Non-fullerene Small Molecule Acceptors Research Articles

Exploring structure-property landscape of non-fullerene acceptors for organic solar cells.

We present a comprehensive analysis of the structure-property relationship in small molecule non-fullerene acceptors (NFAs) featuring an acceptor-donor-acceptor configuration employing state-of-the-art quantum chemical computational methods. Our focus lies in the strategic functionalization of halogen groups at the terminal positions of NFAs as an effective means to mitigate non-radiative voltage losses and augment photovoltaic and photophysical properties relevant to organic solar cells. Through photophysical studies, we observe a bathochromic shift in the visible region for all halogen-functionalized NFAs, except type-2, compared to the unmodified compound. Most of these functionalized compounds exhibit exciton binding energies below 0.3eV and ΔLUMO less than 0.3eV, indicating their potential as promising candidates for organic solar cells. Selected candidate structures undergo an analysis of charge transport properties using the semi-classical Marcus theory based on hopping transport formalism. Molecular dynamics simulations followed by charge transport simulations reveal an ambipolar nature of charge transport in the investigated NFAs, with equivalent hole and electron mobilities compared to the parent compound. Our findings underscore the crucial role of end-group functionalization in enhancing the photovoltaic and photophysical characteristics of NFAs, ultimately improving the overall performance of organic solar cells. This study advances our understanding of the structure-property relationships in NFAs and provides valuable insights into the design and optimization of organic solar cell materials.

High-efficiency flexible organic solar cells with a polymer-incorporated pseudo-planar heterojunction

Organic solar cells (OSCs) are considered as a crucial energy source for flexible and wearable electronics. Pseudo-planar heterojunction (PPHJ) OSCs simplify the solution preparation and morphology control. However, non-halogenated solvent-printed PPHJ often have an undesirable vertical component distribution and insufficient donor/acceptor interfaces. Additionally, the inherent brittleness of non-fullerene small molecule acceptors (NFSMAs) in PPHJ leads to poor flexibility, and the NFSMAs solution shows inadequate viscosity during the printing of acceptor layer. Herein, we propose a novel approach termed polymer-incorporated pseudo-planar heterojunction (PiPPHJ), wherein a small amount of polymer donor is introduced into the NFSMAs layer. Our findings demonstrate that the incorporation of polymer increases the viscosity of acceptor solution, thereby improving the blade-coating processability and overall film quality. Simultaneously, this strategy effectively modulates the vertical component distribution, resulting in more donor/acceptor interfaces and an improved power conversion efficiency of 17.26%. Furthermore, PiPPHJ-based films exhibit superior tensile properties, with a crack onset strain of 12.0%, surpassing PPHJ-based films (9.6%). Consequently, large-area (1 cm2) flexible devices achieve a considerable efficiency of 13.30% and maintain excellent mechanical flexibility with 82% of the initial efficiency after 1000 bending cycles. These findings underscore the significant potential of PiPPHJ-based OSCs in flexible and wearable electronics.

High-performance nonfullerene polymer solar cells based on chlorinated quinoxaline copolymer with a high short-circuit current density

In organic solar cells, the absorption range and extinction coefficient of the active layer not only affect the charge separation and carrier transfer efficiency of excitons, but also influence the JSC, and thus the device efficiency. Herein, an efficient nonfullerene polymer solar cells (NF–PSCs) based on a medium-bandgap (MBG) polymer donor PBDTTS-TClQx comprising chlorinethiophene quinoxaline (Qx) unit and a small molecule nonfullerene acceptor (SM-NFA) Y6 is developed. The PBDTTS-TClQx shows a strong absorption in the wavelength region of 330∼750 nm with an optical band gaps (Egopt) of 1.68 eV, which is well complementary with that of Y6 (1.33 eV) and facilitates achieving of high short-circuit current (JSC) in PSCs. As a result, the PBDTTS-TClQx:Y6-based PSCs achieved a power conversion efficiency (PCE) of 14.28% with a JSC of 25.9 mA cm−2. The JSC of 25.9 mA cm−2 achieved is among the highest reported for Qx-based polymer donors in PSCs.

