Single-component Organic Solar Cells Research Articles

Three-in-One Strategy Enables Single-Component Organic Solar Cells with Record Efficiency and High Stability.

Single-component organic solar cells (SCOSCs) with covalently bonding donor and acceptor are becoming increasingly attractive because of their superior stability over traditional multicomponent blend organic solar cells (OSCs). Nevertheless, the efficiency of SCOSCs is far behind the state-of-the-art multicomponent OSCs. Herein, by combination of the advantages of three-component and single-component devices, this work reports an innovative three-in-one strategy to boost the performance of SCOSCs. In this three-in-one strategy, three independent components (PM6, D18, and PYIT) are covalently linked together to create a new single-component active layer based on ternary conjugated block copolymer (TCBC) PM6-D18-b-PYIT by a facile polymerization. Precisely manipulating the component ratios in the polymer chains of PM6-D18-b-PYIT is able to broaden light utilization, promote charge dynamics, optimize, and stabilize film morphology, contributing to the simultaneously enhanced efficiency and stability of the SCOSCs. Ultimately, the PM6-D18-b-PYIT-based device exhibits a power conversion efficiency (PCE) of 14.89%, which is the highest efficiency of the reported SCOSCs. Thanks to the aggregation restriction of each component and chain entanglement in the three-in-one system, the PM6-D18-b-PYIT-based SCOSC displays significantly higher stability than the corresponding two-component (PM6-D18:PYIT) and three-component (PM6:D18:PYIT). These results demonstrate that the three-in-one strategy is facile and promising for developing SCOSCs with superior efficiency and stability.

A computational investigation of the effects of changes of donor–acceptor linker length and acceptor on electronic spectra of small-molecule single-component organic solar cells

Small-molecule single-component organic solar cells (SM-SCOSCs) have great potential for commercial application. However, the effects of changes of donor–acceptor linker length and acceptor unit of small molecules of active layers on their photoelectric properties are still not well understood. In this work, four state-of-the-art dyads 1–4 were selected to investigate these effects since dyad 4 created the highest power conversion efficiency (PCE) of 5.34% of SM-SCOSC; and their electronic structures were investigated. The results indicate that increasing the length of the donor–acceptor connecting bridge leads to a decrease in exciton binding energy, and so does replacing the acceptor component PC61BM with PC71BM. Furthermore, the simulated electronic absorption spectrum of dyad 4 is enhanced with respect to others. We also find that the introduction of PC71BM creates more channels for transitions from local excited states to charge transfer states. This work gains a deep insight into the relationship between molecular structure and performance of SM-SCOSC.

Incorporating a Nonfused Electron Acceptor into Double-Cable Conjugated Polymers for Single-Component Organic Solar Cells with a Photo Response up to 900 nm

Incorporating a Nonfused Electron Acceptor into Double-Cable Conjugated Polymers for Single-Component Organic Solar Cells with a Photo Response up to 900 nm

The effect of infrared push pulse on the relaxed exciton in single-component organic solar cells

Ultrafast pump-push-probe/photocurrent experiments have confirmed that free charges can be spontaneously generated in single-component organic solar cells. A deeper understanding of the experimental results is expected to further modulate the charge yield. Herein, the effect of an infrared push pulse on the relaxed exciton in conjugated polymers is theoretically studied. We find that the relaxed exciton can be pushed into different hot excitons depending on the energy of this infrared pulse. In particular, the dynamics of the transition from localized to delocalized excitons is explicitly presented. Moreover, we attempt to demonstrate that the delocalization effect of hot exciton is favorable for charge generation by introducing a driving field. The results suggest that the strength of the driving field and timescale required for the dissociation of hot exciton is significantly reduced compared to this relaxed exciton. Finally, the influence of the photoexcitation conditions on the charge generation is discussed to further elucidate the effect of hot exciton delocalization. Overall, this work has the potential to provide further information for the analysis and control of charge generation by hot exciton dissociation.

