Impact of end-capped engineering on the optoelectronic characteristics of pyrene-based non-fullerene acceptors for organic photovoltaics

Pyrene-based molecules are being explored as prospective fullerene-free acceptors for organic solar cells (OSCs), due to their easy accessibility, structural planarity, and excellent electron delocalization. In this work, we successfully designed and analyzed pyrene-based acceptor materials (QL1–QL8) to investigate their photophysical and electro-optical parameters. Various geometric parameters were computed at the MPW1PW91/6-31G(d,p). Advanced quantum chemical approaches were employed to characterize the molecules. All the tailored molecules (QL1–QL8) exhibit a lower bandgap than the reference (R), signifying their superiority. Among these, QL8 was found to have a maximum absorption (λ_max) at 791.37 nm and an optical bandgap (E_LUMO − E_HOMO) minimum of 2.11 eV. Redshifted absorption spectra are observed in both gaseous and solvent phases for all the designed (QL1–QL8) molecules in contrast to R. Among these, QL4 exhibits the highest light harvesting efficiency (0.9826), and open-circuit voltage. A detailed donor–acceptor investigation of QL8/PBDB-T revealed the marvelous charge switching at the donor–acceptor interface. The approach used in this study is anticipated to facilitate the manufacturing of highly efficient OSC molecules.     

A Pyrene-Fused Dimerized Acceptor for Ternary Organic Solar Cells with 19% Efficiency and High Thermal Stability

A pyrene-fused dimerized electron acceptor has been successfully synthesized and subsequently incorporated as the third component in ternary organic solar cells (OSCs). Diverging from the traditional dimerized acceptors with a linear configuration, this novel electron acceptor displays a distinctive “butterfly-like” structure, comprising two Y-acceptors as wings fused with a pyrene-based backbone. The extended π-conjugated backbone and the electron-donating nature of pyrene enable the new acceptor to show low solubility, elevated glass transition temperature (T_g), and low-lying frontier energy levels. Consequently, the new dimerized acceptor seamlessly integrates as the third component into ternary OSCs, enhancing electron transporting properties, reducing non-radiative voltage loss, and elevating open-circuit voltage. These merits have enabled the ternary OSCs to show an exceptional efficiency of 19.07%, a marked improvement compared to the 17.6% attained in binary OSCs. More importantly, the high T_g exhibited by the pyrene-fused electron acceptor helps to stabilize the morphology of the photoactive layer thermal-treated at 70 °C, retaining 88.7% efficiency over 600 hours. For comparison, binary OSCs experience a decline to 73.7% efficiency after the same duration. These results indicate that the “butterfly-like” design and the incorporation of a pyrene unit is a promising strategy in the development of dimerized electron acceptors for OSCs.     

Evaluating Zn‐Porphyrin‐Based Near‐IR‐Sensitive Non‐Fullerene Acceptors for Efficient Panchromatic Organic Solar Cells

Porphyrin‐based non‐fullerene acceptors (NFAs) have shown pronounced potential for assembling low‐bandgap materials with near‐infrared (NIR) characteristics. Herein, panchromatic‐type porphyrin‐based molecules (POR1–POR5) are proposed by modulating end‐capped acceptors of a highly efficient porphyrin‐based NFA PORTFIC(POR) for organic solar cells (OSCs). Quantum chemical structure‐property relationship has been studied to discover photovoltaic and optoelectronic characteristics of POR1–POR5. Results show that optoelectronic properties of the POR1–POR5 are better in all aspects when compared with the reference POR. All proposed NFAs particularly POR5 proved to be the preferable porphyrin‐based NIR sensitive NFA for OSCs applications owing to lower energy gap (1.56 eV), transition energy (1.11 eV), binding energy (E_b =0.986 eV), electron mobility (λ_e=0.007013E_h ), hole mobility (λ_h =0.004686 E_h), high λ_max =1116.27 nm and open‐circuit voltage (V_oc =1.96 V) values in contrast to the reference POR and other proposed NFAs. This quantum chemical insight provides sufficient evidence about excellent potential of the proposed porphyrin‐based NIR sensitive NFA derivatives for their use in OSCs.     