Trade‐Off Break between the Crystallinity and Phase Separation of Donor/Acceptor via a General Two‐Dimensional Transition‐Metal Phosphorus Trichalcogenides Nanoparticle Dopant Concept for Efficient and Stable All‐Polymer Solar Cells

All‐polymer solar cells (all‐PSCs) demonstrate splendid advantages of thermal and mechanical stability. Nevertheless, the rock‐ribbed trade‐off between the crystallinity and phase separation scale of donor/acceptor (D/A) hinder the power conversion efficiency (PCE) improvement of all‐PSCs. Here, a novel two‐dimensional transition‐metal phosphorus trichalcogenides (TMPTCs) namely Cd0.85PS3Li0.3 is intelligently designed and synthesized, and firstly employed as a nanoparticle dopant for PBDB‐T:N2200‐based all‐PSCs. The two‐dimensional Cd0.85PS3Li0.3 possess enormous surface area that can serve as the nucleation center, inducing the crystallinity of D/A without influencing the original phase separation. Such feature significantly boosted the charge transport, PCE (from 7.18% to 8.79%) and stability of PBDB‐T:N2200‐based device. Moreover, the Cd0.85PS3Li0.3 nanoparticle dopant was proved to be universal in non‐fullerene small molecule acceptor (NFSMA)‐based organic solar cells (OSCs), for which the PCE was boosted from 15.05% to 17.27% for PM6:L8‐BO‐based OSCs and from 17.29% to 19.10% for D18:L8‐BO‐based OSCs. These observations exemplify the significance of two‐dimensional TMPTCs nanoparticle dopant as a tool for breaking the rock‐ribbed trade‐off between the crystallinity and phase separation scale of D/A in OSCs, which may open up a special field for making two‐dimensional TMPTCs work in a unprecedented way in OSCs.

19.32% Efficiency Polymer Solar Cells Enabled by Fine-Tuning Stacking Modes of Y-Type Molecule Acceptors: Synergistic Bromine and Fluorine Substitution of the End Groups.

The success of Y6-type nonfullerene small molecule acceptors (NF-SMAs) in polymer solar cells (PSCs) can be attributed to their unique honeycomb stacking style, which leads to favorable thin-film morphologies. The intermolecular interactions related to the crystallization tendency of these NF-SMAs is closely governed by their electron accepting end groups. For example, the high performance Y6 derivative L8-BO (BTP-4F) presents three types of stacking modes in contrast to two stacking modes of Y6. Hence, it is ultimately interesting to obtain more insight on the packing properties and the preferences influenced by chemical modifications such as end group engineering. This work designs and synthesizes asymmetric and symmetric L8-BO derivatives with brominated end groups and explores the stacking preferences in various modes. The asymmetric BTP-3FBr displays an optimized crystallization tendency and thin film morphology, leading to a decent power conversion efficiency (PCE) of 18.34% in binary devices and a top PCE of 19.32% in ternary devices containing 15 wt% IDIC as the second acceptor.

What We have Learnt from PM6:Y6.

Over the past three years, remarkable advancements in organic solar cells (OSCs) have emerged, propelled by the introduction of Y6-an innovative A-DA'D-A type small molecule non-fullerene acceptor (NFA). This review provides a critical discussion of the current knowledge about the structural and physical properties of the PM6:Y6 material combination in relation to its photovoltaic performance. Weaddress the design principles behind PM6 and Y6, the mechanisms for charge transfer, transport and recombination, before turning to a detailed examination of the blend morphology and mechanisms of degradation, to conclude with considerations of commercialization. Wefocus on presenting the current state of the art, while wealso discuss unresolved contentious issues, such as the blend energetics, the pathways of free charge generation, and the role of triple states in recombination. As such, this review aims to provide a comprehensive understanding of the PM6:Y6 material combination and its potential for further development in the field of organic solar cells. By addressing both the successes and challenges associated with this system, wehope to contribute to the ongoing research efforts towards achieving more efficient and stable organic solar cells. This article is protected by copyright. All rights reserved.

