Application In Organic Solar Cells Research Articles

Dithienobenzothiadiazole (DTBT)-Based Polymers Enable Organic Solar Cells with Ultrahigh VOC of ≈1.3V.

Dithieno[3',2':3,4;2",3":5,6]benzo[1,2-c][1,2,5]thiadiazole (DTBT) is a newly emerging building block to construct effective photovoltaic polymers. Organic solar cells (OSCs) based on DTBT-based polymers have realized power conversion efficiency (PCEs) over 18%, despite their relatively low open-circuit voltage (VOC ) of 0.8-0.95V. To extend the application of DTBT-based polymers in high-voltage OSCs, herein, D18-Cl and PE55 are used to combine with a wide-bandgap non-fullerene acceptor (NFA), BTA3, and achieve ultrahigh VOC of 1.30 and 1.28V, respectively. Compared with D18-Cl based on tricyclic benzodithiophene (BDT) segment, PE55 containing the pentacyclic dithienobenzodithiophene (DTBDT) unit possesses better hole mobility, higher charge-transfer efficiency, and more desirable phase separation. Hence, PE55:BTA3 blend exhibits a higher efficiency of 9.36% than that of D18-Cl: BTA3 combination (6.30%), which is one of the highest values for OSCs at ≈1.3V VOC . This work attests that DTBT-based p-type polymers are ideal for the application in high-voltage OSCs.

Nickel(II) Nitrate Hole‐Transporting Layers for Single‐Junction Bulk Heterojunction Organic Solar Cells with a Record 19.02 % Efficiency

AbstractA facile strategy was developed here to improve the film quality of nickel‐based hole transporting layer (HTL) for efficient organic solar cell (OSC) applications. To prevent the agglomeration of Ni(NO3)2 during film deposition, acetylacetonate was added into the precursor solution, which led to the formation of an amorphous and glass‐like state. After thermal annealing (TA) treatment, the film‐forming ability could be further improved. The additional UV‐ozone (UVO) treatment continuously improved the film quality and increased the work function and conductivity of such HTL. The resulting TA & UVO modified Ni(NO3)2 & Hacac HTL produced highly efficient organic solar cells with exciting power conversion efficiencies of 18.42 % and 19.02 % for PM6 : BTP‐eC9 and D18 : BTP‐Th devices, respectively, much higher than the control PEDOT : PSS devices.

Nickel(II) Nitrate Hole-Transporting Layers for Single-Junction Bulk Heterojunction Organic Solar Cells with a Record 19.02 % Efficiency.

A facile strategy was developed here to improve the film quality of nickel-based hole transporting layer (HTL) for efficient organic solar cell (OSC) applications. To prevent the agglomeration of Ni(NO3 )2 during film deposition, acetylacetonate was added into the precursor solution, which led to the formation of an amorphous and glass-like state. After thermal annealing (TA) treatment, the film-forming ability could be further improved. The additional UV-ozone (UVO) treatment continuously improved the film quality and increased the work function and conductivity of such HTL. The resulting TA & UVO modified Ni(NO3 )2 & Hacac HTL produced highly efficient organic solar cells with exciting power conversion efficiencies of 18.42 % and 19.02 % for PM6 : BTP-eC9 and D18 : BTP-Th devices, respectively, much higher than the control PEDOT : PSS devices.

In Silico modeling and exploration of new acceptor molecules with enhanced power conversion efficiency for high-performance organic solar cell applications

Developing an effective strategy to increase open circuit voltage with maximum PCE is vital to realizing high-performance OPVs (organic photovoltaic). In this report, a novel class of non-fullerene acceptor compounds has been constructed by us (D2APH1 to D2APH4) for high-performance OPVs. End-capped alterations of the JC2 (R) molecules were formed using capable end-capped units. A high Fill factor with FF% has been achieved with PCE of 30.34% for D2APH1 to D2APH4. Redshift and a limited energy band gap relative to the reference molecule, a change in the absorption spectra have been observed for D2APH1 to D2APH4. Further, designed molecules also expressed enhanced open-circuit voltage values and strong electron and hole mobility across metal electrodes. Easy exciton excitation inside an excited state is caused by low excitation energy and strong oscillation strength. The different geometric, photovoltaic, and optoelectronic analyses indicated that engineered molecules provide capable contributions to the creation of highly effective OPVs.

