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Comprehensive Summary: In the last few years, organic solar cells (OSCs) have made significant progress in photovoltaic performance, mainly due to the innovative development of active layer materials, especially Y‐series and related derivatives as acceptors which have become the key factor that boosts the power conversion efficiency. Recently, to achieve high‐performance OSCs, an emerging molecular design strategy of applying flexible alkyl units as linkers to construct non‐fully conjugated acceptors has been developed and addressed great attention. This review highlights the non‐fully conjugated photovoltaic materials with Y‐series backbone that enable high‐performance OSCs. Impressive OSCs have been achieved by some representative non‐fully conjugated material systems. The related molecular design strategies are discussed in detail. Finally, a brief summary and future prospect are provided in advancing the non‐fully conjugated photovoltaic materials with Y‐series backbone towards the brighter future. Key Scientists: [ABSTRACT FROM AUTHOR]

The reproducibility issue is impeding the progress of commercialization in organic photovoltaic (OPV) devices, as the difficulty in precise micro‐nano structure control in bulk heterojunction films, as well as the ineluctable fluctuations of molecular weight and polydispersity index in the synthetic process. Due to such intrinsic properties, the poor regioregularity significantly affects the batch‐to‐batch variation in performance of large‐area or integrative scattered OPV devices. Seeking alternatives as compensatory strategies is expected to reduce the inevitable problem of reproducibility in the fabrication process. Herein, the application potential of a pseudo‐bilayer structure in high‐performance OPVs, by using the solution‐processed method is thoroughly examined, and it is observed that the sequentially‐deposited solar cells enjoy improve device reproducibility in addition to the power conversion efficiency (PCE) enhancement. Importantly, such desirable reproducibility in layer‐by‐layer structures raised from the film formation process provides new opportunities in ternary OPV devices, and an improved PCE of 18.70% can be achieved in a PM6/L8‐BO:PY‐IT device, where the counterpart ternary cases exhibit a decreasing trend in performance with the increasing content of PY‐IT. This work illustrates the spatial effects of pseudo‐bilayer OPV devices in the aspect of charge carrier transport/transfer, morphology and film formation kinetics, and provides a novel perspective to overcome the barriers to commercialization. [ABSTRACT FROM AUTHOR]

The determination of molecular conformations of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of their resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F‐Se and DIBP3F‐S, which bridged two segments of Y6‐derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O‐shaped conformations other than S‐ or U‐shaped counter‐ones. Notably, this O‐shaped conformation is likely governed by a distinctive "conformational lock" mechanism, arising from the intensified intramolecular π–π interactions among their two terminal groups within the dimers. PSCs based on DIBP3F‐Se deliver a maximum efficiency of 18.09 %, outperforming DIBP3F‐S‐based cells (16.11 %) and ranking among the highest efficiencies for OA‐based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high‐performance PSCs. [ABSTRACT FROM AUTHOR]

In organic solar cells with very small energetic‐offset (ΔELE − CT), the charge‐transfer (CT) and local‐exciton (LE) states strongly interact via electronic hybridization and thermal population effects, suppressing the non‐radiative recombination. Here, we investigated the impact of these effects on charge generation and recombination. In the blends of PTO2:C8IC and PTO2:Y6 with very small, ultra‐fast CT state formation was observed, and assigned to direct photoexcitation resulting from strong hybridization of the LE and CT states (i.e., LE‐CT intermixed states). These states in turn accelerate the recombination of both CT and charge separated (CS) states. Moreover, they can be significantly weakened by an external‐electric field, which enhanced the yield of CT and CS states but attenuated the emission of the device. This study highlights that excessive LE‐CT hybridization due to very low , whilst enabling direct and ultrafast charge transfer and increasing the proportion of radiative versus non‐radiative recombination rates, comes at the expense of accelerating recombination losses competing with exciton‐to‐charge conversion process, resulting in a loss of photocurrent generation. [ABSTRACT FROM AUTHOR]

The power conversion efficiency (PCE) of all‐polymer solar cells (all‐PSCs) has ascended rapidly arising from the development of polymerized small‐molecule acceptor materials. However, numerous insulating long alkyl chains, which ensure the solubility of the polymer, result in inferior aggregation and charge mobility. Herein, this study proposes a facile random copolymerization strategy of two small molecule acceptor units with different lengths of alkyl side chains and synthesizes a series of polymer acceptors PYT‐EHx, where x is the percentage of the short alkyl chain units. The aggregation strength and charge mobility of the acceptors rise linearly with increasing the proportion of short alkyl chain units. Thus, the PYT‐EH20 reaches balanced aggregation with the star polymer donor PBDB‐T, resulting in optimal morphology, fastest carrier transport, and reduced recombination and energy loss. Consequently, the PYT‐EH20‐based device yields a 14.8% PCE, a 16% improvement over the control PYT‐EH0‐based device, accompanied by an increase in open‐circuit voltage (Voc), short‐circuit current density (Jsc), and fill factor (FF). This work demonstrates that the random copolymerization strategy with short alkyl chain insertion is an effective avenue for developing high‐performance polymer acceptors, which facilitates further advances in the efficiency of all‐PSCs. [ABSTRACT FROM AUTHOR]

Developing organic solar cells based on a ternary active layer is one of the most effective approaches to improve their photovoltaic performance. However, limited success has been achieved in all‐polymer solar cells (all‐PSCs). In this study, a ternary all‐PSC with improved efficiency and stability is realized by using J71 as the third component to adjust the host system of PBDB‐T:PG1. The deeper highest occupied molecular orbital (HOMO) energy level of J71 downshifts the mixed HOMO energy levels of donors. The two polymer donors (PDs) have good miscibility and present Förster resonance energy transfer. When blended with PG1, the optimized morphology is obtained, showing enhanced crystallinity but meanwhile slightly reduced phase separation with improved exciton dissociation and collection efficiency, suppressed charge recombination, and reduced energy loss (0.55 eV). Combining the benefits mentioned above, the ternary all‐PSC exhibits an excellent efficiency of 12.8% with simultaneously elevated open‐circuit voltage (0.96 V), short‐circuit current density (18.4 mA cm−2), and fill factor (72.2%). Moreover, the optimized ternary all‐PSC shows improved storage and thermal stability. This study demonstrates that the utilization of a ternary all‐polymer system based on two well‐miscible PDs is an effective strategy to enhance the photovoltaic performance and stability of all‐PSCs. [ABSTRACT FROM AUTHOR]

We designed and synthesized an asymmetric non-fullerene small molecule acceptor (NF-SMA) IDT-TNIC with an A–D–π–A structure, based on an indacenodithiophene (IDT) central core, with a unidirectional non-fused alkylthio-thiophene (T) π-bridge, and 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene)malononitrile (NIC) extended terminal groups. IDT-TNIC molecules still maintain a good coplanar structure, which benefits from the non-covalent conformational locks (NCL) between O···S and S···S. The asymmetric structure increases the molecular dipole moment, and the extended terminal group broadens the absorption of the material, resulting in an excellent photovoltaic performance of IDT-TNIC. The photovoltaic device, based on PBDB-T:IDT-TNIC, exhibits an energetic PCE of 11.32% with a high Voc of 0.87 V, high Jsc of 19.85 mA cm−2, and a low energy loss of 0.57 eV. More importantly, IDT-TNICs with asymmetric structures show a superior property compared to symmetric IDT-Ns. The results demonstrate that it is an effectual strategy to enhance the properties of asymmetric A–D–π–A-based NF-SMAs with non-fused NCL π-bridges and extended terminal groups. [ABSTRACT FROM AUTHOR]

