Non‐Volatile Perfluorophenyl‐Based Additive for Enhanced Efficiency and Thermal Stability of Nonfullerene Organic Solar Cells via Supramolecular Fluorinated Interactions

Abstract

A novel non‐volatile additive, fluorinated bis(perfluorophenyl)pimelate (BF7), is demonstrated to effectively improve both the efficiency and thermal stability of a highly efficient organic solar cell (OSC), comprising fluorinated Y6 as the small‐molecule acceptor and PM6 as the polymer donor. Processed with optimized 0.5 wt% BF7 in solution, the PM6:Y6:BF7 device achieves an elevated power conversion efficiency (PCE) of 17.01%, compared to 15.16% of that processed without BF7. Moreover, the BF7‐elevated PCE can sustain 95% of the best PCE over 100 °C annealing for 72 h. Grazing incidence X‐ray scattering and differential scanning calorimetry results consistently indicate that BF7 in the PM6:Y6:BF7 device interacts preferentially with Y6, resulting in improved fractal‐like network structures of the active layer with optimized size and orientation of Y6 nano‐crystallites and elevated thermal stability. Molecular simulation also supports that the observed structure and thermal stability is associated with the F–π noncovalent supramolecular interactions between the perfluorophenyl moieties of BF7 and difluorophenyl‐based FIC‐end‐groups of Y6. Similar bifunctional BF7 effects are also observed in the well‐known PM6:IT‐4F system, suggesting that adding BF7 for concomitantly improved PCE and thermal stability might extend generally to OSCs that feature small molecule acceptors of difluorophenyl end‐groups.

Importance of structural hinderance in performance–stability equilibrium of organic photovoltaics

“…In addition to the photo-oxidation and photocatalyzed nucleophilic reactions that tend to break the NFA’s conjugation to degrade their light absorbing capabilities 20 – 23 , the relationship between their chemical structures and the morphological evolution under external stresses also needs to be concerned. Thermal stress induced instability is a very challenging problem for OPV 24 , because the best-performing BHJ devices are often achieved when the active layer morphology is in the thermodynamically non-equilibrated state 24 , which needs to be maintained during the whole thermal aging process. This can be potentially accomplished by tailoring the backbone planarity and side-group hinderance of NFAs, since these structure features are directly related to the crystallization and diffusion abilities of NFAs and their interactions with polymer matrix 25 , 26 .…”

PBDB-T-Based Binary-OSCs Achieving over 15.83% Efficiency via End-Group Functionalization and Alkyl-Chain Engineering of Quinoxaline-Containing Non-Fullerene Acceptors

“…The energy loss ( E loss ) of all the optimized active layer OSC devices are calculated according to the relation of E loss = E g – qV oc . The bandgap is estimated from the intersection of normalized PL emission and UV–vis absorption spectra of D/A blend in film state, as depicted in Figure S3 . The estimated E loss of PBDB-T:TPQ-eC7-4F-, PBDB-T:TPQ-eC7-4Cl-, and PBDB-T:BTP-eC7-4Cl-based optimized OSC devices are 0.593, 0.596, and 0.691, respectively (Table S5).…”

Promoting the Efficiency and Stability of Nonfullerene Organic Photovoltaics by Incorporating Open-Cage [60]Fullerenes in the Nonfullerene Nanocrystallites

“…Temperature-dependent GIWAXS conducted for the PM6:Y6 device films without and with the 1.0 wt % 8OC 60 Me additive further revealed that the additive effects on the greatly enhanced long-term stability of the device performance (Figure 2e,f). As shown in Figure 4a,b, the convoluted peak centered at q ≈ 0.32 Å −1 , contributed by both Y6 and PM6 ordered nanodomains, in the out-of-plane or inplane direction, 29 changes the peak intensity and position, as temperature elevated from 30 to 80 °C and to 100 °C. The change of the peak positions was attributed to an enhanced phase separation between PM6 and Y6, as suggested in a previous report, 29 which results in an over phase-separation morphology to the device performance.…”

“…0.3 Å −1 , which is attributed to the liquid-crystallike, weakly ordered PM6 layering structure, as most of the reflections of Y6 crystallites are largely oriented. 29 Moreover, the characteristic packing peak at q = 1.4 Å −1 (d spacing = 4.49 Å) of the aggregated 8OC 60 Me additive (Figure S16) was not observed in the GIWAXS pattern of the PM6:Y6 with the additive, suggesting that the additive could be effectively dispersed throughout the thin film.…”