Acceptor Polymers Research Articles

Pronounced Dependence of All-Polymer Solar Cells Photovoltaic Performance on the Alkyl Substituent Patterns in Large Bandgap Polymer Donors.

For all-polymer solar cells which are composed of polymer donors and polymer acceptors, the effect of alkyl side chains on photovoltaic performance is a matter of some debate, and this effect remains difficult to forecast. In this concise contribution, we demonstrate that three alkyls namely branched alkyl 2-butyloctyl (2BO), long linear alkyl n-dodecyl (C12), and double-short linear alkyl n-hexyls (DC6) incorporated into the side chains of large bandgap polymer donor PBDT-TTz can induce considerable, of significance, and different electronic, optical, and morphological parameters. Systematic studies shed light on the critical role of the double-short linear alkyl n-hexyls (DC6) in (i) producing large ionization potential value, (ii) increasing propensity of the polymer to order along the π-stacking direction, (iii) generating polymer crystallites with more preferential "face-on" orientation, consequently, (iv) improvement of carriers transportation, (v) suppression of charge recombination, (vi) reduction of energy loss in all-polymer devices. In parallel, we unearth that the PBDT-TTz with double-short linear alkyl n-hexyls (DC6) represents the highest efficiency of 8.3 %, whereas, the other two PBDT-TTz analogues (2BO, C12) yield efficiencies of less than 3 % in optimized all-polymer solar cells. Though branched or long linear alkyl side chains (2BO, C12) have been applied to provide the solution processability of conjugated polymers, motifs bearing multiple short linear alkyl substituents (DC6) are proved critical to the development of high performing polymers.

Multi-Stimuli-Responsive Field-Effect Transistor with Conjugated Polymer Entailing Spiropyran in the Side Chains

Multi-stimuli-responsive field-effect transistors (FETs) with organic/polymeric semiconductors have received increasing attention. Herein, we report a novel strategy for fabricating multi-stimuli-r...

Rational design of a novel isoindigo-based conjugated terpolymer with panchromatic absorption and its application to polymer solar cells

In this study, a panchromatic absorptive conjugated terpolymer, BDTID-BDT3MT, is synthesized, which consists of electron-donating benzodithiophene (BDT), isoindigo (ID) as a strong electron-accepting unit, and methyl-3-thiophenecarboxylate (3 MT) as a weak electron-accepting unit. By combining these three monomers into the structure of a conjugated terpolymer, the absorption spectrum of BDTID-BDT3MT is induced to exhibit an unusually broad, strong, and uniform band in the wavelength interval from 300 to 750 nm, which helps achieving highly efficient light harvesting under solar illumination. The intriguing panchromatic absorption behavior of BDTID-BDT3MT was explained on the basis of theoretical calculations using simplified repeating units. Polymer solar cells (PSCs) based on BDTID-BDT3MT as a donating polymer and non-fullerene acceptors (e.g., ITIC-4F) exhibited a high power conversion efficiency (PCE) of 5.38%, high open circuit voltage (Voc) of 0.88 V, and short circuit current density (Jsc) of 13.74 mA/cm2, while PSCs based on ternary blend systems consisting of BDTID, BDT3MT, and ITIC-4F exhibited lower PCE and Jsc of 3.74% and 11.15 mA/cm2, respectively. The superior performance of PSCs based on BDTID-BDT3MT can be attributed to their high light harvesting efficiencies and relatively more favorable nano-phase film morphologies. Our results establish that BDT, ID, and 3 MT units serve as useful building blocks in the structure of conjugated terpolymers due to their remarkably broad panchromatic absorption band.

