs) with near infrared (NIR) absorption and different geometries were synthesized by introducing 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) and 4-butyl-1,2,4-triazoline-3,5-dione (BuTAD) to the bay position of PDIs through the Diels–Alder reaction. The compounds with various twisted three-dimensional (3D) structures were obtained through combining different connection units, and their aggregation and domain size of the donor-acceptor blends were adjusted. All of these compounds exhibit broad absorption in the range of 300–860 nm, high thermal stability (with a decomposition temperature over 350 °C), applicable lowest unoccupied molecular orbital energy levels (−3.70 ~ −3.74 eV), and appropriate solubility. Blending with a PM6 polymer donor, bulk heterojunction organic solar cells (BHJ OSCs) based on BDT-SBuTADPDI2 exhibited the highest power conversion efficiency of 2.74%. Their carrier mobility and morphology were investigated by Space-charge-limited current (SCLC) measurements and Atomic Force Microscopy (AFM) measurements respectively. This study provides a promising strategy to construct potential PDI-based acceptors with NIR absorption.

Inherent safety and stability issues arising from the use of traditional organic liquid electrolytes in lithium-based batteries are currently limiting their application to flexible electronics and large-scale energy storage from renewable sources. Gel polymer electrolytes (GPE) with chemical cross-linked structures and green ionic liquids as plasticizers represent a solution to this problem. In this study, a novel type of GPE with an interpenetrating polymer network (IPN-GPE) is prepared by a simple in situ thermally induced free radical polymerization. The as-prepared IPN-GPE with cross-linked structure displays a combination of high flexibility and deformability as well as thermal stability (over 310 °C). Moreover, IPN-GPE possesses a superior electrochemical stability window (5 V vs. Li+/Li) as well as a considerable ionic conductivity of 1.3 × 10−3 S cm−1 at 30 °C. Therefore, with such an IPN-GPE gel electrolyte membrane, Li/IPN-GPE/LiFePO4 devices deliver superior stable charge/discharge profiles and remarkable cycling performance and rate capability. This simple, effective and low-cost in situ synthesis strategy makes IPN-GPE one of the most promising polymer electrolyte candidates for next generation rechargeable lithium-based batteries with highly elevated electrochemical performance and safety.

Mainstream organic solar cells (OSCs) suffer a great variation of photovoltaic performance among different batches of polymers, which brings an opportunity for all-small-molecule OSCs to take leading position of industrialization. In recent years, benzodithiophene terthiophene rhodamine (BTR), as small molecule donor, has played an important role in this field. Here we investigated two typical BTR based all-small-molecule OSCs processed with different annealing methods, to explore the morphology optimization brought by them. As a result, BTR:PC71BM system was optimized by solvent vapor annealing (SVA) reaching an excellent fill factor (FF) of 79.1% via tuning molecular packing intensity, while BTR:Y6 with temperature annealing (TA) yielded a power conversion efficiency (PCE) of 12.125% whose molecular packing orientation had been changed. Additionally, by crossing using SVA and TA methods, we found that these two method can't be utilized together to further improve the PCE for either system. Therefore, our work offers better PCEs for these two reported combinations and further studies the compatibility between specific BTR based active layers and designated annealing methods, providing deeper understanding of device engineering on all-small-molecule OSCs.

Given that the ring-fusion strategy can effectively tail the electrical, optical, and structural properties of π-conjugated materials, we have herein developed Y-series non-fullerene acceptors with a dual acceptor–donor–dual acceptor-type structure, bearing non-fused bare bithiophene (Y–Th2), hexagonal ring-fused bithiophene (Y-BDT), or pentagonal ring-fused bithiophene (Y-CDT) central donor units. Several characterization techniques were applied to perform a comparative investigation of their optical and physical properties and frontier energy levels with respect to the different ring-fusion of the central units. Moreover, for the cascade energy level alignment, the synthesized acceptors were employed as a third component in the PM6:Y6 that served as a binary host platform. The introduction of the optimal amount of Y–Th2 or Y-BDT into the host system improved the device performance. Specifically, Y–Th2 exhibited the best power conversion efficiency (PCE) (16.01%) along with improved photovoltaic parameters, whereas the addition of Y-CDT impaired the PCE. Moreover, the optimized Y–Th2-based ternary organic solar cell achieved a PCE of 22.72% under indoor illumination at 1000 lux. Thus, the in-depth structural, morphological, and electrical analyses not only established a structure–property correlation, but also provided better design criteria for the guest-oriented non-fullerene acceptors for ternary photovoltaic applications, especially for Y6-containing systems.

