Red-shifted Absorption Spectra Research Articles

Quantum chemical and photovoltaic modeling of D-π-A organic dyes based on substituted arylamine electron donors in dye sensitized solar cells

In the present research, we designed four tunable triphenylamine (TPA) based organic dyes by applying various aminated electron donor groups and screened their electron donating effects on the electronic, optical and photovoltaic properties of the dyes for application in dye sensitized solar cells (DSSCs). In this respect, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches were applied to investigate the enhanced electron donating effect of substituted TPA dyes on the strength of conjugation with thiophene and a C–C triple bond in the π-spacer fragment that led to a considerable effect on absorption properties, light harvesting efficiency and panchromatic sensitization of the designed dyes in DSSCs. In fact, since the most significant impediment of TPA-based organic dyes for high photovoltaic performance in DSSCs is their low absorption in the near-infrared spectrum, we aimed our modeling to introduce molecular dyes with reduced frontier molecular orbital energy gaps and hence, the favoured red-shift absorption spectra. Moreover, we have computationally concentrated on the photovoltaic performance of our novel dyes in DSSCs and demonstrated that employing aminated electron donating groups in TPA based organic dyes notably tunes the electron injection and regeneration driving forces and hence leads to higher power conversion efficiencies.

Synthesis and evaluation of photophysical and electrochemical properties of vinyl chalcogenide derivatives of phenothiazines

The Wittig-Horner mediated syntheses of phenothiazines carrying vinylsulfide and vinylselenide motifs attached to the aromatic ring(s) or connected to the central nitrogen atom of the heterocycle, and the subsequent study of their photophysical and electrochemical properties, are reported. These compounds were obtained as mixtures of geometric isomers, in good to excellent yields. To complete the study, a small set of vinylsulfoxide and vinylsulfone derivatives was also prepared from the corresponding oxidized phosphinoxides. The photophysical properties of the compounds were examined in solvents of varying polarity, in which they presented absorption maxima in the UV region, with molar absorptivity coefficients compatible with symmetry-allowed π–π* electronic transitions. The heterocyclic derivatives were fluorescent. Compounds bearing vinylsulfide moieties associated to the nitrogen atom of the heterocycle displayed less intense fluorescence than the phenothiazine derivatives carrying vinylchalcogenides bonded to the aromatic ring; the latter also exhibited more red-shifted absorption spectra, and Stokes shifts in the range 6115–8170 cm−1 with weak dependence of solvent polarity. The sulfoxide and sulfones displayed more red-shifted spectra than the corresponding sulfides. The cyclic voltammograms of all derivatives exhibited a common pattern of reversible or quasi-reversible processes in the anodic region, related to the phenothiazine unit.

Molecular engineering of the fused azacycle donors in the D-A-π-A metal-free organic dyes for efficient dye-sensitized solar cells

Four novel D-A-π-A metal-free organic sensitizers QL1–4 with the fused azacycle units as donors have been designed and synthesized to investigate the relationship between both the sizes and conjugations of azacycle and performances of dye-sensitized solar cells systematically. QL1 with the five-membered azacycle, i.e., with carbazole (Cz) as donor, exhibits the smallest molar extinction coefficients (ε). QL2 and QL3 with the seven-membered azacycle, i.e. with N-phenyl-iminostilbene (ISB) and N-phenyl-iminodibenzyl (IDB) as donors, respectively, show the red-shifted absorption spectra and higher ε compared to QL1. However, QL2 and QL3 with an only distinction in a single or double bond, display distinctive PCEs. QL4 with the six-membered azacycle, i.e., 9,9,10-triphenyl-9,10-dihydroacridine (TDD), exhibits a blue-shifted absorption spectrum due to a big dihedral angle, resulting in a lower photovoltaic performance. Especially, QL3 with the ISB donor is conducive to achieving a PCE of 6.22%, which is higher than QL2, due to its better planar structure and more conjugation. When co-adsorbed with CDCA, QL3 exhibits the highest PCE of 7.14% among all dyes, and up to 8.26% by co-sensitizing with dye WL5, which surpasses that of the reference dye N719 (7.75%). The results indicate that the size and conjugation of the fused azacycle donors may affect the photovoltaic performance significantly, and the ISB unit is demonstrated as a promising donor for efficient organic dyes.

