Acceptors For Polymer Solar Cells Research Articles

(Invited) Reactivity on Endohedral Metallofullerenes

Endohedral metallofullerenes (EMFs) are fullerene molecules with unique host-guest structures that allow chemists to manipulate encapsulated metal ions with the arsenal of organic chemistry, for potential applications including spin-quantum computing, single-molecule magnets, dynamic nuclear polarization, artificial photosynthesis, magnetic resonance imaging contrast agents, and therapeutic agents. To unleash the power to do so, the development of new reactions for EMFs has been an ongoing task.A key step to improve the solubility of EMFs as well as to obtain new materials for multiple applications is via exohedral functionalization. In medicine, for instance, water-soluble gadofullerenols are used as powerful contrast agents.1 Besides, the external groups might impart complementary features to EMFs that tune their physical properties for use as acceptors in polymer solar cells or as donor-acceptor dyad conjugates.2 Among the most used methods to obtain EMF monoadducts are cycloaddition reactions and radical additions, including the Diels-Alder cycloaddition, Bingel-Hirsch cyclopropanation, Prato 1,3-dipolar addition, carbene addition, etc. In these reactions, fullerenes typically play a similar electron-accepting role, thus their reactivity and regioselectivity are highly consistent. However, the reactivity of EMFs is far more complicated than of empty fullerenes due to the relatively low molecular symmetry and the influence of the encapsulated species. To understand the role of metal-cage interactions on the reactivity of EMFs is desirable for tuning their chemical reactivity.Here, we report the functionalization of actinide endofullerenes, in particular, the mono-EMFs U@C s(4)-C82 and U@C 2v(9)-C82, which their chemical reactivities were investigated through the Bingel-Hirsch (nucleophilic addition) and carbene addition (electrophilic addition) reactions. Interestingly, only for U@C 2v(9)-C82, the Bingel-Hirsch reaction leads to mono-adduct and multi-adduct compounds. Another subgroup of EMF that we study its reactivity here is the nitride clusterfullerenes, especially the Lu3N@Ih-C80, with high stability and high production yields, that results its chemical modification to be challenging. In this case, the reaction studied is the inverse-electron demand Diels-Alder (IEDDA) reaction and it will be compared to the corresponding reactivity on C60 fullerene. We show that Lu3N@Ih-C80presents higher reactivity than for C60, as well as, different features. 1Bolskar, R. D.; Benedetto, A. F.; Wilson, L. J.; Alford, J. M. et al. J. Am. Chem. Soc. 2003, 125, 5471-5478. 2Ross, R. B.; Cardona, C. M.; Guldi, D. M. et al. Nature Mater. 2009, 8, 208-212. Figure 1

Recent advances and prospects of asymmetric non-fullerene small molecule acceptors for polymer solar cells

Recently, polymer solar cells developed very fast due to the application of non-fullerence acceptors. Substituting asymmetric small molecules for symmetric small molecule acceptors in the photoactive layer is a strategy to improve the performance of polymer solar cells. The asymmetric design of the molecule is very beneficial for exciton dissociation and charge transport and will also fine-tune the molecular energy level to adjust the open-circuit voltage (V oc) further. The influence on the absorption range and absorption intensity will cause the short-circuit current density (J sc) to change, resulting in higher device performance. The effect on molecular aggregation and molecular stacking of asymmetric structures can directly change the microscopic morphology, phase separation size, and the active layer's crystallinity. Very recently, thanks to the ingenious design of active layer materials and the optimization of devices, asymmetric non-fullerene polymer solar cells (A-NF-PSCs) have achieved remarkable development. In this review, we have summarized the latest developments in asymmetric small molecule acceptors (A-NF-SMAs) with the acceptor–donor–acceptor (A–D–A) and/or acceptor–donor–acceptor–donor–acceptor (A–D–A–D–A) structures, and the advantages of asymmetric small molecules are explored from the aspects of charge transport, molecular energy level and active layer accumulation morphology.

