Non-fullerene Acceptor Materials Research Articles

Highly efficient ternary polymer solar cells based on a novel double-cabled third component with the same molecular fragments of donor and acceptor moieties

The red-shifting absorption of non-fullerene acceptor materials is the most important reason for the increasing efficiency of polymer solar cells (PSCs). However, the low absorption of non-fullerene materials in the short-wave direction and the full width at half maximum (FWHM) of the absorption spectra for active layer materials are only around 100 nm, which limits the further improvement of power conversion efficiency (PCE). Herein, we report a novel double-cabled material ITLYBT with the same molecular fragments of donor and acceptor moieties. The absorption spectra of ITLYBT are the superimpose of the donor backbones and the acceptor pendants with nearly 200 nm blue-shift caused by the enhanced steric hindrance, which works as an ideal third component for highly efficient ternary PSCs to broaden and complement the absorption spectra of the photoactive layer. By introducing ITLYBT into PBDB-T-2F:ITIC-4F blend, the ternary device shows enhanced Jsc and Voc, and the over PCE increases from 12.50% to 13.14% due to the optimized phased separation and reduced charge recombination. These results indicate that double-cabled molecule is an ideal third component for construction high performance ternary PSCs.

Insight into the optoelectronic characteristics of diimide-based acceptors in organic solar cells by performing DFT calculation and molecular dynamics simulation

In order to compare the main difference of two diimide derivatives on the modulation of electronic and optical properties of P3HT-based organic solar cell, the density functional theory and molecular dynamics simulations were implemented to achieve elementary data on geometrical structure, molecular orbital, open-circuit voltage, absorption spectra, energetic driving force, and interface parameter of P3HT/D1 and P3HT/D2 systems. According to the investigation, P3HT/D1 system not only exhibits higher open circuit voltage and enough energetic driving force than P3HT/D2 system, but also possesses low-lying LUMO +1 orbital which can favor the exciton separation efficiency. Moreover, on the basis of some typical interface models choose from MD simulation, the estimation of the interface rate manifests that the P3HT/D1 interface possesses the smaller charge recombination rates and larger charge separation rates than those of the P3HT/D2 interface. It is expect that this work can provide certain guidelines for the further develop the performance of organic solar cell. We hope this work can further study on non-fullerene acceptor materials as a certain guides.

High-Efficiency Organic Solar Cells With Solution Processable Non-Fullerene Acceptor as an Interlayer

Interlayers and interface engineering plays a pivotal role in achieving efficient charge extraction necessary for realizing high power conversion efficiency (PCE) in bulk heterojunction organic solar cells. In this study, we report a novel strategy of combining advantages of both fullerene derivative and non-fullerene acceptor materials by employing solution processable non-fullerene acceptor 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indan-one))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2’,3’-d’]-s-indaceno[1,2-b:5,6-b’]dithiophene (ITIC) to modify the interface between ZnO-based electron transport layer and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl) benzo [1,2-b;4,5-b'] dithiophe-ne-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carb-oxylate-2-6-diyl)] (PTB7-Th): phenyl-C71-butyric acid methyl ester-based photoactive layer. An improvement in PCE from ∼ 7.5% to ∼ 9% has been achieved for the devices with ITIC modified interlayer. Time resolved photoluminescence (PL) via time correlated single photon counting and photo-electrochemical impedance spectroscopy (photo-EIS) measurements were carried out to investigate the causes for improved PCE for the devices with ITIC modified interlayer.

Computational Study on the Search for Non-Fullerene Acceptors, Examination of Interface Geometry, and Investigation of Electron Transfer

Extensive exploration of new non-fullerene acceptor materials in organic photovoltaics has led to enhancements in their power conversion efficiency. However, a comprehensive search for new non-fullerene acceptors with a detailed investigation of non-fullerene organic photovoltaic interface geometries has not been performed. In this study, we theoretically searched for new non-fullerene acceptors, modeled the interface of a non-fullerene acceptor and polymer, and estimated electron transfer rates for charge transfer and charge recombination processes via the Marcus formula. By examining more than 1850 candidate materials, promising acceptors were found. The theoretical investigation of the interface geometry revealed that steric hindrance restricts the possible interface geometries. Examination of the electron transfer rates suggested that the charge transfer process is more dominant than the charge recombination one, which is advantageous for high power conversion efficiency.