The application of chlorine substituted conjugated block copolymers in the single-component organic solar cells

The inferior short-circuit current density (JSC) of the conjugated block copolymers (CBCs) based single component organic solar cells (SCOSCs), compared with that of binary all-polymer systems, is the main reason for their limited power conversion efficiency (PCE). To improve the JSC of SCOSCs by enhancing the light-harvesting ability, we designed and synthesized three narrower bandgap acceptor monomers with different chlorine-substituted terminals, and incorporated them into the CBCs. As the position of chlorine substitution altered, the blend morphology, the device performance, and the physical mechanism changed accordingly. It is worth noting that the PB-b-PYCl-2-based SCOSCs exhibited a significantly improved JSC, accompanied by the best PCE of 13.42 %, and good thermal stability. This study illustrated the terminal chlorination strategy is a promising way to modify the device performance of the SCOSCs.

Incorporating Naphthalene and Halogen into Near-Infrared Double-Cable Conjugated Polymers for Single-Component Organic Solar Cells with Low-Voltage Losses.

The invention of near-infrared pedant-based double-cable conjugated polymers has demonstrated remarkable efficacy in single-component organic solar cells (SCOSCs). This work focuses on the innovative double-cable conjugated polymers aimed at attaining good absorption and suitable energy levels. Specifically, in the aromatic side units, the electron-donating (D) part is designed using a thieno[3,4-c]pyrrole-4,6-dione (TPD) as a core unit, flanked by two cyclopentadithiophene groups on either side. The electron-deficient (A) terminal groups consist of 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene) malononitrile (NC), which can be further modified through fluorination to modulate the physical properties and packing modes of the acceptor material. The resulting double-cable conjugated polymers exhibit broad absorption spectra spanning 500-850 nm and possess lowered Frontier energy levels when incorporating fluorine elements, providing decreased voltage losses in SCOSCs. Therefore, SCOSCs fabricated using these polymers have demonstrated power conversion efficiencies ranging from 7.6 to 10.2%, in which fluorine-containing double-cable conjugated polymers showed higher PCEs due to more favorable crystalline packing, enhanced exciton dissociation probability, and charge-transporting ability.

Regulating the Sequence Structure of Conjugated Block Copolymers Enables Large-Area Single-Component Organic Solar Cells with High Efficiency and Stability.

Single-component organic solar cells (SCOSCs) based on conjugated block copolymers (CBCs) by covalently bonding a polymer donor and polymer acceptor become more and more appealing due to the formation of a favorable and stable morphology. Unfortunately, a deep understanding of the effect of the assembly behavior caused by the sequence structure of CBCs on the device performance is still missing. Herein, from the aspect of manipulating the sequence length and distribution regularity of CBCs, we synthesized a series of new CBCs, namely D18(20)-b-PYIT, D18(40)-b-PYIT and D18(60)-b-PYIT by two-pot polymerization, and D18(40)-b-PYIT(r) by traditional one-pot method. It is observed that precise manipulation of sequence length and distribution regularity of the polymer blocks fine-tunes the self-assembly of the CBCs, optimizes film morphology, improves optoelectronic properties, and reduces energy loss, leading to simultaneously improved efficiency and stability. Among these CBCs, the D18(40)-b-PYIT-based device achieves a high efficiency of 13.4 % with enhanced stability, which is an outstanding performance among SCOSCs. Importantly, the regular sequence distribution and suitable sequence length of the CBCs enable a facile film-forming process of the printed device. For the first time, the blade-coated large-area rigid/flexible SCOSCs are fabricated, delivering an impressive efficiency of 11.62 %/10.73 %, much higher than their corresponding binary devices.