Front Cover: Subphthalocyanine‐Diketopyrrolopyrrole Conjugates: 3D Star‐Shaped Systems as Non‐Fullerene Acceptors in Polymer Solar Cells with High Open‐Circuit Voltage (ChemPlusChem 10/2021)

The Cover shows a toy doll holding an umbrella which represents a non-planar, highly conjugated subphthalocyanine-diketopyrrolopyrrole hybrid molecule for non-fullerene organic solar cells. When the sun shines on the umbrella, it absorbs the light, and the doll slides down a polymeric flexible solar cell like a slide, where electrons are produced and electricity flows into the magic wand to illuminate the room. Cover design by Carlos M. Ramos based on an idea by Tomás Torres and Ángela Sastre-Santos. More information can be found in the Full Paper by A. Sastre-Santos, L. F. Marsal, T. Torres and co-workers.

Subphthalocyanine-Diketopyrrolopyrrole Conjugates: 3D Star-Shaped Systems as Non-Fullerene Acceptors in Polymer Solar Cells with High Open-Circuit Voltage.

Invited for this month's cover are the collaborating groups of Prof. Ángela Sastre-Santos, Universidad Miguel Hernández, Prof. Lluis F. Marsal, Universitat Rovira i Virgili and Prof. Tomás Torres, Universidad Autónoma de Madrid, Spain. The cover shows a toy doll holding an umbrella which represents a non-planar, highly conjugated subphthalocyanine-diketopyrrolopyrrole hybrid molecule for non-fullerene organic solar cells. When the sun shines on the umbrella, it absorbs the light, and the doll slides down a polymeric flexible solar cell like a slide, where electrons are produced and electricity flows into the magic wand to illuminate the room. More information can be found in the Full Paper by Ángela Sastre-Santos, Lluis F. Marsal, Tomás Torres, and co-workers.

Subphthalocyanine-Diketopyrrolopyrrole Conjugates: 3D Star-Shaped Systems as Non-Fullerene Acceptors in Polymer Solar Cells with High Open-Circuit Voltage.

Four star-shaped electron acceptors (C1 -OPh, C3 -OPh, C1 -Cl and C3 -Cl) based on a subphthalocyanine core bearing three diketopyrrolopyrrole wings linked by an acetylene bridge have been synthesized. These derivatives feature two different axial substituents (i. e., 4-tert-butylphenoxy (OPh) or chlorine (Cl)) and for each of them, both the C1 and the C3 regioisomers have been investigated. The four compounds exhibit a broad absorption band in the 450-700 nm region, with bandgap values near to 2 eV. These materials were applied in the active layer of inverted bulk-heterojunction polymer solar cells in combination with the donor polymer PBDB-T. Derivatives bearing the OPh axial group showed the best performances, with C1 -OPh being the most promising with a PCE of 3.27 % and a Voc as high as 1.17 V. Despite presenting the widest absorption range, the photovoltaic results obtained with C1 -Cl turned out to be the lowest (PCE=1.01 %).

Femtosecond Transient Absorption Studies of Polymer Aggregation on Photovoltaic Performance: Role of an Integrated Aggregation Promotor in the Polymer Chain

To establish molecular design rules for the donor polymers matching well with both fullerene and nonfullerene acceptors in polymer solar cells (PSCs), we investigated the effect of polymer aggregat...

A small molecular acceptor based on dithienocyclopentaindenefluorene core for efficient fullerene-free polymer solar cells