(Invited) Efficient Non-Fullerene Polymer Solar Cells

Polymer solar cell (PSCs) haveattracted much interest in the renewable energy field because of their low-cost manufacturing, light weight, flexibility and large-scale production [1, 2]. Conventional PSCs exhibit poor stability and short operational lifetimes under environment conditions, and thus require complex encapsulation process to reduce degradation under oxygen and moisture [3]. To solve those problems, PSCs with an inverted structure (iPSCs) were developed. In iPSCs, transition metal oxides such molybdenum oxide (MoO3) or vanadium oxide (V2O5) are used as the hole transport layer (HTL). On the other hand, titanium oxide (TiOx) and zinc oxide (ZnO) are used as electron transport layer (ETL) [4, 5]. In recent years, iPSCs with power conversion efficiency (PCE) of 11% has been reported [6]. Although fullerene derivatives (e. g PC71BM and PC61BM), have been widely used as acceptor materials, the interest on non-fullerene acceptors have increased because of their high thermal stability, tunable molecular energy levels, excellent optical absorption properties and low-cost synthesis [7, 8]. In this work, we present the fabrication and the analysis of the performance of iPSCs based on the polymer PBDB-T and the non-fullerene acceptor IT-M. All the devices were fabricated on ITO substrate using TiOx as ETL, while the V2O5/Ag bilayer was used as top cathode. The materials PBDB-T:IT-M were dissolved in a mixture of solvents chlorobenzene and 1,8-diiodooctane (99:0.5 v/v) with the total concentration of 20 mg ml-1. The PBDB-T:IT-M blend solution was spin-cast on top of TiOx at two different velocities to analyze the effect of the active layer thickness (100 and 130nm) on the performance parameters of iPSCs. Moreover, the effects of the annealing temperature (0, 100 and 160ºC) on the performance parameters of PBDB-T:IT-M-based devices are also investigated. Current density–voltage (J–V) characteristics were measured under simulated AM1.5G illumination (100mWcm-2) conditions to calculate the performance parameters [open circuit voltage (VOC), short-circuit current density (JSC), fill factor (FF) and power conversion efficiency (PCE)] of all iPSCs. The devices with an active layer with a thickness of 100nm exhibit higher performance parameter than that of devices with an active layer thickness of 130nm. In both type of devices (active layer thickness of 100 and 130 nm), the performance parameter values decrease as the annealing temperature increases. Devices with an active layer thickness of 100nm and without thermal annealing (0ºC) exhibit the highest performance parameters, VOC= 919 mV, JSC= 16.2 mA cm-2, FF = 67% with an a PCE of about 9.9%. The results demonstrated that iPSCs using non-fullerene acceptor allow to reach efficiencies of about 10% after a manufacturing parameters optimization such as thickness of the active layer and annealing temperature.Moreover, we demonstrated that thermal annealing reduces the performance of these devices. Finally, this work shown the fabrication and characterization of high efficiency PSCs using a non-fullerene acceptor material as a promisingalternative to the fabrication of fullerene-based PSC. Acknowledgements This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (MEIC) for grant numbers, TEC2015-71915-REDT and TEC2015-71324-R (MINECO/FEDER), by the ICREA for the ICREA Academia Award, by the Catalan authority for project AGAUR 2017 SGR 1527. References S. Balderrama, F. Avila-Herrera, J. G. Sanchez, J. Pallares, O. Vigil-Galan, L. F. Marsal, M. Estrada, IEEE J. Photovoltaics, 6, 2, 491–497, 2016.D. Nielsen, C. Cruickshank, S. Foged, J. Thorsen, F. C. Krebs, Sol. Energy Mater. Sol. Cells, 94, 10, 1553–1571, 2010.S. Balderrama, M. Estrada, P. L. Han, P. Granero, J. Pallarés, J. Ferré-Borrull, L. F. Marsal, Sol. Energy Mater. Sol. Cells,125, 155–163, 2014.G. Sánchez, V. S. Balderrama, M. Estrada, E. Osorio, J. Ferré-Borrull, L. F. Marsal, J. Pallarès, Sol. Energy,150, 147–155, 2017.G. Sánchez, V. S. Balderrama, S. I. Garduño, E. Osorio, A. Viterisi, M. Estrada, J. Ferré-Borrull, J. Pallarès, L. F. Marsal, RSC Adv., 8, 24, 13094–13102, 2018.S. Balderrama, J. G. Sánchez, G. Lastra, W. Cambarau, S. Arias, J. Pallarès, E. Palomares, M. Estrada, L. F. Marsal, J. Mater. Chem. A, 6, 45, 2018.Cheng, G. Li, X. Zhan, and Y. Yang, Nat. Photonics, 12, 3, 131–142, 2018.Yan, S. Barlow, Z. Wang, H. Yan, A. K.-Y. Jen, S. R. Marder, and X. Zhan, Nat. Rev. Mater., 3, 3, 18003, 2018. Figure 1