Non-fullerene acceptors with thiazole π-bridge for organic solar cells

Intramolecular noncovalent conformational locks (NoCLs) have been found to be effective in increasing the rigidity and planarity of the molecular backbone. This, in turn, leads to reduced recombination energy and improved intramolecular charge transport mobility, resulting in significant enhancements in the photovoltaic performance of organic solar cell (OSC) devices. To take advantage of this effect, we designed and synthesized two small molecule non-fullerene acceptors (NFAs) with A-π-D-π-A structures using thiazole (Tz): IDTz-IC4F and IDTz-IC4Cl. With the synergistic assistance of NoCLs and halogenated end groups, the NFAs IDTz-IC4F and IDTz-IC4Cl exhibited power conversion efficiencies (PCEs) of 6.20 % and 6.06 %, respectively. This study presents a strategy for enhancing the PCE of OSCs by incorporating cooperative NoCLs and halogen end groups, providing an exciting avenue for designing high-performance non-fullerene materials in the future.

Ultra Robust and Highly Efficient Flexible Organic Solar Cells with Over 18 % Efficiency Realized by Incorporating a Linker Dimerized Acceptor

AbstractThe wearable application of flexible organic solar cells (f‐OSCs) necessitates high power conversion efficiency (PCE) and mechanical robustness. However, photoactive films based on efficient non‐fullerene small molecule acceptors (NF‐SMAs) are typically brittle, leading to poor mechanical stability in devices. In this study, we achieved a remarkable PCE of 18.06 % in f‐OSCs while maintaining ultrahigh mechanical robustness (with a crack‐onset strain (COS) of higher than 11 %) by incorporating a linker dimerized acceptor (DOY‐TVT). Compared to binary blends, ternary systems exhibit reduced non‐radiative recombination, suppressed crystallization and diffusion of NF‐SMAs, and improved load distribution across the chain networks, enabling the dissipation of the load energy. Thus, the ternary f‐OSCs developed in this study achieved, high PCE and stability, surpassing binary OSCs. Moreover, the developed f‐OSCs retained 97 % of the initial PCE even after 3000 bending cycles, indicating excellent mechanical stability (9.1 % higher than binary systems). Furthermore, the rigid device with inverted structure based on the optimal active layer exhibited a substantial increase in efficiency retention, with 89.6 % after 865 h at 85 °C and 93 % after more than 1300 h of shelf storage at 25 °C. These findings highlight the potential of the linker oligomer acceptor for realizing high‐performing f‐OSCs with ultrahigh mechanical robustness.

Ultra Robust and Highly Efficient Flexible Organic Solar Cells with Over 18 % Efficiency Realized by Incorporating a Linker Dimerized Acceptor.

The wearable application of flexible organic solar cells (f-OSCs) necessitates high power conversion efficiency (PCE) and mechanical robustness. However, photoactive films based on efficient non-fullerene small molecule acceptors (NF-SMAs) are typically brittle, leading to poor mechanical stability in devices. In this study, we achieved a remarkable PCE of 18.06 % in f-OSCs while maintaining ultrahigh mechanical robustness (with a crack-onset strain (COS) of higher than 11 %) by incorporating a linker dimerized acceptor (DOY-TVT). Compared to binary blends, ternary systems exhibit reduced non-radiative recombination, suppressed crystallization and diffusion of NF-SMAs, and improved load distribution across the chain networks, enabling the dissipation of the load energy. Thus, the ternary f-OSCs developed in this study achieved, high PCE and stability, surpassing binary OSCs. Moreover, the developed f-OSCs retained 97 % of the initial PCE even after 3000 bending cycles, indicating excellent mechanical stability (9.1 % higher than binary systems). Furthermore, the rigid device with inverted structure based on the optimal active layer exhibited a substantial increase in efficiency retention, with 89.6 % after 865 h at 85 °C and 93 % after more than 1300 h of shelf storage at 25 °C. These findings highlight the potential of the linker oligomer acceptor for realizing high-performing f-OSCs with ultrahigh mechanical robustness.