In recent years, acceptor–donor–acceptor (A–D–A) type of small molecules have become very promising non-fullerene acceptors (NFAs) to overcome the energy levels and absorption drawbacks of the fullerene-based acceptors in polymer solar cells (PSCs). A non-fullerene small-molecular acceptor named DTIF-IC with dithienocyclopentaindenefluorene (DTIF) as the electron-donating core sealed with 2-(3-oxo-indane-1-ylidene)-malononitrile as the electron-withdrawing groups was developed. The molecule exhibits strong absorption in the range from 550 to 720 nm and relatively high-lying lowest unoccupied molecular orbital (LUMO) energy level (−3.86 eV). Due to its up-shifted LUMO energy levels, high and balanced charge mobility and the homogeneous nanophase separations, the inverted polymer solar cells blending with the donor polymer poly[[2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]-[3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl]] (PTB7-Th) and DTIF-IC deliver a best power conversion efficiency (PCE) of 7.84% with relatively high open circuit voltage (Voc) of 0.95 V by thermal annealing treatment, which demonstrated that the DTIF-type small molecule could be the promising electron acceptor for high-performance polymer solar cells with a high Voc.

A Pyrrole‐Fused Asymmetrical Electron Acceptor for Polymer Solar Cells with Approaching 16% Efficiency

Selecting suitable aromatic rings to develop asymmetric small‐molecule acceptors (SMAs) is of great significance. Herein, two asymmetric SMAs, namely, BTN‐4F and BTSe‐4F, are successfully synthesized by incorporating pyrrole and selenophene unit into the cores, respectively. Compared with the selenophene‐fused counterpart BTSe‐4F, BTN‐4F displays slightly upshifted energy levels and red‐shifted absorption spectrum (about 40 nm in film) due to the strong electron‐donating ability of N atoms in pyrrole. When matching with PM6, the BTN‐4F‐based device gives a higher power conversion efficiency (PCE) (15.82%) due to the simultaneously enhanced open circuit voltage (VOC), short‐circuit current density (JSC), and fill factor (FF), compared with those of the BTSe‐4F‐based device. The higher VOC coincides with the shallower lowest unoccupied molecular orbital (LUMO) energy level of BTN‐4F; the enhanced JSC mainly results from the broadened and enhanced absorption; the increased FF can be ascribed to the weaker bimolecular recombination, more balance charge transport, and more favorable morphology. It should be mentioned that the BTN‐4F‐based device yields a lower energy loss than that of the BTSe‐4F‐based device. Overall, the work demonstrates that pyrrole‐fused SMAs shows great potential in realizing low Eloss while yielding high JSC and PCE, which paves a new way to develop high‐performance SMAs.

Enhancement of photovoltaic efficiency through fine adjustment of indacene‐based non‐fullerene acceptor by minimal chlorination for polymer solar cells

AbstractTwo non‐fullerene small molecule acceptors (NFSMAs, BThIND‐Cl and BThIND) with an A–D–A configuration containing indacenedithiophene donor core unit and terminal unit with IC (BThIND) and chlorinated IND were synthesized for their application as an acceptor in polymer solar cells (PSCs). Compared to BThIND, the chlorinated molecule BThIND‐Cl exhibits lower energy levels and red‐shifted absorption spectrum but also exhibits improved crystallinity and molecular packing. These two NFSMAs are used as acceptors along with a well‐known conjugated polymer PM6, that exhibits complementary absorption to both NFSMAs, and has suitable frontier energy levels (highest occupied molecular orbital at –5.47 eV and lowest unoccupied molecular orbital at 3.61 eV) as a donor, in fabricating PSCs. Having optimized the active layers, the PSC based on PM6: BThIND‐Cl showed higher power conversion efficiency (PCE) of 12.36% and a fill factor (FF) of 0.71 than that of PM6: BThIND counterpart (PCE = 8.04% with a FF of 0.66). Moreover, for the PM6: BThIND‐Cl based PSC a quite high open‐circuit voltage of 0.96 V was achieved in addition to a low energy loss of 0.53. Notably higher short circuit current and FF value were found for the BThIND‐Cl based PSCs that are attributed to originate from the measured high values of charge carrier mobilities (and more balanced), to an advantageous nanoscale morphology, and finally to increased efficiency of exciton dissociation as compared to BThIND counterparts. These results demonstrate that substitution of the single chlorine atom in the IC terminal unit of A–D–A NFSMA is sufficient to enhance the PCE of PSCs