Visible to Near‐Infrared Photodetection Based on Ternary Organic Heterojunctions

AbstractOrganic semiconductors have attracted tremendous attention in the past few years, thanks to their excellent flexibility, solution‐processability, low‐cost, chemical versatility, etc. Particularly, organic solar cells based on ternary heterojunctions have shown remarkable device performance, with the recent development of nonfullerene acceptor materials. These novel materials are also promising for photodetection. However, there are several key limits facing organic photodetectors, such as relatively large bandgaps, poor charge transport, and stability. In this work, a novel nonfullerene acceptor—COi8DFIC—is introduced, blended with a fullerene derivative and a donor to form ternary heterojunctions. After optimization, photodiodes based on such ternary blends exhibit compelling performance metrics, including low dark current, decent responsivity, large linear dynamic range, fast response, and excellent stability. This device performance is actually on a par with the established silicon technology, suggesting great potential for photodetection and imaging.

The binding energy and dynamics of charge-transfer states in organic photovoltaics with low driving force for charge separation

Recent progress in organic photovoltaics (OPVs) has been enabled by optimization of the energetic driving force for charge separation, and thus maximization of open-circuit voltage, using non-fullerene acceptor (NFA) materials. In spite of this, the carrier dynamics and relative energies of the key states controlling the photophysics of these systems are still under debate. Herein, we report an in-depth ultrafast spectroscopic study of a representative OPV system based on a polymer donor PffBT4T-2OD and a small-molecule NFA EH-IDTBR. Global analysis of the transient absorption data reveals efficient energy transfer between donor and acceptor molecules. The extracted kinetics suggest that slow (∼15 ps) generation of charge carriers is followed by significant geminate recombination. This contrasts with the "reference" PffBT4T-2OD:PC71BM system where bimolecular recombination dominates. Using temperature-dependent pump-push-photocurrent spectroscopy, we estimate the activation energy for the dissociation of bound charge-transfer states in PffBT4T-2OD:EH-IDTBR to be 100 ± 6 meV. We also observe an additional activation energy of 14 ± 7 meV, which we assign to the de-trapping of mobile carriers. This work provides a comprehensive picture of photophysics in a system representing new generation of OPV blends with a small driving force for charge separation.

Key Parameters Requirements for Non-Fullerene-Based Organic Solar Cells with Power Conversion Efficiency >20.

The reported power conversion efficiencies (PCEs) of nonfullerene acceptor (NFA) based organic photovoltaics (OPVs) now exceed 14% and 17% for single‐junction and two‐terminal tandem cells, respectively. However, increasing the PCE further requires an improved understanding of the factors limiting the device efficiency. Here, the efficiency limits of single‐junction and two‐terminal tandem NFA‐based OPV cells are examined with the aid of a numerical device simulator that takes into account the optical properties of the active material(s), charge recombination effects, and the hole and electron mobilities in the active layer of the device. The simulations reveal that single‐junction NFA OPVs can potentially reach PCE values in excess of 18% with mobility values readily achievable in existing material systems. Furthermore, it is found that balanced electron and hole mobilities of >10−3 cm2 V−1 s−1 in combination with low nongeminate recombination rate constants of 10−12 cm3 s−1 could lead to PCE values in excess of 20% and 25% for single‐junction and two‐terminal tandem OPV cells, respectively. This analysis provides the first tangible description of the practical performance targets and useful design rules for single‐junction and tandem OPVs based on NFA materials, emphasizing the need for developing new material systems that combine these desired characteristics.

Molecular designing of four high performance pyrazine-based non-fullerene acceptor materials with naphthalene diimide-based small organic solar cells.

