Structure–Property Relationships: Asymmetric Alkylphenyl‐Substituted Anthracene Molecules for Use in Small‐Molecule Solar Cells

Abstract

Two asymmetric anthracene-based organic molecules, NDHPEA and TNDHPEA, were prepared without or with a thiophene spacer between the anthracene and naphthalene units. These asymmetric oligomers displayed different degrees of coplanarity, as evidenced by differences in the dihedral angles calculated by using DFT. Differential scanning calorimetry and XRD studies were used to probe the crystallization characteristics and molecular packing structures in the active layers. The coplanarity of the molecules in the asymmetric structure significantly affected the crystallization behavior and the formation of crystalline domains in the solid state. The small-molecule crystalline properties were correlated with the device physics by determining the J-V characteristics and hole mobilities of the devices.

Impact of the Crystalline Packing Structures on Charge Transport and Recombination via Alkyl Chain Tunability of DPP-Based Small Molecules in Bulk Heterojunction Solar Cells

“…First, all of the three small-molecule-based devices showed substantially higher device performances (ca. 2-fold higher values) when they were processed in CF rather than in CB; similar results have been previously reported for other small molecule OPVs. − For the three devices spin-coated from CF, the maximum PCEs of 4.53% (open circuit voltage ( V oc ) = 0.92 V, short circuit current ( J sc ) = 10.3 mA cm –2 , fill factor (FF) = 54%), 2.67% ( V oc =0.91 V, J sc =5.26 mA cm –2 , FF = 46%), and 0.88% (V oc =0.86 V, J sc =2.75 mA cm –2 , FF = 37%) were achieved for the SM1- , SM2- , and SM3- based devices. Although the backbone structures of the compounds were identical, differences in the alkyl side chains on the DPP moiety had a marked effect on their photovoltaic device performances in solution-processed BHJ solar cells.…”

Symmetry-breaking charge separation in weakly coupled anthracene dimers

“…Then, phenylacetylene Grignard reagent reacted with 2-bromoanthraquinone under the Grignard reaction condition and a further reductive acidification to yield the most important reaction intermediate Br-BPEA. 36 This intermediate reacted with phenylboronic acid to produce the monomer Ph-BPEA via a Suzuki coupling reaction.…”

“…However, p -dimer (1/55 ps −1 ) had a much faster CS rate in comparison with m -dimer (1/165 ps −1 ). According to Marcus’ theory , 36,37 the CS rate ( k CS ) not only relies on the free energy change (Δ G CS ) and total reorganization energy ( λ ) but also on the electronic coupling ( V ). Considering that the difference in λ between these three dimers in the same solvent was very small, the inconsistency between Δ G CS and k CS for m -dimer and p -dimer should be mainly caused by the electronic coupling V .…”

Markedly different molecular formation in DPP-based small-molecule solar cells probed by grazing-incidence wide-angle X-ray scattering

“…Solution-processed small-molecule-based bulk heterojunction (SM-BHJ) solar cells currently have a power conversion efficiency (PCE) close to 10% (Wang et al, 2016;Zhang et al, 2015). While all top-performance devices are at present processed using polymer donor materials (Li, Ye et al, 2016;Baran et al, 2017), they have evolved steadily through their advantages such as well defined structures, synthetically high purity and high crystallinity (Min et al, 2016;Coughlin et al, 2014;Kim et al, 2015;Cheon, Kim, Back et al, 2014).…”