Electronic and photovoltaic properties of triphenylamine-based molecules with D-π-A-A structures

Four organic dyes (AP25, AP26, AP27, and AP28) with triphenylamine (T) as a donor coupled with different bridge groups of cyclopentadithiophene (CPDT) and quinacridone (QA), the auxiliary acceptor groups thienothiophene (TT) and benzothiadiazole (BTZ), are theoretically investigated in this paper for dye-sensitized solar cells (DSSC). DFT is used to calculate the ground-state properties of dyes, and TDDFT provides an understanding of the excited-state properties of dyes. The parameters affecting photoelectric conversion efficiency (PCE) of DSSC, correlating with Voc and Jsc were calculated to compare the photovoltaic performance of investigated dyes. Among those dyes, the results show that AP27 molecule has better photoelectric properties due to redshift absorption spectrum, larger LHE, longer fluorescent lifetime (τ1) and excited-state lifetime (τ2), and the higher μnormal. These results suggest that the CPDT-bridge linked with BTZ auxiliary acceptor is a promising design to develop PCE on DSSC.

Effects of Aromatic Thiol Capping Agents on the Structural and Electronic Properties of CdnTen (n = 6,8 and 9) Quantum Dots

Thiols are efficient capping agents used for the synthesis of semiconductor and metal nanoparticles. Commonly, long-chain thiols are used as passivating agents to provide stabilization to nanoparticles. Theoretical methods rarely reported aromatic thiol ligands’ effects on small-sized CdTe quantum dots’ structural and electronic properties. We have studied and compared the structural and electronic properties of (i) bare and (ii) aromatic thiols (thiophenol, 4-methoxybenzenethiol, 4-mercaptobenzonitrile, and 4-mercaptobenzoic acid) capped CdnTen quantum dots (QDs). Aromatic thiols are used as thiol-radical because of the higher tendency of thiol-radicals to bind with Cd atoms. This work provides an understanding of how the capping agents affect specific properties. The results show that all aromatic thiol-radical ligands caused significant structural distortion in the geometries. The aromatic thiol-radical ligands stabilize LUMOs, stabilize or destabilize HOMOs, and decrease HOMO-LUMO gaps for all the capped QDs. The stabilization of LUMOs is more pronounced than the destabilization of HOMOs. We also studied the effect of solvent on structural and electronic properties. TD-DFT calculations were performed to calculate the absorption spectra of bare and capped QDs, and all the capping ligands resulted in the redshift of absorption spectra.

Mono-/Bimetallic Neutral Iridium(III) Complexes Bearing Diketopyrrolopyrrole-Substituted N-Heterocyclic Carbene Ligands: Synthesis and Photophysics.

The synthesis and photophysics (UV-vis absorption, emission, and transient absorption) of four neutral heteroleptic cyclometalated iridium(III) complexes (Ir-1-Ir-4) incorporating thiophene/selenophene-diketopyrrolopyrrole (DPP)-substituted N-heterocyclic carbene (NHC) ancillary ligands are reported. The effects of thiophene versus selenophene substitution on DPP and bis- versus monoiridium(III) complexation on the photophysics of these complexes were systematically investigated via spectroscopic techniques and density functional theory calculations. All complexes exhibited strong vibronically resolved absorption in the regions of 500-700 nm and fluorescence at 600-770 nm, and both are predominantly originated from the DPP-NHC ligand. Complexation induced a pronounced red shift of this low-energy absorption band and the fluorescence band with respect to their corresponding ligands due to the improved planarity and extended π-conjugation in the DPP-NHC ligand. Replacing the thiophene units by selenophenes and/or biscomplexation led to the red-shifted absorption and fluorescence spectra, accompanied by the reduced fluorescence lifetime and quantum yield and enhanced population of the triplet excited states, as reflected by the stronger triplet excited-state absorption and singlet oxygen generation.