We design four high performance non-fullerene acceptor materials by applying strong electron withdrawing groups at the end of A-D-A-D-A type organic solar cells molecules and compute their different opto-electronic and photovoltaic properties, including absorption spectrum, electron density, solubility strength, charge mobilities for electrons and holes, stability of HOMO/LUMO energy orbitals, excitation energies required for charge transfer mechanisms, and morphology of device with the help of DFT approaches using the principles of quantum mechanics. The newly designed molecules showed strong absorption bands between 420 to 650nm, low HOMO energy values from -7.24 to -7.28eV, large % ETC from 35 to 65%, and small excitation energies from 2.28 to 2.47eV in the organic solvent chloroform; 410 to 620nm, 31 to 64%, and 2.42 to 2.56eV, respectively, in gas phase conditions. Solubility strengths of the newly designed molecules were also high, varying from 5.3039 to 18.4749 Debye in the ground and excited states. Power conversion efficiencies of the designed molecules are expected to be high because they show better results than the R molecule. Open circuit voltages of designed molecules range from 3.67 to 3.54V with respect to the PCBM. Reorganization energies for electron transport vary from 0.0153 to 0.0175eV and for hole transport from 0.0231 to 0.0254eV. This computational study proves that the newly designed molecules with non-fullerene acceptors are superior and thus are recommended for the future construction of high performance organic solar cells devices. Graphical Abstract Orbital's energy comparisons of four newly designed non-fullerene acceptor materials with naphthalene diimide-based small organic solar cells.

Correction: Quad-rotor-shaped non-fullerene electron acceptor materials with potential to enhance the photoelectric performance of organic solar cells

Correction for ‘Quad-rotor-shaped non-fullerene electron acceptor materials with potential to enhance the photoelectric performance of organic solar cells’ by Chuang Yao et al., J. Mater. Chem. A, 2019, DOI: 10.1039/c9ta04084f.

Quad-rotor-shaped non-fullerene electron acceptor materials with potential to enhance the photoelectric performance of organic solar cells

We proposed two novel quad-rotor-shaped non-fullerene electron acceptor materials, which exhibit much better optoelectronic properties than that of the widely used non-fullerene acceptor ITIC.

Constructing a donor–acceptor linear-conjugation structure for heterologous perylene diimides to greatly improve the photovoltaic performance

Th-4PDI, a new donor–acceptor-type non-fullerene electron acceptor material, was designed and synthesized for high efficiency organic solar cells.

High lying energy of charge-transfer states and small energetic offsets enabled by fluorinated quinoxaline-based alternating polymer and alkyl-thienyl side-chain modified non-fullerene acceptor

Abstract Significant driving forces are the prerequisite to achieve fast and efficient charge separation in fullerene derivatives-based polymer solar cells to achieve high power conversion efficiency (PCE). However, the large driving forces both in photo-induced hole transfer (PHT) and in photo-induced electron transfer (PET) processes lead to significant energy losses, resulting in low open-circuit voltage in the devices. Recent studies indicate the driving forces in non-fullerene acceptors-based devices can be reduced to very low values but still with high PCE and low energy losses. Herein, we report a new donor:acceptor system with high lying energy of charge-transfer excitons (ECT) of 1.50 eV and very small driving forces (PHT of 0.28 eV and PET of 0.11 eV), in which a fluorinated quinoxaline-based alternating polymer (FTQ) and an alkyl-thienyl side-chain modified small molecule (ITIC-Th) are taken as the donor material and non-fullerene acceptor material, respectively. A high power conversion efficiency (PCE) of 8.19% with maximal external quantum efficiency of 71% are achieved successfully in FTQ:ITIC-Th-based device after appropriate thermal annealing treatment, indicating FTQ can be further applied as donor materials with other highly efficient NF-acceptors to achieve enhanced performances and low energy losses.

Ternary blend organic solar cells with a non-fullerene acceptor as a third component to synergistically improve the efficiency

Ternary blends, where an additional component is added to a donor/acceptor blend, represent a promising route to improve upon the performance of organic solar cells. Non-fullerene acceptor materials are particularly suited for this application due to their relatively stronger absorption coefficients and tuneable molecular energy levels. This paper demonstrates a ternary blend solar cell by incorporating a promising non-fullerene acceptor, IDFBR, into a PffBT4T-2OD:PC71BM blend. The addition of IDFBR to this blend leads to the formation of a cascading energy band structure in the device, which is required for the operation of an efficient ternary system. Ternary blend solar cells with an IDFBR concentration of 5 wt% demonstrated improved photovoltaic performance, when compared to the host binary blends. This improved performance was attributed to a reduction in energetic disorder and improved charge carrier transport in the ternary blend.

