Phenyl‐1,3,5‐Trithienyl‐Diketopyrrolopyrrole: A Molecular Backbone Potentially Affording High Efficiency for Solution‐Processed Small‐Molecule Organic Solar Cells through Judicious Molecular Design

Abstract

Finding new molecular backbones is necessary for further advances in solution-processed small-molecule organic solar cells (SM-OSCs). Increasing molecular π conjugation generally enhances the light-harvesting ability, and the resulting strong π-π-stacking interactions improve the charge-carrier transport ability; both increase the efficiency. In this study, we focus on the phenyl-1,3,5-trithienyl (3T-P) backbone because of its C3 symmetry, planarity, and particularly high conjugation between the three arms through the core phenyl unit. When the three arms were functionalized with diketopyrrolopyrrole (DPP) units to afford 3D-T-P, only modest efficiency was achieved (1.16%). Introduction of 4,8-bis(2-(2-ethylhexylthienyl)) benzodithiophene (BDT) between the 3T-P and DPP units to give 3D-B-T-P enhanced the light-harvesting ability, and particularly improved the hole mobility by 1.5 orders of magnitude (5.91×10(-2) versus 1.05×10(-3) cm(2) V(-1) s(-1)). When using PC71BM as the acceptor material, 3D-B-T-P gave the best power conversion efficiency (PCE) of 2.27%, which is about 1.9 times higher than the best efficiency from 3D-T-P (≈1.16%). The efficiency can be improved up to 3.60% with 3% (v/v) of 1,8-diiodooctane (DIO) as the cosolvent and thermal annealing at 100 °C for 10 min. This PCE is, to the best of our knowledge, the highest efficiency reported to date among the phenyl-1,3,5-based C3-symmetric molecules. Removing one DPP unit from 3D-T-P to form 2D-T-P, or from 3D-B-T-P to form 2D-B-T-P both decreased the light-harvesting ability and the hole mobility, thereby affording lower efficiency. Taken together, our results demonstrate that the planar phenyl-1,3,5-trithienyl-based C3 -symmetric structure can be a promising backbone, and enhancing the conjugation of the 3D-T-P backbone can effectively improve the device performance.

Comparative Study of Effects of Terminal Non‐Alkyl Aromatic and Alkyl Groups on Small‐Molecule Solar Cell Performance

“…Several categories of electron-rich units are reported: Oligothiophene, [ 1 ] benzo [1,2-b:4,5- [ 3 ] phenyl-1,3,5-trithiophene derivative, [ 4 ] triarylamines, [ 5 ] porphyrin, [ 6 ] phthalocyanine, [ 7 ] squaraines, [ 8 ] merocyanine, [ 9 ] etc. The second consideration is the solubility of the molecule.…”

Design and characteration of planar star-shaped oligomer electron donors for organic solar cells: a DFT study

“…On the other hand, although the special propeller structure is easy to form amorphous materials and contact closely with fullerene acceptor, enhancing the charge dissociation efficiency, and it also lead to the poor phase separation and charge recombination. 17,18 Very recently, Zhang et al 5,6,19 synthesized a series of star-shaped donor molecules with fused aromatic ring as core, aiming to find an ideal molecular skeleton for the improvement of cell performance. Among them, when introducing the benzodithiophene (BDT) unit into the arms of phenyl-1,3,5-trithienyl-diketopyrrolopyrrole (3T-P-DPP) backbone (Fig.…”

“…1), the conjugation of the prototype molecule was enhanced, which improves the molecular optoelectronic properties, and the efficiency of the cell blended with PC 71 BM, increased from 1.16% to 2.2%. 19 To further improve the material performance and the device efficiency, we remodified the 3T-P-DPP backbone 5 by replacing core (3T-P) with other four fused planar aromatic rings (BTT, TTT, DIC and DIF) which are widely used building-blocks in experimental synthesis, to construct new molecules (2, 3, 4 and 5), as shown in Fig.1. …”

“…The former is widely used in solution process and has good solubility and film quality, while the latter has well-defined chemical structure and well-understood structure-property relation. Besides the above two materials, oligomers gradually go into people's research scope because they combine the strong points of polymer and small molecule, and are therefore extremely attractive al- [19]. Table 2.…”

Synthesis and photovoltaic properties of two star-shaped molecules involving phenylquinoxaline as core and triphenylamine and thiophene units as arms

“…So far, the PCE exceeding 5.81% with using star-shaped small molecule donor materials in BHJ-OSCs has been achieved [19], representing a promising important advance in the development of solution processable OSCs. In particular, compared to the linear small molecule donor materials, the star-shaped small molecule donor materials present a wider spectral absorption that can absorb more sunlight to improve the PCEs of small-molecule donors [22].…”