Fluorination Triggered New Small Molecule Donor Materials for Efficient As-Cast Organic Solar Cells

Fluorination or Not in Small Molecule Solar Cells: Achieving a Higher Efficiency with Halogen-Free End Group

Fluorination is an efficient strategy for improving organic solar cells (OSCs) efficiency, particularly by fluorinating the end group of emerging nonfullerene acceptors. Here, the fluorination effect was investigated by using small molecule donors with fluorine-free (SBz) and fluorinated (SBz-F) end groups, paired with the emerging nonfullerene acceptor Y6. Interestingly and unexpectedly, fluorination of the end group negatively affects OSCs efficiency, with fluorine-free SBz:Y6 OSCs achieving a higher power conversion efficiency (PCE) of 11.05 % compared to the fluorine-containing SBz-F:Y6 blends (PCE=9.61 %). Analysis of space-charge limited currents reveals lower and unbalanced hole/electron mobility in SBz-F:Y6 compared to the SBz:Y6 blends. These findings are further supported by charge recombination dynamics and donor-acceptor miscibility analyses.

Synergistic non-bonding interactions based on diketopyrrolo-pyrrole for elevated photoacoustic imaging-guided photothermal therapy

Synergistic non-bonding interactions in fluorine and chalcogen-substituted diketopyrrolopyrrole nanoagents for elevated photoacoustic imaging-guided photothermal therapy.

Dynamics of Photoinduced Energy Transfer in Fully and Partially Conjugated Polymers Bearing π-Extended Donor and Acceptor Monomers

The photophysical properties of donor (D)-acceptor (A) polymers were studied by designing two types of polymers, (D-σ-A)_n and (D-π-A)_n, with non-conjugated alkyl (sp³) and π-conjugated (sp²) linkers using π-extended donor and acceptor monomers that exhibit planar A-D-A structures. The non-conjugated alkyl linker provides structural flexibility to the (D-σ-A)_n polymers, while the π-conjugated linker retains the rigid structure of the (D-π-A)_n polymers. Photoinduced energy transfer occurs from the large donor to acceptor units in both polymers. However, the photoinduced energy transfer dynamics are found to be dependent on the conformation of the polymers, where the difference is dictated by the types of linkers between the donor and acceptor units. In solution, intramolecular energy transfer is relatively favorable for the (D-σ-A)_n polymers with flexible linkers that allow the donor and acceptor units to be proximally located in the polymers. On the other hand, intermolecular (or interchain) energy transfer is dominant in the two polymer films because the π-extended donor and acceptor units in polymers are closely packed. The structural flexibility of the linkers between the donor and acceptor repeating units in the polymers affects the efficiency of energy transfer between the donor and acceptor units and the overall photophysical properties of the polymers.

Crucial Role of Fluorine in Fully Alkylated Ladder-Type Carbazole-Based Nonfullerene Organic Solar Cells

Two fused ladder-type nonfullerene acceptors, DTCCIC and DTCCIC-4F, based on an electron-donating alkylated dithienocyclopentacarbazole core flanked by electron-withdrawing nonfluorinated or fluorinated 1,1-dicyanomethylene-3-indanone (IC or IC-4F), are prepared and utilized in organic solar cells (OSCs). The two new molecules reveal planar structures and strong aggregation behavior, and fluorination is shown to red-shift the optical band gap and downshift energy levels. OSCs based on DTCCIC-4F exhibit a power conversion efficiency of 12.6%, much higher than that of DTCCIC-based devices (6.2%). Microstructural studies reveal that while both acceptors are highly crystalline, bulk heterojunction blends based on the nonfluorinated DTCCIC result in overly coarse domains, while blends based on the fluorinated DTCCIC-4F exhibit a more optimal nanoscale morphology. These results highlight the importance of end group fluorination in controlling molecular aggregation and miscibility.

Surface Modification of SnO2 via MAPbI3 Nanowires for a Highly Efficient Non-Fullerene Acceptor-Based Organic Solar Cell

These days, organic-inorganic hybrid perovskites (OIHP) and non-fullerene acceptor (NFA) molecules are all at the frontiers of research and development in the domain of photovoltaics. A careful design and use of inorganic transparent metal oxides with wide band gaps as electron and hole transport layers are critically important for highly efficient and stable solar cells. As one of the most favorable electron transport materials, tin oxide (SnO₂), which has been frequently utilized in highly efficient OIHP solar cells, is rarely seen in the application of NFA organic bulk heterojunction (BHJ) solar cells. To appropriately tailor an interface of SnO₂ and an organic blend, while to make them compatible and useful may offer some opportunities for achieving higher efficiencies and longer lifetimes. In fact, there is still a lack of a method to solve the problem. Herein, a unique way is developed by implementing a surface decoration nanostructure such as low dimensional MAPbI₃ perovskite nanowires (PeNWs) at the interface of SnO₂ and the organic blend such as PBDB-T-SF:IT-4F. Such an interface functions well for the improvement of photovoltaic performance for the organic solar cell of the structure ITO(glass)/SnO₂/PeNWs/PBDB-T-SF:IT-4F/MoO₃/Ag. Experimental results indicate that the electron-hole dissociation, charge extraction, and photo-absorption ability of the organic solar cell can be improved significantly. The inside generation of the photocurrent is explored by the magneto-photocurrent method. Finally, the solar cell exhibits more than 80% power conversion efficiencies even after 20 days, which suggests the merits of having both SnO₂ and PeNWs in the NFA-based organic solar cell.

Energy level tuning of ‘Z’-shaped small molecular non-fullerene electron acceptors based on a dipyrrolo[2,3-b:2′,3′-e]pyrazine-2,6(1H,5H)-dione acceptor unit for organic photovoltaic applications: a joint experimental and DFT investigation on the effect of fluorination

Three dipyrrolo[2,3-b:2′,3′-e]pyrazine-2,6(1H,5H)-dione based small molecule non-fullerene acceptors with various end-capped fluorine units have been investigated.