Angular-Shaped 4,9-Dialkylnaphthodithiophene-Based Octacyclic Ladder-Type Non-Fullerene Acceptors for High Efficiency Ternary-Blend Organic Photovoltaics

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

Nonfullerene Acceptor Molecules for Bulk Heterojunction Organic Solar Cells.

The bulk-heterojunction blend of an electron donor and an electron acceptor material is the key component in a solution-processed organic photovoltaic device. In the past decades, a p-type conjugated polymer and an n-type fullerene derivative have been the most commonly used electron donor and electron acceptor, respectively. While most advances of the device performance come from the design of new polymer donors, fullerene derivatives have almost been exclusively used as electron acceptors in organic photovoltaics. Recently, nonfullerene acceptor materials, particularly small molecules and oligomers, have emerged as a promising alternative to replace fullerene derivatives. Compared to fullerenes, these new acceptors are generally synthesized from diversified, low-cost routes based on building block materials with extraordinary chemical, thermal, and photostability. The facile functionalization of these molecules affords excellent tunability to their optoelectronic and electrochemical properties. Within the past five years, there have been over 100 nonfullerene acceptor molecules synthesized, and the power conversion efficiency of nonfullerene organic solar cells has increased dramatically, from ∼2% in 2012 to >13% in 2017. This review summarizes this progress, aiming to describe the molecular design strategy, to provide insight into the structure-property relationship, and to highlight the challenges the field is facing, with emphasis placed on most recent nonfullerene acceptors that demonstrated top-of-the-line photovoltaic performances. We also provide perspectives from a device point of view, wherein topics including ternary blend device, multijunction device, device stability, active layer morphology, and device physics are discussed.

Recent Progress in Ternary Organic Solar Cells Based on Nonfullerene Acceptors

AbstractThe use of a ternary component is a facile and effective method to further improve the device performances of binary organic solar cells (OSCs) comprising one donor and one acceptor. Recently, the rapid progress of highly efficient nonfullerene acceptor materials has offered a new opportunity for studying ternary OSCs because of the flexibility of ternary components, and the photovoltaic performance of ternary OSCs has been promoted quickly. In this research news article, some strategies for materials selection of the ternary components are concisely summarized and the recent progress in ternary OCSs based on nonfullerene acceptors, and the challenges and perspectives of ternary OSCs are also presented.

Triplet Tellurophene-Based Acceptors for Organic Solar Cells.

Triplet materials have been employed to achieve high-performing organic solar cells (OSCs) by extending the exciton lifetime and diffusion distances, while the triplet non-fullerene acceptor materials have never been reported for bulk heterojunction OSCs. Herein, for the first time, three triplet molecular acceptors based on tellurophene with different degrees of ring fusing were designed and synthesized for OSCs. Significantly, these molecules have long exciton lifetime and diffusion lengths, leading to efficient power conversion efficiency (7.52 %), which is the highest value for tellurophene-based OSCs. The influence of the extent of ring fusing on molecular geometry and OSCs performance was investigated to show the power conversion efficiencies (PCEs) continuously increased along with increasing the extent of ring fusing.

Improved photovoltaic performance of bilayer small molecular solar cells via geometrical rearrangement of active materials

Nowadays, non-fullerene electron transport material for the fabrication of organic photovoltaic devices has become one of extensive issue of research. But unfortunately, it has been observed that the replacements of the fullerene acceptors with non-fullerene acceptor materials typically led down the device efficiency. In this article, improvement in photovoltaic response of bilayer solar cells based on small molecular Zinc Phthalocyanine (ZnPc) and non-fullerene acceptor material (Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)) is reported via their geometrical rearrangement. The structural and optical property of ZnPc and PTCDA thin films were investigated using SEM, AFM, XRD and UV–vis absorption spectroscopy and their role on device performance is discussed in detail. It has been observed that the photovoltaic performance of the devices in PTCDA/ZnPc layer sequence exhibits 8 times higher value of JSC with almost double VOC that collectively shows 15 times higher value of the device efficiency as compared to the devices with ZnPc/PTCDA layer sequence. The results show that ZnPc and PTCDA exhibit complimentary absorption spectra but it would be efficient only if the materials are deposited in right sequence.

Morphological characterization of fullerene and fullerene-free organic photovoltaics by combined real and reciprocal space techniques

Abstract