Non-fullerene acceptor pre-aggregates enable high efficiency pseudo-bulk heterojunction organic solar cells

Pseudo-bulk heterojunction(BHJ)fabricated by sequential casting of donor and acceptor layers has been recently demonstrated as a superior structure to prepare organic solar cells(OSCs)with enhanced efficiency compared to the conventional BHJ OSCs cast from a common solution of donors and acceptors.However,molecular diffusion and aggregation within the pseudo-BHJ layer bring great challenges to fully realize the advantage of pseudo-BHJ structure.Herein,a solution-incubated pre-aggregation strategy is employed to tune the nanoscale aggregates of non-fullerene acceptor(NFA)BTP-e C11 and N3 to substantially enhance device power-conversion efficiency(PCE).NFA pre-aggregates are incubated in solutions via aging or adding antisolvent,and then sequentially cast onto D18 fibrillar network,which then penetrate to form a pseudo-BHJ structure with appropriate domain sizes to ensure superior charge mobilities.While the conventional pseudo-BHJ OSCs obtain inferior PCEs below 17%compared with normal BHJ OSCs,NFA pre-aggregates help to achieve remarkable PCEs of 17.7%and 17.5%for D18/BTP-e C11 and D18/N3 pseudo-BHJ OSCs.This work demonstrates that the solution-incubated nanoscale pre-aggregation is an efficient approach to regulate molecular diffusion and aggregation to guarantee high performance pseudo-BHJ OSCs.     

Achieving 16.68% efficiency ternary as-cast organic solar cells

State-of-the-art organic solar cells(OSCs)often require the use of high-boiling point additive or post-treatment such as temperature annealing and solvent vapor annealing to achieve the best efficiency.However,additives are not desirable in largescale industrial printing process,while post-treatment also increases the production cost.In this article,we report highly efficient ternary OSCs based on PM6:BTP-Cl Br1:BTP-2O-4Cl-C12(weight ratio=1:1:0.2),with 16.68%power conversion efficiency(PCE)for as-cast device,relatively close to its annealed counterpart(17.19%).Apart from obvious energy tuning effect and complementary absorption spectra,the improved PCE of ternary device is mainly attributed to improved morphological properties including the more favorable materials miscibility,crystallinity,domain size and vertical phase separation,which endorse suppressed recombination.The result of this work provides understanding and guidance for high-performance as-cast OSCs through the ternary strategy.     

A chlorinated low-bandgap small-molecule acceptor for organic solar cells with 14.1% efficiency and low energy loss

A new acceptor-donor-acceptor(A-D-A) type small-molecule acceptor NCBDT-4 Cl using chlorinated end groups is reported.This new-designed molecule demonstrates wide and efficient absorption ability in the range of 600–900 nm with a narrow optical bandgap of 1.40 eV. The device based on PBDB-T-SF:NCBDT-4 Cl shows a power conversion efficiency(PCE) of 13.1%without any post-treatment, which represents the best result for all as-cast organic solar cells(OSCs) to date. After device optimizations, the PCE was further enhanced to over 14% with a high short-circuit current density(Jsc) of 22.35 m A cm-2 and a fill-factor(FF) of 74.3%. The improved performance was attributed to the more efficient photo-electron conversion process in the optimal device. To our knowledge, this outstanding efficiency of 14.1% with an energy loss as low as 0.55 eV is among the best results for all single-junction OSCs.     

Electron-deficient core fused-ring based non-Fullerene acceptor enables over 15% efficiency in single junction organic solar cells

<正>Organic solar cells (OSCs) are promising to access flexible,light weight and semi-transparent photovoltaic devices by low-cost solution fabrication. Recently, the fused-ring nonfullerene acceptors play an important role in promoting the research progress of the OSCs. The power conversion efficiencies (PCEs) have been rapidly boosted to over 14%in single junction OSCs with the development of new nonfullerene acceptors and the related devices [1–3]. Although     

Achieving over 16% efficiency for single-junction organic solar cells

To achieve high photovoltaic performance of bulk hetero-junction organic solar cells(OSCs), a range of critical factors including absorption profiles, energy level alignment, charge carrier mobility and miscibility of donor and acceptor materials should be carefully considered. For electron-donating materials, the deep highest occupied molecular orbital(HOMO) energy level that is beneficial for high open-circuit voltage is much appreciated. However, a new issue in charge transfer emerges when matching such a donor with an acceptor that has a shallower HOMO energy level. More to this point, the chemical strategies used to enhance the absorption coefficient of acceptors may lead to increased molecular crystallinity, and thus result in less controllable phase-separation of photoactive layer. Therefore, to realize balanced photovoltaic parameters, the donor-acceptor combinations should simultaneously address the absorption spectra, energy levels, and film morphologies. Here, we selected two non-fullerene acceptors, namely BTPT-4F and BTPTT-4F, to match with a wide-bandgap polymer donor P2F-EHp consisting of an imidefunctionalized benzotriazole moiety, as these materials presented complementary absorption and well-matched energy levels. By delicately optimizing the blend film morphology, we demonstrated an unprecedented power conversion efficiency of over 16% for the device based on P2F-EHp:BTPTT-4F, suggesting the great promise of materials matching toward high-performance OSCs.     