To fabricate organic solar cells (OSCs) via slot‐die coating, solvent additives are essential to induce an optimized phase‐separated and order morphology. It is critical to determine the morphological evolution from solution to solid state and understand the crystallization kinetics in slot‐die coating. Using in situ grazing‐incidence wide‐angle X‐ray scattering characterization, the morphological evolution in PM6‐ and ITIC‐based systems without or with 0.3% 1,8‐diiodooctane (DIO) as additive can be monitored in real‐time during slot‐die coating. As a result, DIO weakens the planarization of the PM6 backbone and splits the backbone ordering into fragments to form ordered crystallites. DIO also induces surface crystallization to reinforce the tie‐chain connections between the crystallites. Furthermore, in the ITIC system, DIO triggers the formation of an interconnected fibril network morphology and concurrently promotes the stacking of ITIC molecules in between the polymer network. Thus, an optimized morphology with a refined crystal structure is formed with the help of DIO. As a result, the power conversion efficiency is improved from 8.77% to 9.59% in slot‐die‐coated OSCs. These findings provide guidelines for optimizing the morphology in slot‐die‐coated OSCs and accelerate the transition of laboratory‐scale fabrication to industrial production. [ABSTRACT FROM AUTHOR]

Due to their high transparency, electrodes fabricated from conductive polymers are often implemented in semitransparent organic solar cells. Opaque solar cells usually employ metal back electrodes with high reflectivity for best photon confinement in the light‐harvesting layer. Herein, a bilayer back electrode comprising conductive polymers and nanofoamed poly(methyl methacrylate) (PMMA) is investigated, the latter of which creates diffuse reflection of the incoming light. By tuning the thickness of the nanofoamed PMMA layer, absorption and transmission of the solar cells can be tailored from opaque to vastly transparent. Due to its diffusive character, this versatile electrode enhances the light absorption in the wavelength regimes with lower absorption coefficient. The solar cells are particularly suited for deployment in frosted window applications. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Recently, the asymmetric nonfullerene acceptors (NFAs) with acceptor‐donor‐acceptor (A‐D‐A) structure have been developed rapidly, especially for the modification of asymmetric core, asymmetric side chains and asymmetric end groups. In this work, a novel asymmetric A‐D‐π‐A type NFA with a noncovalently fused‐ring core named PIST‐4F is synthesized, containing an indacenodithieno[3,2‐b]dithiophene (IDT), two strong electron‐withdrawing end groups and an alkylthio‐substituted thiophene π‐bridge. Benefiting from the S···S noncovalent interaction between the sulfur atom on π‐bridge and the adjacent thiophene in IDT, the PIST‐4F presents nearly planar geometry and extended conjugated area, resulting in the optimized electronic properties, charge transport, and film morphology compared to the symmetric NFA PI‐4F. As a result, PM6:PIST‐4F‐based devices achieve a higher power conversion efficiency (PCE) of 13.8%, while the PM6:PI‐4F‐based devices only show a PCE of 7.1%. Notably, the PM6:PIST‐4F‐based devices processed with nonhalogen solvent toluene exhibit an excellent PCE as high as 13.1%. These results indicate that PIST‐4F is an effective acceptor for high‐efficiency organic solar cells. [ABSTRACT FROM AUTHOR]

How to simultaneously achieve both high open‐circuit voltage (Voc) and high short‐circuit current density (Jsc) is a big challenge for realising high power conversion efficiency (PCE) in all‐small‐molecule organic solar cells (all‐SM OSCs). Herein, a novel small molecule (SM)‐donor, namely FYSM−SiCl, with trialkylsilyl and chlorine substitutions was designed and synthesized. Compared to the original SM‐donor FYSM−H, FYSM−Si with trialkylsilyl substitution showed a decreased crystallinity and lower highest occupied molecular orbital (HOMO) level, while FYSM−SiCl had an improved crystallinity, more ordered packing arrangement, significantly lower HOMO level, and predominant "face‐on" orientation. Matched with a SM‐acceptor Y6, the FYSM−SiCl‐based all‐SM OSCs exhibited both high Voc of 0.85 V and high Jsc of 23.7 mA cm−2, which is rare for all‐SM OSCs and could be attributed to the low HOMO level of FYSM−SiCl donor and the delicate balance between high crystallinity and suitable blend morphology. As a result, FYSM−SiCl achieved a high PCE of 13.4 % in all‐SM OSCs, which was much higher than those of the FYSM−H‐ (10.9 %) and FYSM−Si‐based devices (12.2 %). This work demonstrated a promising method for the design of efficient SM‐donors by a side‐chain engineering strategy via the introduction of trialkylsilyl and chlorine substitutions. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Side‐chain engineering as one of the most important molecular design strategies has been widely used to improve photovoltaic efficiency of active layer materials. Herein, a series of acceptor‐π‐donor‐π‐acceptor typed small molecule (SM)‐donors (SL1, SL2, SL3, and SL4), on the basis of high‐performance SM‐donor BTTzR (SL1) with thiazolo[5,4‐d]thiazole as the π‐bridging units and 3‐butylrhodanine as the terminal electron‐withdrawing groups, were designed and synthesized to study the effect of the side‐chain substitutions of BDT‐T on the photovoltaic performance. The investigation shows that the side‐chain engineering has no obvious effect on the molecular absorption spectrum and energy levels but significantly influences on the molecular orientation and packing, and the compatibility with the acceptor Y6. Among these SM‐donors neat films, SL1 and SL3 with two mixed branched and straight alkyl chains exhibit stronger crystallization in the face‐on direction, and SL4 with two shorter alkyl chains achieves more compact packing. In the Y6‐based blend films, three SM‐donors (SL1, SL3, and SL4) with double alkyl chains on thienyl of BDT‐T have much better compatibility compared to SL2 with single long alkyl chain, while their compatibility increases with the increase of alkyl chain length. The stronger crystallization, moderate molecular packing, and better blend compatibility of SL1 offer higher Jsc of 23.2 mA·cm–2 and fill factor (FF) of 0.68 in the Y6‐based all‐small‐molecule organic solar cells (all‐SM‐OSCs). Ultimately, the SL1:Y6‐based devices achieved a promising power conversion efficiency of 13.9%, which is much higher than that of 11.5% from the SL2:Y6‐based devices (Jsc = 21.5 mA·cm–2 and FF = 0.60). This work indicates that modulating the side chain of SM‐donors is a promising strategy to obtain efficient all‐SM‐OSCs. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Recently, the polymer solar cells (PSCs) based on the PM6 and small molecular acceptor (SMA) Y6 have attracted considerable attention in this community for their outstanding photovoltaic performance. As well known, the molecular weight of polymer has dramatic impact on the blend morphology and photovoltaic performance in the polymer solar cells, especially for those polymers with temperature‐dependent aggregation (TDA) behavior. In this work, a series of PM6 polymers with different weight‐average molecular weights (Mw = 41, 67, 74, 84 and 114 kDa) were synthesized, and the effects of the Mw on the morphology and photovoltaic performance were systematically investigated. Notably, molecular weight induces dramatic influences on the aggregation behaviors of the polymers and their corresponding blend morphology, which were explored by the temperature‐dependent UV‐vis absorptions (TD‐Abs), grazing incidence wide‐angle X‐ray scattering (GIWAXS) and resonant soft X‐ray scattering (R‐SoXS) measurements. Increasing Mw promoted the strong face‐on molecular packing and reduced the blend film domain sizes for enhanced donor‐acceptor interfacial areas, resulting in increased short‐circuit current densities (Jsc) and fill factor (FF). However, polymer donor with high Mw value processed stronger tendency of forming excessive pure donor aggregate, which hampered forming the intermixed phase for efficient charge transport, resulting in the inferior FF. Therefore, the optimized OSCs based on PM6 with moderate molecular weight (Mw = 74 kDa) and Y6 exhibited suitable size and purity of the domains, facilitating well‐balanced charge transport, reducing trap‐assisted recombination and leading to significant enhancement of photovoltaic performance with the optimal PCE of 17.1%. This work indicates that proper and precisely tuning the molecular weight of polymer donor is critical to enhance the photovoltaic performance in PSCs. [ABSTRACT FROM AUTHOR]

