Non-fullerene Molecular Acceptors Research Articles

Effect of terminal fluorination of indenoindene-cored non-fullerene molecular acceptors for photovoltaic application

Two new non-fullerene molecule acceptors (NFAs), IDTIC and IDTIC-4F, based on a 5,10-dihydroindeno[2,1-a]indene core and 4H-cyclopenta[1,2-b:5,4-b']dithiophene (CPDT) bridges, were designed and synthesized. The fluorine-terminated IDTIC-4F shows a larger bathochromic shift than the non-fluorinated IDTIC. When blending with a PBDB-T polymer donor to fabricate organic solar cells, the IDTIC and IDTIC-4F acceptors respectively showed power conversion efficiencies (PCEs) of 5.60% and 6.77%. The PBDB-T:IDTIC-4F device performed better on Jsc and FF, which was attributed to the morphological evolution due to terminal fluorinated design of NFAs. Comparatively, the terminal fluorinated IDTIC-4F contributes to the formation of a more uniform film with less traps, which improves the charge transport and reduces the bimolecular recombination within the device. The work demonstrates that terminal fluorination of NFAs is an efficient design to modifying the morphology and performance of non-fullerene organic photovoltaics.

Machine learning of atomic force microscopy images of organic solar cells.

The bulk heterojunction structures of organic photovoltaics (OPVs) have been overlooked in their machine learning (ML) approach despite their presumably significant impact on power conversion efficiency (PCE). In this study, we examined the use of atomic force microscopy (AFM) images to construct an ML model for predicting the PCE of polymer : non-fullerene molecular acceptor OPVs. We manually collected experimentally observed AFM images from the literature, applied data curing and performed image analyses (fast Fourier transform, FFT; gray-level co-occurrence matrix, GLCM; histogram analysis, HA) and ML linear regression. The accuracy of the model did not considerably improve even by including AFM data in addition to the chemical structure fingerprints, material properties and process parameters. However, we found that a specific spatial wavelength of FFT (40-65 nm) significantly affects PCE. The GLCM and HA methods, such as homogeneity, correlation and skewness expand the scope of image analysis and artificial intelligence in materials science research fields.

Efficient wide-band-gap copolymer donors for organic solar cells with perpendicularly placed benzodithiophene units

The working horses for the drastically improved power conversion efficiency (PCE) of organic solar cells (OSCs) were the small-band-gap molecular non-fullerene acceptors. This development not only removed the low performance obstacle for OSCs but also raised needs for wide-band-gap polymers for donor/acceptor mix with complimentary absorptions. Benzodithiophene (BDT) is one of the mostly used unit for constructing donor polymers. Here, we introduced one type of donor polymer with two BDT units placed perpendicularly. This exploration is aimed to reduce the complexity of molecule design, potentially to reduce the cost of donor materials. We also explored the halogenation of BDT side group to optimize the performances of the copolymers. The chlorinated donor polymer PvBDT-Cl delivered a decent PCE of 8.23% with Y6-T. This work explored the possibility of using only BDT unit to construct high performance donor polymers, which is a crucial insight for future low-cost donor polymer design.

Oxygen heterocycle-fused indacenodithiophenebithiophene enables an efficient non-fullerene molecular acceptor

Fusing oxygen heterocycles into an indacenodithiophenebithiophene core contributes to realizing low bandgap non-fullerene molecular acceptors with a power conversion efficiency exceeding 8%.

Effect of Replacing Alkyl Side Chains with Triethylene Glycols on Photovoltaic Properties of Easily Accessible Fluorene-Based Non-Fullerene Molecular Acceptors: Improve or Deteriorate?

Hydrophilic oligo(ethylene glycol) (OEG) side chains are more flexible than alkyl chains and can facilitate the π–π stacking of conjugated polymer backbones, which has been proven to be a key structural feature leading to better device performance in polymer:fullerene blend polymer solar cells (PSCs). So far, little has been known about the influence of OEG side chains on the performance of non-fullerene acceptors in polymer:non-fullerene acceptor blends. Based on an easily accessible conjugated backbone of dicyanomethylene indanone–thiophene–fluorene–thiophene–dicyanometnylene indanone (DICTF), two non-fullerene molecular acceptors were synthesized with decyl (DICTF-C10) and triethylene glycol monoether (DICTF-TEG) side chains to blend with the polymer donor of PTB7-Th for PSCs. Replacing the decyl side chains with the TEGs on DICTF does improve the π–π stacking between the conjugated backbones as expected. For DICTF-TEG, nevertheless, forming the BHJ blend with the PTB7-Th donor leads to unfavorable fil...

Investigating charge generation in polymer:non-fullerene acceptor bulk heterojunction films

Non-fullerene acceptors are now capable of being used in high efficiency bulk heterojunction (BHJ) donor-acceptor organic solar cells. Acceptors comprising single or multiple linked chromophores have been used. We have developed a new non-fullerene molecular acceptor as well as two non-polymeric macromolecular materials that contain four equivalents of a similar chromophore, but can adopt different spatial arrangements of the chromophores. We compare the effect of having single and multiple chromophores within a macromolecule on the charge generation processes in P3HT:non-fullerene acceptor BHJ films using Transient Absorption Spectroscopy (TAS) and Time Resolved Microwave Conductivity (TRMC) measurements. It was found from the TAS measurements that at low weight percent (5 wt%) the single chromophore formed more polarons than the acceptors in which chromophores were linked, due to it having a more even distribution within the film. At higher concentrations (50 wt%) the trend was reversed due to the single chromophore forming crystalline domains, which reduced the interface area with the P3HT donor. The TRMC measurements showed that more mobile carriers were formed in the macromolecular acceptors when used at low concentrations in the blend and, independent of concentration, mobile carriers had a longer lifetime when compared to films containing the molecular material, which we ascribe to the charges being able to sample more than one chromophore and thus reduce recombination events.

Effect of Replacing Alkyl Side Chains with Triethylene Glycols on Photovoltaic Properties of Easily Accessible Fluorene-Based Non-Fullerene Molecular Acceptors: Improve or Deteriorate?

Effect of Replacing Alkyl Side Chains with Triethylene Glycols on Photovoltaic Properties of Easily Accessible Fluorene-Based Non-Fullerene Molecular Acceptors: Improve or Deteriorate?

Unprecedented low energy losses in organic solar cells with high external quantum efficiencies by employing non-fullerene electron acceptors

Non-fullerene molecular acceptors in combination with a polymeric donor gave well performing BHJSCs with energy losses below 0.4 eV concomitant with outstanding external quantum efficiencies in the NIR-regime.

Phthalimide end-capped thienoisoindigo and diketopyrrolopyrrole as non-fullerene molecular acceptors for organic solar cells

Two acetylene-bridged molecules, built by grafting phthalimides on thienoisoindigo (TII) and diketopyrrolopyrrole (DPP) blocks, have been synthesized, characterized and evaluated as electron acceptor materials in air-processed inverted organic solar cells.