Studies of New 2,7-Carbazole (CB) Based Donor-Acceptor-Donor (D-A-D) Monomers as Possible Electron Donors in Polymer Solar Cells by DFT and TD-DFT Methods

The new donor-acceptor-donor (D-A-D) monomers have been studied using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods to evaluate the optoelectronic and electronic properties for bulk heterojunction (BHJ) organic solar cells. The TD-DFT method is combined with a hybrid exchange-correlation functional using the B3LYP method in conjunction with a polarizable continuum model (PCM) and a 6–311G basis set to predict the excitation energies and absorption spectra of all monomers. The predicted bandgap (E_g) of the monomers decreasing in the following order D1<D2<D3<D4<D5<D6<D7<D9<D8. Furthermore, open-circuit voltage (V_OC) estimates for monomers with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) acceptor. The V_OC of the studied monomers ranges from 0.976 to 1.398 eV in the gas and from 1.109 to 1.470 eV in the solvent phase with PC71BM acceptor, which is sufficient for efficient electron injection into the acceptor‘s LUMO. The results show that theoretically, a maximum energy conversion efficiency of roughly 5 % for D8 and 5.8 5 % for D7.     

The Synthesis of a Multiple D–A Conjugated Macrocycle and Its Application in Organic Photovoltaic

As a novel class of materials, D–A conjugated macrocycles hold significant promise for chemical science. However, their potential in photovoltaic remains largely untapped due to the complexity of introducing multiple donor and acceptor moieties into the design and synthesis of cyclic π-conjugated molecules. Here, we report a multiple D–A ring-like conjugated molecule ( RCM ) via the coupling of dimer molecule DBTP-C3 as a template and thiophenes in high yields. RCM exhibits a narrow optical gap (1.33 eV) and excellent thermal stability, and shows a remarkable photoluminescence yield (Φ_PL) of 11.1 % in solution, much higher than non-cyclic analogues. Organic solar cell (OSC) constructed with RCM as electron acceptor shows efficient charge separation at donor-acceptor band offsets and achieves a power conversion efficiency (PCE) of 14.2 %-approximately fourfold higher than macrocycle-based OSCs reported so far. This is partly due to low non-radiative voltage loss down to 0.20 eV and a high electroluminescence yield (Φ_EL) of 4×10⁻⁴. Our findings emphasize the potential of D–A cyclic conjugated molecules in advancing organic photovoltaic technology.     

Lead Halide Perovskite Quantum Dots To Enhance the Power Conversion Efficiency of Organic Solar Cells

The facile synthesis, solution‐processability, and outstanding optoelectronic properties of emerging colloidal lead halide perovskite quantum dots (LHP QDs) makes them ideal candidates for scalable and inexpensive optoelectronic applications, including photovoltaic (PV) devices. The first demonstration of integrating CsPbI₃ QDs into a conventional organic solar cell (OSC) involves embedding the LHP QDs in a donor–acceptor (PTB7‐Th:PC₇₁BM) bulk heterojunction. Optimizing the loading amount at 3 wt %, we demonstrate a power conversion efficiency of 10.8 %, which is a 35 % increase over control devices, and is a record amongst hybrid ternary OSCs. Detailed investigation into the mechanisms behind the performance enhancement shows that increased light absorption is not a factor, but that increased exciton separation in the acceptor phase and reduced recombination are responsible.     

Exploring the potential of tetraazaacene derivatives as photovoltaic materials with enhanced photovoltaic parameters

A series of D-π-A type molecules have been designed for their potential use in organic photovoltaic devices. Photovoltaic and optoelectronic properties of newly designed molecules have been explored by comparing with a reference molecule R comprising of the central core (2,3,8,9-tetrakis(thiophen-2-ylethynyl)-5,7,10,12-tetrakis((trimethylsilyl)ethynyl)pyrazino[2,3-b]phenazine) and π-bridge (thiophene). The end groups are (2-(2-ethylidene-3-oxo-2,3-dihydro-1H-inden-1 ylidene)malononitrile), (2-ethylidenemalonitrile), (methyl 2-cyanoacrylate) and (3-methyl-5-methylene-2-thioxothiazolidin-4-one) in the newly designed molecules. Among the investigated molecules M1 and M2 exhibit a broad absorption range of 627 and 626 nm with respect to the reference. All the designed molecules exhibited a lower bandgap as compared to R which indicates a better transfer of electron density from highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO). The reorganization energy values show that all designed molecules have efficient charge transport capability. This study proves that end-capped acceptor modification is an effective strategy for designing optimistic molecule for high performance future organic solar cells fabrication.     