In non‐fullerene‐based photovoltaic devices, it is unclear how excitons efficiently dissociate into charge carriers under small driving force. Here, we developed a modified method to estimate dielectric constants of PM6 donor and non‐fullerene acceptors. Surprisingly, most non‐fullerene acceptors and blend films showed higher dielectric constants. Moreover, they exhibited larger dielectric constants differences at the optical frequency. These results are likely bound to reduced exciton binding energy and bimolecular recombination. Besides, the overlap between the emission spectrum of donor and absorption spectra of non‐fullerene acceptors allowed the energy transfer from donor to acceptors. Hence, based on the synergistic effect of dielectric property and energy transfer resulting in efficient charge separation, our finding paves an alternative path to elucidate the physical working mechanism in non‐fullerene‐based photovoltaic devices. [ABSTRACT FROM AUTHOR]

Regulating molecular structure to optimize the active layer morphology is of considerable significance for improving the power conversion efficiencies (PCEs) in organic solar cells (OSCs). Herein, we demonstrated a simple ternary copolymerization approach to develop a terpolymer donor PM6‐Tz20 by incorporating the 5,5′‐dithienyl‐2,2′‐bithiazole (DTBTz, 20 mol%) unit into the backbone of PM6 (PM6‐Tz00). This method can effectively tailor the molecular orientation and aggregation of the polymer, and then optimize the active layer morphology and the corresponding physical processes of devices, ultimately boosting FF and then PCE. Hence, the PM6‐Tz20: Y6‐based OSCs achieved a PCE of up to 17.1% with a significantly enhanced FF of 0.77. Using Ag (220 nm) instead of Al (100 nm) as cathode, the champion PCE was further improved to 17.6%. This work provides a simple and effective molecular design strategy to optimize the active layer morphology of OSCs for improving photovoltaic performance. [ABSTRACT FROM AUTHOR]

A non‐conjugated polymer acceptor PF1‐TS4 was firstly synthesized by embedding a thioalkyl segment in the mainchain, which shows excellent photophysical properties on par with a fully conjugated polymer, with a low optical band gap of 1.58 eV and a high absorption coefficient >105 cm−1, a high LUMO level of −3.89 eV, and suitable crystallinity. Matched with the polymer donor PM6, the PF1‐TS4‐based all‐PSC achieved a power conversion efficiency (PCE) of 8.63 %, which is ≈45 % higher than that of a device based on the small molecule acceptor counterpart IDIC16. Moreover, the PF1‐TS4‐based all‐PSC has good thermal stability with ≈70 % of its initial PCE retained after being stored at 85 °C for 180 h, while the IDIC16‐based device only retained ≈50 % of its initial PCE when stored at 85 °C for only 18 h. Our work provides a new strategy to develop efficient polymer acceptor materials by linkage of conjugated units with non‐conjugated thioalkyl segments. [ABSTRACT FROM AUTHOR]

Two wide‐bandgap (WBG) conjugated polymers (PBPD‐p and PBPD‐m) based on phenyl‐substituted benzodithiophene (BDT) with the different substitution position of the alkyl side chain and benzodithiophene‐4,8‐dione (BDD) units are designed and synthesized to investigate the influence of alkyl substitution position on the photovoltaic performance of polymers in polymer solar cells (PSCs). The thermogravimetric analysis, absorption spectroscopy, molecular energy level, X‐ray diffraction, charge transport and photovoltaic performance of the polymers are systematically studied. Compared with PBPD‐p, PBPD‐m exhibits a slight blue‐shift but a deeper highest occupied molecular orbital (HOMO) energy level, a tighter alkyl chain packing and a higher hole mobility. The PBPD‐m‐based PSCs blended with acceptor IT‐4F shows a higher power conversion efficiency (PCE) of 11.95% with a high open‐circuit voltage (Voc) of 0.88 V, a short‐circuit current density (Jsc) of 19.76 mA cm−2 and a fill factor (FF) of 68.7% when compared with the PCE of 6.97% with a Voc of 0.81 V, a Jsc of 15.97 mA cm−2 and an FF of 53.9% for PBPD‐p. These results suggest that it is a feasible and effective strategy to optimize photovoltaic properties of WBG polymers by changing the substitution position of alkyl side chain in PSCs. [ABSTRACT FROM AUTHOR]

Molecular ordering and miscibility of donor and acceptor materials play critical roles in developing high‐performance as‐cast polymer solar cells (PSCs). In this work, a highly crystalline nonfullerene small molecular acceptor, namely, C8‐IT‐4F, based on alkylated indacenodithieno[3,2‐b]thiophene as the aromatic core and 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile moieties as end groups, is selected and synthesized. The π–π stacking distance in C8‐IT‐4F film can be tuned from 3.88 Å to a more compact (3.48 Å) state by a film‐formation process and the confinement induced by the preaggregated polymer donor PM7, leading to broadened absorption and fine phase separation in the blend film. The optimal morphology with a framework of preaggregated polymer donor, J‐type face‐on π–π stacked acceptor, and appropriate donor/acceptor miscibility facilitates charge generation and transport and reduces charge recombination. As a result, the best PSC based on the as‐cast PM7:C8‐IT‐4F blend film exhibits power conversion efficiency of 14.3%, with an open‐circuit voltage of 0.82 V, a short‐circuit current density of 22.7 mA cm−2, a fill factor of 77.1%, and good photostability with a stabilized fill factor. [ABSTRACT FROM AUTHOR]