Organic solar cell (OSC) has achieved great progress in the past few years. Power conversion efficiency (PCE) has stepped into a new stage due to the evolution of non-fullerene acceptors (NFAs). The gap between lowest unoccupied molecular orbit of acceptor and highest occupied molecular orbit of donor (|ELUMOA-EHOMOD|) is proportional to the value of open circuit voltage (VOC). Applying two similar polymeric donors with different energy levels offers possibility of changing VOC without significantly impacting short circuit current (JSC) and fill factor (FF). Here we chose halogenated polymers PM6 and PM7 as donors to cope with a newly design asymmetric molecule TPIC-4Cl derived from IT-4Cl. As a result, the PM7:TPIC-4Cl device achieved a PCE of 15.1% than its PM6:TPIC-4Cl counterparts (14.4%), wherein the improvement of VOC from 0.855 V to 0.885 V contributed most. Our work proves the feasibility of improving photovoltaic performance of NFA OSCs by utilizing polymeric donors with similar structure yet different HOMOs. Besides, the PCE over 15% of OSCs involving no Y6 or its derivatives sheds light on another direction of OSC research.

Organic-inorganic hybrid heterostructures have attracted considerable attentions due to their wide application in electronics and optoelectronics. In this study, a high-performance red light photodetector based on organic-inorganic heterostructure was successfully fabricated after a systematical optimization in material and device constitution. The conjugated polymer (P(PDI-BDT-O)) with narrow band gap used as light absorber was combined with a layer of indium gallium zinc oxide (IGZO) to construct a bi-layered phototransistor achieving a high mobility as well as high photoresponsivity. Benefiting from both the high absorption coefficient of the polymer over a wide range of wavelength and the perfect matching of band level between polymer and IGZO, the device exhibits an ultrahigh photoresponsivity (212 A/W) and specfic detectivity (2 × 1012 Jones) for red light at the wavelength of 633 nm. These results demonstrate the great potential of organic-inorganic heterostructures in the application of long-wavelength photodetectors.

High-efficiency organic solar cells (OSCs) can be produced through optimization of component molecular design, coupled with interfacial engineering and control of active layer morphology. However, vertical stratification of the bulk-heterojunction (BHJ), a spontaneous activity that occurs during the drying process, remains an intricate problem yet to be solved. Routes toward regulating the vertical separation profile and evaluating the effects on the final device should be explored to further enhance the performance of OSCs. Herein, we establish a connection between the material surface energy, absorption, and vertical stratification, which can then be linked to photovoltaic conversion characteristics. Through assessing the performance of temporary, artificial vertically stratified layers created by the sequential casting of the individual components to form a multilayered structure, optimal vertical stratification can be achieved. Adjusting the surface energy offset between the substrate results in donor and acceptor stabilization of that stratified layer. Further, a trade-off between the photocurrent generated in the visible region and the amount of donor or acceptor in close proximity to the electrode was observed. Modification of the substrate surface energy was achieved using self-assembled small molecules (SASM), which, in turn, directly impacted the polymer donor to acceptor ratio at the interface. Using three different donor polymers in conjunction with two alternative acceptors in an inverted organic solar cell architecture, the concentration of polymer donor molecules at the ITO (indium tin oxide)/BHJ interface could be increased relative to the acceptor. Appropriate selection of SASM facilitated a synchronized enhancement in external quantum efficiency and power conversion efficiencies over 10.5%.