Effects of the Reduction and/or Fluorination of the TT‐Units in BDT‐TT Polymers on the Photostability of Polymer:Fullerene Solar Cells

Abstract

Polymer solar cells have a promising future for applications in our day to day usage of energy in small appliances and portable devices. However, their performance in terms of efficiency is limited by a number of factors, among which is their low open circuit voltage (Voc). It is, therefore, understandable that much effort is channeled by the scientific community in improving the Voc. One way to achieve this goal is the development of novel materials, for example, polymers, through chemical structure modification. Typical examples are addition (chlorination, fluorination, or sulfonylation) and/or reduction (from alkyl‐ester to ketone substituents) mechanisms. This paper reports on the study of the effect of these structural changes for Voc enhancement on the performance of the polymers in polymer:fullerene solar cells. In particular, it looks at seven polymers of the polybenzodithiophene‐thienothiophene family, identifying the structural changes in the thienothiophene units or their moieties as a function of Voc behavior in relation to their UV‐stability. The findings reveal that the fluorination of the TT‐units or having alkyl‐ester groups as substituents on the TT‐units is bad for photostability. However, when these alkyl‐ester groups are reduced into ketone substituents, the photostability behavior improves.

Improved photostability in ternary blend organic solar cells: the role of [70]PCBM

“…1. To ascertain our finding, PTB7-Th workhorse low bandgap polymer [33][34][35] was also employed in place of PBDB-T. Under the same experimental conditions, the ternary blend OSCs outperform by far the [70]PCBM binary blend OSC in terms of PCE and are slightly better in PCE than the ITIC binary blend OSC.…”

“…The same concentrations are used for the ternary devices, by varying the acceptor ratio (A 1 : A 2 ) from 0 to 1. The ratio was varied between 1 : 1 to the best known 1 : 1.5 as used before for PBDT-TT polymer with [70]PCBM 34,35 when PTB7-Th is used. Zinc oxide solution was prepared by dissolving zinc acetate (109.67 mg) in 2-methoxyethanol (1 mL) and ethanolamine (30.2 mL).…”

Polyolefin Elastomer as the Anode Interfacial Layer for Improved Mechanical and Air Stabilities in Nonfullerene Solar Cells

“…The result illustrates that POE contributes to reducing the ideality factor ( n ) of the solar cells when used either as a dopant to the active layer or spin-coated as a layer atop the active layer. Thus, a decrease in n suggests a reduction in trap-assisted recombination. , In Figure e, the photocurrent density ( J ph ) versus effective voltage ( V eff ) curves were further measured to determine the exciton dissociation efficiency ( P diss ) . The device doped with POE and with a spin-coated POE layer exhibit P diss values of 98 and 97%, which are higher than the 93% of the device without the anode interfacial layer (w/o AIL).…”

“…Thus, a decrease in n suggests a reduction in trap-assisted recombination. 43,44 In Figure 2e, the photocurrent density (J ph ) versus effective voltage (V eff ) curves were further measured to determine the exciton dissociation efficiency (P diss ). 45 The device doped with POE and with a spin-coated POE layer exhibit P diss values of 98 and 97%, which are higher than the 93% of the device without the anode interfacial layer (w/o AIL).…”

Dual Interface Protection for High Performance and Excellent Long-Term Stability of Organic Solar Cells

“…This result suggests that PVDF and PS-r-PMMA can contribute to reducing the parameter n, showing a clear reduction in trap-assisted recombination. 53,54 In addition, the relationship curves of photocurrent density (J ph ) and effective voltage (V eff ) were further measured to determine the photoexciton dissociation efficiency (P diss ), as shown in Figure 4d. 55 The devices with a PVDF spin-coating layer and dual interface protection show enhanced P diss values of 98.2 and 98.4%, while the device without a cathode interlayer exhibits a comparatively lower P diss value of 94.6%.…”