Summary of main observation and conclusion: Small molecular acceptors (SMAs) BTC‐2F and BTH‐2F, based on heptacyclic benzodi(cyclopentadithiophene) electron‐donating core (CBT) with chlorinated‐thienyl conjugated and thienyl conjugated side chains, respectively, are designed and synthesized. Compared with non‐chlorine acceptor BTH‐2F, BTC‐2F exhibits slightly blue‐shifted absorption spectra, similar the lowest unoccupied molecular orbital (LUMO) (–3.91 eV), deeper highest occupied molecular orbital (HOMO) energy level and higher electron mobility than that of BTH‐2F. PM6, a wide bandgap polymer, is selected as the donor material to construct bulk heterojunction polymer solar cells processed with nonhalogenated solvent toluene. The optimized PM6:BTC‐2F‐based device presents a 12.9% power conversion efficiency (PCE), while the PCE of PM6:BTH‐2F‐based device is only 11.3%. The results suggest that it is an effective strategy to optimize the photoelectric properties of SMAs by incorporating chlorine atom into the conjugated side chains. [ABSTRACT FROM AUTHOR]

The prosperous period of polymer solar cells (PSCs) has witnessed great progress in molecule design methods to promote power conversion efficiency (PCE). Designing asymmetric structures has been proved effective in tuning energy level and morphology, which has drawn strong attention from the PSC community. Two hepta‐ring and octa‐ring asymmetric small molecular acceptors (SMAs) (IDTP‐4F and IDTTP‐4F) with S‐shape and C‐shape confirmations are developed to study the relationship between conformation shapes and PSC efficiencies. The similarity of absorption and energy levels between two SMAs makes the conformation a single variable. Additionally, three wide‐bandgap polymer donors (PM6, S1, and PM7) are chosen to prove the universality of the relationship between conformation and photovoltaic performance. Consequently, the champion PCE afforded by PM7: IDTP‐4F is as high as 15.2% while that of PM7: IDTTP‐4F is 13.8%. Moreover, the S‐shape IDTP‐4F performs obviously better than their IDTTP‐4F counterparts in PSCs regardless of the polymer donors, which confirms that S‐shape conformation performs better than the C‐shape one. This work provides an insight into how conformations of asymmetric SMAs affect PCEs, specific functions of utilizing different polymer donors to finely tune the active‐layer morphology and another possibility to reach an excellent PCE over 15%. [ABSTRACT FROM AUTHOR]

Keywords: Acceptor; Molecular Conformation; Oligomer; Selenophene; Solar Cells EN Acceptor Molecular Conformation Oligomer Selenophene Solar Cells 1 1 1 10/31/23 20231106 NES 231106 B Two dimeric acceptors b , DIBP3F-Se and DIBP3F-S were synthesized by linking two Y6-derivative segments using different central linking bridges: selenophene and thiophene. Acceptor, Molecular Conformation, Oligomer, Selenophene, Solar Cells Paired with the state-of-the-art polymer donor PM6, optimized solar cells employing DIBP3F-Se showcase remarkable performance with a power conversion efficiency of 18.09 %, as demonstrated by Donghong Yu, Thomas D. Anthopoulos, Ergang Wang et al. in their Research Article (e202302888). [Extracted from the article]

Keywords: Acceptor; Molecular Conformation; Oligomer; Selenophene; Solar Cells EN Acceptor Molecular Conformation Oligomer Selenophene Solar Cells 1 1 1 10/31/23 20231106 NES 231106 B Two dimeric acceptors b , DIBP3F-Se and DIBP3F-S were synthesized by linking two Y6-derivative segments using different central linking bridges: selenophene and thiophene. Paired with the state-of-the-art polymer donor PM6, optimized solar cells employing DIBP3F-Se showcase remarkable performance with a power conversion efficiency of 18.09 %, as demonstrated by Donghong Yu, Thomas D. Anthopoulos, Ergang Wang et al. in their Research Article (e202302888). Back Cover: On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18 % (Angew. [Extracted from the article]

Over the past decade, organic solar cells (OSCs) have achieved a dramatic boost in their power conversion efficiencies from about 6 % to over 16 %. In addition to developments in device engineering, innovative photovoltaic materials, especially fluorinated donors and acceptors, have become the dominant factor for improved device performance. This minireview highlights fluorinated photovoltaic materials that enable efficient OSCs. Impressive OSCs have been obtained by developing some important molds of fluorinated donor and acceptor systems. The molecular design strategy and the matching principle of fluorinated donors and acceptors in OSCs are discussed. Finally, a concise summary and outlook are presented for advances in fluorinated materials to realize the practical application of OSCs. [ABSTRACT FROM AUTHOR]

Nonfullerene polymer solar cells (PSCs) are fabricated with a perylene monoimide-based n-type wide-bandgap organic semiconductor PMI-F-PMI as an acceptor and a bithienyl-benzodithiophene-based wide-bandgap copolymer PTZ1 as a donor. The PSCs based on PTZ1:PMI-F-PMI (2:1, w/w) with the treatment of a mixed solvent additive of 0.5% N-methyl pyrrolidone and 0.5% diphenyl ether demonstrate a very high open-circuit voltage ( Voc) of 1.3 V with a higher power conversion efficiency (PCE) of 6%. The high Voc of the PSCs is a result of the high-lying lowest unoccupied molecular orbital (LUMO) of −3.42 eV of the PMI-F-PMI acceptor and the low-lying highest occupied molecular orbital (HOMO) of −5.31 eV of the polymer donor. Very interestingly, the exciton dissociation efficiency in the active layer is quite high, even though the LUMO and HOMO energy differences between the donor and acceptor materials are as small as ≈0.08 and 0.19 eV, respectively. The PCE of 6% is the highest for the PSCs with a Voc as high as 1.3 V. The results indicate that the active layer based on PTZ1/PMI-F-PMI can be used as the front layer in tandem PSCs for achieving high Voc over 2 V. [ABSTRACT FROM AUTHOR]

A new fluorinated polythiophENe (PT) derivative, PBDD ‐ ff4T, is designed and synthesized. The PBDD ‐ ff4T/PC71BM ‐ based device without any extra treatmENt exhibits a high efficiENcy of 9.2%, under the irradiation of AM 1.5G, 100 mW cm−2, which is the highest power conversion efficiENcy reported for PT derivative ‐ based polymer solar cells. [ABSTRACT FROM AUTHOR]

A new broad bandgap and 2D-conjugated D-A copolymer, PBDTBTz-T, based on bithienyl-ben zodithiophene donor unit and bithiazole (BTz) acceptor unit, is designed and synthesized for the application as donor material in polymer solar cells (PSCs). The polymer possesses highly coplanar and crystalline structure with a higher hole mobility and lower HOMO energy level which is beneficial to achieve higher open circuit voltage (Voc) of the PSCs with the polymer as donor. The PSCs based on PBDTBTz-T:PC71BM blend film with a lower PC71BM content of 40% demonstrate a power conversion efficiency (PCE) of 6.09% with a relatively higher Voc of 0.92 V. These results indicate that the lower HOMO energy level of the BTz-based D-A copolymer is beneficial to a high Voc of the PSCs. The polymer, with highly coplanar and crystalline structure, can effectively reduce the content of fullerene acceptor in the active layer and can enhance the absorption and PCE of the PSCs. [ABSTRACT FROM AUTHOR]

