Evaluation of photovoltaic properties and effective conjugated length of DTTTD-based polymers as donor in BHJ solar cells; quantum chemical approach. (22nd September 2017)

• Record Type: Journal Article
• Authors: Ostovan, Azar; Mahdavifar, Zabiollah; Bamdad, Mehrdad
• Is Part Of: Polymer. Volume 126(2017)
• Page Start: 162
• Page End: 176
• Publication Date: 2017-09-22
• Subjects: DTTTD -- Effective conjugated length -- Optical properties -- Light-harvesting efficiency -- TDDFT; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2017.08.044
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: Different chain length of conjugated polymers based on 4, 6-dithien-2-ylthieno [3, 4-c] [1, 2, 5]-thiadiazole (DTTTD) have been extended to investigate the structural, electronic and optical properties of (DTTTD)N donors in both vacuum and solvent environments using density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The calculated results reveal that the bond length alternation (BLA), the HOMO–LUMO energy gap (Eg ), Fermi energy level position (EF ) and optical band gap (Eopt ) of corresponding donors with N ≥ 5 (where N = 5 is the effective conjugated length (ECL) of DTTTD-based extended polymers) become size-consistent. The moderately-polar solvent environment cause of more stabilizing HOMO and LUMO energy levels, lower transition energy (TE), larger transition dipole moment (μij ) and higher oscillator strength ( f ) of DTTTD investigated polymers. Therefore, the red-shifted in absorption spectra is occurred with respect to the vacuum state. In addition, the external electric field (Fext ) smoothly affects optical properties of investigated donors. Based on our calculations, it was found that the trimer of DTTTD-based extended polymers is the most suitable donor to design the high-performance organic solar cells (OSCs) possessing a narrow HOMO–LUMO energy gap, highest exciton life time, broad and intense absorption spectra that cover the solar spectrum leads to maximum light-harvesting efficiency (LHE), higher charge transfer (CT) ability and high open-circuit voltage (VOC ). On the other hand, the value of VOC of larger extended polymers decreased due to the HOMO upward-shifted. Graphical abstract: Highlights: Optoelectronic properties of (DTTTD)N donors in both vacuum and solvent environments were studied using TD-DFT calculations. Based on obtained results the ECL, BLA and HOMO–LUMO energy gap of corresponding donors become size-consistent. The external electric field (Fext ) smoothly affects the electronic and optical properties of (DTTTD)N . The (DTTTD)3 is the most suitable donor to design the high-performance organic solar cells. Highest exciton life time, broad and intense absorption spectra that cover the solar spectrum leading to maximum LHE.