Fine‐Tuning the Photovoltaic Performance of Organic Solar Cells by Collaborative Optimization of Structural Isomerism and Halogen Atom

Fused‐ring acceptors based on an electron‐deficient core, such as Y6, have become a successful strategy in bulk heterojunction (BHJ) organic solar cells (OSCs) for high power conversion efficiencies (PCEs). Here, five fused‐ring electron acceptors (Y9, Y9‐2F, Y9‐2Cl, i‐Y9‐2F, i‐Y9‐2Cl) are synthesized using fused dithienothiophen[3,2‐b]pyrrolobenzotriazole and halogenated 1,1‐dicyanomethylene‐3‐indanone (IC) to investigate the effect of end‐group (EG) halogenation and structural isomerism on BHJ photovoltaic performance. Due to the strong electronegativity of halogens, all the acceptors with halogenated terminal units possess redshifted absorption spectra and deeper frontier energy levels compared with Y9. Different from asymmetric molecules i‐Y9‐2F and i‐Y9‐2Cl, Y9‐2F and Y9‐2Cl exhibit slightly lower bandgaps. Moreover, the devices based on fluorinated acceptors show more efficient charge collection, obtaining relatively high short‐circuit current density (J sc) and fill factor (FF). The lowest unoccupied molecular orbital energy levels of halogenated acceptors are similar. As a result, OSCs based on poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithio‐phene))‐alt‐(5,5‐ (1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethyl‐hexyl) benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))] (PBDB‐T):Y9‐2F obtain more balanced J sc and open‐circuit voltage (V oc), and thus an optimal PCE of 15.49% is demonstrated with a V oc of 0.84 V, J sc of 26.30 mA cm−2, and FF of 70.05%.

Monomer driven growth of catalytically active AgAu plasmonic nanoalloys

Ag–Au alloy nanoparticles were effortlessly synthesized with the seed Ag nanoparticles acting as sacrificial template for the effective reduction of Au3+ ions to Au0 atoms, augmented in the presence of the monomer, NVP (N-vinyl pyrrolidone) assimilated in specific solvents. The conventional spherical morphology of the different Ag–Au alloy molar compositions confirmed using TEM corroborates their red-shifted optical absorption spectra along with the strain induced XRD patterns in accordance with Vegard's law. FTIR spectroscopy depicts clearly the solvation property of NVP and also its respective molecular interaction of individual metal and alloy nanostructures. The amine group of NVP despite its possible steric hindrance seems to coordinate well with monometallic Ag nanoparticles; while for bimetallic Ag–Au nanoparticles, the combined amine and carbonyl groups plays a major role in stabilizing the nanostructure. No evidence of oligomerization/polymerization is observed even after the formation of respective nanoparticles, representing the intriguing configuration of the monomer NVP, the behavior of which seems equivalent to that of its long chain polymer counterpart, PVP. The catalytic properties of the as-synthesized Ag–Au alloy nanoparticles were carefully analyzed in comparison with other polymer/surfactant coated alloy nanoparticles and their significance is established in a cohesive manner.

Near-infrared small molecule acceptors based on 4H-cyclopenta[1,2-b:5,4-b']dithiophene units for organic solar cells