A new D–A copolymer, poly(thieno[3,2-b]thiophene-alt-bithiazole) (PTTBTz),based on thieno[3,2-b]thiophene donor unit and bithiazoleacceptor unit, wassynthesized by the Pd-catalyzed Stille-coupling reaction for the applicationas donor material in polymer solar cells (PSCs). PTTBTzfilm possesses high thermal stability with 5% weight-loss temperatureat 450 °C, a lower-lying HOMO energy level at −5.20 eV,a higher hole mobility of 6.45 × 10–3cm2/(V s), and a crystalline structure. Photovoltaic performanceof the polymer was investigated with [6,6]-phenyl-C71-butyricacid methyl ester (PC70BM) or indene-C60bisadduct(ICBA) as acceptor and with 3% DIO additive. The power conversionefficiency (PCE) of the PSC based on PTTBTz:ICBA (1:1w/w) reached 5.35% with a high Vocof1.03 V, a Jscof 8.55 mA/cm2, and an FF of 0.608, whereas the PCE of the PSC based on PTTBTz:PC70BM (1:1 w/w) was 4.57% with a Vocof 0.82 V, a Jscof 9.89 mA/cm2, and an FF of 0.563, under the illumination of AM1.5, 100mW/cm2. PTTBTzis one of the D–A copolymersthat shows better photovoltaic performance with ICBA as acceptor thanPC70BM. PTTBTz/ICBA could be a promising frontactive layer for high-efficiency tandem PSC because of its high Voc. [ABSTRACT FROM AUTHOR]

Two poly(thiazole vinylene) derivatives, poly(4-hexylthiazole vinylene) (P4HTzV) and poly(4-nonylthiazole vinylene) (P4NTzV), were synthesized by Pd-catalyzed Stille coupling method. The polymers are soluble in common organic solvents such as o-dichlorobenzene and chloroform, and possess good thermal stability. P4HTzV and P4NTzV films exhibit broad absorption bands at 400-720 nm with an optical bandgap of 1.77 eV and 1.74 eV, respectively. The HOMO (the highest occupied molecular orbital) energy levels of P4HTzV and P4NTzV are −5.11 and −5.12 eV, respectively, measured by cyclic voltammetry. Preliminary results of the polymer solar cells based on P4HTzV : PC61BM ([6,6]-phenyl-C-61-butyric acid methyl ester) (1 : 1, w/w) show a power conversion efficiency of 0.21% with an open-circuit voltage of 0.55 V and a short circuit current density of 1.11 mA cm−2, under the illumination of AM1.5G, 100 mW cm−2. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Abstract: Two D–A copolymers containing dithienosilole (DTS) donor unit and phthalimide (Ph) acceptor unit, PDTSPh and PDTSBTPh, were synthesized by the Pd-catalyzed Stille-coupling method. The copolymers have a strong absorption ranging from 350 to 650nm, exhibit good solubility and thermal stability. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the copolymers determined by cyclic voltammetry were about −5.2 and −3.0eV, respectively. The power conversion efficiency of the polymer solar cells based on PDTSBTPh:PC70BM (1:2, w/w) reached 2.1% with open-circuit voltage of 0.83V and a short-circuit current of 6.27mA/cm2, under the illumination of AM1.5, 100mW/cm2. [Copyright &y& Elsevier]

A new benzodithiophene (BDT)‐based polymer, poly(4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene vinylene) (PBDTV), was synthesized by Pd‐catalyzed Stille‐coupling method. The polymer is soluble in common organic solvents and possesses high thermal stability. PBDTV film shows a broad absorption band covering from 350 nm to 618 nm, strong photoluminescence peaked at 545 nm and high hole mobility of 4.84 × 10−3 cm2/Vs. Photovoltaic properties of PBDTV were studied by fabricating the polymer solar cells based on PBDTV as donor and PC70BM as acceptor. With the weight ratio of PBDTV: PC70BM of 1:4 and the active layer thickness of 65 nm, the power conversion efficiency of the device reached 2.63% with Voc = 0.71 V, Isc = 6.46 mA/cm2, and FF = 0.57 under the illumination of AM1.5, 100 mW/cm2. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1822–1829, 2010 [ABSTRACT FROM AUTHOR]

We study the ultrafast photoexcitation dynamics in PBDTTT-C-T (P51, poly(4,8-bis(5-(2-ethylhexyl)-thiophene-2-yl)-benzo[1,2-b:4,5-b′]dithiophene-alt-alkylcarbonyl-thieno[3,4-b]thiophene)) film (~100 nm thickness) and PBDTTT-C-T:PC71BM (P51:PC71BM, phenyl-C71-butyric-acid-methyl ester) nanostructured blend (∼100 nm thickness) with/without DIO(1,8-diiodooctane) additives with sub-10 fs transient absorption (TA). It is revealed that hot-exciton dissociation and vibrational relaxation could occur in P51 with a lifetime of ~160 fs and was hardly affected by DIO. However, the introduction of DIO in P51 brings a longer lifetime of polaron pairs, which could make a contribution to photocarrier generation. In P51:PC71BM nanostructured blends, DIO could promote the Charge Transfer (CT) excitons and free charges generation with a ~5% increasement in ~100 fs. Moreover, the dissociation of CT excitons is faster with DIO, showing a ~5% growth within 1 ps. The promotion of CT excitons and free charge generation by DIO additive is closely related with active layer nanomorphology, accounting for Jsc enhancement. These results reveal the effect of DIO on carrier generation and separation, providing an effective route to improve the efficiency of nanoscale polymer solar cells. [ABSTRACT FROM AUTHOR]

A strong electron-withdrawing unit, naphtho[2,3-c]thiophene-4,9-dione, was copolymerized with dithienosilole to get a D–A copolymer, PDTSNTDO, with a narrow bandgap and lower-lying HOMO level. The PCE of the PDTSNTDO-based device reached 5.21%, with a high open circuit voltage of 0.88 V. [ABSTRACT FROM AUTHOR]

A new copolymer of dithienosilole and dithienylthiazolo[5,4-d]thiazole with a hexyl side chain on the 4-position of thiophene units was designed and synthesized. Polymer solar cells based on the polymer as a donor and PC70BM as an acceptor demonstrated a power conversion efficiency up to 5.88% with a high fill factor of 71.6%. [ABSTRACT FROM AUTHOR]

