Backbone Engineering with Fluoroarene to Mitigate Morphological Disorder for High-Performance Polymer Solar Cells

Abstract

Three random terpolymers were synthesized by subtle incorporation of fluoroarenes as the third monomer into the popular PTB7-Th backbone and utilized for photovoltaic applications. By substituting 5% of 3-fluorothieno­[3,4-b]­thiophene-2-carboxylate in the PTB7-Th backbone using monomers such as 2,5-difluorobenzene, 2,3-difluorobenzene, and 2,3,5,6-tetrafluorobenzene, random terpolymers M1, M2, and M3 were synthesized, respectively. The presence of fluorinated monomers deepened the highest occupied molecular orbital (HOMO) energy level of terpolymers, which substantially enhanced the open circuit voltage (V OC) of polymer solar cells (PSCs). The power conversion efficiency (PCE) for M1- and M2-based PSCs reached up to 9.48 and 8.80% from 8.19% for the PTB7-Th:PC71BM blend. However, M3-based blend exhibited an inferior PCE of 8.13% majorly due to its weaker absorption in the higher-wavelength region and lower carrier mobility. The M1 polymer also exhibited an enhanced PCE of 9.01% compared to 7.68% for PTB7-Th with ITIC, a non-fullerene acceptor. Moreover, the fluoroarenes induced intra/intermolecular non-covalent interactions in blend films. These interactions acted as a conformational lock to tune the morphology that also improved the phase domain stability. M1:PC71BM-based PSC displayed superior capability to sustain under ambient conditions and it retained 82% of its initial PCE after 1000 h of ambient exposure in comparison to 51% of the PTB7-Th blend under a relative humidity of 45 ± 5%. This generic approach can be utilized in finely modulating the property of photovoltaic materials to enhance the performance along with the stability of PSCs.

The effect of non-covalent conformational locks on intra-molecular charge transport of OPV units

“…3b), we can explain its highest conductance among the three molecules. Thus, instead of the molecule planarity as the driving force for improving device scale charge transport, 13,16 the more efficient charge conducting channels contributed to improving intra-molecule charge transport in the case here. This work may contribute to providing new insights into the role of NCLs to improve the charge transport of solar cells at the molecule level.…”

“…9 Consequently, NCLs were employed with great success to prepare various types of functional materials of highly efficient charge transporting ability, which had been mostly evaluated through investigation of their charge transport behaviour in the condensed solid state. 13–16 However, the influence of NCLs on charge transfer at the single molecule level has not been directly addressed and revealed before, which could potentially provide new insights into the role of NCLs to improve the charge transport of solar cells at the molecular scale.…”

Radical reactions enabled by polyfluoroaryl fragments: photocatalysis and beyond

“…[1][2][3] While processes relying on specific fluorine effects associated with fluoroalkyl moieties have been extensively reviewed, the ability of fluorinated aromatic groups to serve as reactivity-enabling functionality has long been neglected, and existing reviews focus on the functionalization of the polyfluoroarene core. [4][5][6][7][8][9][10][11][12][13][14][15][16] At the same time, polyfluoroarenes are widely used for different purposes of catalysis, [17][18][19][20][21] analytical chemistry, 22,23 biochemistry, [24][25][26][27] and materials science [28][29][30][31] and their applications are well beyond the C-F bond activation. This review aims to highlight the known applications of polyfluoroarenes in organic chemistry of free radicals.…”

Manipulating the Alkyl Chains of Naphthodithiophene Imide-Based Polymers to Concurrently Boost the Efficiency and Stability of Organic Solar Cells

“…In the blend film, the separated NFA domains are dispersed between the interconnecting polymer domains and the physical property of the polymer donor should play a key role in the morphology stability of the interpenetrating D/A domains. − However, very limited attention was paid to study the relationship between the polymer structure, crystallinity, and morphology stability, although it is crucially important. ,, Consequently, how to design polymer donors with high efficiency and excellent morphology stability remains challenging currently. The chemical structure of the monomer significantly affects the intermolecular interaction, crystallinity, and film forming properties of polymers. − The units with a large conjugated backbone benefit strong intermolecular interactions, which probably could provide additional strength against polymer chain movement. − Therefore, developing polymer donors based on multifused aromatic units should be a wise option to address the morphology stability issue of OSCs.…”