Two small-molecule non-fullerene acceptors (NFAs) CPDT-Me-2Eh and CPDT-4Cl-2Eh based on 4H-cyclopenta[1,2-b:5,4-b′] dithiophene as the electron-donating unit 2-(5/6-methyl-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile and 2-(5,6-dichloro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile as the end group respectively were developed. Compared with CPDT-Me-2Eh, CPDT-4Cl-2Eh possesses red-shift absorption spectrum, lower HOMO and LUMO energy level, and higher electron mobility. Non-fullerene polymer solar cells based on PBDB-T: CPDT-4Cl-2Eh gave a power conversion efficiency (PCE) of 7.52%, with a fill factor (FF) of 64.46%, and a short-circuit current (Jsc) of 16.90 mA/cm2. As contrast, the cell based on PBDB-T: CPDT-Me-2Eh got a PCE value of 4.39%. Our results indicate that the small molecule acceptor containing the CPDT core can effectively extend the absorption spectrum to the near-infrared (NIR) region by chlorination of the capping group. Our work provides an easy routine to broaden the field of new NIR NFAs with high PCE based on non-fullerene OSCs.

Effect of positional isomerism on the functional properties of carbazole-phenanthroimidazole-triphenylamine triads

A series of bipolar 2, 6 or 2, 7 substituted carbazole-based isomeric hybrids featuring phenanthroimidazole as acceptor and N-phenylcarbazole or triphenylamine as donor are synthesized. Structure-property relationship of these blue-emitting materials is established by detailed investigation of physiochemical, thermal and electroluminescence characteristics. The materials showed tunable absorption and emission spectra depending upon nature and position of chromophores attached to carbazole core. The triphenylamine substituted isomers exhibited red-shifted absorption and emission spectra when compared to their respective N-phenylcarbazole-based analogs. It is attributed to the increased intramolecular charge transfer (ICT) in the electron-rich triphenylamine derivatives as further confirmed in solvatochromism studies. However, the N-phenylcarbazole derivatives showed less solvent dependence in spectra attesting less polar ground and excited state due to comparatively poor donor strength of N-phenylcarbazole. Similarly, dyes containing electron-rich chromophores showed facile removal of electron with low oxidation potentials. The thermal robustness of the compounds was attested by high thermal decomposition temperatures (Td) which varied from 438 to 481 οC. The EL performance of 3 wt% doped device fabricated with emitter derived from 2,7-disubstituted carbazole featuring N-phenylcarbazole and PI chromophores showed deep-blue CIE coordinates of (0.16, 0.06) and maximum external quantum efficiency of 5.3%.

Polymerized small-molecule acceptors based on vinylene as π-bridge for efficient all-polymer solar cells

Two near-infrared (NIR) polymer acceptors (PAs, PYV, and PYV-Tz) based on fused-ring 2,1,3-benzothiadiazole (BT)- or benzotriazole (BTz)-based A′-DAD-A′ structure as electron-deficient-core and vinylene as the linking units, were designed and synthesized. The structure-property relationships of the all-polymer solar cells (all-PSCs) with a wide bandgap PBDB-T as donor were investigated systematically. Compared to the BT-based PA PYV, using BTz unit as the central core in PA PYV-Tz leads to the red-shifted absorption spectra and higher absorption coefficient in the PYV-Tz neat film. In addition, PYV-Tz also exhibits a higher lowest unoccupied molecular orbital (LUMO) energy level and better electron mobility. Consequently, the PBDB-T:PYV-Tz all-PSCs displayed a PCE of 13.02%, under the illumination of AM 1.5G, 100 mW cm-2, which is much higher than that of the PBDB-T:PYV device (11.51%). The measurements of relevant physical dynamics and blend morphologies further demonstrated the photovoltaic performance differences between PBDB-T:PYV and PBDB-T:PYV-Tz. This result indicates that PYV-Tz is a promising polymer acceptor material for the potential application of all-PSCs.