A wide-bandgap nonplanar small molecule acceptor having indenofluorene core for non-fullerene polymer solar cells

Recently, the nonplanar non-fullerene acceptors (NFAs) are attractive in active layers in highly efficient polymer solar cells (PSCs) because of their up-shifted energy levels, improved absorption as well as charge transportation performances. However, presently nonplanar NFAs always absorb the lights in the long-wavelength region and even to near-infrared (NIR) region, which limits their further utilization in low-bandgap polymer donor-based PSCs. To further probe the performances of nonplanar NFAs in low-bandgap polymer-based PSCs, a new twisted NFA (i-IF-4F) having indenofluorene derivatives as the electron-donating fused-ring core was synthesized. Due to the relatively weak electron-donating ability of the indenofluorene core, this newly designed NFA has wide optical bandgap (1.79 eV) with absorption spectrum ranged from 450 to 690 nm, suitable lowest unoccupied molecular orbital (LUMO, −3.71 eV) and highest occupied molecular orbital (HOMO, −5.55 eV) energy levels, which ensure its matching well with the typically low-bandgap polymer (PTB7-Th) to achieve complementary absorption and proper differences in energy levels. After thermal annealing treatment, the film morphologies, charge transfer properties and charge recombination performances of i-IF-4F:PTB7-Th-based device was improved to a certain degree, leading to an optimized power conversion efficiency (PCE) of 6.47%. The work in this manuscript demonstrates the applicability of wide-bandgap twisted acceptors in PSCs and the possible approach to further improve the performances of wide-bandgap nonplanar acceptors in PSCs.

Introduction of Siloxane-Terminated Side Chains into Semiconducting Polymers To Tune Phase Separation with Nonfullerene Acceptor for Polymer Solar Cells.

In this work, five PTB7-Th-based conjugated polymers (PTB7-Th, PTBSi20, PTBSi25, PTBSi33, and PTBSi100) with different contents of siloxane-terminated pentyl side chain were synthesized, and properties of corresponding blend films with narrow band gap nonfullerene IEICO-4F acceptor were extensively investigated. According to the contact angle testing, the PTB7-Th with 100% alkyl side chain and PTBSi100 100% siloxane-terminated side chain on the benzodithiophene unit showed surface energy values of 40.04 and 34.52 mJ/m2, respectively. The results demonstrate that relative to alkyl side chain in PTB7-Th, the siloxane-terminated side chain could effectively reduce the surface energy of a resulting polymer. Based on Flory-Huggins interaction parameter estimations, the miscibility between the polymer and IEICO-4F would vary in an order of PTB7-Th > PTBSi20 > PTBSi25 > PTBSi33 > PTBSi100, suggesting that siloxane-terminated side chain would afford a tunable driving force for phase separation. Transmission electron microscopy and Raman mapping could confirm large bulk domains inside the PTBSi100:IEICO-4F blend film. In polymer solar cells, the blend film of the PTBSi100 with the lowest miscibility to IEICO-4F showed an undesirable power conversion efficiency (PCE) of 8.52%, which was significantly lower than that of 11.23% for PTB7-Th, suggesting that too large phase separation driving force is not beneficial for the device performance. Side-chain random copolymers PTBSi20, PTBSi25, and PTBSi33 for fine tuning could display PCEs of 11.94, 12.61, and 11.80%, respectively, all higher than that of PTB7-Th. Our results not only reveal the big surface energy difference between the siloxane-terminated side chain and the common alkyl side chain but also provide a guideline for side chain engineering of conjugated polymer donors with tunable morphology and optimal matching with a nonfullerene acceptor.