A novel AH-D-A-type phase junction material to improve photovoltaic performance and device stability in fullerene OSCs

In order to boost power conversion efficiency (PCE) and operation stability of organic solar cells (OSCs), we propose a new idea of phase junction materials (PJMs) used as a photoactive layer component to improve device performance and stability. For this purpose, a novel PJM of H-TRC8 based on rhodanine unit was designed with a conjugated A_H-D-A framework. Here, A_H is a hydrogen-donating electron acceptor unit, D-A is an electron donor-acceptor unit. It is found that H-TRC8 has a good carrier-transporting ability, as well as definite hydrogen-bond and D-A interaction with donor/acceptor materials. While H-TRC8 is added into the PBDB-T/PC₆₀BM blend film with 1.0 vol% DIO (1,8-diiodooctane), the resulting blend film exhibited an enhanced absorption and improved morphology. The intermolecular hydrogen bond between H-TRC8 and PBDB-T plays an important role for them, which is confirmed via FT-IR spectra and 2D ¹H NMR. As a result, the PBDB-T/PC₆₀BM-based devices with 1.25 wt% H-TRC8 and 1.0 vol% DIO exhibit a significantly improved PCE of 8.06%, which is increased by 20.6% in comparison to that in the binary devices with 1.0 vol% DIO only (PCE = 6.68%). Furthermore, the device stability is significantly enhanced with only 43% PCE roll-off at 150 °C for 120 h. This work indicates that A_H-D-A-type PJMs are promising photovoltaic materials used as photoactive-layer components to achieve high-performance fullerene OSCs with high device stability.     

A New Small-Molecule Donor Containing Non-Fused Ring π-Bridge Enables Efficient Organic Solar Cells with High Open Circuit Voltage and Low Acceptor Content

To achieve high open-circuit voltage (V_oc) and low acceptor content, the molecular design of a small-molecule donor with low energy loss (E_loss) is very important for solution-processable organic solar cells (OSCs). Herein, we designed and synthesized a new coplanar A−D−A structured organic small-molecule semiconductor with non-fused ring structure π-bridge, namely B2TPR , and applied it as donor material in OSCs. Owing to the strong electron-withdrawing effect of the end group and the coplanar π-bridge, B2TPR exhibits a low-lying highest occupied molecular orbital and strong crystallinity. Furthermore, benefiting from the coplanar molecular skeleton, the high hole mobility, balanced charge transport and reduced recombination were achieved, leading to a high fill factor (FF). The OSCs based on B2TPR : PC₇₁BM blend film (w/w=1 : 0.35) demonstrates a moderate power conversion efficiency (PCE) of 7.10 % with a remarkable V_oc of 0.98 V and FF of 64 %, corresponding to a low fullerene content of 25.9 % and a low E_loss of 0.70 eV. These results demonstrate the great potential of small-molecule with structure of B2TPR for future low-cost organic photovoltaic applications.     

Unidirectional Sidechain Engineering to Construct Dual-Asymmetric Acceptors for 19.23 % Efficiency Organic Solar Cells with Low Energy Loss and Efficient Charge Transfer

Achieving both high open-circuit voltage (V_oc) and short-circuit current density (J_sc) to boost power-conversion efficiency (PCE) is a major challenge for organic solar cells (OSCs), wherein high energy loss (E_loss) and inefficient charge transfer usually take place. Here, three new Y-series acceptors of mono-asymmetric asy-YC11 and dual-asymmetric bi-asy-YC9 and bi-asy-YC12 are developed. They share the same asymmetric D₁AD₂ (D₁=thieno[3,2-b]thiophene and D₂=selenopheno[3,2-b]thiophene) fused-core but have different unidirectional sidechain on D₁ side, allowing fine-tuned molecular properties, such as intermolecular interaction, packing pattern, and crystallinity. Among the binary blends, the PM6 : bi-asy-YC12 one has better morphology with appropriate phase separation and higher order packing than the PM6 : asy-YC9 and PM6 : bi-asy-YC11 ones. Therefore, the PM6 : bi-asy-YC12-based OSCs offer a higher PCE of 17.16 % with both high V_oc and J_sc, due to the reduced E_loss and efficient charge transfer properties. Inspired by the high V_oc and strong NIR-absorption, bi-asy-YC12 is introduced into efficient binary PM6 : L8-BO to construct ternary OSCs. Thanks to the broadened absorption, optimized morphology, and furtherly minimized E_loss, the PM6 : L8-BO : bi-asy-YC12-based OSCs achieve a champion PCE of 19.23 %, which is one of the highest efficiencies among these annealing-free devices. Our developed unidirectional sidechain engineering for constructing bi-asymmetric Y-series acceptors provides an approach to boost PCE of OSCs.     