The Influence of the Central Metal Ion on the Electronic and Photovoltaic Properties of Metalloporphyrins [M= Zn(II), Ni(II), Cu(II), Au(III)] Systems

Although the pioneering use of porphyrins in organic solar cells (OSCs) was disappointing as reported efficiencies were very low, the situation has changed over the last five years as Zn-porphyrins with ABAB structures linked to acceptor units through triple bonds have been applied as donors resulting in efficiencies of up to 12% in binary OSCs and more than 15% in ternary OSCs.The optical and electrochemical properties of porphyrins can be adjusted by molecular design and functionalization on the b or meso positions of the porphyrin ring as well as by introduction of different central metal ions. The choice of the centrally bounded metal cation within the porphyrin core plays an important role in the electronic properties allowing the modulation of the frontier orbital levels and thereby use the porphyrin-based molecule as donor or acceptor component of the device.Due to the high HOMO level of Zn-Porphyrin derivatives, the Voc of OSCs using this family of compounds are lower than 0.9 V limiting the PCE of devices.We have described that Ni-porphyrins derivatives allow the design of OSCs with voltage higher than 1V. These systems present slightly higher optical bandgaps but the deeper highest occupied molecular orbital (HOMO) energy level make available to reach good PCE values of the solar devices.While porphyrins and their derivatives have been extensively used as donor component in the BHJ active layer of OSCs, the investigation of porphyrin-based materials as electron acceptor is very limited. Recently, we designed a new A2-D-A1-D-A2 non fullerene small molecule acceptor (NFSMA) with broad absorption up to 920 nm and a great absorption coefficient where A1 core is Au(III) porphyrin. This molecule, when used in OSC with a polymer donor yielded a PCE=9.24%. Nevertheless, the use of other central metals such as Cu(II) in the porphyrin core has been scarcely used in OSCs, the studied devices presented low efficiencies (≤ 3%). These outcomes demonstrated that metalloporphyrins, which is different from Zn-porphyrins, also have great potential for the design of NFSMAs for efficient OSCs. Also, we have studied A-π-D-π-A small molecules based on Cu(II) Porphyrin, scarcely used in OSCs, presenting an ambipolar behaviour, as donor and as acceptor. Here, I´ll present our recent work in design, synthesis, and application of porphyrin-based small molecules with different central metal for highly efficient OSCs.References V. Cuesta, M. Vartanian, P. de la Cruz, R. Singhal, G. D. Sharma and F. Langa. J. Mater. Chem. A, 2017, 5, 1057.S. Arrechea, A. Aljarilla, P. de la Cruz, M. K. Singh, G. D. Sharma and F. Langa. J. Mater. Chem. C, 2017, 5, 4742.M. Vartanian, R. Singhal, P. de la Cruz, S. Biswas, G. D. Sharma and F. Langa. ACS Appl. Energy, Mater., 2018, 1, 1304.M. Vartanian, P. de la Cruz, F. Langa, S. Biswas and G. D. Sharma. Nanoscale, 2018, 10, 12100.M. Vartanian, R. Singhal, P. de la Cruz, G. D. Sharma and F. Langa. Chem. Commun., 2018, 54, 14144.V. Cuesta, R. Singhal, P. de la Cruz, G. D. Sharma and F. Langa. ACS Appl. Mater. Interfaces, 2019, 11, 7216.Cuesta, R. Singhal, P. de la Cruz, G. D. Sharma and F. Langa, ChemSusChem, 2021, 14, 3439.H. Dahiya, V. Cuesta, P. de la Cruz, F. Langa and G. D. Sharma ACS Appl. Energy Mater., 2021, 4, 4498. Figure 1

Green-Solvent-Processed High-Performance Broadband Organic Photodetectors.