14.4% efficiency all-polymer solar cell with broad absorption and low energy loss enabled by a novel polymer acceptor

Abstract All-polymer solar cells (All-PSCs) offer several distinct merits including superior thermal stability and flexibility. Here, we report a novel polymer acceptor PJ1 that exhibits a narrow band gap around 1.4 eV and a high extinction coefficient about 1.39 × 105 cm−1. When PJ1 is blended with donor polymer PBDB-T, all-PSC with a record power conversion efficiency (PCE) of 14.4% is achieved, which is mainly attributed to the broad absorption, efficient charge separation and collection, and low energy loss. The synergetic effects of molecular weight of PJ1 on the photovoltaic performance are also investigated. It is found that the increase in molecular weight can result in the red-shift of absorption along with slight enhancement of extinction coefficient, which therefore benefits photocurrent. In addition, all-PSC based on PJ1 demonstrate much better thermal stability than the control device based on small molecule acceptor (TTPBT-IC), as evidenced by the insignificant morphology change of PBDB-T:PJ1 versus excessive phase separation of PBDB-T:TTPBT-IC when annealed at 150 °C. Of particular interest is that the all-PSCs based on PBDB-T:PJ1 can retain high PCEs even when the thickness of photoactive layer is increased over 300 nm (PCE of 12.1%) or the device area is enlarged to 1 cm2 (PCE of 13.0%).

Half‐Fused Diketopyrrolopyrrole‐Based Conjugated Donor–Acceptor Polymer for Ambipolar Field‐Effect Transistors

AbstractA novel building block, denoted as half‐fused diketopyrrolopyrrole (DPP) (9‐(3‐octadecylhenicosyl)‐8‐(thiophen‐2‐yl)‐7H‐pyrrolo[3,4‐a]thieno[3,2‐g]indolizine‐7,10(9H)‐dione), in which one of the flanking thiophene units is fused to one of the DPP rings via a carbon‐carbon double bond at the N‐position is reported. The half‐fused DPP is successfully utilized as an electron acceptor to prepare the conjugated donor–acceptor polymer PTFDFT, which exhibits ambipolar semiconducting behavior in ambient air. Theoretical calculations and absorption spectral studies show that the backbone of PTFDFT is more planar compared to the reference polymer with conventional DPP units. As a result, PTFDFT shows a narrow bandgap and low lowest unoccupied molecular orbital level. The more planar backbone with fewer side chains favors the dense packing of the polymer chains of PTFDFT with a short π–π stacking distance (3.49 Å). Grazing‐incidence wide‐angle X‐ray scattering data further confirm the predominant edge‐on packing mode of the PTFDFT polymer chains on the substrate. As expected, the PTFDFT thin film shows excellent ambipolar semiconducting properties under ambient conditions, reaching 2.23 and 1.08 cm2 V−1 s−1 for the n‐ and p‐channels, respectively. In addition, complementary‐like inverter with gain value as high as 141 is successfully constructed using the PTFDFT thin film.

Simultaneous enhanced efficiency and thermal stability in organic solar cells from a polymer acceptor additive

The thermal stability of organic solar cells is critical for practical applications of this emerging technology. Thus, effective approaches and strategies need to be found to alleviate their inherent thermal instability. Here, we show a polymer acceptor-doping general strategy and report a thermally stable bulk heterojunction photovoltaic system, which exhibits an improved power conversion efficiency of 15.10%. Supported by statistical analyses of device degradation data, and morphological characteristics and physical mechanisms study, this polymer-doping blend shows a longer lifetime, nearly keeping its efficiency (t = 800 h) under accelerated aging tests at 150 oC. Further analysis of the degradation behaviors indicates a bright future of this system in outer space applications. Notably, the use of polymer acceptor as a dual function additive in the other four photovoltaic systems was also confirmed, demonstrating the good generality of this polymer-doping strategy.

Impact of Polymer Backbone Fluorination on the Charge Generation/Recombination Patterns and Vertical Phase Segregation in Bulk Heterojunction Organic Solar Cells.