High-Performance Organic Solar Cells Containing Pyrido[2,3-b]quinoxaline-Core-Based Small-Molecule Acceptors with Optimized Orbit Overlap Lengths and Molecular Packing

The central core in A-DA₁D-A-type small-molecule acceptor (SMAs) plays an important role in determining the efficiency of organic solar cells (OSCs), while the principles governing the efficient design of SMAs remain elusive. Herein, we developed a series of SMAs with pyrido[2,3-b]quinoxaline (PyQx) as new electron-deficient unit by combining with the cascade-chlorination strategy, namely Py1, Py2, Py3, Py4 and Py5. The introduction of chlorine atoms reduces the intramolecular charge transfer effects but elevates the LUMO values. Density functional theory (DFT) reveals that Py2 with ortho chlorine substituted PyQx and Py5 with two chlorine atoms yield larger dipole moments and smaller π⋅⋅⋅π stacking distances, as compared with the other three acceptors. Moreover, Py2 shows the strongest light absorption capability induced by extended orbit overlap lengths and more efficient packing structures in the dimers. These features endow the best device performance of Py2 due to the better molecular packing and aggregation behaviors, more suitable domain sizes with better exciton dissociation and charge recombination. This study highlights the significance of incorporating large dipole moments, small π⋅⋅⋅π stacking distances and extended orbit overlap lengths in dimers into the development of high-performance SMAs, providing insight into the design of efficient A-DA₁D-A-type SMAs for OSCs.     

A‐D‐A Type Small Molecules Based on Boron Dipyrromethene for Solution‐Processed Organic Solar Cells

The unique properties of boron dipyrromethene (BODIPY) dyes including facile synthesis, high absorption coefficients, and delocalized molecular orbitals as well as excellent photochemical and thermal stability, make them promising as materials for organic solar cells. Accordingly, in this study three A‐D ‐A structural small molecules of BDTT‐BODIPY, FL‐BODIPY, and TT‐BODIPY have been synthesized, in which two BODIPY acceptor units are symmetrically conjugated to 4,8‐bis(5‐(2‐ethylhexyl) thiophen‐2‐yl)benzo[1,2‐b:4,5‐b]dithiophene (BDTT), 9,9‐dioctyl‐9H‐fluorene (FL), and thieno[3,2‐b]thiophene (TT) donor cores, respectively. The manipulation of the structural parameters significantly improves the performances of the BHJ OSCs, which show power conversion efficiencies of 4.75 %, 1.51 %, and 1.67 % based on [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM) as the acceptor material and BDTT‐BODIPY, FL‐BODIPY, and TT‐BODIPY as the donor materials, respectively.     

Tightly Bound Double‐Caged [60]Fullerene Derivatives with Enhanced Solubility: Structural Features and Application in Solar Cells

A series of novel highly soluble double‐caged [60]fullerene derivatives were prepared by means of lithium‐salt‐assisted [2+3] cycloaddition. The bispheric molecules feature rigid linking of the fullerene spheres through a four‐membered cycle and a pyrrolizidine bridge with an ester function CO₂R (R=n ‐decyl, n ‐octadecyl, benzyl, and n ‐butyl; compounds 1 a – d , respectively), as demonstrated by NMR spectroscopy and X‐ray diffraction. Cyclic voltammetry studies revealed three closely overlapping pairs of reversible peaks owing to consecutive one‐electron reductions of fullerene cages, as well as an irreversible oxidation peak attributed to abstraction of an electron from the nitrogen lone‐electron pair. Owing to charge delocalization over both carbon cages, compounds 1 a – d are characterized by upshifted energies of frontier molecular orbitals, a narrowed bandgap, and reduced electron‐transfer reorganization energy relative to pristine C₆₀. Neat thin films of the n ‐decyl compound 1 a demonstrated electron mobility of (1.3±0.4)×10⁻³ cm² V⁻¹ s⁻¹, which was comparable to phenyl‐C₆₁‐butyric acid methyl ester (PCBM) and thus potentially advantageous for organic solar cells (OSC). Application of 1 in OSC allowed a twofold increase in the power conversion efficiencies of as‐cast poly(3‐hexylthiophene‐2,5‐diyl) (P3HT)/ 1 devices relative to the as‐cast P3HT/PCBM ones. This is attributed to the good solubility of 1 and their enhanced charge‐transport properties — both intramolecular, owing to tightly linked fullerene cages, and intermolecular, owing to the large number of close contacts between the neighboring double‐caged molecules. Test P3HT/ 1 OSCs demonstrated power‐conversion efficiencies up to 2.6 % ( 1 a ). Surprisingly low optimal content of double‐caged fullerene acceptor 1 in the photoactive layer (≈30 wt %) favored better light harvesting and carrier transport owing to the greater content of P3HT and its higher degree of crystallinity.     