Finely Tuned Molecular Packing Realized by a New Rhodanine-Based Acceptor Enabling Excellent Additive-Free Small- and Large-Area Organic Photovoltaic Devices Approaching 19 and 12.20% Efficiencies.

A new nonfullerene acceptor (NFA), BTA-ERh, was synthesized and integrated into a PM6:Y7:PC71BM ternary system to regulate the blend film morphology for enhanced device performance. Due to BTA-ERh's good miscibility with host active blend films, an optimized film morphology was obtained with appropriate phase separation and fine-tuning of film crystallinity, which ultimately resulted in efficient exciton dissociation, charge transport, lower recombination loss, and decreased trap-state density. The resulting additive-free quaternary devices achieved a remarkable efficiency of 18.90%, with a high voltage, fill factor, and current density of 0.87 V, 76.32%, and 28.60 mA cm-2, respectively. By adding less of a new small molecule with high crystallinity, the favorable nanomorphology shape of blend films containing NFAs might be adjusted. Consequently, this strategy can enhance photovoltaic device performance for cutting-edge NFA-based organic solar cells (OSCs). In contrast, the additive-free OSCs exhibited good operational stability. More importantly, large-area modules with the quaternary device showed a remarkable efficiency of 12.20%, with an area as high as 55 cm2 (substrate size, 100 cm2) in an air atmosphere via D-bar coating. These results highlight the enormous research potential for a multicomponent strategy for future additive-free OSC applications.

Intramolecular and Intermolecular Interaction Switching in the Aggregates of Perylene Diimide Trimer: Effect of Hydrophobicity

The research on perylene diimide (PDI) aggregates effectively promotes their applications in organic photovoltaic solar cells and fluorescent sensors. In this paper, a PDI fabricated with three peripheral PDI units (N, N'-bis(6-undecyl) perylene-3,4,9,10-bis(dicarboximide)) is investigated. The trimer shows different absorption and fluorescence properties due to hydrophobicity when dissolved in the mixed solvent of tetrahydrofuran (THF) and water. Through comprehensive analysis of the fluorescence lifetime and transient absorption spectroscopic results, we concluded that the trimer underwent different excited state kinetic pathways with different concentrations of water in THF. When dissolved in pure THF solvent, both the intramolecular charge-transfer and excimer states are formed. When the water concentration increases from 0 to 50% (v/v), the formation time of the excimer state and its structural relaxation time are prolonged, illustrating the arising of the intermolecular excimer state. It is interesting to determine that the probability of the intramolecular charge-transfer pathway will first decrease and then increase as the speed of intermolecular excimer formation slows down. The two inflection points appear when the water concentration is above 10% and 40%. The results not only highlight the importance of hydrophobicity on the aggregate properties of PDI multimers but also guide the further design of PDI-based organic photovoltaic solar cells.

Flexible, stripe-patterned organic solar cells and modules based on multilayer-printed Ag fibers for smart textile applications