Developing a high-performance donor polymer is critical for achieving efficient non-fullerene organic solar cells (OSCs). Currently, most high-efficiency OSCs are based on a donor polymer named PM6, unfortunately, whose performance is highly sensitive to its molecular weight and thus has significant batch-to-batch variations. Here we report a donor polymer (named PM1) based on a random ternary polymerization strategy that enables highly efficient non-fullerene OSCs with efficiencies reaching 17.6%. Importantly, the PM1 polymer exhibits excellent batch-to-batch reproducibility. By including 20% of a weak electron-withdrawing thiophene-thiazolothiazole (TTz) into the PM6 polymer backbone, the resulting polymer (PM1) can maintain the positive effects (such as downshifted energy level and reduced miscibility) while minimize the negative ones (including reduced temperature-dependent aggregation property). With higher performance and greater synthesis reproducibility, the PM1 polymer has the promise to become the work-horse material for the non-fullerene OSC community. The batch reproducibility of polymer donor materials limits the performance of polymer solar cells. Here Wu et al. develop a polymer donor PM1 by random terpolymerization strategy with a high efficiency of 17.6% in the device and excellent batch-to-batch reproducibility. [ABSTRACT FROM AUTHOR]

Two new wide bandgap block copolymers (PL1 and PL2) with porphyrin‐incorporated side chains are designed and used as electron donors for solution‐processed bulk heterojunction polymer solar cells. The photophysical, electrochemical, and photovoltaic properties, charge transport mobility and film morphology of these two block copolymers are investigated. Detailed investigations reveal that the different alkyl groups and electron‐withdrawing substituents on the porphyrin pendant units have significant influence on the polymer solubility, absorption energy level, band gap, and charge separation in the bulk‐heterojunction thin films, and thus the overall photovoltaic performances. Organic photovoltaic devices derived from these copolymers and ([6,6]‐phenyl‐C71‐butyric acid methyl ester) (PC71BM) acceptor show the best power conversion efficiencies of 5.83% and 7.14%, respectively. These results show that the inclusion of a certain proportion of side chain porphyrin group as a pendant in the traditional donor‐acceptor (D‐A) type polymer can broaden the molecular absorption range and become a full‐color absorbing molecule. The size of the porphyrin pendant also has an obvious effect on the properties of the molecule. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: In the last few years, organic solar cells (OSCs) have made significant progress in photovoltaic performance, mainly due to the innovative development of active layer materials, especially Y‐series and related derivatives as acceptors which have become the key factor that boosts the power conversion efficiency. Recently, to achieve high‐performance OSCs, an emerging molecular design strategy of applying flexible alkyl units as linkers to construct non‐fully conjugated acceptors has been developed and addressed great attention. This review highlights the non‐fully conjugated photovoltaic materials with Y‐series backbone that enable high‐performance OSCs. Impressive OSCs have been achieved by some representative non‐fully conjugated material systems. The related molecular design strategies are discussed in detail. Finally, a brief summary and future prospect are provided in advancing the non‐fully conjugated photovoltaic materials with Y‐series backbone towards the brighter future. Key Scientists: [ABSTRACT FROM AUTHOR]

Nonfullerene polymer solar cells (PSCs) are developed based on a fluorinated thienyl‐based wide‐bandgap (WBG) polymer PBBF as the electron donor and nonfullerene small molecule IDIC as the electron acceptor. PBBF exhibits a strong absorption in the range of 300–605 nm with a wide optical bandgap of 2.05 eV, which is complementary with that of IDIC. Meanwhile, it possesses a deeper highest occupied molecular orbital energy level of  −5.52 eV and a higher hole mobility of 7.3 × 10−4 cm2 V−1 s−1 compared to the nonfluorinated polymer PBDTT. The PSCs based on PBBF:IDIC without extra treatment show a power conversion efficiency (PCE) of 8.5% with a Voc of 0.95 V, a Jsc of 15.3 mA cm−2, and an FF of 58.8%, which is much higher than that of the devices based on PBDTT:IDIC (a PCE of 5.3% with a Voc of 0.88 V, a Jsc of 13.7 mA cm−2, and an FF of 43.9%). These results indicate that PBBF is a promising WBG polymer donor material for the photovoltaic applications in nonfullerene PSCs. Nonfullerene polymer solar cells (PSCs) based on a new wide‐bandgap polymer PBBF and a narrow bandgap acceptor IDIC exhibit a power conversion efficiency (PCE) of 8.5% without extra treatment, which is much higher than that of the devices based on PBDTT:IDIC. The result indicates that PBBF is a promising wide‐bandgap polymer donor material for photovoltaic applications in nonfullerene PSCs. [ABSTRACT FROM AUTHOR]

Abstract: Fluorination of conjugated polymers is one of the effective strategies to tune the molecular energy levels and morphology for high efficient polymer solar cells (PSCs). Herein, two novel donor‐acceptor conjugated polymers, PffBT and PBT, based on bis(3,5‐bis(hexyloxy)phenyl)benzo[1,2‐ b:4,5‐b']dithiophene and benzo[c][1,2,5]thiadiazole (BT) with or without fluorination, respectively, were synthesized, and their photovoltaic properties were compared. The polymer PffBT based on fluorinated BT showed lower frontier energy levels, improved polymer ordering, and a well‐developed fibril structure in the blend with PC71BM. As a result, the PSCs based on PffBT/PC71BM exhibit a superior power conversion efficiency (PCE) of 8.6% versus 4.4% for PBT‐based devices, due to a high space charge limit current (SCLC) hole mobility, mixed orientation of polymer crystals in the active layer, and low bimolecular recombination. [ABSTRACT FROM AUTHOR]

The morphology of the active layer plays a crucial role in the device performance and stability of organic solar cells (OSCs). To obtain the optimized blend film morphology, numerous solvent additives have been developed and utilized. Nevertheless, the commonly used high boiling point solvent additives have strict volume control and residual problems, which are not conducive to the development of OSCs. To alter the situation, it is urgent to develop highly volatile additives to minimize the unfavorable effect. Here, a volatile aromatic small molecule, benzoylacetate (BA), is used as a solid additive to control the morphology of the active layer during the post-treatment procedure. More importantly, BA has an apparent positive interaction with Y6, leading to more favorable molecular arrangement in the blend film and enhanced charge transfer properties. Finally, the BA-treated PM6:Y6 device exhibits improved device performance and photostability. Moreover, BA could be used as a universal solid additive for different OSC systems. Specifically, a superior PCE of 18.5 % is achieved in BA-processed PM6:L8-BO binary system with good photostability. Our work demonstrates an approach of applying a volatile solid additive to improve the device performance and photostability. [Display omitted] • High-performance organic solar cells (OSCs) were fabricated by introducing benzoylacetone (BA), a volatile aromatic small molecule, into the non-fullerene acceptor (NFA) systems. • The addition of BA can be used to control the blend morphology and obtain improved crystallinity and appropriate phase separation. Meanwhile, good volatility of BA is beneficial to improve the photostability of OSCs. • For the binary PM6:L8-BO device, a notable PCE of 18.5 % was yielded after treatment with the BA additive, which is much higher than that of the device treated with DIO. [ABSTRACT FROM AUTHOR]

