Development of Organic Dye‐Based Molecular Materials for Use in Fullerene‐Free Organic Solar Cells

Abstract

This personal account describes the pursuit of non‐fullerene acceptors designed from simple and accessible organic pi‐conjugated building blocks and assembled through efficient direct (hetero)arylation cross‐coupling protocols. Initial materials development focused on isoindigo and diketopyrrolopyrrole organic dyes flanked by imide‐based terminal acceptors. Efficiencies in solution‐processed organic solar cells were modest but highlighted the potential of the material design. Materials performance was improved through structural engineering to pair perylene diimide with these organic dyes. Optimization of active layer processing and solar cell device fabrication identified the perylene diimide flanked diketopyrrolopyrrole structure as the best framework, with fullerene‐free organic solar cells achieving power conversion efficiencies above 6 %. This material has met our criteria for a simple wide band gap fullerene alternative for pairing with a range of donor polymers.

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

“…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.…”

“…[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.…”

Columnar Mesomorphism of Board‐Shaped Perylene, Diketopyrrolopyrrole, Isoindigo, Indigo, and Quinoxalino‐Phenanthrophenazine Dyes

“…Reviewed here is the columnar mesomorphism of five board-shaped dyes perylene (PBI and PTE), [21][22][23][24] indigo (IND), [25,26] isoindigo (IIND), [25,[27][28][29] diketopyrrolopyrrole (DPP), [28,[30][31][32][33][34][35] and quinoxalinophenanthrophenazine (QPP) [36,37] ( Figure 2). They were selected because of their significant industrial importance (perylene, IND, and DPP) and their specific mesomorphism has not been reviewed except for perylene.…”

Optimization of the Bulk Heterojunction of All-Small-Molecule Organic Photovoltaics Using Design of Experiment and Machine Learning Approaches

“…27,28 Efficient non-fullerene acceptors now dominate the recent OPV literature with a growing list of members that includes Y6 and the extensive ITIC family of derivatives. 24,27,[29][30][31][32][33] These acceptors offer excellent tunability of absorption properties through well-developed modular organic chemistry. 34,35 The devices optimized in this study contain the donor DRCN5T and one of three acceptors, ITIC, IT-M or IT-4F.…”