Designing of benzodithiophene acridine based Donor materials with favorable photovoltaic parameters for efficient organic solar cell

https://doi.org/10.1016/j.comptc.2021.113238Get rights and content

Highlights

  • Four small molecule donors (M1-M4) have been designed for photovoltaic applications.

  • Designed molecules have superior optoelectronic and photophysical parameters.

  • These molecules showed high charge mobility characteristics.

Abstract

To enhance the charge transfer properties in organic materials, four π-conjugated donor compounds, namely DR3TBDTC-M1, DR3TBDTC-M2, DR3TBDTC-M3, and DR3TBDTC-M4 are formulated and studied. The central core of the molecules is composed of benzodithiophene acridine connected with the terminal groups using three thiophene rings as a spacer. The optoelectronic analysis has indicated that from all the donors DR3TBDTC-M3 is better which has a greater λmax value of 505.4 nm than the reference molecule (DR3TBDTC) having a λmax value of 463.4 nm. Examination of the frontier molecular orbitals, the binding energy, transition density matrix, the reorganization energy, and open-circuit voltage are implemented that offered the fundamental knowledge on the transmission of charges and electronic excitation. With a small band gap (Eg = 3.97 eV), the DR3TBDTC-M3 compound excellently transfers its electron density from the HOMO to LUMO. In the reported compounds, the λe value of DR3TBDTC-M1 (0.01358 eV), DR3TBDTC-M3 (0.01680 eV), and DR3TBDTC-M4 (0.01169 eV) are found to be less than the reference having λe = 0.01795 eV. Likewise, DR3TBDTC-M3 provides the lowest λh = 0.01566 eV relative to DR3TBDTC λh = 0.01578 eV. It has been observed that the structural adaptation at the terminal modifies the charge transfer property in the molecule as all the designed molecules have shown better VOC and Eg as compared to the reference.

Graphical abstract

All the donor molecules have depicted better results compared to a reference molecule, but DR3TBDTC-M3 give exceptionally best results compared to other novel designed molecules. All designed donors were analysed as a donor acceptor interface with PCBM acceptor for charge interaction. The results depicted them as an efficient donor acceptor interface.

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Introduction

Recent sources of energy used worldwide include water, petroleum loading products, and coal even though these sources have a lot of threats for all over the world environment. Also, these energy sources are depleting day by day due to over-usage [1]. So, it is the need for time to switch toward environmentally friendly renewable sources. Photovoltaic devices are the most efficient in this regard as a huge amount of energy can be produced through them [2]. In the last few years, the power conversion efficiency (PCE) of photovoltaics is being enhanced quite significantly. Amorphous and mono-crystalline silicon is quite efficient but has a rigid structure which decreases its limit of utilization. Scientists are working on the easy production of organic solar cells (OSCs) which have high flexibility, very little cost to fabricate, low weight, and compatible devices [3]. Bulk heterojunction (BHJ) devices are also compatible, as 8% efficiency has been achieved by these cells. These are higher in flexibility but have some drawbacks as these are not reproducible and not easily be synthesized [4].

Organic photovoltaic solar devices hold astonishing optical and electronic characteristics [5], [6], [7], [8], [9], [10]. Fullerene-type materials engaged in OSCs, have outstanding sort of characters, such as strong electronic conductivity, an isotropic transition of electrons, and low reorganization energy [11], [12]. Despite these benefits, fullerenes utilization is reduced due to many variables such as energy level adjustment difficulties, mild absorption of the visible radiations, and high cost of production with poor solubility and instability [13], [14].