Zn(II)-DPA Coordinative fluorescent probe for enhancing G4 DNA binding

Novel dipicolylamino functionalized styryl-carbazole derivative (YCJ) was designed and synthesized. This derivative in combination with Zn(II) has exhibited large fluorescence intensity enhancement and prominent red-shift in absorption spectra with G4 DNA. Systematical analysis indicats that YCJ-Zn(II) complex shows much higher binding affinity and spectral response to G4 DNA than our previously reported styryl-carbazole scaffold (E1) due to the incorporationc of a Zn(II)-DPA moiety which could decrease the carbazole core electron density and consequently enhance the ability to display π-π stacking interaction with G4 DNA. Spectroscopic and molecular docking studies have unraveled YCJ-Zn(II) complex can stack both 3′ and 5′-ends and an associated with partial loop/groove interactions. The application of this Zn(II) complex as a fluorescent agent for living cell imaging was also demonstrated. The conjugation of the Zn-DPA moiety results in good cell permeability, endogenous DNA labeling, which is suitable for monitoring of nucleus activities.

A mechanochromic donor-acceptor torsional spring

Mechanochromic polymers are intriguing materials that allow to sense force of specimens under load. Most mechanochromic systems rely on covalent bond scission and hence are two-state systems with optically distinct “on” and “off” states where correlating force with wavelength is usually not possible. Translating force of different magnitude with gradually different wavelength of absorption or emission would open up new possibilities to map and understand force distributions in polymeric materials. Here, we present a mechanochromic donor-acceptor (DA) torsional spring that undergoes force-induced planarization during uniaxial elongation leading to red-shifted absorption and emission spectra. The DA spring is based on ortho-substituted diketopyrrolopyrrole (o-DPP). Covalent incorporation of o-DPP into a rigid yet ductile polyphenylene matrix allows to transduce sufficiently large stress to the DA spring. The mechanically induced deflection from equilibrium geometry of the DA spring is theoretically predicted, in agreement with experiments, and is fully reversible upon stress release.

Modulation of Aromaticity and Properties of Porphyrins By Peripheral Heterole-Fused Structures

Porphyrins are macrocyclic 18π aromatic molecules that have been actively studied in various fields owing to their intriguing properties for diverse applications. The introducing peripheral fused structures are quite effective for electronic perturbations and realizing red-shifted absorption spectra because of their expanded π-conjugated networks. In particular, the introduction of heteroles, i.e., five-membered π-conjugated molecules with main group elements, has attracted attention as heteroatom-embedded porphyrins. Because the properties of heterole derivatives can be modulated by main group elements and their oxidation states, we envisioned that the properties of fused porphyrins would also be modulated by heterole-fused structures. Herein, we report new synthetic strategies for heterole-fused porphyrins using [2+2+1] cyclization of bis(alkynyl)porphyrin, e.g., phosphole- and pyrrole-fused porphyrins. The oxidation state of the phosphorus atom had a clear influence on the aromatic character and the resultant electronic properties. In addition, the pyrrole-fused structure exhibited larger perturbation compared to the phosphole-fused structure. Therefore, we demonstrated the modulation of their aromaticity and physicochemical properties by control of main group elements and their oxidation states.

Influence of (Li/Na/K) doping and point defect (VAl, Hi) on the magnetic and photocatalytic performance of AlN: A first-principles study

Although extensive reports on the influence of Li/Na/K doping on the physical properties of AlN systems exist, the effects of Li/Na/K doping and point defects (VAl, Hi) coexisting in AlN systems on magneto-optical properties are often neglected. Experimentally, Li/Na/K doping and point defects (VAl, Hi) cannot be precisely controlled. In this study, the generalized gradient approximation (GGA) plane wave ultrasoft pseudopotential + U method based on spin density functional theory is adopted to solve the abovementioned problem. The first-principles method is utilized to study the effects of point defects (VAl, Hi) and Li/Na/K doping on the photocatalytic performance of AlN systems. Compared with the Al34MN36 (M = Li/Na/K) system, the Al34MHiN36 (M = Li/Na/K) system presents reduced formation energy and improved stability. The Al34NaHiN36 system has the smallest formation energy and the highest stability. In particular, compared with all doped systems, the Al34NaHiN36 system has the best absorption spectrum redshift, the best carrier activity, the longest carrier lifetime, and the strongest oxidation capacity, that is, the best photocatalytic performance. The first-principles study indicates that N atoms in all Al34MN36 (M = Li/Na/K) and Al34MHiN36 (M = Li/Na/K) systems have acceptor and donor characteristics. The magnetic source of all doped systems is related to the double exchange of carriers as mediators, the itinerant electron polarization of unpaired N2− atoms and electric polarization. This study has certain theoretical guidance for the experimental design and preparation of new AlN magneto-optical functional materials.

