Fluorination Enables Tunable Molecular Interaction and Photovoltaic Performance in Non-Fullerene Solar Cells Based on Ester-Substituted Polythiophene

Abstract

Owing to the advantages of low synthetic cost and high scalability of synthesis, polythiophene and its derivatives (PTs) have been of interest in the community of organic photovoltaics (OPVs). Nevertheless, the typical efficiency of PT based photovoltaic devices reported so far is much lower than those of the prevailing push-pull type conjugated polymer donors. Recent studies have underscored that the excessively low miscibility between PT and nonfullerene acceptor is the major reason accounting for the unfavorable active layer morphology and the inferior performance of OPVs based on a well-known PT, namely PDCBT-Cl and a non-halogenated nonfullerene acceptor IDIC. How to manipulate the miscibility between PT and acceptor molecule is important for further improving the device efficiency of this class of potentially low-cost blend systems. In this study, we introduced different numbers of F atoms to the end groups of IDIC to tune the intermolecular interaction of the hypo-miscible blend system (PDCBT-Cl:IDIC). Based on calorimetric, microscopic, and scattering characterizations, a clear relationship between the number of F atoms, miscibility, and device performance was established. With the increased number of F atoms in IDIC, the resulting acceptors exhibited enhanced miscibility with PDCBT-Cl, and the domain sizes of the blend films were reduced substantially. As a result, distinctively different photovoltaic performances were achieved for these blend systems. This study demonstrates that varying the number of F atoms in the acceptors is a feasible way to manipulate the molecular interaction and the film morphology toward high-performance polythiophene:nonfullerene based OPVs.

Manipulating the Intermolecular Interactions through Side Chain Engineering and Unilateral π‐Bridge Strategy for Efficient Small Molecular Photovoltaic Acceptor

“…This side chain approach to moderately enhance the D/A interactions could be appealing because it would not sacrifice the V OC of devices, which often happened in halogenated SMAs for the enhancement of D/A interactions. [ 55 ]…”

Over 19% Efficiency Organic Solar Cells by Regulating Multidimensional Intermolecular Interactions

“…According to a previous study, reasonably miscible D/A blends are preferred to balance exciton dissociation and charge transport, which occur in D/A interfaces and connected pure phases, respectively. [48,49] The relatively smaller binding energies between PM6-and LA-series acceptors did not affect the exciton dissociation capacity, which had reasonable dissociation probabilities (η diss ) of over 99% (Figure S15, Supporting Information). Instead, the moderate D/A interactions and restrained miscibility help refine the phase separation with larger CCL values.…”

p-Tetrafluorophenylene Divinylene-Bridged Nonfullerene Acceptors as Binary Components or Additives for High-Efficiency Organic Solar Cells

“…Fluorinated conjugated polymers or molecular acceptors could enhance the PCE of OPV devices. , Donors and acceptors incorporating fluoro-substitution may be used to improve the PCE of devices because of their corresponding electron-deficient natures, thereby the frontier molecular orbital (FMO) energy of donors can be tuned. Acceptors incorporating fluoro-substituted moieties could exhibit enhanced compatibility with donors; thus, phase morphology parameters such as the fibril structure, carrier mobility, and charge extraction can be improved. , To the best of our knowledge, some oligomeric fused-ring electron acceptors containing more than one fused-ring unit exhibited an improved device efficiency with electron-deficient bridges, − and some literatures reported that fluorination has a beneficial effect on the morphology, miscibility, and crystallinity of the active layer. − Inspired by the semiconducting self-assembled nanofibers from photostable octafluorinated bisanthene derivatives and enhancement of PCE by a σ-hole solid additive, 1,4-diiodotetrafluorobenzene, we designed a molecular acceptor by tethering the fused-ring core structure of indacenodithienothiophene ( IDTT ) with a p -tetrafluorophenylene divinylene moiety. In this system, the electron-deficient p -tetrafluorophenylene divinylene ( FB ) moiety served as an electron-deficient core (A′), in which two IDTT donors were tethered and end-capped with two electron-withdrawing 2-(5,6-dichloro-3-oxo-2,3-dihydro-1 H -inden-1-ylidene)­malononitriles ( ClIN ); thus, the conjugation and tethering of IDTT with an A′ unit enabled the tuning of the FMO energy levels.…”