Visible to Near‐Infrared‐Absorbing Polymers Containing Bithiazole and 2,3‐Didodecyl‐6,7‐Difluoroquinoxaline Derivatives for Polymer Solar Cells

Electron donor and electron acceptor materials for solution‐processable polymer solar cells (PSCs) should ideally exhibit a narrow band gap (Eg) and high solubility for improved performance. Herein, we synthesized two new near‐infrared‐absorbing alternating polymers, namely P(BTz‐FQ) and P(BTz‐DTFQ), via Stille polymerization of 4‐butoxy‐5‐(4‐butoxy‐2‐(trimethylstannyl)thiazol‐5‐yl)‐2‐(trimethylstannyl)thiazole and 5,8‐dibromo‐2,3‐didodecyl‐6,7‐difluoroquinoxaline or 5,8‐bis(5‐bromothiophen‐2‐yl)‐2,3‐didodecyl‐6,7‐difluoroquinoxaline. The absorption spectra of P(BTz‐FQ) and P(BTz‐DTFQ) ranged from 300 to 900 nm with two distinct absorption maxima at 718 and 800 nm and 665 and 718 nm, respectively. Both polymers exhibited an identical Eg of 1.41 eV, which is the lowest value reported for quinoxaline‐based polymers to date. Their highest occupied (−5.04 and −5.09 eV) and lowest unoccupied (−3.63 and −3.68 eV) molecular orbital levels were suitable for their use as electron donors along with the fullerene derivative, [6,6]‐phenyl C71 butyric acid methyl ester, as the electron acceptor in PSCs. The maximum power conversion efficiencies obtained for the PSCs utilizing P(BTz‐FQ) and P(BTz‐DTFQ) were 0.51% and 0.71%, respectively. These findings demonstrate that thiazole and fluoroquinoxaline derivatives are promising materials for PSCs and other optoelectronic devices.

Polymer solar cells based on spontaneously-spreading film with double electron-transporting layers

Abstract Although metal oxides such as ZnO are frequently used in inverted polymer solar cells (PSCs) to serve as an electron-transporting layer, how to effectively improve its interface with the photoactive layer is still an open question. In this study, we exploited small-molecule (SM) compounds usually used as electron acceptors in PSCs to act as an interlayer on ZnO and constructed an SM/ZnO double electron-transporting layer to improve the device's photovoltaic performance. To avoid the solvent erosion to SM interlayer during the deposition of upper-layer film, spontaneously-spreading-film technique was employed to prepare the photoactive layer. We used two SM acceptors (ITIC and IDT-BOC6) with different energy levels to serve as the interlayer. Results show that devices based on ITIC interlayer, which has similar LUMO level with materials in its adjacent layers, possess a better electron-transporting ability than IDT-BOC6 based ones which lack of such an energy-level structure. Moreover, SM interlayer is beneficial to flatten the interface and improves the contact between the electron-transporting layer and the photoactive layer. Consequently, we demonstrate a new way to improve the collection of electrons in PSCs by using commonly available electron acceptors, which provides a large choosability in interfacial materials.

A conjugated polymer based on alkylthio-substituted benzo[1,2-c:4,5-c’]dithiophene-4,8-dione acceptor for polymer solar cells

In this work, the 2,5-di(alkyl)thiophene unit was replaced with a 2,5-di(alkylthio)thiophene moiety on benzo [1,2-c:4,5-c’]dithiophene-4,8-dione (BDD) unit. The di(alkylthio) substituted BDD was used to obtain a novel copolymer PSBDB-T via Stille polymerization. PSBDB-T shows good solubility and excellent thermal stability. The opto-electronic properties of PSBDB-T were investigated. PSBDB-T has a broad absorption range from 300 nm to 700 nm and deep highest occupied molecular orbital (HOMO) level due to the alkylthio units, which can improve the open-circuit voltage. A solar cell based on PSBDB-T as donor and a near infrared absorbing non-fullerene acceptor achieves a power conversion efficiency (PCE) of 5.0%, which is lower than its analogous polymer PBDB-T with a PCE of 8.8%. The studies of organic field-effect transistors and space charge limited current (SCLC) measurement indicate that PSBDB-T shows a significantly low hole mobility, which is responsible for the low photocurrent and fill factor in solar cells.