Rapid advancement in the fabrication technologies of stripe/fiber-shaped optoelectronic devices has driven the performance of smart textile electronics to a new height. In the development of high-performance smart textile electronics, indium tin oxide (ITO)-free flexible transparent conductive electrodes (TCEs) are particularly desirable because they offer superior flexibility and lower manufacturing cost than the brittle ITO-based counterparts. Herein, we innovatively combine spin-coating and three-dimensional direct-ink writing (three-dimensional-DIW) techniques to develop large-area (5 × 5 cm2) PEDOT:PSS/Ag-fibers hybrid TCEs (denoted as DIW-TCEs) for application in flexible organic solar cells (OSCs). Through a multilayer printing strategy, high aspect-ratio Ag-fibers are successfully deposited on top of the planar PEDOT:PSS film. The resulting DIW-TCEs, when fully embedded in a colorless polyimide substrate, exhibit excellent electrical conductivity (sheet resistance ∼ 4 Ω/□), superior optical transmittance, and mechanical flexibility. One-dimensional stripe-patterned OSCs (stripe-OSCs) based on DIW-TCEs achieved power conversion efficiency of 9.3% and 8.2% at an active area of 0.11 cm2 and 0.31 cm2, respectively. For real-life application, a flexible power module was constructed using eight stripe-OSCs. When attached on textile, the module successfully lit up a commercial light-emitting diode upon photocharging. The unique DIW-TCE fabricated herein can be the ITO-free alternative for the production of smart textile electronics.

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.

High‐Efficiency Binary Organic Solar Cells Enabled by Pseudo‐Bilayer Configuration in Dilute Solution

Forming proper film morphology in organic solar cells (OSCs) is important to govern the exciton dissociation and charge transport. Herein, high‐performance pseudo‐bilayer heterojunction (PBHJ) OSCs with donor:acceptor (D:A) bilayer architecture are reported by sequentially depositing two layers of diluted active solution with different D:A ratios. Such pseudo‐bilayer films can not only enable the cascaded components distributed in the vertical direction, but also afford large donor and acceptor (D/A) interfaces for efficient exciton dissociation. Additionally, the D:A active layer on the bottom substrate can act as a seed to promote the crystallization process of the upper film during the sequential casting process. The PBHJ strategy on two representative D:A blends, PM6:Y6 and PTQ10:Y6, is implemented. Benefiting from the synergetic effects of efficient exciton dissociation and balanced charge transport, the devices based on PM6:Y6 and PTQ10:Y6 show high power conversion efficiencies of 17.73% and 17.81%, respectively. Notably, the presented PBHJ devices are fabricated by using dilute chloroform solution (4 mg mL−1 for donor), demonstrating the excellent potential for poorly soluble donors and acceptors in future OSCs applications.

State-of-the-Art Techniques on Asymmetrical Perylene Diimide Derivatives: Efficient Electron-Transport Materials for Perovskite Solar Cells

Electron-transport materials (ETMs) play an important role in the injection and transfer of electrons at the interface of perovskite solar cells (PSCs). In this work, four PDI (perylene diimide) derivatives (PDI-3, PDI-4, PDI-5, and PDI-6) were designed on the basis of two asymmetrical PDIs (PDI-1 and PDI-2), which were found to have potential application in organic solar cells. State-of-the art techniques were used to investigate the molecular geometry, crystal packing, and electronic properties of these PDIs. The quantum chemical calculations reveal that designed PDIs have more matching energy level with MAPbI3, which will promote the efficient electron extraction and block undesirable hole transport from perovskite to the ETM layer. The crystal structures of asymmetrical PDIs exhibit a quasi-two-dimensional (2D) π–π stacking motif ascribed to the strong interaction of oxygen atoms in alkoxy benzamide/benzoate groups and hydrogen atoms in the molecule. A largely improved electron mobility of PDI-3 to PDI-6 (0.24, 0.41, 0.40, and 0.15 cm2 V–1 s–1, respectively) was obtained compared to the values for PDI-1 and PDI-2 (6.53 × 10–10 and 1.35 × 10–10 cm2 V–1 s–1, respectively). The calculated electron mobility of the designed PDI-4 and PDI-5 (0.41 and 0.40 cm2 V–1 s–1, respectively) is higher than that of a symmetrical PDI derivative (PDI-0, 0.30 cm2 V–1 s–1). The interface property of PDI-4/MAPbI3 and PDI-5/MAPbI3 is better than that of PDI-0/MAPbI3 due to the reinforced O···Pb interaction between the oxygen atom in the branched chain of PDI-4/PDI-5 and Pb of the perovskite surface. The enhanced defect (methylammonium vacancy, lead vacancy, and iodine substituted at the lead site) passivation ability for perovskite was also found in PDI-4 and PDI-5, which will lead to a high-performance perovskite layer. The current investigation not only offers a few promising ETMs but also provides a useful strategy for introducing asymmetrical functional groups into PDIs to obtain more efficient ETMs of PSCs.