Incorporating fluorine (–F) substituents along the main-chains of polymer donors and acceptors is an effective strategy toward efficient bulk-heterojunction (BHJ) solar cells. Specifically, F-substituted polymers often exhibit planar conformations, leading to favorable packing, and electronic coupling. However, the effects of fluorine substituents on the charge generation and recombination characteristics that determine the overall efficiency of BHJ active layers remain critically important issues to examine. In this report, two PBDT[2X]T polymer analogs –poly[4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4, 5-b′]dithiophene-thiophene] [PBDT[2H]T] and its F-substituted counterpart poly[4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene-3,4-difluoro-thiophene] [PBDT[2F]T]—are studied to systematically examine how –F substituents impact the blend morphology, charge generation, carrier recombination and extraction in BHJ solar cells. Considering the large efficiency differences between PBDT[2H]T- and PBDT[2F]T-based BHJ devices, significant emphasis is given to characterizing the out-of-plane morphology of the blend films as vertical phase-separation characteristics are known to have dramatic effects on charge transport and carrier extraction in polymer-fullerene BHJ solar cells. Herein, we use electron energy loss spectroscopy (EELS) in tandem with charge transport characterization to examine PBDT[2X]T-fullerene blend films. Our analyses show that PBDT[2H]T and PBDT[2F]T possess very different charge generation, recombination and extraction characteristics, resulting from distinct aggregation, and phase-distribution within the BHJ blend films.

Mechanically Robust All-Polymer Solar Cells from Narrow Band Gap Acceptors with Hetero-Bridging Atoms

Summary We developed three narrow band-gap polymer acceptors PF2-DTC, PF2-DTSi, and PF2-DTGe with different bridging atoms (i.e., C, Si, and Ge). Studies found that such different bridging atoms significantly affect the crystallinity, extinction coefficient, electron mobility of the polymer acceptors, and the morphology and mechanical robustness of related active layers. In all-polymer solar cells (all-PSCs), these polymer acceptors achieved high power conversion efficiencies (PCEs) over 8.0%, while PF2-DTSi obtained the highest PCE of 10.77% due to its improved exciton dissociation, charge transport, and optimized morphology. Moreover, the PF2-DTSi-based active layer showed excellent mechanical robustness with a high toughness value of 9.3 MJ m−3 and a large elongation at a break of 8.6%, which is a great advantage for the practical applications of flexible devices. As a result, the PF2-DTSi-based flexible all-PSC retained >90% of its initial PCE (6.37%) after bending and relaxing 1,200 times at a bending radius of ∼4 mm.

Enhanced photocatalytic hydrogen evolution from organic semiconductor heterojunction nanoparticles.

Photocatalysts formed from a single organic semiconductor typically suffer from inefficient intrinsic charge generation, which leads to low photocatalytic activities. We demonstrate that incorporating a heterojunction between a donor polymer (PTB7-Th) and non-fullerene acceptor (EH-IDTBR) in organic nanoparticles (NPs) can result in hydrogen evolution photocatalysts with greatly enhanced photocatalytic activity. Control of the nanomorphology of these NPs was achieved by varying the stabilizing surfactant employed during NP fabrication, converting it from a core-shell structure to an intermixed donor/acceptor blend and increasing H2 evolution by an order of magnitude. The resulting photocatalysts display an unprecedentedly high H2 evolution rate of over 60,000 µmol h-1 g-1 under 350 to 800 nm illumination, and external quantum efficiencies over 6% in the region of maximum solar photon flux.

Understanding the Interplay of Transport‐Morphology‐Performance in PBDB‐T‐Based Polymer Solar Cells

Polymer–polymer blends have been reported to exhibit exceptional thermal and ambient stability. However, power conversion efficiencies (PCEs) from devices using polymeric acceptors have been recorded to be significantly lower than those based on conjugated molecular acceptors. Herein, two organic nonfullerene bulk heterojunction (BHJ) blends ITIC:PBDB‐T and N2200:PBDB‐T, together with their fullerene counterpart, PCBM:PBDB‐T, are adopted to understand the effect of electron acceptors on device performance. Free charge carrier properties using time‐resolved microwave conductivity (TRMC) measurements are comprehensively investigated. The nonfullerene devices show an improved PCE of 10.06% and 6.65% in the ITIC‐ and N2200‐based cells, respectively. In comparison, the PCBM:PBDB‐T‐based devices yield a PCE of 5.88%. The optimal N2200:PBDB‐T produced the highest TRMC mobility, longest lifetime, and greatest free‐carrier diffusion length. It is found that such phenomena can be associated with the unfavorable morphology of the all‐polymer BHJ microstructure. In contrast, the solar cells using either the PCBM or ITIC acceptors display a more balanced donor and acceptor phase separation, leading to more efficient free‐carrier separation and transport in the operating device. By sacrificing efficiency for superior stability, it is shown that the improved structure in all‐polymer blend can deliver a more stable morphology under thermal stress.