Significant Difference in Semiconducting Properties of Isomeric All‐Acceptor Polymers Synthesized via Direct Arylation Polycondensation

The direct arylation polycondensation (DArP) appeared as an efficient method for producing semiconducting polymers but often requires acceptor monomers with orienting or activating groups for the reactive carbon‐hydrogen (C‐H) bonds, which limits the choice of acceptor units. In this study, we describe a DArP for producing high‐molecular‐weight all‐acceptor polymers composed of the acceptor monomers without any orienting or activating groups via a modified method using Pd/Cu co‐catalysts. We thus obtained two isomeric all‐acceptor polymers, P1 and P2, which have the same backbone and side‐chains but different positions of the nitrogen atoms in the thiazole units. This subtle change significantly influences their optoelectronic, molecular packing, and charge‐transport properties. P2 with a greater backbone torsion has favorable edge‐on orientations and a high electron mobility μ_e of 2.55 cm² V^?1 s^?1. Moreover, P2‐based transistors show an excellent shelf‐storage stability in air even after the storage for 1 month.     

Benzotriazole-Based 3D Four-Arm Small Molecules Enable 19.1 % Efficiency for PM6 : Y6-Based Ternary Organic Solar Cells

A third component featuring a planar backbone structure similar to the binary host molecule has been the preferred ingredient for improving the photovoltaic performance of ternary organic solar cells (OSCs). In this work, we explored a new avenue that introduces 3D-structured molecules as guest acceptors. Spirobifluorene (SF) is chosen as the core to combine with three different terminal-modified (rhodanine, thiazolidinedione, and dicyano-substituted rhodanine) benzotriazole (BTA) units, affording three four-arm molecules, SF-BTA1, SF-BTA2, and SF-BTA3, respectively. After adding these three materials to the classical system PM6 : Y6, the resulting ternary devices obtained ultra-high power-conversion efficiencies (PCEs) of 19.1 %, 18.7 %, and 18.8 %, respectively, compared with the binary OSCs (PCE=17.4 %). SF-BTA1-3 can work as energy donors to increase charge generation via energy transfer. In addition, the charge transfer between PM6 and SF-BTA1-3 also acts to enhance charge generation. Introducing SF-BTA1-3 could form acceptor alloys to modify the molecular energy level and inhibit the self-aggregation of Y6, thereby reducing energy loss and balancing charge transport. Our success in 3D multi-arm materials as the third component shows good universality and brings a new perspective. The further functional development of multi-arm materials could make OSCs more stable and efficient.     

Impact of A–D–A-Structured Dithienosilole- and Phenoxazine-Based Small Molecular Material for Bulk Heterojunction and Dopant-Free Perovskite Solar Cells

Herein, the synthesis of the novel acceptor–donor–acceptor (A–D–A)-structured small molecule Si-PO-2CN based on dithienosilole (DTS) as building block flanked by electron-rich phenoxazine (POZ) units, which are terminated with dicyanovinylene, is presented. Si-PO-2CN showed unique electrochemical and photophysical properties and has been successfully employed in perovskite solar cells (PSCs) as well as in bulk heterojunction organic solar cells (OSCs). The PSCs fabricated with dopant-free Si-PO-2CN as hole-transport material (HTM) exhibited a power conversion efficiency (PCE) of 14.1 % (active area=1.02 cm²). Additionally, a PCE of 5.6 % has been achieved for OSCs, which employed Si-PO-2CN as p-type donor material when blended with a [6,6]-phenyl C71 butyric acid methyl ester (PC₇₁BM) acceptor. The versatile application of Si-PO-2CN provides a pathway for further implementation of DTS-based building blocks in solar cells for designing new molecules.     