Recently, a chemical compound, (4Z,4′Z)-5,5′- ((5″,5-(4,8-bis(9-(2-Ethylhexyl)-9H-carbazol-3-yl)benzo[1,3-b:4,5-b′]trithiophene-2,5-diyl)bis(3,2″-dioctyl[2,2′:5′,2″ -terthiophene]-5″,5-diyl))bis(methanylylidene))bi(2-ethyl-3-thioxothiazolidin-5-one), specified as (DR3TBDTC), was discovered as a donor specie. This system was able to sustain 88% of all its original PCE following thermal annealing of the absorber region at 170 °C for 9 days. This type of thermal solidity is impressively better than the standard OSCs. Due to the small energy difference between HOMO-LUMO, high charge transmission efficiency, and low reorganization energy, DR3TBDTC is an attractive material for study. In DR3TBDTC, the central core implements donor character, and the terminals have acceptor character while the donor core and acceptor terminals are connected through the spacer. The spacer moiety is named to three thiophene rings which provide a smooth π-conjugated path for the transport of charge from donor to the acceptor. So, this molecule has a scheme; A-D-A type means acceptor-donor-acceptor type molecule [15], [16], [17], [18].

In the DR3TBDTC molecule, the acceptor fragment contains sulphur, oxygen, and nitrogen. Due to these atoms, the acceptor regions have shown high intra-molecular charge transfer (ICT) properties. To get high efficiency, the reference molecule was modified and compared with the four molecules namely, DR3TBDTC-M1, DR3TBDTC-M2, DR3TBDTC-M3, and DR3TBDTC-M4 by replacing the acceptor groups of the reference DR3TBDTC with 2-methylenemalononitrile, methylenemethcrylate, 3-(2-methylene-4-oxo-2, 3-dihydroinder-1-ylidene) malononitrile and 4-(thiophene-2-yl) benzo [1], [2], [6] thiadiazol, respectively. Their structures are shown in Fig. 1. The band gap of designed molecules between HOMO and LUMO is studied to check the credibility of charge transfer. The density of states (DOS), reorganization energy (RE), and density of transitions was analyzed theoretically. Also, open-circuit voltage (VOC) was calculated by matching with well-known acceptor PCBM.

Section snippets

Computational details

All analyses were carried out with the help of the software Gaussian 09 [19]. The Three - dimensional assembly of designed complexes was originally developed with the GuassView 5.0 [20]. Density functional theory (DFT) was utilized for theoretical analysis by ωB97XD [21], B3LYP [22], CAM-B3LYP [23], and MPW1PW91 methods. The configuration optimization and all other analysis were executed by 6-31 G* diffused set [24]. 6-31G* split valence polarized basis set was employed for all analysis, due to

UV–Vis spectral properties

In chlorobenzene solvent, the optical profile of absorption coefficient of the reference compound DR3TBDTC was analyzed by computation with various functions such that B3LYP, MPW1PW91, CAM-B3LYP, as well as ωB97XD for the molar absorption coefficient (λmax) which was come to be 713 nm, 463 nm, 641 nm, and 434 nm, accordingly, as described in Table 1). The experimental molar absorption of DR3TBDTC is 509 nm [29], correlated with the absorption band recorded under-tested methods that could be

Conclusions

The four donor molecules (DR3TBDTC-M1 to DR3TBDTC-M4) were designed with configuration A-D-A types such as donor at the core and two acceptors at the two terminal positions of the spacer, as thiophene spacer was in between the donor and the acceptor. All the theoretical analyses were executed by taking into the consideration DFT method CAM-B3LYP/6-31 G*. These donors have marked far greater charge transfer properties than the reference (DR3TBDTC) that presented the smaller λmax as compared to

CRediT authorship contribution statement

Qurat ul Ain: Data curation, Formal analysis, Writing - original draft. Rao AqilShehzad: Data curation, Formal analysis, Writing - original draft. Umer Yaqoob: Data curation, Formal analysis, Writing - original draft. Arooba Sharif: Data curation, Formal analysis, Writing - original draft. Zubia Sajid: Data curation, Formal analysis, Writing - original draft. Sidra Rafiq: Data curation, Formal analysis, Writing - original draft. Saleem Iqbal: Data curation, Formal analysis, Writing - original

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

All the computational work is accomplished in the computational laboratory of Punjab Bioenergy Institute, University of Agriculture (UAF), 38000, Faisalabad Pakistan funded by Govt. of the Punjab, Pakistan.

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