In this research, the structural, electronic and optical properties of oligoselenophene (OS)n=1-15 with syn andanti configuration and oligo(3,4-ethylenedioxyselenophene) (OEDOS)n=1-12 with anti configuration as donor in the hetero-junction solar cells are studied by means of quantum calculations. The structural and electronic properties of investigated materials are evaluated using B3LYP/6-311g(d) level of theory. The TDDFT method in the same level of theory is also applied to consider optical properties. The bond length alternation (BLA), HOMO–LUMO energy levels, electronic band gap (Eg,ele), optical band gap (Eopt), UV-vis absorption spectrum, maximum wavelength (λmax), light harvesting efficiency (LHE) and exciton life time (τ) properties of entitled compounds are considered.Obtained results indicated that with increase in the chain length of the oligomers in syn and anti configuration, theBLA parameter is decreased. In other words, increasing the chain length caused the increased of π- electron delocalization and improvement the conjugation degree. As a result, the HOMO and LUMO energy levels closer to each other and therefore electronic energy gap (Eg,ele) as well asoptical energy gap (Eg,opt) will be decreased. Also, with increasing in the chain length, the red shift in the maximum of wavelength is occurred and thus the light harvesting efficiency (LHE) is increased. Furthermore, the exciton life time of (OS)n=2-15 and (OEDOS)n=2-12 with anti configuration is decreased when the chain length is increased whereas there is no particular trend is observed for the (OS)n=2-15 with syn configuration. Based on obtained results, it can be concluded that the (OS)n=14,15 oligomers with syn configuration can be act as suitable donors in the bulk hetero-junction solar cells (BHJ). In continue, the effect of electron donor and electron acceptor substitutions such as C4H9, F, CN and NO2 on the HOMO-LUMO energy levels and electronic band gap (Eg,ele) of (OEDOS)n=2 are considered. Results show that the NO2 substitution has a favorable effect on the electronic properties.
In order to model the active layer in the hetero-junction solar cells, the fullerene structures such as C60, C70, PC60BM, PCBDAN as acceptor were considered. The (OS)n=14/C60, (OS)n=14/C70, (OS)n=14/PC60BM and (OS)n=14/PCBDANblends (complexes) as a model of the active layer in the BHJ solar cell were chosen and the optoelectronic properties were studied. Results demonstrated that the efficiency of these complexes calculated based on Scharber diagram were obtained as 8%, 8.2%, 9.3% and 9.7% respectively. Obtained results indicate that the (OS)n=14/PCBDAN is a favorable candidate as solar cell than that of the other blends. In order to investigate the effect of chain length of oligomers on the solar cell properties, the optoelectronic properties of (OS)n=12/C60 blend was also studied. In comparison, the electronic and optical properties and the obtained efficiency values for (OS)n=12/C60 and(OS)n=14/C60 (7.7% and 8% respectively) indicated that (OS)n=14/C60 complex is more suitable candidate than the (OS)n=12/C60 for modeling the active layer in the BHJ solar cells.
 

In this study the structural and electronic properties of C59M [ M = B, Al, Ga, Si, Ge, N, P, As] Heterofullerenes and C60 fullerene using density functional theory calculations (MPW1PW91/6-31G (d)) were investigated. Investigation of energy gap and binding energy show that the thermodynamic stability of all structures slightly decreased compared with C60 and reactivity of them increased. Besed on the obtained results, in each group the heterofullerenes with smaller heteroatom have more thermodynamic stability and heterofullerenes with heavier heteroatoms have less reactivity. The most binding energy is obtained for C59N and C59B structures and the C59Ga has the most energy gap. Also the atomic partial charges of atoms with three methods included Hirshfeld, Mulliken and NBO were calculated for all structures. The obtained results showed that the charge transfer take placed from heteroatoms to carbon atoms and heteroatoms have partial positive charge. It should be mentioned in C59N because of the high electronegativity of nitrogen atom with respect to Carbon atom, Nitrogen has negative charge and carbon atoms have positive partial charge. Furthermore, the bond lengths for all of the structures increased compared with C60 and the bond orders decreased, with one exception, C59N. In the second part, due to the damaging effects of air pollutants such as SO2 and CO2, the interaction of pure fullerene and heterofullerenes with entitled molecules was investigated. Three different modes of SO2 were considered (a: from the oxygen, b: from the sulfur, C: horizontally). The SO2 molecule was located without any constraints about 2 Å above the heterofullerenes. The most interaction was found for those structures in with the molecule were closed to the heteroatoms through its oxygen atoms. Results show that the SO2 molecule can be adsorbed onto the C60 fullerene with adsorption energy about -4.758 kJ/mol. On the other hand, the interaction of C59Al, C59Ga and C59Si with SO2 molecule exhibit adsorption energies in the range of -98.275 kJ/mol to -193.675 kJ/mol which means that the strong chemically adsorption is occurred. Also, C59Ge and C59P structures reveal that a strong physically adsorption for SO2 more than -40 kJ/mol take place. Next to explore the ability of structures for adsorption of a nonpolar molecule, CO2 investigated. Only C59Ga and C59Al structures show a good physically adsorption. In conclusion, the heteroatoms in the C60 structure have higher impact to the adsorption of SO2 compared to the adsorption of CO2. The HOMO-LUMO energy gap decreases with increasing the interaction between SO2 or CO2 molecules and heterofullerene.