Doping High‐Mobility Donor–Acceptor Copolymer Semiconductors with an Organic Salt for High‐Performance Thermoelectric Materials

AbstractOrganic semiconductors (OSCs) are attractive for fabrication of thermoelectric devices with low cost, large area, low toxicity, and high flexibility. In order to achieve high‐performance organic thermoelectric devices (OTEs), it is essential to develop OSCs with high conductivity (σ ), large Seebeck coefficient (S), and low thermal conductivity (κ ). It is equally important to explore efficient dopants matching the need of thermoelectric devices. The thermoelectric performance of a high‐mobility donor–acceptor (D–A) polymer semiconductor, which is doped by an organic salt, is studied. Both a high p‐type electrical conductivity approaching 4 S cm−1 and an excellent power factor (PF) of 7 µW K−2 m−1 are obtained, which are among the highest reported values for polymer semiconductors. Temperature‐dependent conductivity, Seebeck coefficient and power factor of the doped materials are systematically investigated. Detailed analysis on the results of thermoelectric measurements has revealed a hopping transport in the materials, which verifies the empirical relationship: S ∝ σ−1/4 and PF ∝ σ1/2. The results demonstrate that D–A copolymer semiconductors with proper combination of dopants have great potential for fabricating high‐performance thermoelectric devices.

Recent progress of all-polymer solar cells – From chemical structure and device physics to photovoltaic performance

Single junction organic solar cells (OSCs) have now achieved power conversion efficiencies (PCEs) exceeding 17 %. Most of these high performance OSCs contain fullerene acceptors (FAs) and non-fullerene small-molecule acceptors (NFSMAs). In contrast, there are very limited usages of polymer acceptors. Recently, there are escalating recognition among perylene-diimide/naphthalene-diimide (PDI/NDI) and B⟵N-unit n-type polymers as electron acceptors in the all-polymer solar cells. FAs like PC71BM suffer from multiple limitations. They include restricted energy level tuning, weak absorptions in visible region, narrow spectral breadth, and morphological instability. In contrast to FAs, NFSMAs offer numerous advantages. They include strong and broad absorption in the visible and even the NIR region, tunable energy levels, and simple synthesis and purification procedures. Despite these advantages, the long-term device stability and large-area roll-to-roll (R2R) fabrication remain the major issues for the commercialization for NFSMA-based OSCs. All-polymer solar cells, on the other hand, largely address the problems of device stability and large-area film processing. Many all-polymer solar cells have been demonstrated to possess long-term thermal, photo and mechanical stability. Meanwhile, the precursor solutions for all-polymer solar cells enjoy superior control in the solution viscosity, which is an important factor for the solution processing of large-scale OSCs. Before 2015, all-polymer solar cells received little attention due to their disappointing device performance. Afterwards, PCEs of all-polymer solar cells are picking up. Currently, the best cells have achieved PCEs in excess of 11 %. Here, we provide a systematic review on the evolution of n-type polymeric acceptors used in OSCs. In addition, we summarize the morphological and charge carrier transport properties of all-polymer solar cells and compare with their small molecule acceptor counterparts. The outstanding properties of all-polymer solar cells are discussed from the perspectives of morphology and electron transport in bulk heterojunctions (BHJs). The concept of electron percolation in all-polymer BHJs is introduced and correlated with the excellent device stability. This review should have a broad appeal and enable researchers in comprehending the achievements, challenges, and future directions of all-polymer solar cells.

Near-infrared absorbing pyrrolopyrrole aza-BODIPY-based donor–acceptor polymers with reasonable photoresponse

Designing near-infrared (NIR) absorbing donor–acceptor (D–A) polymers with photoresponse beyond 900 nm has remained a challenge in the area of organic photovoltaics (OPV) owing to the limited kinds of strong electron acceptors.

