Naphthodithiophene-Based Conjugated Polymer with Linear, Planar Backbone Conformation and Strong Intermolecular Packing for Efficient Organic Solar Cells

Abstract

Two donor-acceptor copolymers, PBDT and PNDT, containing 4,8-bis(2-ethylhexyloxy)benzo[1,2-b:3,4-b']dithiophene (BDT) and 4,9-bis(2-ethylhexyloxy)naphtho[1,2-b:5,6-b']dithiophene (NDT), respectively, as an electron-rich unit and 5,6-difluoro-2,1,3-benzothiadiazole (2FBT) as an electron-deficient unit, were synthesized and compared. The introduction of the NDT core into the conjugated backbone was found to effectively improve both light harvesting and the charge carrier mobility by enhancing chain planarity and backbone linearity; the NDT copolymer has stronger noncovalent interactions and smaller bond angles than those of the BDT-based polymer. Moreover, the introduction of the NDT core brings about a drastic change in the molecular orientation into the face-on motif and results in polymer:PCBM blend films with well-mixed interpenetrating nanofibrillar bulk-heterojunction networks with small-scale phase separation, which produce solar cells with higher short-circuit current density and fill factor values. A conventional optimized device structure containing PNDT:PC71BM was found to exhibit a maximum solar efficiency of 6.35%, an open-circuit voltage of 0.84 V, a short-circuit current density of 11.92 mA cm(-2), and a fill factor of 63.5% with thermal annealing, which demonstrates that the NDT and DT2FBT moieties are a promising electron-donor/acceptor combination for high-performance photovoltaics.

Microwave-assisted synthesis of 4,9-linked pyrene-based ladder conjugated polymers

“…Planar conjugated polymers such as ladder poly( p ‐phenylene)‐type polymers (LPPP) and graphite ribbon are special members of conjugated polymer family . The unique rigid and planar structure endows materials with good conjugation, carrier mobility, and luminescence intensity, so ladder conjugated polymers are widely applied as organic light emitting diodes and field‐effect transistor materials. LPPP polymer was first reported by Scherf and Müllen, graphite ribbon polymer was reported by Goldfinger and Swager .…”

Subtle Polymer Donor and Molecular Acceptor Design Enable Efficient Polymer Solar Cells with a Very Small Energy Loss

“…[43] However, only very few NDT-based polymer donors have been reported due to the difficulty of synthesis, which are paired all with the traditional fullerene acceptors. [44][45][46][47] No work indicated that the NDT-based polymers have been used for matching the more superior NFAs at present.…”

Effect of Semi‐Fluorinated Alkyl Side Chains on Conjugated Polymers with Planar Backbone in Organic Field‐Effect Transistors

“…The 2D patterns of the as‐cast, 200 °C, and 300 °C annealed films show both ( h 00) and (010) reflections along the out‐of‐plane direction, corresponding to lamellar and π–π stacking diffraction peaks, along both the out‐of‐plane and the in‐plane direction, respectively. These indicate that the crystalline textures of the polymer films are bimodal structures with coexisting edge‐on and face‐on crystallites . Two diffraction crystallographic peaks of β‐phase, α‐phase in the in‐plane direction are also observed from the polymer films with SFA side chains.…”