A ternary organic solar cell with 300 nm thick active layer shows over 14% efficiency

In order to meet the requirements for making organic solar cells(OSCs) through solution printing techniques, great efforts have been devoted into developing high performance OSCs with relatively thicker active layers. In this work, a thick-film(300 nm)ternary OSC with a power conversion efficiency of 14.3% is fabricated by introducing phenyl-C_(61)-butyric-acid-methyl ester(PC_(61)BM) into a PBDB-T-2Cl:BTP-4 F host blend. The addition of PC_(61)BM is found to be helpful for improving the hole and electron mobilities, and thus facilitates charge transport as well as suppresses charge recombination in the active layers, leading to the improved efficiencies of OSCs with relatively thicker active layers. Our results demonstrate the feasibility of employing fullerene derivative PC_(61)BM to construct a high-efficiency thick-film ternary device, which would promote the development of thick layer ternary OSCs to fulfill the requirements of future roll to roll production.     

Short-axis substitution approach on ladder-type benzodithiophene-based electron acceptor toward highly efficient organic solar cells

Short-axis substitution, as an effective way to change the optical and electronic properties of the organic semiconductors for organic photovoltaics(OPVs), is a readily approach to modify non-fullerene acceptors, especially for the linear fused rings system. Here, two new fused-ring electron acceptors(CBT-IC and SBT-IC) were designed and developed by short-axis modification based on the dithienyl[1,2-b:4,5-b′]benzodithiophene(BDCPDT) system. Combined with a medium bandgap polymer donor J71, both of the OPV devices exhibit high power conversion efficiency(PCE) over 11%, and ～70% external quantum efficiencies. To better understand how this kind of substitution affects the BDCPDT based acceptors, a comparative analysis is also made with the the plain acceptor BDT-IC without this modification. We believe this work could disclose the great potential and the versatility of BDCPDT block and also enlighten other ladder-type series for further optimization.     

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.     

High efficiency ternary organic solar cells enabled by compatible dual-donor strategy with planar conjugated structures

Ternary organic solar cells(OSCs) have received extensive attention for improving the power conversion efficiency(PCE) of organic photovoltaics(OPVs). In this work, a novel donor material(ECTBD) consisting of benzodithiophene(BDT) central electron donor unit was developed and synthesized. The small molecular donor has the same central unit as PM6. The addition of ECTBD into PM6:Y6 system could improve the morphology of active blend layer. In addition, ECTBD showed good morphologically compatibility when blending with PM6:Y6 host, resulting in the improvement of fill factor and current density. As a result, the ternary devices based on PM6:ECTBD:Y6 ternary system achieved a highest PCE of 16.51% with fill factor of 76.24%, which was much higher than that of the binary devices(15.7%). Overall, this work provided an effective strategy to fabricate highly efficient ternary organic solar cells through design of the novel small molecular donor as the third component.     

Morphology optimization in ternary organic solar cells

Ternary organic solar cells have drawn great attention because the highest power conversion efficiencies have reached ~12%, showing a promising prospect for the future applications. However, most reported ternary solar cells focus on the increase of light absorption and the optimization of energy alignment, but ignore the importance of morphology. Herein, we summarize the morphology optimization on the ternary blends with different structural aspects, such as controlling crystallinity, crystal orientation, domain size, and domain purity. Furthermore, the fundamental mechanism of ternary solar cells which is related to the morphology has been described. The efforts here will provide a guiding role for the morphology optimization on the ternary solar cells in the future.     

A chlorinated non-fullerene acceptor for efficient polymer solar cells

After additive and thermal annealing treatment, the PM6:Y15 based device obtains a high power conversion efficiency of 14.13%.     

A new non-fullerene acceptor based on the heptacyclic benzotriazole unit for efficient organic solar cells

正Non-fullerene acceptors (NFAs) become an interesting family of organic photovoltaic materials, and have attracted considerable interest for their great potential in manufacturing large-area flexible solar panels by low cost coating methods [1–5]. Recently, our group proposed in the first time an A-DA’D-A molecular strategy and synthesized a new class of non-fullerene acceptor Y6 with a record efficiency above 15%with single junction organic solar cells (OSCs)[6]. To further improve the photovoltaic performance     

