High-performance Non-fullerene Organic Solar Cells Research Articles

Random Terpolymer Based on Simple Siloxane-functionalized Thiophene Unit Enabling High-performance Non-fullerene Organic Solar Cells

Random Terpolymer Based on Simple Siloxane-functionalized Thiophene Unit Enabling High-performance Non-fullerene Organic Solar Cells

Fluorescent Conversion Agent Embedded in Zinc Oxide as an Electron-Transporting Layer for High-Performance Non-Fullerene Organic Solar Cells with Improved Photostability.

Zinc oxide (ZnO) is widely used as an electron transporting layer (ETL) for organic solar cells (OSCs). Here, a low-cost commercial water/alcohol-soluble fluorescent conversion agent, sodium 2,2'-([1,1'-biphenyl]-4,4'-diyldivinylene)-bis(benzenesulfonate) (CBS), is incorporated into ZnO to develop a novel organic-inorganic hybrid ETL for high-performance OSCs. The photoinduced charge transfer from CBS to ZnO significantly improves the charge transport properties of ZnO, resulting in faster electron extraction and reduced charge recombination in OSC devices with ZnO:CBS ETLs. ZnO:CBS-based devices exhibit higher power conversion efficiencies (PCEs) than their pure ZnO-based counterparts, especially in devices with a thicker ETL, which is more suitable for roll-to-roll and large-area module processing. Furthermore, the strong ultraviolet-light absorption capability of CBS inhibits the photodegradation of the active layer, improving the photostability of ZnO:CBS based OSC devices. Therefore, this work provides a simple and effective strategy for realizing high-performance OSCs with high PCE and good photostability, which can further facilitate the commercialization of OSCs.

Near 0 eV HOMO offset enable high-performance nonfullerene organic solar cells with large open circuit voltage and fill factor

Blending the donor and acceptor with a near zero HOMO offset can realize high-performance nonfullerene organic solar cells with large open circuit voltage and fill factor.

High photogeneration and low recombination rate leading to high-performance non-fullerene organic solar cells

TPV/TPC, EQE/IQE measurements and simulation modeling reveal that the high-performance organic solar cells originate from both an increasing charge generation and a reducing recombination rate coefficient, with PCE potentially exceeding 21%.

High-Performance Non-fullerene organic solar cells enabled by noncovalent Conformational locks and Side-Chain engineering

Three novel small molecular acceptors (SMAs) BO-2F, BO-C8-2F and BO-C2C6-C8-2F were designed and synthesized. These acceptors all possess planar molecular backbone because of the introduction of intramolecular noncovalent interaction. Among them, BO-C2C6-C8-2F with four side chains, which has the highest solubility, can form more appropriate nanomorphology when blending with PBDB-T. Hence, organic solar cells (OSCs) based on PBDB-T:BO-C2C6-C8-2F displayed an outstanding power convesion efficiency (PCE) of 14.25%, which is higher than BO-2F and BO-C8-2F based ones. To the best of our knowledge, the PCE of 14.25% is one of the highest for the OSCs based on A-π-D-π-A type SMAs. Our results have demonstrated that the combination of side-chain engineering and intramolecular conformation lock has a great prospect in the design of high performance SMAs for OSCs.

Quantum chemical designing of banana-shaped acceptor materials with outstanding photovoltaic properties for high-performance non-fullerene organic solar cells

Non-Fullerene acceptors (NFAs) are getting a huge attention from the researchers across the globe to develop bulk-heterojunction organic solar cells (BHJ-OSC). In contrast with fullerene counterparts, the electronic energy levels as well as their optical properties can be tuned easily which ultimately helps to further enhance the power conversion efficiency of BHJ-OSC devices. By considering this crucial phenomenon of NFAs in OSCs, here we have designed a series of new banana-shaped NFAs (BS1-BS5) by doing end-capped modifications of BDTP-4F (R). Structural-property relationship, photo-physical, and optoelectronic properties of newly designed molecules are extensively studied by using density functional theory (DFT) and time dependent-density functional theory (TD-DFT). Furthermore, some geometric parameters like frontier molecular orbitals (FMOs), excitation and binding energy, hole-electron overlap, density of states, molecular electrostatic potential, open circuit voltage, transition density matrix, and reorganizational energy of electron and hole are also studied and compared with BDTP-4F (R). All of the designed materials (BS1-BS5) showed a red-shifting in absorption spectrum, higher electronic charge mobility, while, lower binding and excitation energies in-contrast to BDTP-4F. Much narrower HOMO-LUMO energy gaps (Eg= 1.89–1.98 eV) has been observed among all of the newly designed materials, suggesting their higher charge shifting behavior from HOMO to LUMO. In last, complex study of PTB7-Th/BS2 and PM6/BS2 also investigated in order to understand the charge shifting between donor and acceptor molecules. From all reported analysis, we concluded that our theoretical designed molecules are better than BDTP-4F (R), thus we recommend these molecules to experimentalist for future development of highly-efficient OSCs devices.

