Toward a Universally Compatible Non‐Fullerene Acceptor: Multi‐Gram Synthesis, Solvent Vapor Annealing Optimization, and BDT‐Based Polymer Screening

Abstract

To highlight the benefits of the organic dye PDI-DPP-PDI for use in fullerenefree organic solar cells, herein is demonstrated how this material can meet scalability demands through a multigram scale direct heteroarylation coupling reaction, and performance demands through a post-deposition solvent vapor annealing treatment. A solvent vapor annealing method has been utilized to screen a comprehensive selection of ethereal, aromatic, and chlorinated solvents. Upon transitioning to these eight alternative solvents, significant performance increase over the chloroform standard is noted for all solvents, with tetrahydrofuran and o-dichlorobenzene leading to the highest performance devices post-treatment. This trend, including an open-circuit voltage greater than 1 V proved to be consistent with four different BDT-based donor polymers, PTB7-Th, PBDB-T, J61, and TTFQx-T1. The highest performing devices are achieved with PTB7-Th and TTFQx-T1, with PCEs reaching 6.2 and 5.7%, respectively, when tetrahydrofuran solvent vapor annealing is combined with interfacial modification of the ZnO electron-transport layer.

Diketopyrrolopyrrole Derivatives Functionalized with N‐Annulated PDI and Se‐Annulated PDI by Direct (Hetero)Arylation Methods

“…[13,15] Blends of NPDIÀ DPPÀ NPDI with various donor polymers also displayed changes in the absorption profile after annealing with various solvents. [17] These changes were accompanied by a large increase in OPV device performance. The largest increase in performance was seen in blends with the donor polymer PTB7-Th with THF SVA treatment for 5-10 minutes where PCE increased from 1.3% with no treatment to 5.7% with THF SVA.…”

“…Previous work with thin films of NPDIÀ DPPÀ NPDI showed that they respond to SVA treatment with CHCl 3 and THF, reflected by changes in solid-state absorption profile. [13,17] Given the similarities in the optical properties between NPDIÀ DPPÀ NPDI, SePDIÀ DPPÀ NPDI, and SePDIÀ DPPÀ SePDI, it is likely SVA treatment would also have similar effects on the thin films of SePDIÀ DPPÀ NPDI and SePDIÀ DPPÀ SePDI. For NPDIÀ DPPÀ NPDI, SVA treatment induces a change in the solid-state morphology that is reflected in the absorption profile.…”

“…Following our previously established protocols, [13,[16][17][18]25] proofof-concept OPV devices were fabricated to further characterize and compare the two new compounds SePDIÀ DPPÀ NPDI and Figure 8. Thin film absorption spectra of NPDIÀ DPPÀ NPDI, [13] SePDIÀ DPPÀ NPDI, and SePDIÀ DPPÀ SePDI spun-cast from 1.0 wt/v% CHCl 3 solutions and treated with a THF SVA step for 5 minutes.…”

“…A 3 : 7 donor to acceptor ratio was used considering all blends showed changes in the optical absorption profile at this ratio (vide supra) and having a higher acceptor loading has previously led to best results. [13,17,46] OPV devices based on PTB7-Th : SePDIÀ DPPÀ NPDI and PTB7-Th : SePDIÀ DPPÀ SePDI active layers without SVA treatment gave best power conversion efficiency (PCE) values of 0.5% and 1.3%, respectively ( Figure 10, Table 2). The low PCE is consistent with previously reported devices based on PTB7-Th : NPDIÀ DPPÀ NPDI active layers where a disorganized, amorphous nanomorphology persisted.…”

“…[13] This material is readily synthesized on multi-gram scale using direct (hetero)arylation (DHA) methods, exhibits strong visible light absorption, and has relatively higher lying frontier molecular orbital energy levels compared to related PDI materials enabling the fabrication of OPV devices with open circuit voltages (V OC ) greater than 1 V. Linear aliphatic sidechains on the DPP core direct the self-assembly of this molecule upon solvent vapour annealing, [14] in the presence of donor polymers, leading to crystallization of thin-films and enhanced photovoltaic performance, [15] and thus has been used as a universal NFA. [16][17][18] The material NPDIÀ DPPÀ NPDI incorporates the N-annulated PDI chromophore, [19] for which the pyrrolic N-position adds an extra site for side-chain engineering to alter solubility and selfassembly, and lowers the electron affinity. [20,21] The brominated N-annulated PDI has proved quite effective for use as a substrate in DHA cross-coupling reactions, where symmetrical, [22,23] unsymmetrical, [24,25] and tetrameric [26,27] molecules have been readily constructed.…”