Interfacial engineering is crucial to improve the photovoltaic performance of polymer solar cells (PSCs). In this study, we demonstrate efficient inverted non-fullerene PSCs with ZnO modified by nontoxic glycine (Gly) as the electron transport layer (ETL). With the modification of Gly, work function of the ETL interlayer was decreased from 4.11 eV for ZnO to 4.02 eV for ZnO/Gly, which effectively increased the built-in electric field and hence improved the electron extraction. Furthermore, the surface energy of interlayer was also reduced from 69.1 mJ/m2 for ZnO to 52.5 mJ/m2, which is beneficial for the enrichment of the acceptor at the interface and hence facilities the electron transport and collection at cathode electrode. Therefore, the device based on PM6:IT-4F with ZnO/Gly as ETL exhibited a remarkably enhanced power conversion efficiency (PCE) of 14.0% relative to 12.9% for the control device with ZnO ETL, indicating a ∼9% increase of the PCE with the simple molecular modification of the ETL. Meanwhile, this strategy can also be successfully applied to other non-fullerene and fullerene based inverted PSCs. Our work provides an effective approach to modify ZnO for high performance PSCs. Nontoxic glycine modified ZnO was used as the electron transport layer (ETL), which shows fewer defects, lower work function and lower surface energy, and therefore promote the photovoltaic performance of the inverted non-fullerene polymer solar cells. Image 1 • Nontoxic glycine modified ZnO is used as the electron transport layer in inverted non-fullerene polymer solar cells (PSCs). • The glycine modified ZnO interlayer shows lower work function, fewer defects and lower surface energy. • With the glycine modified ZnO interlayer, higher efficiencies are obtained in the inverted non-fullerene PSCs. [ABSTRACT FROM AUTHOR]

Abstract In this work, we designed and synthesized a new acceptor-π-donor-π-acceptor (A-π-D-π-A) type small molecule (SM) donor material, BBDDR, based on thienyl-substituted benzo[1,2-b:4,5-b']dithiophene (BDT-T) as the electron-donating core, the benzo[1,2-c:4,5-c']dithiophene-4,8-dione (BDD) along with two thiophene units as π-bridge and rhodanine as the end group. BBDDR exhibits a strong absorption in the visible range of 300–700 nm with an optical bandgap (E g opt) of 1.79 eV, deep-lying HOMO energy level of −5.40 eV and high hole mobility of 1.1 × 10−3 cm2 V−1 s−1. The organic solar cells (OSCs) based on BBDDR: IDIC exhibited an optimized power conversion efficiency (PCE) of 7.8% with a high open-circuit voltage (V oc) of 1.01 V, a short circuit current density (J sc) of 14.6 mA cm−2, and a fill factor (FF) of 53% under the illumination of AM 1.5G, 100 mW cm−2. Graphical abstract By introducing BDD unit into small molecule, non-fullerene organic solar cell based on BBDDR: IDIC with a high V oc of 1.01 V was obtained. Image 1 Highlights • The novel A-π-D-π-A small molecule donor material BBDDR was synthesized. • BBDDR showed a deep-lying HOMO energy level of -5.40 eV and a high hole mobility of 1.1×10-3 cm2 V−1 s−1. • The organic solar cells based on BBDDR:IDIC exhibited a high open-circuit voltage (V oc) of 1.01 V. [ABSTRACT FROM AUTHOR]

Abstract Two non-fullerene electron acceptors (BT-SFIC and BT-FIC) bearing a dithienyl[1,2-b:4,5-b']benzodithiophene core were designed and synthesized. Due to the strong electron-withdrawing ability of fluorine atoms, these two non-fullerene acceptors both show near-infrared absorption around 900 nm, with a narrow bandgap of 1.44 and 1.39 eV for BT-SFIC and BT-FIC, respectively. BT-SFIC and BT-FIC have complementary absorption and matched energy level with PTB7-Th. PSCs based on PTB7-Th donor and these two acceptors both show good charge dissociation and collection, small charge recombination and good active layer morphology. However, BT-FIC bearing much more fluorine have much higher electron mobility. And the PSCs based on PTB7-Th: BT-FIC gives a maximum PCE of 10.10% with a V OC of 0.73 eV, a J SC of 21.28 mA cm−2 and an FF of 65%, which is among in the high-performance polymer organic solar cells based on PTB7-Th. Graphical abstract Image 1 Highlights • Florination can narrow the optical bandgap of non-fullerene acceptors. • BT-SFIC and BT-FIC can increase the PCE to 9.52% and 10.10% respectively. • High-performance PSCs basd on PTB7-Th:non-fullerene system are achived. [ABSTRACT FROM AUTHOR]

Abstract Polymer solar cells (PSCs) based on narrow bandgap (NBG) photovoltaic materials have attracted significant attention due to their unique applications in semitransparent devices and organic tandem solar cells. In this work, we design and synthesize a new NBG polymer PBTT based on 2-(2-ethylhexyl)-thienyl substituted benzodithiophene (BDT-T) and n-octyl-3-fluorothieno[3,4-b]thiophene-2-carboxylate (TT) as donor material for the applications in non-fullerene PSCs. Compared with the widely used NBG polymer PTB7-Th, PBTT exhibited higher film extinction coefficient of 9.27 × 10 4 cm−1, higher-lying energy levels, more ordered molecule packing and higher hole mobility of 2.13 × 10 −3 cm2 V−1 s −1. The PSCs based on PBTT : IEICO obtained a power conversion efficiency (PCE) of 9.5% with a V oc of 0.86 V, a J sc of 17.9 mA cm−2 and a FF of 61.3%, which is significantly enhanced over that (7.3%) of the corresponding devices with PTB7-Th as donor. The significantly improved PCE could be attributed to the higher charge mobility and the improved morphology of the PBTT : IEICO blend film. These results demonstrate that PBTT is a very promising NBG polymer donor material for the applications in non-fullerene PSCs. Graphical abstract Image 1 Highlights • A new narrow-bandgap polymer with high mobility was developed. • The optimal PSCs devices demonstrated a PCE of 9.5%. [ABSTRACT FROM AUTHOR]

Abstract A new planar A-D-A structured organic small molecule semiconductor (O-SMS) with dialkyl-thiophene substituted benzodithiophene (BDT) as central electron-rich core flanked by relatively electron-deficient units of [1,2,5]thiadiazolo[3,4-c]pyridine (PTz) and terminated with alkyl-bithiophene as π-conjugated end-caps, BDTDPTz , was designed and synthesized for the application as donor material in organic solar cells (OSCs). BDTDPTz possesses wider absorption spectra with an optical bandgap of 1.65 eV, lower the highest occupied molecular orbital (HOMO) energy level of −5.42 eV and highly crystalline structures in solid films. The OSCs based on BDTDPTz :PC 71 BM blend film with a lower PC 71 BM content of 40% demonstrate a power conversion efficiency (PCE) of 6.28% with a relatively higher open-circuit voltage of 0.868 V and short circuit current density of 12.83 mA cm−2. These results indicate that highly coplanar and crystalline structure of BDTDPTz can effectively reduce the content of fullerene acceptor in the active layer and then enhance the absorption and PCE of the OSCs. Graphical abstract Image 1 A new planar A-D-A structured organic molecule, BDTDPTz , was designed and synthesized for the application as donor material in organic solar cells (OSCs). The OSCs based on BDTDPTz :PC 71 BM with a weight ratio of 1.5:1 and 0.25% 1-Phenylnaphthalene treatment exhibit higher power conversion efficiency (PCE) of 6.28%. The optimized PC 71 BM content of 40% is one of the lowest acceptor content in the active layer reported so far for the high photovoltaic performance OSCs, and BDTDPTz could be promising high performance donor materials in solution-processable OSCs. Highlights • BDTDPTz with A-D-A structured was synthesized for the application in Solar Cells. • The OSCs shows a PCE of 6.28% with a lower PC 71 BM content of 40%. • PC 71 BM content of 40% is one of the lowest acceptor content in the active layer. • BDTDPTz could be promising high performance donor in solution-processable OSCs. [ABSTRACT FROM AUTHOR]

