Spectroscopic Studies on Intramolecular Charge-Transfer Characteristics in Small-Molecule Organic Solar Cell Donors: A Case Study on ADA and DAD Triad Donors

Abstract

To explore the efficient way of assembling electron-donating (D) and -accepting (A) moieties in small-molecule donors for organic solar cells (OSCs), ADA- and DAD-type triad donor molecules were synthesized and investigated using indolo­[3,2-b]­indole and diketopyrrolopyrrole (DPP) as D and A moieties, respectively. Designing D–A-type donor materials possessing intramolecular charge-transfer (ICT) characteristics is important to facilitate exciton dissociation and retard charge-carrier recombination at the donor and acceptor (PC61BM) interface of bulk heterojunction OSCs. While ADA and DAD triad donors showed similar absorption spectra, their photoinduced ICT nature in the excited state monitored by the transient absorption spectroscopy was quite different. Both molecules exhibit strong electronegativity and abundance of electrons on DPP moieties, facilitating interaction with the neighboring molecules. However, ADA exhibits stronger ICT character than DAD because of the spatially more delocalized lowest unoccupied molecular orbital and abundant electron density at the end-capping DPP moieties. Owing to its stronger ICT character in the excited state, the ADA:PC61BM blend showed more favorable charge separation and reduced charge-carrier recombination at the donor/PC61BM interface. Consequently, ADA:PC61BM devices exhibited higher J SC than DAD:PC61BM OSCs.

Designing Well-Organized Donor-Bridge-Acceptor Conjugated Systems Based on Cyclopentadithiophene as Donors in Bulk Heterojunction Organic Solar Cells: DFT-Based Modeling and Calculations

“…In order to explore the photo-physical properties of the considered compounds, the optical absorption spectra were simulated using TD-DFT approach as costeffective method [54,55]. TD-DFT simulations were performed at the optimized ground state (S 0 ) geometries in gaseous phase (See Figure 6) and the related optical parameters are listed in Table 2.…”

A novel donor–π–acceptor halochromic 2,6-distyrylnaphthalene chromophore: synthesis, photophysical properties and DFT studies

“…[1][2][3][4][5][6] On the other hand, organic molecules that possess intramolecular charge transfer (ICT) character are important in a large number of areas, such as organic solar cells, polarity probes and nonlinear optics. 7,8 Donor-p-acceptor (D-p-A; where D is an electron-donating group, A is an electron-accepting group, and p is a conjugating moiety) systems with different congurations have been extensively developed because their absorption spectra and energy gaps can be readily tuned by controlling the ICT character using different electron-donor and electron-acceptor groups. This belonging plays an important role in the improvement of the photophysical properties of photonic devices.…”

Synthesis of some new distyrylbenzene derivatives using immobilized Pd on an NHC-functionalized MIL-101(Cr) catalyst: photophysical property evaluation, DFT and TD-DFT calculations

“…Stilbene compounds are a signicant class of uorescent organic p-conjugated compounds, which are widely used in the above mentioned applications. [17][18][19][20][21][22][23][24][25][26] Due to the systematic relationship between the uorescence properties of the uorescent materials and their chemical structures, stilbenes are an interesting class of compounds which permit us to simply ne tune the photophysical properties via available chemical modications. [27][28][29][30][31] To synthesize stilbenes, different organic methodologies such as Wittig reaction, [32][33][34] Horner-Wadsworth-Emmons reaction, 35 catalytic aldehyde olenations, 36 and Mizoroki-Heck reaction 37,38 have been developed.…”