Indoor Single‐Component Organic Solar Cells Based on Double‐Cable Conjugated Polymers with Pendant A‐π‐D‐π‐A Electron Acceptors

Herein, three double‐cable conjugated polymers are developed for indoor single‐component organic solar cells (SCOSCs). The new double‐cable conjugated polymers contain pendent nonfused electron acceptors with A‐π‐D‐π‐A configuration, in which group A uses 1H‐indene‐1,3(2H)‐dione (ID) as an electron‐withdrawing end group. The innovative design enables the double‐cable polymer to show absorption spectra in the range of 400–700 nm, which is matched with the spectra of indoor light‐emitting diode lights. In addition, the ID units at the acceptor side units and the introduction of halogen atoms make the double‐cable polymers show high photovoltage (>1.0 V) in SCOSCs. As a result, SCOSCs based on the new double‐cable polymers exhibit a high efficiency of 18% under indoor light illumination. The findings present a novel modular design approach for wide‐bandgap double‐cable conjugated polymers that can be utilized for indoor photovoltaics.

Low temperature, non-halogen solvent processed single-component organic solar cells with 10% efficiency

A double-cable conjugated polymer DCPIC-BO is designed via introducing a long-branched alkyl chains 2-buthyloctyl into the acceptor side unit. Compared with the double-cable polymer (DCPIC-EH) with the 2-ethylhexyl alkyl chains, the solubility of the DCPIC-BO in non-halogen solvents is substantially improved. Therefore, a power conversion efficiency (PCE) of 9.77% can be obtained by the devices processed from o-xylene at 40 °C, while the DCPIC-EH cannot be processed due to its poor solubility under this condition. Moreover, PCEs of 10.10% for small-area (0.04 cm2) devices and nearly 9% for devices with an area of 1 cm2 are achieved using a non-halogenated solid additive in o-xylene, realizing the "absolutely halogen-free" OSC fabrication.

13% Single-Component Organic Solar Cells based on Double-Cable Conjugated Polymers with Pendent Y-Series Acceptors.

Double-cable conjugated polymers with pendent electron acceptors, including fullerene, rylene diimides, and nonfused acceptors, have been developed for application in single-component organic solar cells (SCOSCs) with efficiencies approaching 10%. In this work, Y-series electron acceptors have been firstly incorporated into double-cable polymers in order to further improve the efficiencies of SCOSCs. A highly crystalline Y-series acceptor based on quinoxaline core and the random copolymerized strategy are used to optimize the ambipolar charge transportand the nanophase separation of the double-cable polymers. As a result, an efficiency of 13.02% is obtained in the random double-cable polymer, representing the highest performance in SCOSCs, while the regular double-cable polymer only provides a low efficiency of 2.75%. The significantly enhanced efficiencies are attributed to higher charge carrier mobilities, better ordering conjugated backbones and Y-series acceptors in random double-cable polymers.

Alkyl-thiophene-alkyl linkers to construct double-cable conjugated polymers for single-component organic solar cells

In this work, semirigid linkers of the alkyl-thiophene-alkyl structure are developed to construct double-cable polymers. Three alkyl units, propyl (C3H6), hexyl (C6H12), and dodecyl (C12H24), are applied as semirigid linkers, yielding three double-cable polymers: PBC6-T, PBC12-T, and PBC24-T, respectively. PBC12-T which uses C6H12-thiophene-C6H12 linkers is found to exhibit the best device efficiency of 5.56%, while PBC6-T and PBC24-T with shorter or longer linkers yield device efficiencies of only 2.65% and 1.09% in single-component organic solar cells (SCOSCs). Further studies reveal that PBC12-T exhibits higher crystallinity and improved charge transport, resulting in better efficiencies. Our work provides an approach to construct double-cable conjugated polymers with long alkyl linkers, and it shows the importance of the linker length for the photovoltaic performance of SCOSCs.