Chlorination of dithienobenzodithiophene (DTBDT) based polymers to simultaneously improve the VOC, JSC and FF of non-fullerene organic solar cells

Two donor–π–acceptor polymers (PE64 and PE65) with dithienobenzodithiophene (DTBDT) as the electron-donating unit and quinoxaline as the electron-accepting unit were designed to extend the application of DTBDT in non-fullerene organic solar cells.

A compatible polymer acceptor enables efficient and stable organic solar cells as a solid additive

Polymer acceptors with acceptor–donor–acceptor (A–D–A) building blocks have demonstrated great potential in achieving excellent power conversion efficiency (PCE) and stability in the field of organic solar cells (OSCs).

Organic solar cells based on small molecule donors and polymer acceptors operating at 150 °C

An organic solar cell based on a small molecule donor and a polymer acceptor exhibits a PCE of 9.5% and can operate at high temperature. It retains 84% of its PCE after thermal treatment at 150 °C for three days.

Recent advances of polymer acceptors for high-performance organic solar cells

Recent advances in polymer acceptors that focus on structure–property relationships, which may provide guidance for photovoltaic materials, were systematically summarized.

A thieno-isoindigo derivative-based conjugated polymer nanoparticle for photothermal therapy in the NIR-II bio-window.

Photothermal therapy (PTT), a powerful tool for non-invasive cancer treatment, has been recognized as an alternative strategy for cancer therapy in the clinic, and it is promoted by optical absorbing agents (photothermal agents) that can intensively convert near-infrared (NIR) light into thermal energy for cancer ablation. Conjugated polymer nanoparticles (CPNs) have recently attracted extensive attention owing to their excellent photothermal properties. However, the absorption of typical CPNs is mostly located in the traditional near-infrared region (NIR-I, 700-900 nm), which suffers from low tissue penetration, so the penetration depth is still limited and severely restricts their further applications. Compared with the NIR-I light, the second near-infrared window light (NIR-II, 1000-1700 nm) could efficiently enhance the tissue penetration depth, however, CPNs which absorb NIR-II region light are still especially limited and need further exploration. Here, a thieno-isoindigo derivative-based Donor-Acceptor (D-A) polymer (BTPBFDTS), which exhibited excellent absorption characteristics from the NIR-I to NIR-II window, was prepared. After formation of nanoparticles and surface functionalization, the prepared nanoparticles (NPsBTPBFDTS@HA NPs) exhibited obvious targeting ability, high photothermal conversion efficiency and photoacoustic imaging effects under 1064 nm irradiation. Both in vitro and in vivo studies demonstrate that our obtained NPsBTPBFDTS@HA nanoparticles possess excellent PTT efficacy including extremely high cancer cell killing ability and admirable tumor elimination efficiency. Hence, this work developed a promising photothermal conversion agent based on CPNs for cancer ablation.

Effect of curvature and placement of donor and acceptor units in cycloparaphenylenes: a computational study.

Cycloparaphenylenes have promise as novel fluorescent materials. However, shifting their fluorescence beyond 510 nm is difficult. Herein, we computationally explore the effect of incorporating electron accepting and electron donating units on CPP photophysical properties at the CAM-B3LYP/6-311G** level. We demonstrate that incorporation of donor and acceptor units may shift the CPP fluorescence as far as 1193 nm. This computational work directs the synthesis of bright red-emitting CPPs. Furthermore, the nanohoop architecture allows for interrogation of strain effects on common conjugated polymer donor and acceptor units. Strain results in a bathochromic shift versus linear variants, demonstrating the value of using strain to push the limits of low band gap materials.

Side chain independent photovoltaic performance of thienopyrroledione conjugated donor–acceptor polymers

This work highlights a unique TPD-based donor polymer system which exhibits robust photovoltaic tolerance regardless of acceptor unit side chain, presenting a distinct avenue for polymer structure and BHJ morphology manipulation.