Solution-processed organic photodetectors with broadband activity have been demonstrated with an environmentally benign solvent, ortho-xylene (o-xylene), as the processing solvent. The organic photodetectors employ a wide band gap polymer donor PBDB-T and a narrow band gap small-molecule non-fullerene acceptor CO1-4F, both dissolvable in o-xylene at a controlled temperature. The o-xylene-processed devices have shown external quantum efficiency of up to 70%, surpassing the counterpart processed with chlorobenzene. With a well-suppressed dark current, the device can also present a high specific detectivity of over 1012 Jones at -2 V within practical operation frequencies and is applicable for photoplethysmography with its fast response. These results further highlight the potential of green-solvent-processed organic photodetectors as a high-performing alternative to their counterparts processed in toxic chlorinated solvents without compromising the excellent photosensing performance.

Boosting the efficiency of organic solar cells via dual non-fullerene acceptors

To prepare high-performance organic solar cells (OSCs), incorporating a third component into the binary blend is a feasible and convenient strategy. Here, IDIC, a non-fullerene small molecule acceptor with medium bandgap and good compatibility, was added to the PM6:BTP-eC9 system to prepare high-performance ternary OSCs. The good absorption, compatibility and energy level of IDIC can contribute to enhance light-harvesting, obtain better nanofiber structures, promote the exciton dissociation and charge transport, and suppress recombination. Finally, the optimized ternary OSCs achieves a high power conversion efficiency (PCE) up to 18.53%, which is higher than that of the binary system (17.09%). Additionally, IDIC was also used as a third component to build efficient OSCs in other binary systems and achieved enhanced photovoltaic performance. This work proves that selecting a third component having appropriate absorption and good compatibility to fabricate high-performance ternary OSCs is an effective and convenient strategy.

From Solution to Thin Film: Molecular Assembly of π-Conjugated Systems and Impact on (Opto)electronic Properties.

The assembly of conjugated organic molecules from solution to solid-state plays a critical role in determining the thin film morphology and optoelectronic properties of solution-processed organic electronics and photovoltaics. During evaporative solution processing, π-conjugated systems can assemble via various forms of intermolecular interactions, forming distinct aggregate structures that can drastically tune the charge transport landscape in the solid-state. In blend systems composed of donor polymer and acceptor molecules, assembly of neat materials couples with phase separation and crystallization processes, leading to complex phase transition pathways which govern the blend film morphology. In this review, we provide an in-depth review of molecular assembly processes in neat conjugated polymers and nonfullerene small molecule acceptors and discuss their impact on the thin film morphology and optoelectronic properties. We then shift our focus to blend systems relevant to organic solar cells and discuss the fundamentals of phase transition and highlight how the assembly of neat materials and processing conditions can affect blend morphology and device performance.

Exploring the photovoltaic properties of promising non-fullerene acceptors with different degrees of asymmetry due to halogenations of terminal groups

Over the past few years, the strategy of asymmetric modification has become popular for designing new photovoltaic materials because it can effectively improve optoelectronic performance and morphology, therefore power conversion efficiency (PCE). However, how the halogenations (to further change asymmetry) of terminal groups (TGs) of an asymmetric small-molecule non-fullerene acceptor (Asy-SM-NFA) influence optoelectronic properties is still not very clear. In this work, we have selected a promising Asy-SM-NFA IDTBF (the OSC based on it has a PCE of 10.43 %), exacerbated the asymmetry through fluorinations of TGs, and finally designed six new molecules. Based on density functional theory (DFT) and time-dependent DFT calculations, we systematically examine how the changed asymmetry impacts the optoelectronic properties. We find that the halogenations of TGs may significantly affect the molecular planarity, dipole moment, electrostatic potential, exciton binding energy, energy loss, and absorption spectrum. And the results show that newly designed BR-F1 and IM-mF (m = 1,3, and 4) are potential Asy-SM-NFAs because they all have enhanced absorption spectra in the visible region. Therefore, we provide a meaningful direction for the design of asymmetric NFA.