Impact of symmetry-breaking of non-fullerene acceptors for efficient and stable organic solar cells

The concurrent enhancement of short-circuit current (J_SC) and open-circuit voltage (V_OC) is a key problem in the preparation of efficient organic solar cells (OSCs). In this paper, we report efficient and stable OSCs based on an asymmetric non-fullerene acceptor (NFA) IPC-BEH-IC2F. The NFA consists of a weak electron-donor core dithienothiophen[3,2-b]-pyrrolobenzothiadiazole (BEH) and two kinds of strong electron-acceptor (A) units [9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile (IPC) with a tricyclic fused system and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC2F)]. For comparison, the symmetric NFAs IPC-BEH-IPC and IC2F-BEH-IC2F were characterised. The kind of flanking A unit significantly affects the light absorption features and electronic structures of the NFAs. The asymmetric IPC-BEH-IC2F has the highest extinction coefficient among the three NFAs owing to its strong dipole moment and highly crystalline feature. Its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels lie between those of the IPC-BEH-IPC and IC2F-BEH-IC2F molecules. The IPC group also promotes molecular packing through the tricyclic π-conjugated system and achieves increased crystallinity compared to that of the IC2F group. Inverted-type photovoltaic devices based on p-type polymer:NFA blends with PBDB-T and PM6 polymers as p-type polymers were fabricated. Among all these devices, the PBDB-T:IPC-BEH-IC2F blend device displayed the best photovoltaic properties because the IPC unit provides balanced electronic and morphological characteristics. More importantly, the PBDB-T:IPC-BEH-IC2F-based device exhibited the best long-term stability owing to the strongly interacting IPC moiety and the densely packed PBDB-T:IPC-BEH-IC2F film. These results demonstrate that asymmetric structural modifications of NFAs are an effective way for simultaneously improving the photovoltaic performance and stability of OSCs.

A 9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile (IPC) moiety in asymmetric non-fullerene acceptors promotes the formation of a densely packed crystalline structure, enabling efficient and long-term stable organic solar cells.     

Dithieno[2,3‐d:2',3'‐d']benzo[1,2‐b:4,5‐b']dithiophene (DTBDAT)‐based copolymers for high‐performance organic solar cells

P(BDT‐TCNT) and P(DTBDAT‐TCNT) , which has an extended conjugation length, were designed and synthesized for applications in organic solar cell (OSCs). The solution absorption maxima of P(DTBDAT‐TCNT) with the extended conjugation were red‐shifted by 5–15 nm compared with those of P(BDT‐TCNT) . The optical band gaps and highest occupied molecular orbital (HOMO) energy levels of both P(BDT‐TCNT) and P(DTBDAT‐TCNT) were similar. The structure properties of thin films of these materials were characterized using grazing‐incidence wide‐angle X‐ray scattering and tapping‐mode atomic force microscopy, and charge carrier mobilities were characterized using the space‐charge limited current method. OSCs were formed using [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as the electron acceptor and 3% diphenylether as additive suppress aggregation. OSCs with P(BDT‐TCNT) as the electron donor exhibited a power conversion efficiency (PCE) of 4.10% with a short‐circuit current density of J_SC = 9.06 mA/cm², an open‐circuit voltage of V_OC = 0.77 V, and a fill factor of FF = 0.58. OSCs formed using P(DTBDAT‐TCNT) as the electron donor layer exhibited a PCE of 5.83% with J_SC = 12.2 mA/cm², V_OC = 0.77 V, and FF = 0.62. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3182–3192     

Macrocyclic Encapsulation in a Non-fused Tetrathiophene Acceptor for Efficient Organic Solar Cells with High Short-Circuit Current Density

Non-fullerene acceptors have shown great promise for organic solar cells (OSCs). However, challenges in achieving high efficiency molecular system with conformational unicity and effective molecular stacking remain. In this study, we present a new design of non-fused tetrathiophene acceptor R4T-1 via employing the encapsulation of tetrathiophene with macrocyclic ring. The single crystal structure analysis reveals that cyclic alkyl side chains can perfectly encapsulate the central part of molecule and generate a conformational stable and planar molecular backbone. Whereas, the control 4T-5 without the encapsulation restriction displays cis- and twisted conformation. As a result, R4T-1 based OSCs achieved an outstanding power conversion efficiency (PCE) exceeding 15.10 % with a high short-circuit current density (J_sc) of 25.48 mA/cm², which is significantly improved by ≈30 % in relative to that of the control. Our findings demonstrate that the macrocyclic encapsulation strategy could assist fully non-fused electron acceptors (FNEAs) to achieve a high photovoltaic performance and pave a new way for FNEAs design.