“Double-Cable” Conjugated Polymers with Linear Backbone toward High Quantum Efficiencies in Single-Component Polymer Solar Cells

Abstract

A series of "double-cable" conjugated polymers were developed for application in efficient single-component polymer solar cells, in which high quantum efficiencies could be achieved due to the optimized nanophase separation between donor and acceptor parts. The new double-cable polymers contain electron-donating poly(benzodithiophene) (BDT) as linear conjugated backbone for hole transport and pendant electron-deficient perylene bisimide (PBI) units for electron transport, connected via a dodecyl linker. Sulfur and fluorine substituents were introduced to tune the energy levels and crystallinity of the conjugated polymers. The double-cable polymers adopt a "face-on" orientation in which the conjugated BDT backbone and the pendant PBI units have a preferential π-π stacking direction perpendicular to the substrate, favorable for interchain charge transport normal to the plane. The linear conjugated backbone acts as a scaffold for the crystallization of the PBI groups, to provide a double-cable nanophase separation of donor and acceptor phases. The optimized nanophase separation enables efficient exciton dissociation as well as charge transport as evidenced from the high-up to 80%-internal quantum efficiency for photon-to-electron conversion. In single-component organic solar cells, the double-cable polymers provide power conversion efficiency up to 4.18%. This is one of the highest performances in single-component organic solar cells. The nanophase-separated design can likely be used to achieve high-performance single-component organic solar cells.

The Effect of Aromatic Diimide Side Groups on the π-Conjugated Polymer Properties

“…The results of BHJ OPV based on these polymers show the efficiency typically much less than 1%. However, recent research shows that such structures have great potential leading to devices with good efficiency exceeding 4% [30,31]. Moreover, according to our knowledge, there are no reported polymers with NDI side groups employed as the electron acceptor.…”

The Dawn of Single Material Organic Solar Cells

“…[79] The degree of polymerization estimated from 1 H NMR data was limited to 3-4 units. [82] The polymers show number-average molecular weights of 42.8, 37.0, and 26.3 kDa for 10a, 10b, and 10c, respectively. The absorption edge at ≈750 nm corresponds to a bandgap of 1.65 eV for the film.…”

“…[78] Koyuncu et al reported the synthesis of a highly crystalline D-A low bandgap polymer with oligothiophene-diketopyrrolopyrrole (DPP) as the donor and PBI as the acceptor (8) using a DPP-based macroinitiator and acryloyl-based PBI. [82] The use of a linear π-conjugated backbone of poly(DTBDT) was motivated by an expected improved crystallinity and nanophase separation. The UV-vis absorption spectrum of dichloromethane solutions presents a broad absorption in the visible and near infrared (NIR) region in which the DPP macroinitiator and PBI exhibit complementary absorptions.…”

“…Photovoltaic devices of structure ITO/ PEDOT:PSS/8/LiF/Al were fabricated and characterized under a AM 1.5 solar simulator at 100 mW cm −2 . [82] Replacement of chloroform by chlorobenzene, reduction of the film thickness from 120 to 70 nm, and solvent annealing with dichloromethane led to a large improvement of PCE to 0.89% with J sc increasing to 4.30 mA cm −2 .…”

“…PBDTPBI: 10a, S-PBDTPBI: 10b, SF-PBDTPBI: 10c.Reproduced with permission [82]. b) EQE of optimized SMOSCs.…”