Eco-Friendly Solvent-Processed Dithienosilicon-Bridged Carbazole-Based Small-Molecule Acceptors Achieved over 25.7% PCE in Ternary Devices under Indoor Conditions.

Terminal acceptor atoms and side-chain functionalization play a vital role in the construction of efficient nonfullerene small-molecule acceptors (NF-SMAs) for AM1.5G/indoor organic photovoltaic (OPV) applications. In this work, we report three dithienosilicon-bridged carbazole-based (DTSiC) ladder-type (A-DD'D-A) NF-SMAs for AM1.5G/indoor OPVs. First, we synthesize DTSiC-4F and DTSiC-2M, which are composed of a fused DTSiC-based central core with difluorinated 1,1-dicyanomethylene-3-indanone (2F-IC) and methylated IC (M-IC) end groups, respectively. Then, alkoxy chains are introduced in the fused carbazole backbone of DTSiC-4F to form DTSiCODe-4F. From solution to film absorption, DTSiC-4F exhibits a bathochromic shift with strong π-π interactions, which improves the short-circuit current density (Jsc) and the fill factor (FF). On the other hand, DTSiC-2M and DTSiCODe-4F display up-shifting lowest unoccupied molecular orbital (LUMO) energy levels, which enhances the open-circuit voltage (Voc). As a result, under both AM1.5G/indoor conditions, the devices based on PM7:DTSiC-4F, PM7:DTSiC-2M, and PM7:DTSiCOCe-4F show power conversion efficiencies (PCEs) of 13.13/21.80%, 8.62/20.02, and 9.41/20.56%, respectively. Furthermore, the addition of a third component to the active layer of binary devices is also a simple and efficient strategy to achieve higher photovoltaic efficiencies. Therefore, the conjugated polymer donor PTO2 is introduced into the PM7:DTSiC-4F active layer because of the hypsochromically shifted complementary absorption, deep highest occupied molecular orbital (HOMO) energy level, good miscibility with PM7 and DTSiC-4F, and optimal film morphology. The resulting ternary OSC device based on PTO2:PM7:DTSiC-4F can improve exciton generation, phase separation, charge transport, and charge extraction. As a consequence, the PTO2:PM7:DTSiC-4F-based ternary device achieves an outstanding PCE of 13.33/25.70% under AM1.5G/indoor conditions. As far as we know, the obtained PCE results under indoor conditions are one of the best binary/ternary-based systems processed from eco-friendly solvents.

Improving the Efficiency of Organic Solar Cells via the Molecular Engineering of Simple Fused Non-Fullerene Acceptors

The development of novel non-fullerene small-molecule acceptors (NFAs) with a simple chemical structure for high-performance organic solar cells (OSCs) remains an urgent research challenge to enable their upscaling and commercialization. In this work, we report on the synthesis and comprehensive investigation of two new acceptor molecules (BTPT-OD and BTPT-4F-OD), which have one of the simplest fused structures among the Y series of NFAs, along with the medium energy bandgap (1.85 eV–1.94 eV) and strong absorption in the visible and near-IR spectral range (700–950 nm). The novel NFAs have high thermal stability, good solubility combined with a high degree of crystallinity, and deep-lying levels of the lowest unoccupied molecular orbital (up to −3.94 eV). The BTPT-OD with indan-1-one-3-dicyanvinyl terminal acceptor group is superior to its counterpart BTPT-4F-OD with 5,6-difluorindan-1-one-3-dicyanvinyl group both in the number of synthetic steps and in the photovoltaic performance in OSCs. PM6:BTPT-OD systems exhibit superior photovoltaic performance due to the higher charge mobility and degree of photoresponsiveness, faster carrier extraction, and longer carrier lifetime. As a result, BTPT-OD has almost two times higher photovoltaic performance with PM6 as a donor material due to the higher JSC and FF than BTPT-4F-OD systems. The results obtained indicate that further development of OSCs can be well achieved through a rational molecular design.