Tuning the molecular packing and energy levels of fullerene acceptors for polymer solar cells

Two novel fullerene acceptors were synthesized and applied in polymer solar cells, and the importance of functional groups in tuning the molecular packing and energy levels for the design of fullerene acceptors was demonstrated.

Polythiophene derivatives compatible with both fullerene and non-fullerene acceptors for polymer solar cells

In this work we report three novel polythiophene derivatives which perform well in both fullerene- and non-fullerene-based polymer solar cells.

Bithiazole-based copolymer with deep HOMO level and noncovalent conformational lock for organic photovoltaics

To match with the state-the-art-of non-fullerene acceptor for polymer solar cells (PSCs), it is urgent to develop high performance wide-bandgap (WBG) copolymer donors with deep highest occupied molecular orbital (HOMO) level and highly planar backbone to further promote the device efficiency. A new WBG copolymer PBDTBTz, poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithi ophene))-alt-(5,5’-(-4,4’-dinonyl-2,2’-bithiazole))], which is based on benzodithiophene (BDT) as donor unit and 4,4’-dinonyl-2,2’-bithiazole (BTz) as acceptor unit is prepared for non-fullerene PSCs. Due to the strong electron-withdrawing effect, BTz unit can dramatically lower the HOMO level of PBDTBTz to −5.60 eV. Notably, double noncovalent conformational locks (N⋯S) of BTz are formed in the backbone to reduce the steric hindrance and favor a highly planar geometry for efficient charge transport and molecular packing. As a result, the device based on PBDTBTz as donor and 3,9-bis(2-methylene-((3-(1,1-dic-yanomethylene)-6,7-difluoro)-indanone))-5,5,11, 11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d']-s-indaceno[1,2-b:5,6-b']dithiophen e(IT-4F) as acceptor afforded a high open circuit voltage (Voc) of 0.92 V, which is the highest value for IT-4F-based PSCs reported so far. Furthermore, the device operated well with a negligible driving force (ΔEHOMO) of as small as 0.06 eV. These results revealed that combination of electron-withdrawing bithiazole and double noncovalent conformational lock of N⋯S is a promising molecular design concept of polymer donor with deep and planar structure for high performance PSCs.

Recent Progress in Fused-Ring Based Nonfullerene Acceptors for Polymer Solar Cells.

The progress of bulk-heterojunction (BHJ) polymer solar cells (PSCs) is closely related to the innovation of photoactive materials (donor and acceptor materials), interface engineering, and device optimization. Especially, the development of the photoactive materials dominates the research filed in the past decades. Photoactive materials are basically classified as p-type organic semiconductor donor (D) and an n-type organic semiconductor acceptor (A). In the past two decades, fullerene derivatives are the dominant acceptors for high efficiency PSCs. Nevertheless, the limited absorption and challenging structural tunability of fullerenes hinder further improve the efficiency of PSCs. Encouragingly, the recent progresses of fused-ring based A-D-A type nonfullerene acceptors exhibit great potential in enhancing the photovoltaic performance of devices, driving the power conversion efficiency to over 13%. Such kind of nonfullerene acceptors is usually based on indacenodithiophene (IDT) or its extending backbone core and end-caped with strong electron-withdrawing group. Owing to the strong push-pulling effects, the acceptors possess strong absorption in the visible-NIR region and low-lying HOMO (highest occupied molecular orbital) level, which can realize both high open-circuit voltage and short-circuit current density of the devices. Moreover, the photo-electronic and aggregative properties of the acceptors can be flexibly manipulated via structural design. Many strategies have been successfully employed to tune the energy levels, absorption features, and aggregation properties of the fused-ring based acceptors. In this review, we will summarize the recent progress in developing highly efficient fused-ring based nonfullerene acceptors. We will mainly focus our discussion on the correlating factors of molecular structures to their absorption, molecular energy levels, and photovoltaic performance. It is envisioned that an analysis of the relationship between molecular structures and photovoltaic properties would contribute to a better understanding of this kind of acceptors for high-efficiency PSCs.

