Effect of Benzothiadiazole-Based π-Spacers on Fine-Tuning of Optoelectronic Properties of Oligothiophene-Core Donor Materials for Efficient Organic Solar Cells: A DFT Study

Abstract

In this work, five novel A-π-D-π-A type molecules D1–D5 were designed by adding unusual benzothiadiazole derivatives as π-spacer blocks to the efficient reference molecule DRCN5T for application as donor materials in organic solar cells (OSCs). Based on a density functional theory approach, a comprehensive theoretical study was performed with different functionals (B3LYP, B3LYP-GD3, B3LYP-GD3BJ, CAM-B3LYP, M06, M062X, and wB97XD) and with different solvent types (PCM and SMD) at the extended basis set 6-311+g(d,p) to evaluate the structural, optoelectronic, and intramolecular charge transfer properties of these molecules. The B3LYP-GD3BJ hybrid functional was used to optimize the studied molecules in CHCl 3 solution with the SMD model solvent as it provided the best results compared to experimental data. Transition density matrix maps were simulated to examine the hole–electron localization and the electronic excitation processes in the excited state, and photovoltaic parameters including open-circuit photovoltage and fill factor were investigated to predict the efficiency of these materials. All the designed materials showed promising optoelectronic and photovoltaic characteristics, and for most of them, a red shift. Out of the proposed molecules, [1,2,5]thiadiazolo[3,4- d ]pyridazine was selected as a promising π-spacer block to evaluate its interaction with PC 61 BM in a composite to understand the charge transfer between the donor and acceptor subparts. Overall, this study showed that adding π-spacer building blocks to the molecular structure is undoubtedly a potential strategy to further enhance the performance of donor materials for OSC applications.

Theoretical Insights into the Structural and Optical Properties of D−π–A-based Cyanostilbene Systems of α and β Variants

“…Cyanostilbene appended donor–π–acceptor (D−π–A) type systems, where the cyano moiety acts as the acceptor (A), are the more straightforward model for a comprehensive understanding of the effect of positional isomerism of α and β analogs of cyanostilbene because it allows flexibility in molecular design by changing either conjugating moiety (π) or donor unit (D) systematically. ,− Such systems are capable of fabricating excellent hole and electron transport facilities and executing push–pull effects, allowing electron transfer from the donor to the acceptor through the conjugated π-units. − Furthermore, D−π–A architecture having functionalized acrylonitrile compounds offers better nonlinear optical (NLO) performance. − For example, Singh and co-workers recently synthesized a series of cyanostilbene-based D−π–A systems containing the 9,9-dimethyl-9 H -fluoren-2-amine type of chromophores and observed a significant enhancement in the first hyperpolarizability and related intrinsic hyperpolarizability by modulating the π-conjugation pathways . In a continued work, the same group compared the first hyperpolarizabilities by extending the π-conjugation of D−π–A systems and found that lengthening of π-conjugation beyond a certain limit hardly improves the NLO response.…”

“…In a continued work, the same group compared the first hyperpolarizabilities by extending the π-conjugation of D−π–A systems and found that lengthening of π-conjugation beyond a certain limit hardly improves the NLO response. Therefore, improving the efficiency through structural tuning to design better NLO candidates attracts a lot of attention. − In recent years, organic heterocyclic luminophores have made great progress as a new-generation functional material. − These findings triggered our curiosity to computationally design cyanostilbene-based NLO materials with various heterocyclic rings as π-linkers. , More importantly, it would also serve as the optimal candidate to study the effect of positional isomerism on the cyanostilbene derivatives.…”

“… 6 , 22 − 24 Such systems are capable of fabricating excellent hole and electron transport facilities and executing push–pull effects, allowing electron transfer from the donor to the acceptor through the conjugated π-units. 25 − 29 Furthermore, D−π–A architecture having functionalized acrylonitrile compounds offers better nonlinear optical (NLO) performance. 30 − 32 For example, Singh and co-workers recently synthesized a series of cyanostilbene-based D−π–A systems containing the 9,9-dimethyl-9 H -fluoren-2-amine type of chromophores and observed a significant enhancement in the first hyperpolarizability and related intrinsic hyperpolarizability by modulating the π-conjugation pathways.…”

“… 37 − 39 These findings triggered our curiosity to computationally design cyanostilbene-based NLO materials with various heterocyclic rings as π-linkers. 29 , 40 More importantly, it would also serve as the optimal candidate to study the effect of positional isomerism on the cyanostilbene derivatives.…”

Designing of π‐Bridge for Metal Free Dye‐Sensitized Solar Cell and Optoelectronic Properties: An ab initio DFT Perspective

“…[20] It also plays a vital role in optimizing electron transfer processes, enhancing light-harvesting efficiency, and improve charge transport characteristics within the solar cell. [21] Consequently researcher is concentrating to design and tune the various π-spacers to enhance the efficiency of DSSCs. L. Giribabu and his research group recently demonstrated how πspacers regulate the photovoltaic performance of dye sensitized solar cell.…”