Photophysical properties of fluorescent nucleobase P-analogues expected to monitor DNA replication

In this work, we computationally design a series of fluorescent purine analogues based on the 2-amino-8-(1′-β-D-2′-deoxyribofuranosyl)-imidazo[1,2-a]-1,3,5-triazin-4(8H)-one (P) to monitor the DNA replication process with merely a minimal perturbation to the natural structure of nucleic acid. The P-modified fluorescent probes present red-shifted absorption spectra and enhanced photoluminescence due to the additional π-conjugation resulting from the fluorophore modification and the ring-expansion. Efficient fluorescence quenching of P-analogues occurs upon pairing with the complementary 6-amino-5-nitro-3-(1′-β-D-2′-deoxyribofuranosyl)-2(1H)-pyridone (Z) due to the nonradiative relaxation from the low-lying dark excited state to the ground state of Z moiety. Especially, the P3 and the P7, which have high fluorescence intensity in both gas and liquid phases, are proposed as the sensors for studying conformational switching in the presence and absence of a complementary sequence. Also examined are the influences of hydration and the linking to deoxyribose on absorption and emission processes. Besides, the potential phosphorescence emission of these modified base pairs is taken into account by constructing the relaxed potential energy curves of S0, T1 and S1 states.

Electrostatic Control of Photoisomerization in Channelrhodopsin 2.

Channelrhodopsin 2 (ChR2) is the most commonly used tool in optogenetics. Because of its faster photocycle compared to wild-type (WT) ChR2, the E123T mutant of ChR2 is a useful optogenetic tool when fast neuronal stimulation is needed. Interestingly, in spite of its faster photocycle, the initial step of the photocycle in E123T (photoisomerization of retinal protonated Schiff base or RPSB) was found experimentally to be much slower than that of WT ChR2. The E123T mutant replaces the negatively charged E123 residue with a neutral T123 residue, perturbing the electric field around the RPSB. Understanding the RPSB photoisomerization mechanism in ChR2 mutants will provide molecular-level insights into how ChR2 photochemical reactivity can be controlled, which will lay the foundation for improving the design of optogenetic tools. In this work, we combine ab initio nonadiabatic dynamics simulation, excited state free energy calculation, and reaction path search to comprehensively characterize the RPSB photoisomerization mechanism in the E123T mutant of ChR2. Our simulation agrees with previous experiments in predicting a red-shifted absorption spectrum and significant slowdown of photoisomerization in the E123T mutant. Interestingly, our simulations predict similar photoisomerization quantum yields for the mutant and WT despite the differences in excited-state lifetime and absorption maximum. Upon mutation, the neutralization of the negative charge on the E123 residue increases the isomerization barrier, alters the reaction pathway, and changes the relative stability of two fluorescent states. Our findings provide new insight into the intricate role of the electrostatic environment on the RPSB photoisomerization mechanism in microbial rhodopsins.

Selenophene-containing semiconducting polymers for high-performance ambipolar thin film transistor application

The development of high-performance and well-balanced ambipolar conjugated polymers are critical to next generation optoelectronic devices. Herein, we report the synthesis and characterization of two APBDOPV polymers containing alternative bis-thiophene, and bis-selenophene as comonomers. The relationship between the structure and opto-electrical property, thin film morphology, molecular packing and solution processing thin film transistors have been investigated systemically. Our results showed that by increasing the size of the chalcogen atom, a stronger red-shifted absorption spectrum, higher IP and a reduced optical band gap are observed for selenophene-containing polymers. The enhanced EA and the planar backbone make both polymers as ambipolar charge transport behaviors under ambient conditions. Particularly, selenophene-containing polymer exhibits much higher and well-balanced hole/electron mobilities up to 0.11/0.15 cm2 V−1 s−1 under ambient conditions with a BGTC device configuration. After further optimization of the TGBC configuration, higher hole/electron mobility of 0.19/0.76 cm2 V−1 s−1 are achieved. Our results also demonstrate that introducing the chalcogen atom into the conjugated backbone is an effective approach to tune the property of the semiconducting polymers.

