Photocurrent Enhancement of BODIPY-Based Solution-Processed Small-Molecule Solar Cells by Dimerization via the Meso Position

Abstract

Three 4,4-difluoro-4-bora-3a,4a-diaza-s-indancene (BODIPY)-based small molecule donors H-T-BO, Br-T-BO, and DIMER were synthesized and fully characterized. Although modification at the meso position has a subtle influence on the light-harvesting ability, energy levels, and phase sizes, it has a striking effect on the packing behavior in solid film as two-dimension grazing incidence X-ray diffraction (2D GIXRD) and X-ray diffraction (XRD) confirm. Br-T-BO exhibits better packing ordering than H-T-BO in pristine film, which is beneficial from reinforced intermolecular interaction from halogen atoms. However, when [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) is blended, no diffraction patterns corresponding to the monomeric donor can be seen from the XRD data and both H-T-BO- and Br-T-BO-based blend films give a slightly blue-shifting absorption peak with respect to their neat ones, both of which imply destruction of the crystalline structure. As for DIMER, the enhancement of the intermolecular interaction arises not only from the expansion of the backbone but the "steric pairing effect" brought on by its twisted structure. When blended with PC71BM, the diffraction patterns of DIMER are, however, kept well and the absorption peak position remains unchanged, which indicates the ordered packing of DIMER is held well in blend film. In coincidence with the fact that packing ordering improves from H-T-BO to Br-T-BO and DIMER in pristine films and the ordered packing of DIMER even in blend film, DIMER-based devices show the highest and most balanced hole/electron mobility of 1.16 × 10(-3)/0.90 × 10(-3) cm(2) V(-1) s(-1)with respect to Br-T-BO (4.71 × 10(-4)/2.09 × 10(-4) cm(2) V(-1) s(-1)) and H-T-BO (4.27 × 10(-5)/1.00 × 10(-5) cm(2) V(-1) s(-1)) based ones. The short-circuit current density of the three molecule-based cells follows the same trend from H-T-BO (6.80) to Br-T-BO (7.62) and then to DIMER (11.28 mA cm(-2)). Finally, the H-T-BO-, Br-T-BO-, and DIMER-based optimal device exhibits a power conversion efficiency of 1.56%, 1.96%, and 3.13%, respectively.

Low-Bandgap Near-IR Conjugated Polymers/Molecules for Organic Electronics

“…138−141 Yao et al reported three BODIPY-based near-IR small molecules, S18, S19, and S20 ( Figure 19). 142 All of these small molecules show broad absorption bands with onset absorption extending to 880−900 nm. They found that S19 tends to pack in a more ordered way than S18 in the pristine film, which might benefit from the intermolecular interaction from the halogen bond.…”

BODIPY‐Based Semiconducting Materials for Organic Bulk Heterojunction Photovoltaics and Thin‐Film Transistors

“…Liu et al. synthesized and fully characterized three new BODIPY‐based small molecular donors 15 – 17 (Figure ) . Modification at the meso ‐position showed slight influence on the light‐harvesting ability, energy levels, and domain sizes, but it was very effective in tuning the packing behavior in the solid state.…”

“… UV‐vis absorption spectra of the three donors in the blend films (dashed lines) (1 : 2 for 15 (H‐T‐BO) : PC 71 BM and 1 : 2.5 for 16(Br‐T‐BO) : PC 71 BM and 17(DIMER) : PC 71 BM, w/w) . The absorption spectra (solid lines) for the neat films are also displayed for comparison.…”

Series of Quinoidal Methyl-Dioxocyano-Pyridine Based π-Extended Narrow-Bandgap Oligomers for Solution-Processed Small-Molecule Organic Solar Cells

“…So far, the popular electron-rich units contain benzodithiophene (BDT), 1-5 dithienosilole, 6-8 oligthiophene, [9][10][11] triarylamine, 12-14 phenyl-1,3,5-trithiophene derivative, 15 porphyrin, 16,17 etc. Diketopyrrolopyrrole (DPP), [18][19][20] isoindigo (ID), 21,22 benzothiadiazole (BT), 23,24 thiazole, 25 dipyrromethene boron difluoride (BODIPY), [26][27][28] etc. are used as the electron-deficient units.…”

“…6 Interestingly, the two α-positions π-extending BODIPY-donor film shows the onset absorption beyond 900 nm. 28 4,8-bis (2-(2-ethylhexylthienyl) benzo[1,2-b:4,5-b']dithiophene (BDT) is a good electron-donating unit and has been widely used to construct efficient donor materials. 1-5 For example, the DPP-BDT-DPP typed small molecule shows a power conversion efficiency of close to 6%, which is the top values of the DPP based small-molecules.…”