A chlorinated non-fullerene acceptor for efficient polymer solar cells

Improving the performance and reducing the manufacturing costs are the main directions for the development of organic solar cells in the future. Here, the strategy that uses chemical structure modification to optimize the photoelectric properties is reported. A new narrow bandgap (1.30 eV) chlorinated non-fullerene electron acceptor (Y15), based on benzo[d][1,2,3] triazole with two 3-undecyl-thieno[2′,3′:4,5] thieno[3,2-b] pyrrole fused -7-heterocyclic ring, with absorption edge extending to the near-infrared (NIR) region, namely A-DA'D-A type structure, is designed and synthesized. Its electrochemical and optoelectronic properties are systematically investigated. Benefitting from its NIR light harvesting, the fabricated photovoltaic devices based on Y15 deliver a high power conversion efficiency (PCE) of 14.13%, when blending with a wide bandgap polymer donor PM6. Our results show that the A-DA'D-A type molecular design and application of near-infrared electron acceptors have the potential to further improve the PCE of polymer solar cells (PSCs).     

Manipulating active layer morphology of molecular donor/polymer acceptor based organic solar cells through ternary blends

The development of molecular donor/polymer acceptor blend(MD/PA)-type organic solar cells(OSCs) lags far behind other type OSCs. It is due to the large-size phase separation morphology of MD/PAblend, which results from the high crystallinity of molecular donors. In this article, to suppress the crystallinity of molecular donors, we use ternary blends to develop OSCs based on one polymer acceptor(P-BNBP-f BT) and two molecular donors(DR3 TBDTT and BTR) with similar chemical structures.The ternary OSC exhibits a power conversion efficiency(PCE) of 4.85%, which is higher than those of the binary OSCs(PCE=3.60% or 3.86%). To our best knowledge, it is the first report of ternary MD/PA-type OSCs and this PCE is among the highest for MD/PA-type OSCs reported so far. Compared with the binary blends, the ternary blend exhibits decreased crystalline size and improved face-on orientation of the donors. As a result, the ternary blend exhibits improved and balanced charge mobilities, suppressed charge recombination and increased donor/acceptor interfacial areas, which leads to the higher shortcircuit current density. These results suggest that using ternary blend is an effective strategy to manipulate active layer morphology and enhance photovoltaic performance of MD/PA-type OSCs.     

A non-fullerene acceptor enables efficient P3HT-based organic solar cells with small voltage loss and thickness insensitivity

The large D core of DFPCBR results in efficient P3HT-based OSCs with a high V_OC and thickness insensitivity.     

Additive-free non-fullerene organic solar cells with random copolymers as donors over 9% power conversion efficiency

The PBDB-TBT1:ITIC-based device obtains PCE of 9.09%, and is insensitive to additive and thermal annealing, and forms microstructural morphology.     

A donor-acceptor-acceptor molecule for vacuum-processed organic solar cells with a power conversion efficiency of 6.4%

A D-A-A-type molecular donor (DTDCTP) featuring electron-accepting pyrimidine and dicyanovinylene blocks has been synthesized for vacuum-deposited planar-mixed heterojunction solar cells with C(70) as the acceptor, giving a power conversion efficiency as high as 6.4%.     

High-performance polymer solar cells with >13% efficiency

正In the last three years,polymer solar cells(PSCs)based on ntype organic semiconductor(n-OS)acceptor have become the focus of attention and made great progress.In 2017,the power conversion efficiencies(PCEs)have been boosted to~13%for PSCs with single-junction and~14%for PSCs     

High-performance polymer solar cells with >10% efficiency

<正>Polymer solar cells(PSCs)with bulky heterojunction structure have attracted considerable attention due to their advantages in making flexible,light weight and large area solar cell panels through the low cost roll-to-roll printing technologies.In the past decades,tremendous efforts have been devoted to developing new materials and device fabrication methods to improve the power conversion efficien-     

Breaking 12% efficiency in flexible organic solar cells by using a composite electrode

The performance of flexible organic solar cells(OSCs)significantly relies on the quality of transparent flexible electrode.Here,we used silver nanowires(AgNWs)with various weight ratios to dope high-conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate(PH1000)to optimize the optical and electronic properties of PH1000 film.A high-quality flexible composite electrode PET/Ag-mesh/PH1000:AgNWs-20 with smooth surface,a low sheet resistance of 6Ω/sq and a high transmittance of 86%at 550-nm wavelength was obtained by doping 20 wt%AgNWs to PH1000(PH1000:AgNWs-20).The flexible OSCs based on the PET/Ag-mesh/PH1000:AgNWs-20 electrode delivered a power conversion efficiency(PCE)of12.07%with an open circuit voltage(V_(oc))of 0.826 V,a short-circuit current density(J_(sc))of 20.90 m A/cm~2and a fill factor(FF)of69.87%,which is the highest reported PCE for the flexible indium-tin oxide(ITO)-free OSCs.This work demonstrated that the flexible composite electrodes of PET/Ag-mesh/PH1000:AgNWs are promising alternatives for the conventional PET/ITO electrode,and open a new avenue for developing high-performance flexible transparent electrode for optoelectronic devices.