Abstract A new n -type organic semiconductor (n -OS) acceptor with (E)-5-(2-(5-(2-ethylhexyl)thiophen-2-yl)vinyl)-thiophene-2-yl (TVT) functional group as π-bridge to link indacenodithiophene (IDT) core and 3-(dicyanomethylidene)indan-1-one (IC) terminals, named ITVT, was synthesized and applied in polymer solar cells (PSCs). It is the first time employing TVT unit in n -OS small molecule acceptor. Benefited from the conjugated TVT side groups, the small molecule ITVT shows a strong absorption at the short wavelength range (300–500 nm). In addition, ITVT exhibits a low optical band gap (E g opt) of 1.48 eV and a medium electron mobility of 1.85 × 10−4 cm2 V-1 s-1. A wide band gap polymer PBZ was chosen as donor to fabricate an inverted BHJ PSCs because of the complementary absorption and matched molecular energy levels. The as-cast PSCs yield a power conversion efficiency (PCE) of 5.84% with an open-circuit voltage (V oc) of 0.96 V and a short-circuit current density (J sc) of 14.22 mA cm−2 under the illumination of AM 1.5 G at 100 mW cm−2. Graphical abstract A new small molecule acceptor ITVT containing Alkylthienylenevinylene thiophene unit was synthesized. The as-cast PSCs yield a power conversion efficiency (PCE) of 5.84% under the illumination of AM 1.5 G at 100 mW cm−2. Image 1 Highlights • A new molecule with thienylenevinylene thiophene as π bridge was synthesized. • ITVT exhibits appropriate optoelectronic properties used as an electron acceptor. • The as-cast solar cells based on ITVT yield a power conversion efficiency of 5.84%. [ABSTRACT FROM AUTHOR]

Herein, we synthesized a new acceptor-π-donor-π-acceptor (A-π-D-π-A) type small molecule donor material BTTR based on thienyl-substituted benzo[1,2- b :4,5- b ′]dithiophene (BDT-T) as the electron-donating core, thieno[3,2- b ]thiophene (TT) along with two thiophene units as the π-bridge, and 3-ethylrhodanine (TR) as the electron-deficient end group. The optical, electrical, thermal properties and photovoltaic performance were investigated. BTTR shows strong absorption in the range of 300–700 nm, deep-lying HOMO energy level of −5.32 eV and high hole mobility of 1.01 × 10 −3 cm 2 V −1 s −1 . The organic solar cells (OSCs) based on BTTR :PC 71 BM (1:0.8, w/w) blend with tetrahydrofuran (THF) solvent vapor annealing (SVA) exhibited an optimized power conversion efficiency (PCE) of 8.0% with an open circuit voltage ( V oc ) of 0.93 V, a short circuit current density ( J sc ) of 13.2 mA cm −2 , and a fill factor (FF) of 65.4% under the illumination of AM 1.5G, 100 mW cm −2 . The good photovoltaic performance indicates BTTR could be a promising donor material in solution-processed OSCs. [ABSTRACT FROM AUTHOR]

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

A new ultra-narrow bandgap and 2D-conjugated D-A copolymer, PBDTT-TIID , based on bithienyl-benzodithiophene (BDTT) donor unit and ( E )-4,4′-bis(2-ethylhexyl)-[6,6′-bithieno[3,2 -b ]pyrrolylidene]-5,5′(4H,4′H)-dione (TIID) acceptor unit was designed and synthesized for the application as donor material in polymer solar cells (PSCs). The polymer demonstrates two absorption peaks at around 450 nm and 900 nm respectively, and possesses a very narrow bandgap ( E g ) of 1.17 eV and a higher hole mobility of 4.48 × 10 −3 cm 2 /V s. The PSCs based on PBDTT-TIID :PC 71 BM (1:1, w/w) demonstrate a higher V oc of 0.59 V even though the polymer has a very narrow E g of 1.17 eV, which is corresponding to a low energy loss ( E loss ) of 0.58 eV. In addition, an optimal PCE of 2.40% was achieved with 1% DIO as additive. [ABSTRACT FROM AUTHOR]

The interlayers, including hole transporting layer (HTL) and electron transporting layer (ETL), segregating photoactive layer and the electrodes play an important role in charge extraction and transportation in perovskite solar cells (pero-SCs). Two novel copolymers, PDTSTTz and PDTSTTz-4, for the first time were applied as HTL in the n-i-p type pero-SCs, with the device structure of ITO/compact TiO 2 /CH 3 NH 3 PbI 3-x Cl x /HTL/MoO 3 /Ag. The highest occupied molecular orbitals (HOMO) levels of PDTSTTz and PDTSTTz-4 exhibit a suitable band alignment with the valence band edge of the perovskite. Both of them lead to improved device performances compared with reference pero-SCs based on P3HT as HTL. To further balance the charge extraction and the diffusion length of charge carriers, pristine C 60 was introduced at the cathode side of the pero-SCs, working together with TiO 2 as ETL. With insertion of both the HTL and ETL, the performance of pero-SCs was greatly enhanced. The optimized devices exhibited impressive PCEs of 14.4% and 15.8% for devices based on PDTSTTz and PDTSTTz-4. The improved performance is attributed to better light harvest ability, decreased interface resistance and faster decay time due to the introduction of the interlayers. [ABSTRACT FROM AUTHOR]

Two electron-donating sides chain (octylthio and methoxy) were strategically attached on BDTT unit to develop two new polymers ( PBDTT-OS-TT-EF and PBDTT-OS-TT-CF ) as donor materials for polymer solar cells. PBDTT-OS-TT-EF and PBDTT-OS-TT-CF show broad absorption spectra with narrow optical band-gap of 1.52 and 1.56 eV, and low-lying HOMO energy level of −5.34 and −5.46 eV, respectively. A high V oc of 0.92 V was obtained from the PSC devices based on PBDTT-OS-TT-EF . Particularly, the V oc of PSC device based on PBDTT-OS-TT-CF is as high as 1.00 V, which is the highest value for the devices based on TT-base polymers. The results indicate that the engineering two electron-donating side chains in BDTT unit is an effective strategy to narrow the band-gap and manipulate the energy levels of polymers, which can be potentially applied to design polymer donor materials with high V oc values. [ABSTRACT FROM AUTHOR]