Efficient Diketopyrrolopyrrole‐Based Small‐Molecule Bulk‐Heterojunction Solar Cells with Different Electron‐Donating End‐Groups

Abstract

A series of small molecules that contained identical π-spacers (ethyne), a central diketopyrrolopyrrole (DPP) unit, and different aromatic electron-donating end-groups were synthesized and used in organic solar cells (OSCs) to study the effect of electron-donating groups on the device performance. The three compounds, DPP-A-Ph, DPP-A-Na, and DPP-A-An, possessed intense absorption bands that covered a wide range, from 350 to 750 nm, and relatively low HOMO energy levels, from -5.50 to -5.55 eV. DPP-A-An, which contained anthracene end-groups, demonstrated a stronger absorbance and a higher hole mobility than DPP-A-Ph, which contained phenyl groups, and DPP-A-Na, which contained naphthalene units. The power-conversion efficiencies (PCEs) of OSCs based on organic:PC71BM blends (1:1, w/w) with a processed DIO additive were 3.93% for DPP-A-An, 3.02% for DPP-Na, and 2.26% for DPP-A-Ph. These findings suggest that a DPP core that is functionalized with electron-donating capping groups constitutes a promising new class of solution-processable small molecules for OSC applications.

Organic solar cells based on acceptor-functionalized diketopyrrolopyrrole derivatives

“…To help promote planarity of the derivatives, the electron-withdrawing moieties [18][19][20][21][22] were introduced using Sonogashira-coupling reactions of DPP-Br 2 and 4-ethynylbenzaldehyde. 23 Further, Knoevenagel condensation of DPP-BZ with 2-ethylhexyl-2-cyanoacetate and N-(2-ethylhexyl)-2-cyanoacetamide afforded DPP-ES and DPP-AM, respectively. CV was used to estimate the HOMO and LUMO energies of the DPP derivatives from the half-wave potentials of their redox waves (Table 1).…”

Synthesis of 3H‐Benzo[e]indoline and Its Application to Small‐Molecule Organic Solar Cells

“…[3] Indoline, as an electron-richer indole derivative, has received increasing attention in the field of dye-sensitized solar cells and organic solar cells, [3a] and most of their derivativesh ave achieved high performance. [5] Squaraine dyes have drawn much attention for small-molecule organic solarc ell (SMOSCs), due to their intense absorption in the visible-NIR region, their good photochemical/photophysicals tability, and, most importantly, their facile synthetic access without involving highly toxic reagents, which are very importantf or commercial application. [5] Squaraine dyes have drawn much attention for small-molecule organic solarc ell (SMOSCs), due to their intense absorption in the visible-NIR region, their good photochemical/photophysicals tability, and, most importantly, their facile synthetic access without involving highly toxic reagents, which are very importantf or commercial application.…”

“…[9] In comparison with non-benzene-ring-fused ASQ-5, USQ-BI shows about5times higherh ole-mobility (9.57 10 À5 vs. 2.00 10 À5 cm 2 V À1 s À1 )i n pristine film, andt he corresponding photovoltaic devices exhibitedahigher performance of 5.35 %, with a J sc of over 15 mA cm À2 ,w hich is the highest value for the squaraine-based OSCs. 3H-Benzo[e]indole was synthesized throughF ischeri ndole synthesis, then it wasc onverted into 3H-benzo[e]indoline (5). Allt he synthetic and characterization details can be found in the Supporting Information.…”

“…[5] For the ratio of 1:3, the PCE of 5.35 %w as achieved with after thermal annealed at 70 8Cf or 20 min ( Table 2), 33 % highert han that of the as-castd evices,w hich is originated from the significantly increasing of J sc and as lightly increasing of FF and V oc .P lease note that the J sc is high to 15.64 mA cm À2 , to the best of our knowledge,w hich is the highest value among squaraine-based OPVs. As shown in Tables 2a nd S2 (Supporting Information), the devices with a1 :3 ratio show the highest PCE of 4.68 % among all the devices without TA.Upon TA,the devices exhibit 5-15 %i ncrease for the same ratio except 1:3, which is similar to mosts quaraines-based organic photovoltaic (OPV) including ASQ-5.…”

“…[3a, 4] Here, to promote more effective intermolecular p-p stacking, we designed and synthesized 3H-benzo[e]indoline, an ovel benzene-ring-fused indoline, to enhancet he charge transport for the organic semiconductors. [5] Squaraine dyes have drawn much attention for small-molecule organic solarc ell (SMOSCs), due to their intense absorption in the visible-NIR region, their good photochemical/photophysicals tability, and, most importantly, their facile synthetic access without involving highly toxic reagents, which are very importantf or commercial application. [3c, 4b, 6] In 2014, we designed and synthesized an unsymmetrical squaraine (USQ)based small molecule using indoline (ASQ-5)a sa ne lectron donor for organics olar cells.…”