A solution-processed, ultraviolet-irradiation-derived WO3 film as anode interface layer for high-performance non-fullerene organic solar cells

Tungsten(VI) oxide (WO3) with excellent charge transport properties and intrinsic thermal and chemical robustness is a promising anode interface material instead of PEDOT:PSS in organic solar cells (OSCs). Herein, a solution-processed, ultraviolet-irradiation-derived WO3 film as anode interface layer (AIL) is developed based on tungsten(VI) chloride (WCl6) as precursor. The WO3 film is derived from the solution-processed precursor film with simple ultraviolet-irradiation treatment, and the preparation process without high-temperature annealing is very compatible with large-scale production and flexible substrate. The composition of the WO3 film is analyzed by X-ray photoelectron spectroscopy. ITO modified by the WO3 film, namely ITO/WO3, exhibits similarly high optical transmittance as that of bare ITO. The work function of ITO/WO3 measured by ultraviolet photoelectron spectroscopy is obviously lower than that of bare ITO, which can facilitate effective holes extraction. In addition, the WO3 film possesses relatively smooth and hydrophobic surface, beneficial to form excellent interface contact with active layer. Moreover, non-fullerene OSCs based on the WO3 film as AIL are studied with typical and relatively low-cost PBDB-T:ITIC as active layer. The optimal efficiency (8.70%) of the device based on ITO/WO3 is dramatically higher than that (3.32%) of the device based on bare ITO, and comparable to that (8.80%) of the device based on ITO/PEDOT:PSS. Therefore, the solution-processed, ultraviolet-irradiation-derived WO3 film as AIL should have great potential to realize high-performance non-fullerene OSCs, which can also inspire a novel and promising route to prepare other transition metal oxide films in optoelectronic devices.

Optimizing the energy levels and crystallinity of 2,2′-bithiophene-3,3′-dicarboximide-based polymer donors for high-performance non-fullerene organic solar cells

BTI-based polymer donors greatly affect the active layer morphology by adjusting energy levels and crystallinity, so as to optimize the phase separation, which is important for the construction and development of organic solar cells.

A-DA′D-A non-fullerene acceptors for high-performance organic solar cells

Since the world-record power conversion efficiency of 15.7% was achieved for organic solar cells (OSCs) in 2019, the newly developed non-fullerene acceptor (NFA) Y6 with an A-DA′D-A structure (A denotes an electron-accepting moiety, D denotes an electron-donating moiety) has attracted increasing attention. Subsequently, many new A-DA′D-A NFAs have been designed and synthesized, and the A-DA′D-A NFAs have played a significant role in the development of high-performance non-fullerene organic solar cells (NF-OSCs). Compared with the classical A-D-A-type acceptors, A-DA′D-A NFAs contain an electron-deficient core (such as benzothiadiazole (BT), benzotriazole (BTA), quinoxaline (Qx), or their derivatives) in the ladder-type fused rings to fine-tune the energy levels, broaden light absorption and achieve higher electron mobility of the NFAs. This review emphasizes the recent progress on these emerging A-DA′D-A (including Y-series) NFAs. The synthetic methods of DA′D-fused rings are introduced. The relationships between the chemical structure of the A-DA′D-A NFAs and the photovoltaic performance of the corresponding OSCs are summarized and discussed. Finally, issues and prospects for further improving photovoltaic performance of the OSCs are also proposed.

Efficient Non-Fullerene Organic Solar Cells Based on a Wide-Bandgap Polymer Donor Containing an Alkylthiophenyl-Substituted Benzodithiophene Moiety.

Two wide-bandgap polymer donors containing an alkylthiophenyl substituted benzo[1,2-b : 4,5-b']dithiophene moiety, namely PTZPO and PTZPS, were designed and synthesized. Both polymers exhibit relatively wide optical bandgap of 1.95 V with similar absorption profiles. The polymer PTZPS with alkylthiophenyl substituted benzo[1,2-b : 4,5-b']dithiophene units showed enhanced light-harvesting capabilities, leading to improved short-circuit current densities. The PTZPS : ITIC film shows more appreciable film morphology and phase separation than the film composed of a blend of ITIC with alkoxyl substitutions containing copolymer PTZPO, which facilitates exciton dissociation and charge transport. The PTZPS : ITIC-based non-fullerene organic solar cells show clearly improved short-circuit current density and an impressively high power conversion efficiency of more than 11 %. These observations demonstrate the great promise of using PTZPS as electron-donating materials for high-performance non-fullerene organic solar cells.

Ternary System with Intermolecular Hydrogen Bond: Efficient Strategy to High-Performance Nonfullerene Organic Solar Cells.

