Charge Transfer and Aggregation Effects on the Performance of Planar vs Twisted Nonfullerene Acceptor Isomers for Organic Solar Cells

Abstract

Newly synthesized perylene diimide dimers were investigated as nonfullerene electron acceptors for organic solar cells. In particular, two analogous positional isomers exhibiting twisted vs planar geometries were prepared to make a direct comparison of their optical and electronic properties. These properties were investigated to provide information regarding the impact of the nonfullerene acceptor geometry on the ultimate photovoltaic performance. The two isomers exhibited strikingly different optical and photophysical properties in solution as well as in film. The ultrafast spectroscopic investigation in solution revealed the occurrence of charge transfer upon photoexcitation, which takes place more efficiently in the planar isomer. This is also supported by theoretical simulations. The planar conformation exhibits higher aggregation in the neat film as well as in the blend. However, our results suggest that the dominance of intramolecular charge transfer in the planar isomer is the crucial factor in determining the improved power conversion efficiency of organic solar cells.

Activating intramolecular singlet exciton fission by altering π-bridge flexibility in perylene diimide trimers for organic solar cells

“…More rigid molecular structures are indeed known to exhibit enhanced uorescence capability. 33,38 This result suggests that the excited state deactivation of these trimer compounds takes place mainly through non-radiative pathwayspossibly triplet production/decay, in competition with the uorescence decay pathway. This non-radiative deactivation is more efficient for the twisted b compound, whose uorescence quantum yield is almost negligible.…”

“…The extremely broad emission spectrum and the large Stokes shi suggest a drastic rearrangement of this exible molecule in the excited state. 33,34 Fig. 1 Normalized absorption and emission spectra of the trimers in chloroform.…”

Synthesis and Nonlinear Optical Studies on Organic Compounds in Laser-Deposited Films

“…Perylene diimides (PDIs) are a new class of nonfullerene electron acceptors for organic solar cells with many attracting features, like low cost; significant thermal, chemical, and light stability; good electron-accepting ability; and excellent electron mobility [96]. Carlotti et al investigated PDI dimers as nonfullerene electron acceptors [96] for organic solar cells. Two isomers 5 and 6 have planar and twisted geometries, which determined very diverse spectral and photophysical properties (see Figure 3).…”

Small-Molecule Electron Acceptors for Efficient Non-fullerene Organic Solar Cells

“…Compound 3 with a planar conformation utilized weak electron acceptor (thieno-pyride-thieno-isoquinoline-dione) bridge for the lateral PDIs. When blended with PTB7-Th, the devices delivered a PCE of 5.03% (Carlotti et al, 2018 ).…”