 In this research the stability of Boron fullerenes is investigated. The structure of molecules were optimized with B3LYP and/or B3PW91 method and the basis set of 6-31g(d) for all atoms except for transition metals (the calculations for transition metals are accomplished by LANL2DZECP method). Time dependent DFT is applied to survey the optical characteristics of complexes at CAM-B3LYP method. All the calculations were actuated by Gaussian09 software. In the first phase of the research, five boron fullerenes with C1, C2, Ci, C2h, and D2h symmetries were investigated to find the most suitable option for encapsulating single metallic atom and/or metallic cluster. Among these fullerenes the B80 fullerene with D2h symmetry showed the maximum stability energy and therefore was found to be thermodynamically the most stable fullerene. On the other hand the B80 fullerene with C1 symmetry turned out to have the biggest energy gap and therefore to have less reactivity and best fit because of its preeminent kinetic stability among the five alterative fullerenes. In the second phase of the research, metal encapsulation was studied as an option to enhance the fullerene stability. In order to investigate the effect of the capsulated metallic atom on the stability and structural characteristics of the B80 fullerene, Li and Be were used. Encapsulating Be atom made a slight increase in the energy gap of B80 empty cage and perhaps makes the Be@B80 complex less reactive, but encapsulating Li decreased the energy gap and therefore causes higher reactivity. It was found that Be@B80 has a higher energy gap than Li@B80 and therefore it is predicted to be kinetically more stable. Comparing the stability energies of these complexes showed that, Li@B80 is thermodynamically more stable; therefore it was understood that kinetic and thermodynamic behaviors vary in two divergent patterns. Within the third phase of the research we focused on the encapsulating La3N, Sc3N, and Sc2C2 metallic clusters in the B80(C1) fullerene by investigating the structural and electronic parameters. It was unfolded that encapsulating Nitride cluster Sc3N causes a smaller decrease in energy band gap as compared with its carbide type Sc2C2. Therefore it was deduced that Sc3N@B80 has less reactivity than Sc2C2@B80. Also between the Sc3N@B80 and La3N@B80, the former exhibited less decrease in energy band gap and eventually it was predicted to be at less reactivity. By comparing the stability energies it was found that encapsulating Sc3N nitride cluster in B80(C1) fullerene causes more negative stability energy than carbide cluster Sc2C2. Therefore Sc3N@B80 is thermodynamically more stable than Sc2C2@B80. Sc3N@B80 has a higher stability energy than La3N@B80 and therefor is predicted to be more thermodynamically stable. Eventually the most stable complex is recognized as Sc3N@B80 and this issue is verified by thermodynamic and kinetic viewpoint simultaneously.

In this research, the optical and electronic properties of heterojunction polymer-fullerene as model for organic solar cells in the gas and solvent phases are investigated. The
(1D), (2D) and (3D) are used as donors and C₆₀, C₇₀, PC₆₀BM and PC₆₀BE are used as acceptores. In this study the energy levels, HOMO-LUMO gaps and reorganization energy are obtained within the framework of Density Functional Theory (DFT). The time-depended DFT (TDDFT) is employed to calculate their excited state properties. The B3LYP, hybrid exchange-correlation functional, and the 6-311G (d ,p) basis set is used to determine optimized ground state structures of the above mentioned molecular systems. For solvent effect we make use of the conductor-like polarizable continuum model (CPCM). The calculations are carried out using G09 package.
The study of size effect of polymer show that the HOMO-LUMO gap decrease and the maximum wavelength increase with increasing the polymer size. The solvent effect caused red shifted in the maximum wavelength and increase the absorbance in the polymers and complexes. On the other hand, the size effect of polymer on the optical properties of C₆₀/(1D)_n complexes with n=1,2,3 is investigated. The result show that if the size of polymer is increased the maximum wavelength is also increased. Furtheremore, with increasing the polymer size the open circuit voltage (V_OC) is decreased. According to the above mentioned result and investigation of other electronic properties, we can conclude that the C60/(1D)_n=1 complex has better condition as heterojunction solar cell compared with C₆₀/(1D)_n=2,3 complexes.
To explore the effect of acceptor on the solar cell properties, we investigated the three different type of acceptors instead of C₆₀ such as C₇₀, PC₆₀BM and PC₆₀BE. It should be mentioned that the donor in the above situations is 1D monomer. Obtained results indicate that the C₇₀/(1D)_n=1 is a better candidate as solar cell than that of the complexes.
If the 2D and 3D polymers (with n=3) are used as donor, so the PC₆₀BM and PC₆₀BE are the best acceptors between entiteled acceptor materials. To investigate the ability of PC₆₀BM/(2D)_n=3 and PC₆₀BE/(2D)_n=3 complexes as heterojunction solar cell, the various quantities of these complexes are calculated in both gas and Chlorobenzene phases. The calculated electronic and optical properties of above complexes indicate that the entitled complexes are suitable candidate as solar cell in the gas and solvent phases as well as PC₆₀BM/(3D)_n=3 and PC60BE/(3D)n=3 that are suitable candidate in the gas phase