In Silico Designing of Thieno[2,3-b]thiophene Core-Based Highly Conjugated, Fused-Ring, Near-Infrared Sensitive Non-fullerene Acceptors for Organic Solar Cells.

The performance of organic solar cells (OSCs) has been improving steadily over the last few years, owing to the optimization of device fabrication, fine-tuning of morphology, and thin-film processing. Thiophene core containing fused ring-type non-fullerene acceptors (NFAs) achieved significant proficiency for highly efficient OSCs. Quantum chemical computations are utilized herein with the motive of suggesting new NIR sensitive, highly efficient low-band gap materials for OSCs. A series of extended conjugated A-π-D-π-A architectured novel fused-ring NFAs (FUIC-1-FUIC-6) containing thieno[2,3-b]thiophene-based donor core are proposed by substituting the end-capped units of synthesized molecule F10IC. Different properties including frontier molecular orbital analysis, density of states analysis, transition density matrix analysis, excitation energy, reorganizational energies of both holes (λh) and electrons (λe), and open-circuit voltage (V oc) were performed employing the density functional theory approach. Charge transfer analysis of the best-designed molecule with the donor complex was analyzed to comprehend the efficiency of novel constructed molecules (FUIC-1-FUIC-6) and compared with the reference. End-caped acceptor alteration induces the reduction of the energy gap between HOMO-LUMO (1.88 eV), tunes the energy levels, longer absorption in the visible and near-infrared regions, larger V oc, smaller reorganizational energies, and binding energy values in designed structures (FUIC-1-FUIC-6) in comparison to reference (FUIC). The designed molecules show the best agreement with the PTBT-T donor polymer blend and cause the highest charge from the HOMO to the LUMO orbital. Our findings predicted that thieno[2,3-b] thiophene-based newly designed molecules would be efficient NFAs with outstanding photovoltaic characteristics and can be used in future applications of OSCs.

Efficient and Thermally Stable Organic Solar Cells via a Fully Halogen-Free Active Blend and Solvent

The state-of-the-art organic solar cells (OSCs) are basically based on halogenated active materials and solvents. However, halogens/halides could be detrimental to the stability of OSCs due to their corrosiveness to the interface and the electrode. On the other hand, the introduction of halogens, especially the use of halogen solvents, could cause hazards to the environment, further limiting the application of OSCs. Thus, it is meaningful to explore and develop efficient and stable OSCs based on halogen-free materials and solvents. It is demonstrated that fully halogen-free OSCs deliver efficient performance as well with an efficiency of 10.42%, based on the nonhalogenated active blend PBDB-T:ITIC and the nonhalogenated processing solvent CS2. More importantly, superior thermal stability is achieved for the halogen-free cells, with 95% of the initial efficiency retained in 1400 h under 85 °C in a N2 atmosphere, due to the stabilized blend morphology and impeded corrosion of the metal electrode. These results provide insights into the thermal degradation of OSCs and suggest possible rules/directions for the design of active materials and selection of solvents to achieve efficient and thermally stable OSCs.

Star-shape non-fullerene acceptor featuring an aza-triangulene core for organic solar cells.