To boost organic solar cell (OSC) performance, numerous approaches have been developed, such as synthesizing new materials, using post-annealing (thermal or solvent annealing) or fabricating ternary devices. The ternary strategy is usually used as an uncomplicated and effective way, but how to choose the third component and the effect of interactions between materials on OSC performance still need to be clarified. Herein, we proposed a new finding that the carbonyl group of 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b'] dithiophene (ITIC) end groups can react with the dye molecule SR197 to form the N-H···O noncovalent interaction. The existence of intermolecular hydrogen bonds was confirmed using Fourier transform infrared spectra and two-dimensional proton nuclear magnetic resonance. The power conversion efficiency (PCE) was improved to 10.29% via doping SR197 into blends of PTB7-Th:ITIC, which exhibited a huge enhancement of approximately 30% compared with the binary OSCs (PCE = 7.92%). The ternary OSCs of PBDB-T:SR197:ITIC could also achieve high PCE (11.03%) without post-thermal or solvent annealing. Transmission electron microscopy and grazing-incidence wide-angle X-ray scattering showed the optimized morphology and enhanced crystallinity of ternary systems, which is facilitated to exciton dissociation and charge transmission. These conclusions mean that the H-bonding strategy is an effective way for selecting the third component and could achieve high-performance OSCs.

Isomerization of Perylene Diimide Based Acceptors Enabling High-Performance Nonfullerene Organic Solar Cells with Excellent Fill Factor.

A strategy that employs the central‐core regiochemistry to develop two isomeric perylene diimide (PDI)‐based small molecular acceptors (SMAs), BPT‐Se and BPT‐Se1, is introduced, and the effect of the central‐core regiochemistry on the optical, electronic, charge‐transport, photovoltaic, and morphological properties of the molecules and their devices is investigated. The PDBT‐T1:BPT‐Se1‐based device delivers a power conversion efficiency (PCE) of 9.54% with an excellent fill factor (FF) of 73.2%, while the BPT‐Se‐based device yields a PCE of 7.78%. The large improvement of PCE upon isomerization of BPT‐Se should be ascribed to the concurrent enhancement of FF, short circuit current ( J SC), and open circuit voltage (V OC) of the PDBT‐T1:BPT‐Se1 devices. The higher FF of the organic solar cells (OSCs) based on PDBT‐T1:BPT‐Se1 can be attributed to the higher charge dissociation and charge collection efficiency, less bimolecular combination, more balanced µ h/µ e, better molecular packing and a more favorable morphology. It is worth mentioning that the FF of 73.2% is the highest value for PDI‐based SMAs OSCs to date. The result shows that regiochemistry of the central core in PDI‐based SMAs greatly affects the physicochemical properties and photovoltaic performance. The success of the isomerization strategy offers exciting prospects for the molecular design of PDI‐based SMAs.

Polymer Donors for High-Performance Non-Fullerene Organic Solar Cells.

Over the past few years, non-fullerene organic solar cells have been a focus of research and their power conversion efficiencies have been improved dramatically from about 6 % to over 14 %. In addition to innovations in non-fullerene acceptors, the ongoing development of polymer donors has contributed significantly to the rapid progress of non-fullerene organic solar cell performance. This Minireview highlights the polymer donors that enable high-performance non-fullerene organic solar cells. We show the impressive photovoltaic devices results achieved by some of important classes of conjugated polymer systems in non-fullerene organic solar cells. We discuss the molecular design strategies as far as developing matching polymer donors for non-fullerene acceptors. We conclude with a brief summary and outlook for advances in donor polymers required for commercialization.

A universal layer-by-layer solution-processing approach for efficient non-fullerene organic solar cells

A universal layer-by-layer solution-processing approach is proven to be effective for the fabrication of high-performance non-fullerene organic solar cells.

Diblock conjugated polyelectrolyte electron transport layer modulating the morphology of the active layer for efficient nonfullerene organic solar cells

To acquire high-performance nonfullerene organic solar cells (OSCs), the effective approach is to explore new interfacial layer that not only can modulate the interfacial contact, but can also tune the morphology of the active layer. A diblock CPE PFEO-b-PTNBr with polyfluorene and polythiophene backbone, quaternary ammonium salt and ethylene oxy polar side chains, has been used to modify ZnO as ETL for PBDB-T:ITIC OSCs. The influences of the diblock CPE PFEO-b-PTNBr electron transport layer (ETL) on the morphology and crystalline properties of the PBDB-T:ITIC, exciton diffusion and transfer, and the device performances have been thoroughly investigated. Remarkably, the self-assembled diblock polymer PFEO-b-PTNBr can really induce the corresponding PBDB-T:ITIC active layer to obtain an ordered nano-fiber morphology. Consequently, in sharp comparison to the OSC utilizing ZnO as ETL, the performances of the device with the ZnO/PFEO-b-PTNBr ETL have been simultaneously enhanced, exhibiting a remarkably superior power conversion efficiency of 10.8%. These findings manifest that the diblock CPE PFEO-b-PTNBr is a promising ETL in nonfullerene OSCs.

Extension of indacenodithiophene backbone conjugation enables efficient asymmetric A–D–A type non-fullerene acceptors

Three non-fullerene acceptors are developed by extending the conjugation of the indacenodithiophene (IDT) core for the fabrication of high-performance non-fullerene organic solar cells.

Terminal π–π stacking determines three-dimensional molecular packing and isotropic charge transport in an A–π–A electron acceptor for non-fullerene organic solar cells

Three-dimensional molecular packing and isotropic charge transport can be achieved through local π–π stacking between terminal acceptor units for A–π–A electron acceptors toward high-performance non-fullerene organic solar cells.