Double-Cable Conjugated Polymers Based on Simple Non-Fused Electron Acceptors for Single-Component Organic Solar Cells

In this work, a non-fused electron acceptor with near-infrared absorption was introduced into double-cable conjugated polymers for single-component organic solar cells (SCOSCs). The non-fused electron acceptor contains a simple thienyl-phenyl-thienyl core with 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) as the end group, which was used as the side unit to create double-cable conjugated polymers. In addition, poly(benzodithiophene) was selected as the conjugated backbone, in which the number of chlorine (Cl) atoms was varied to tune the optical and electronic properties. The new double-cable polymers were successfully applied in SCOSCs, providing an efficiency of over 8% with a broad photoresponse from 300 to 800 nm. When the number of Cl atoms on the repeat unit was increased from 2 to 3, the open-circuit voltage was enhanced to 1.01 V, yielding a low voltage loss of 0.59 eV, while the efficiency was reduced to 5.28%. The reduced performance is explained by the increased charge recombination in this polymer, as observed by transient absorption spectroscopy. This work reports a set of IC-based NIR double-cable conjugated polymers, which inspire material design toward more efficient SCOSCs.

Desirable Uniformity and Reproducibility of Electron Transport in Single-Component Organic Solar Cells.

Despite the simplified fabrication process and desirable microstructural stability, the limited charge transport properties of block copolymers and double-cable conjugated polymers hinder the overall performance of single-component photovoltaic devices. Based on the key distinction in the donor (D)-acceptor (A) bonding patterns between single-component and bulk heterojunction (BHJ) devices, rationalizing the difference between the transport mechanisms is crucial to understanding the structure-property correlation. Herein, the barrier formed between the D-A covalent bond that hinders electron transport in a series of single-component photovoltaic devices is investigated. The electron transport in block copolymer-based devices is strongly dependent on the electric field. However, these devices demonstrate exceptional advantages with respect to the charge transport properties, involving high stability to compositional variations, improved film uniformity, and device reproducibility. This work not only illustrates the specific charge transport behavior in block copolymer-based devices but also clarifies the enormous commercial viability of large-area single-component organic solar cells (SCOSCs).

Random double-cable conjugated polymers with controlled acceptor contents for single-component organic solar cells

The random double-cable conjugated polymers pendent with near-infrared acceptors with tunable contents have been synthesized, exhibiting a high efficiency of 9.4% in single-component organic solar cells.

Single-component organic solar cells-Perspective on the importance of chemical precision in conjugated block copolymers.

Organic photovoltaics (OPV) present a promising thin-film solar cell technology with particular benefits in terms of weight, aesthetics, transparency, and cost. However, despite being studied intensively since the mid 90's, OPV has not entered the mass consumer market yet. Although the efficiency gap with other thin-film photovoltaics has largely been overcome, active layer stability and performance reproducibility issues have not been fully resolved. State-of-the-art OPV devices employ a physical mixture of electron donor and acceptor molecules in a bulk heterojunction active layer. These blends are prone to morphological changes, leading to performance losses over time. On the other hand, in "single-component" organic solar cells, the donor and acceptor constituents are chemically connected within a single material, preventing demixing and thereby enhancing device stability. Novel single-component materials affording reasonably high solar cell efficiencies and improved lifetimes have recently emerged. In particular, the combination of donor and acceptor structures in conjugated block copolymers (CBCs) presents an exciting approach. Nevertheless, the current CBCs are poorly defined from a structural point of view, while synthetic protocols remain unoptimized. More controlled synthesis followed by proper structural analysis of CBCs is, however, essential to develop rational structure-property-device relations and to drive the field forward. In this perspective, we provide a short overview of the state-of-the-art in single-component organic solar cells prepared from CBCs, reflect on their troublesome characterization and the importance of chemical precision in these structures, give some recommendations, and discuss the potential impact of these aspects on the field.

Chlorine-Substituted Double-Cable Conjugated Polymers with NearInfrared Absorption for Low Energy Loss Single-Component Organic Solar Cells

Chlorine-Substituted Double-Cable Conjugated Polymers with NearInfrared Absorption for Low Energy Loss Single-Component Organic Solar Cells

Squaraine-fullerene conjugate for single component organic solar cells

The donor (D) acceptor (A) architecture of squaraine-fullerene conjugate (SQ-Full) was developed for single-component organic solar cell (SC–OSCs) devices. The SQ-Full dyad showed three absorption bands centered around 330 nm, 396 nm, and 712 nm, extending to 850 nm. We have fabricated SC-OSCs and achieved an overall power conversion efficiency of 5.21% after solvent vapor annealing (SVA) of the active layer. This is the highest efficiency available in the reported literature for small molecules and squaraine-based SC-OSC.