We present the simple synthesis of a star-shape non-fullerene acceptor (NFA) for application in organic solar cells. This NFA possesses a D(A)3 structure in which the electron-donating core is an aza-triangulene unit and we report the first crystal structure for a star shape NFA based on this motive. We fully characterized this molecule's optoelectronic properties in solution and thin films, investigating its photovoltaic properties when blended with PTB7-Th as the electron donor component. We demonstrate that the aza-triangulene core leads to a strong absorption in the visible range with an absorption edge going from 700 nm in solution to above 850 nm in the solid state. The transport properties of the pristine molecule were investigated in field effect transistors (OFETs) and in blends with PTB7-Th following a Space-Charge-Limited Current (SCLC) protocol. We found that the mobility of electrons measured in films deposited from o-xylene and chlorobenzene are quite similar (up to 2.70 × 10-4 cm2 V-1 s-1) and that the values are not significantly modified by thermal annealing. The new NFA combined with PTB7-Th in the active layer of inverted solar cells leads to a power conversion efficiency of around 6.3% (active area 0.16 cm2) when processed from non-chlorinated solvents without thermal annealing. Thanks to impedance spectroscopy measurements performed on the solar cells, we show that the charge collection efficiency of the devices is limited by the transport properties rather than by recombination kinetics. Finally, we investigated the stability of this new NFA in various conditions and show that the star-shape molecule is more resistant against photolysis in the presence and absence of oxygen than ITIC.

S,N-Heteropentacene-based molecular donor–acceptor dyads: structure–property relationships and application in single-material organic solar cells

Molecular donor–acceptor dyads D11–D18 using S,N-heteropentacenes SN5′ and fullerenic acceptors were synthesized and applied in solution-processed single-material organic solar cells reaching power conversion efficiencies of up to 2.8%.

Rational design of non-fullerene acceptors via side-chain and terminal group engineering: a computational study.

We investigated the optoelectronic and photovoltaic properties of three types of acceptor-donor-acceptor-based non-fullerene acceptor (NFA) molecules for organic solar cell (OSC) applications. Density functional theory and its time-dependent variant were employed to compute the quadrupole moment perpendicular to the π-system (Q20), open circuit voltage (VOC), and other relevant solar cell parameters. The role of functionalization in the acceptor unit on the overall device performance was explored by incorporating halogen and methoxy-based electron-withdrawing groups. The electronegativity differences between the halogen atoms and the methoxy group demonstrated contrasting effects on the energy levels, molecular orbitals, and absorption maximum. We observed a trade-off between short-circuit current (JSC) and VOC, which was further substantiated by an inverse correlation between Q20 and VOC. We found an optimum value of Q20 in the range of 80 to 130 ea02 to achieve an optimized solar cell performance. Among the designed systems, Se-derived NFAs with a small band gap, red-shifted absorption maximum, high-oscillator strength, small exciton binding energy, and optimum Q20 turned out to be potential candidates for future applications. These criteria can be generalized to design and screen next-generation non-fullerene acceptors to achieve improved OSC performance.

Heteroatom (boron, nitrogen, and fluorine) quantum dot-doped polyaniline-photoactive film preparation and characterization for organic solar cell applications

Carbon quantum dots (CQDs) play a significant role in various applications, such as solar cells, bio-imaging, batteries, sensing, and therapy, thanks to their outstanding optical and electrical properties.

Self-Assembled Biomolecule Interlayer for Enhanced Efficiency and Stability of Inverted Organic Solar Cells

Interlayers play a vital role in achieving high efficiency and stability of organic solar cells (OSCs). Zinc oxide (ZnO) has been widely used as an electron transport layer (ETL) in inverted OSCs; however, its high structural defects and intrinsic photocatalytic nature toward nonfullerene acceptors limit its applications in OSCs. Herein, a low-cost, environmentally-friendly biomolecule, potassium aspartic acid (PAA), is introduced as the interlayer on top of the ZnO ETL. Through experimental results and theoretical calculations, we find PAA not only can tune energy alignments and passivate oxygen vacancy defects and zinc interstitial dangling bonds but also can promote the π–π stacking strength of the active layer, leading to enhanced charge collection and photovoltaic performance in both IT series (e.g., PM6:IT-4F) and Y series (e.g., PM6:BTP-4F-C5-16) OSCs. Moreover, benefiting from the reduced surface defects of ZnO, OSCs based upon the ZnO/PAA ETL exhibit superior stabilities under continuous operation as well as UV-light irradiation, leading to an improved T80 lifetime of around 4 times compared to OSCs fabricated without the PAA interlayer. This work provides a universal solution to fabricate efficient and stable inverted OSCs.

