Effects of Electron-Donating and Electron-Accepting Substitution on Photovoltaic Performance in Benzothiadiazole-Based A–D–A′–D–A-Type Small-Molecule Acceptor Solar Cells

Abstract

A–D–A′–D–A-type nonfused-ring acceptors (NFRAs) have recently received extensive attention because of their suitable tuning of absorption spectra, frontier energy levels, and promising sunlight harvesting capability. However, no attention has yet been paid to the effects of A′ core substitutions on optoelectronic, morphological, and photovoltaic properties in high-performance organic solar cells (OSCs). In this work, to deeply understand the effects of electron-donating and electron accepting substitutions on the A′ core, we designed and synthesized three A–D–A′–D–A-type NFRAs, BTCPDT, BTCPDTO4, and BTCPDTF, with different substitutions on the benzo­[c]­[1,2,5]­thiadiazole core, such as hydrogen, alkoxy, and fluorine groups, respectively. Based on the characterization results, BTCPDT, BTCPDTO4, and BTCPDTF showed considerable variations in optical, electrochemical, and morphological properties because of their different electronegativity, steric hindrance, and intramolecular charge transfer effects. Among the NFRAs in this study, BTCPDTO4 showed the highest absorption coefficient, a high-lying frontier energy level, well-mixed and interpenetrating network morphology with enhanced charge transfer/transport, and suppressed charge recombination, which result in an impressive efficiency of 11.85% in an NFRA-OSC.

Design of Nonfused Nonfullerene Acceptors Based on Pyrido- or Benzothiadiazole Cores for Organic Solar Cells

“…To understand the charge recombination behaviors, the J – V characteristics of the devices were explored with respect to the light intensity. The tendency of bimolecular recombination can be monitored by the power law dependence of J SC on the light intensity . The J SC vs light intensity, power-law relationship can be related as J SC ∝ P light α , where α denotes the degree of bimolecular recombination.…”

“…The tendency of bimolecular recombination can be monitored by the power law dependence of J SC on the light intensity. 52 The J SC vs light intensity, power-law relationship can be related as J SC ∝ P light α , where α denotes the degree of bimolecular recombination. When the value of α is close to unity, it ascribes a negligible bimolecular recombination expected under short-circuit conditions.…”

A new insight into the push‐pull effect of substituents via the stilbene‐like model compounds

“…Push‐pull effect of substituents is an important concept, which is often employed to improve the properties of organic compounds [1–24], such as UV absorption [4, 15], fluorescence emission [6, 16], intramolecular charge transfer [1, 3, 14], nonlinear optical properties [5, 13], photovoltaic performance [10], organic light‐emitting diode [19], and so on. If we input the word “push‐pull effect” into the Web of Science, we will obtain more than 100,000 items, which implies that the push‐pull effect of substituents is widely used in physics and chemistry.…”

Femtosecond Transient Absorption Studies of Polymer Aggregation on Photovoltaic Performance: Role of an Integrated Aggregation Promotor in the Polymer Chain

“…Polymer solar cells (PSCs) have been extensively investigated as a competitive technology for renewable energy due to their advantages of light weight, low cost of fabrication, and capability of flexible devices with large area and roll-to-roll method fabrication. , Based on these advantages of PSCs, power conversion efficiencies (PCEs) of over 17% have been achieved. − In decades, considerable attention has been paid to the fullerene derivatives in the early development stage of PSCs with their distinct advantages such as an isotropic electron transport in three dimension, high electron mobility, and multiple reversible electrochemical reductions. , However, fullerene derivatives also have inherent drawbacks of weak absorption in the region of the solar spectrum and restricted energy level tunability, which definitely limit the photocurrent in PSCs. , Recently, enormous progress has been reported for nonfullerene acceptor (NFA) PSCs with great advantages such as tunable energy levels and strong absorption in the near-IR region, which are beneficial to cover the broad absorption range of PSCs by sharing with those of donor materials. − With the development of NFAs, the structure of donor polymers matching well with both fullerene and NFAs is much more important. − For the ideal donor/acceptor (D/A) blend morphology, too small domain or oversized phase segregation should be avoided for the efficient exciton dissociation, charge separation, and transport in PSCs. − In order to obtain a morphology with an appropriate domain size, several strategies of material design have been studied on the donor characteristics by modifying the polymer backbone curvature, solution aggregation, and surface energy matching with the acceptor. − However, despite the importance of the donor polymer design and D/A blend morphology, their effects on the excited state dynamics and charge carrier generation have barely been investigated in the viewpoint of the professional photophysical study. Therefore, correlating the charge generation and recombination processes monitored by the time-resolved spectroscopic studies with those by the PSC device characteristics in terms of the blend morphology is greatly important to obtain high-performance bulkheterojunction (BHJ) PSCs.…”