Medium Bandgap Nonfullerene Acceptor for Efficient Ternary Polymer Solar Cells with High Open-Circuit Voltage.

We have designed a new medium bandgap non-fullerene small-molecule acceptor consisting of an IDT donor core flanked with 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]-thiophene-4-ylidene) malononitrile (TC) acceptor terminal groups (IDT-TC) and compared its optical and electrochemical properties with the IDT-IC acceptor. IDT-TC showed an absorption profile from 300 to 760 nm, and it has an optical bandgap of 1.65 eV and HOMO and LUMO energy levels of -5.55 and -3.83 eV, respectively. In contrast to IDT-IC, IDT-TC has an upshifted LUMO energy level, which is advantageous for achieving high open-circuit voltage. Moreover, IDT-TC showed higher crystallinity and high electron mobility than IDT-IC. Using a wide bandgap D-A copolymer P as the donor, we compared the photovoltaic performance of IDT-TC, IDT-IC, and IDT-IC-Cl nonfullerene acceptors (NFAs). Polymer solar cells (PSCs) using P: IDT-TC, P: IDT-IC, and P:IDT-IC-Cl active layers achieved a power conversion efficiency (PCE) of 14.26, 11.56, and 13.34%, respectively. As the absorption profiles of IDT-IC-Cl and IDT-TC are complementary to each other, we have incorporated IDT-TC as the guest acceptor in the P: IDT-IC-Cl active layer to fabricate the ternary (P:IDT-TC: IDT-IC-Cl) PSC, demonstrating a PCE of 16.44%, which is significantly higher than that of the binary BHJ devices. The improvement in PCE for ternary PSCs is attributed to the efficient exploitation of excitons via energy transfer from IDT-TC to IDT-IC-Cl, suitable nanoscale phase separation, compact stacking distance, and more evenly distributed charge transport.

Challenging PM6-like donor polymers for pairing with a Y-type state-of-the-art acceptor in binary blends for bulk heterojunction solar cells.

Being fluorine-free and a high performance material as a small organic acceptor molecule, BTP-eC9 has been well mixed with BDT-based PM6 donor polymers for providing satisfactory photovoltaic properties, especially towards future large scale/large area solar cell production. However, as one of the key electrical outputs from such binary active layer materials, the open circuit voltage (VOC) was limited to ca. 0.84 V, which needs to be further improved for BTP-eC9 to have a bright future. This paper focuses on the molecular design of alkylthio- and alkoxy-phenyl flanked benzo[1,2-b:4,5-b']dithiophene-based conjugated polymers (PBDT-PS-ttTPD or P10 for short and PBDT-PO-ttTPD or P11), which were successfully synthesized and applied as donor materials for pairing with BTP-eC9 in organic photovoltaic (OPV) devices. By fine-tuning the side chains of the benzodithiophene (BDT) moiety, such non-fullerene OPV devices with normal configuration demonstrate an attractively high open circuit voltage (VOC) of 0.89 and 0.87 V in P10/BTP-eC9 and P11/BTP-eC9 based binary single bulk heterojunction OPV devices, while still maintaining an excellent JSC of 22.7 and 20.0 mA cm-2 with a final power conversion efficiency (PCE) of 12.93% and 9.37%, respectively. The alkylthio-phenyl chain substituted BDT polymer exhibits better photovoltaic performance in all aspects than the alternative with alkoxy chains due to the synergistic effect of the alkylthio-phenyl flanked BDT, TPD, and π-bridge (thieno[3,2-b]thiophene).

Organic photovoltaic performance and structural relationship of non-fullerene small molecule acceptors based on a tetraarylphenazine core and perylene diimide

Two small molecular acceptors based on perylene diimide tetramer with a phenazine core and benzene or thiophene linkers are developed.

Design and screening of B–N functionalized non-fullerene acceptors for organic solar cells via multiscale computation

Multiscale computation driven molecular engineering of small molecule non-fullerene acceptors for organic solar cells.