Unusual photodegradation reactions of Asteraceae and Poaceae grass pollen enzymatic extracts on P25 photocatalyst.

In previous studies, it was demonstrated that photocatalysis by TiO2 nanoparticles can be effective for decomposition of pollen grains and pollen allergen extracts (PAEs) for Cupressus arizonica and Platanus hybrida species. In this work, the chemical and photochemical processes of five types of PAEs belonging to family Asteraceae, tribe Astereae, and family Poaceae, tribes Poeae and Triticea, were studied. It was confirmed that the PAEs suffered almost complete decomposition, which likely led to gaseous final products. For the species of Poeae tribe, i.e., Poa pratensis, Festuca pratensis, and Avena sativa, an unusual surface chemical modification of the photocatalyst consisting in the appearance of new bands on fine core level spectra of Ti 2p, C 1s, and O 1s was observed. These changes were associated with possible doping of TiO2 with C and N by pollen extracts. This was accompanied by a red shift of absorption spectra. The results suggest that some components of Poeae pollen can be grafted on TiO2 surface and they can activate the photocatalyst in the visible range. These findings can open a new pathway to eco-friendly chemical engineering of photocatalysts using organic biological compounds.

Quantum chemical design of near‐infrared sensitive fused ring electron acceptors containing selenophene as π‐bridge for high‐performance organic solar cells

AbstractEnd‐capped acceptors modification of fused ring electron acceptors (FREAs) is an attractive strategy to boost the optoelectronic and photovoltaic properties of the materials. FREAs are also proven beneficial due to their tremendous applications in organic solar cells (OSCs). Among fused‐ring electronic species, small fullerene‐free FREAs have already been drawn more attention due to their near‐infrared sensitivity and constantly increasing efficiencies. Therefore, we have designed six new FREAs (K1–K6) having selenophene as π‐bridge in between the central alkylated indaceno[1,2‐b:5,6b]dithiophene (IDT) unit after the incorporations of various end‐capped acceptors on to the recently synthesized IDT2SeC2C4‐4F molecule. Structural–property relationship and photophysical and photovoltaic properties of newly designed molecules are studied with the help of density functional theory (DFT) and time‐dependent DFT (TD‐DFT). Certain critical specifications like frontier molecular orbitals (FMOs) alignment, density of states (DOS), absorption maxima, excitation energy, binding energy (BE) along with transition density matrix (TDM), and the specifically estimated reorganizational energy values of electron and hole and the open circuit voltages of newly designed molecules are computed and compared with reference molecule. Generally, a red‐shifting absorption behavior of FREAs is considered the most important reason for their high efficiencies in OSCs. Our novel designed molecules exhibit red shift in absorption spectrum. Similarly, low excitation and binding energies of designed molecules offer improved power conversion efficiencies (PCEs) with highest possible charge photocurrent density (Jsc) in OSCs devices. Furthermore, study of PTB7‐Th/K1 complex is also done in order to examine charge transfer between within complex. By introducing the efficient end‐capped acceptor moieties in reference molecule, enhancement in charge mobilities is noted. The large open circuit voltage, low reorganizational energies, narrower highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap, lower binding and excitation energies, and highly red shifting in absorption phenomenon indicate an efficient designing of molecules, which could be best fitted for high efficiency OSCs. Finally, theorized molecules are much superior related to their photovoltaic and electronic properties and thus are recommended to experimentalist for their synthesis and out‐looking future developments of highly efficient solar cells devices.