4,4-Bis(2-ethylhexyl)-6-(9-(2-ethylhexyl)-2,3,4,4a,9,9a-hexahydro-1H-carbazol-6-yl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2-carbaldehyde

Dyes with a donor–π–spacer–acceptor (D-π-A) structure containing a dicyanovinyl group as an acceptor have recently been of interest for the production of single-component organic solar cells. The most convenient precursors for their synthesis are the corresponding aldehydes. In this communication, 4,4-bis(2-ethylhexyl)-6-(9-(2-ethylhexyl)-2,3,4,4a,9,9a-hexahydro-1H-carbazol-6-yl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2-carbaldehyde was synthesized by the Suzuki cross-coupling reaction between 4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-dicarbaldehyde and 9-(2-ethylhexyl)-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,3,4,4a,9,9a-hexahydro-1H-carbazole in the presence of tetrakis(triphenylphosphine)palladium(0). The structure of the newly synthesized compound was established by means of high-resolution mass spectrometry, 1H, 13C NMR, IR, and UV spectroscopy.

Over 13% Efficient Single‐Component Organic Solar Cells Enabled by Adjusting the Conjugated‐Length of Intermediate PBDB‐T Block

AbstractBatch‐to‐batch variation widely exists in conjugated donor‐acceptor (D‐A) block copolymer materials and plays a crucial role in photovoltaic performance of organic solar cells (OSCs). To investigate the influence of conjugated‐length of the intermediate block on the performance of single‐component OSC (SCOSCs), herein, four batches of conjugated block copolymers (CBCs, PB‐b‐PY‐1, PB‐b‐PY‐2, PB‐b‐PY‐3, and PB‐b‐PY‐4) are synthesized, which possess different D/A block lengths. As the conjugation length of intermediate D‐block increases, the lamellar packing order of these CBCs shows a monotonically increasing trend, leading to stronger absorption spectra in the visible region, efficient charge transfer, and suppressed carrier recombination loss. Consequently, the PB‐b‐PY‐4 device yields a higher efficiency of 13.28% than those of other CBCs. This study demonstrates the effectiveness of the conjugated length of intermediate D‐blocks in designing high‐performance conjugated D‐A block copolymers, which paves the way toward developing high‐performance SCOSCs.

N-Annulated Perylene Bisimide-Based Double-Cable Polymers with Open-Circuit Voltage Approaching 1.20 V in Single-Component Organic Solar Cells.

In this work, we have introduced single/double-sided N-annulated perylene bisimide (PBI) with deep energy levels into double-cable polymers with poly[1-(5-(4,8-bis(4-chloro-5-(2-ethylhexyl)thiophen-2-yl)-6-methylbenzo[1,2-b:4,5-b']dithiophen-2-yl)thiophen-2-yl)-5,7-bis(2-ethylhexyl)-3-(5-methylthiophen-2-yl)-4H,8H-benzo[1,2-c:4,5-c']dithiophene-4,8-dione] (PBDB-T-Cl) as a donor backbone, marking as s-PPNR and as-PPNR, according to the molecular symmetry. Both double-cable polymers displayed a high open-circuit voltage approaching 1.20 V in light of high energy level discrepancy between electron-donating and electron-withdrawing parts, which is the highest open-circuit voltage among double-cable-based single-component organic solar cell (SCOSC) devices. Additionally, the asymmetric polymer displayed improved absorption spectra, thereby promoting crystallization and phase separation. Consequently, the as-PPNR-based SCOSCs achieved a power conversion efficiency of 5.05% along with a higher short-circuit current density and fill factor than their s-PPNR-based counterparts. In this work, we have successfully incorporated N-annulated PBI into double-cable polymers and revealed the important effects on structural symmetry and phase separation of double-cable polymers for higher SCOSC performance.