Rational synthesis of a polymerizable fullerene–aniline derivative: study of photophysical, morphological and photovoltaic properties $$^{\S }$$ §

This paper describes the synthesis of a polymerizable, aniline appended fullerene derivative, 3-aminobenzyl-phenyl- $$\hbox {C}_{61}$$ -butyrate (PCBAn) and its corresponding polymer (P-PCBAn), and detailed photophysical and morphological analysis towards application as an acceptor in polymer solar cells (BHJ-PSCs). The poly-3-aminobenzyl-phenyl- $$\hbox {C}_{61}$$ -butyrate (P-PCBAn), having a substituted polyaniline (PANI) skeletal structure, was synthesized via $$\hbox {FeCl}_{3}$$ oxidative polymerisation of PCBA in its non-conducting leucoemaraldine state. HOMO and LUMO energies estimated using optical and electrochemical techniques revealed upshifted LUMO levels for PCBAn ( $$-$$ 3.68 eV, $$\Delta \hbox {E} = 0.1$$ eV) and P-PCBAn ( $$-$$ 3.66 eV, $$\Delta \hbox {E} = 0.12$$ eV) compared to the parental fullerene derivative, PCBM ( $$-$$ 3.78 eV). The morphologies of PCBAn and P-PCBAn individually and in polymer blends with P3HT were investigated using AFM and TEM analysis, which showed nanoflake-like aggregates for P3HT/PCBAn and a favourable interconnected nanonetwork structure for P3HT/P-PCBAn. The wide angle X-ray scattering (WAXS) studies of PCBAn films drop-cast from THF/water (3:7) mixture and P-PCBAn films drop-cast from 1,2-dichlorobenzene exhibited plane reflections of lamellar mesophases with d-spacing of 3.4 nm and 3 nm for PCBAn and P-PCBAn, respectively. The fluorescence quenching experiments with P3HT indicated efficient electron transfer from P3HT to P-PCBAn when compared to PCBAn. The fabrication of an inverted BHJ-PSC device using PCBAn and P-PCBAn as an acceptor in combination with P3HT showed PCE of 0.9% and 1.1%, respectively, showing considerable enhancement in the case of the polymeric acceptor. The polymeric acceptor and the rational design strategy used here could open up new opportunities in the PSC device fabrication. Ref.: Ms. No. JCSC-D-18-001042 SYNOPSIS Synthesis of a polymerizable, aniline appended fullerene derivative, 3-aminobenzyl-phenyl- $$\hbox {C}_{61}$$ -butyrate (PCBAn) and its corresponding polymer, and detailed photophysical and morphological analysis towards application as acceptor in polymer solar cells (BHJ-PSCs) are reported. The results suggest bicontinuous interpenetrating network and better charge transport properties for P3HT:P-PCBAn polymer blend compared to P3HT:PCBAn.

Highly twisted ladder-type backbone bearing perylene diimides for non-fullerene acceptors in organic solar cells

A ladder-type π-system PDIPY that bearing perylene diimide and pyrene units have been developed for constructing non-fullerene acceptors. The vinyl bridged PDIPY dimer PDIPY-V and polymer PPDIPY-V have been synthesized via bromonation and Stille coupling recation. PDIPY-V and PPDIPY-V exhibit intense and broad absorption within 400–650 nm that complement the absorption spectra of the narrow bandgap polymeric donors. DFT calculation indicated that PDIPY-V and PPDIPY-V hold highly twisted structure, which prevent the formation of π−π stacking and crystallization in the aggregated states. The grazing-incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM) investigations confirmed the amorphous nature of the pure films and the PDIPY-V/PPDIPY-V:PTB7-Th blend films. The PDIPY-V:PTB7-Th based photovoltaic device showed a poor performance due to the small LUMO offset of donor and acceptor. While the PPDIPY-V:PTB7-Th based device showed a high PCE of 5.20%, indicating the PDIPY derivatives are promising non-fullerene acceptors for polymer solar cells.