Co‐La‐Based Hole‐Transporting Layers for Binary Organic Solar Cells with 18.82 % Efficiency

AbstractPoly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used hole transporting layer (HTL) in organic solar cells (OSCs), but its acidity severely reduces the stability of devices. Until now, very few HTLs were developed to replace PEDOT:PSS toward stable and high‐performance OSCs. Herein, a new cobalt‐lanthanum (Co‐La) inorganic system was reported as HTL to show a high conversion efficiency (PCE) of 18.82 %, which is among the top PCEs in binary OSCs. Since electron‐rich outer shell of La atom can interact with Co atom to form charge transfer complex, the work function and conductivity of the Co‐La system could be simultaneously enhanced compared to Co or La‐based HTLs. This Co‐La system could also be applied into other OSCs to show high performance. All these results demonstrate that binary Co‐La systems as HTL can efficiently tackle the issue in hole transporting and show powerful application in OSCs to replace PEDOT:PSS.

Co-La-Based Hole-Transporting Layers for Binary Organic Solar Cells with 18.82 % Efficiency.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used hole transporting layer (HTL) in organic solar cells (OSCs), but its acidity severely reduces the stability of devices. Until now, very few HTLs were developed to replace PEDOT:PSS toward stable and high-performance OSCs. Herein, a new cobalt-lanthanum (Co-La) inorganic system was reported as HTL to show a high conversion efficiency (PCE) of 18.82 %, which is among the top PCEs in binary OSCs. Since electron-rich outer shell of La atom can interact with Co atom to form charge transfer complex, the work function and conductivity of the Co-La system could be simultaneously enhanced compared to Co or La-based HTLs. This Co-La system could also be applied into other OSCs to show high performance. All these results demonstrate that binary Co-La systems as HTL can efficiently tackle the issue in hole transporting and show powerful application in OSCs to replace PEDOT:PSS.

Dialkyl‐fluoroquinoxaline–based polymeric donor for binary and ternary organic solar cell applications

AbstractHere, we studied the potential of 2,3‐didodecyl‐6‐fluoroquinoxaline–based polymer as an electron‐donor in binary and ternary organic solar cell (OSC) applications. A new wide bandgap polymeric donor, namely poly(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐2,3‐didodecyl‐6‐fluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline) (P(BDTT‐TfQT)), is prepared. Polymer P(BDTT‐TfQT) showed intense absorption between 300 and 650 nm with an optical band gap of 1.83 eV. The determined highest occupied and lowest unoccupied molecular orbitals (highest occupied molecular orbital/lowest unoccupied molecular orbital = −5.28 eV/−3.45 eV) for P(BDTT‐TfQT) are found to be suitable to utilize as an electron donor along with widely used fullerene and non‐fullerene acceptors. The OSCs prepared by using P(BDTT‐TfQT):fullerene blend gave a maximum power conversion efficiency (PCE) of 4.64%, and the PCE further increased to 6.77% by using a non‐fullerene acceptor instead of fullerene. Overall, the improved light absorption results in higher photo‐current and PCE for P(BDTT‐TfQT):non‐fullerene blend compared to that of P(BDTT‐TfQT):fullerene blend. In contrast, the inclusion of 10 vol% of P(BDTT‐TfQT) as a third component in a high energy converting polymer: non‐fullerene blend is found to lower the performance from 16.03% to 14.50% for the resulting ternary OSCs.