Evaluation of acceptor strength in thiophene coupled donor-acceptor chromophores for optimal design of organic photovoltaic materials

Unlocking high-performance near-infrared photodetection: polaron-assisted organic integer charge transfer hybrids

Room temperature femtowatt sensitivity remains a sought-after attribute, even among commercial inorganic infrared (IR) photodetectors (PDs). While organic IR PDs are poised to emerge as a pivotal sensor technology in the forthcoming Fourth-Generation Industrial Era, their performance lags behind that of their inorganic counterparts. This discrepancy primarily stems from poor external quantum efficiencies (EQE), driven by inadequate exciton dissociation (high exciton binding energy) within organic IR materials, exacerbated by pronounced non-radiative recombination at narrow bandgaps. Here, we unveil a high-performance organic Near-IR (NIR) PD via integer charge transfer between Poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (C-14PBTTT) donor (D) and Tetrafluorotetracyanoquinodimethane (TCNQF4) acceptor (A) molecules, showcasing strong low-energy subgap absorptions up to 2.5 µm. We observe that specifically, polaron excitation in these radical and neutral D-A blended molecules enables bound charges to exceed the Coulombic attraction to their counterions, leading to an elevated EQE (polaron absorption region) compared to Frenkel excitons. As a result, our devices achieve a high EQE of ∼107%, femtowatt sensitivity (NEP) of ~0.12 fW Hz-1/2 along a response time of ~81 ms, at room temperature for a wavelength of 1.0 µm. Our innovative utilization of polarons highlights their potential as alternatives to Frenkel excitons in high-performance organic IR PDs.

Unveiling peripheral symmetric acceptors coupling with tetrathienylbenzene core to promote electron transfer dynamics in organic photovoltaics

Non-fullerene organic compounds are promising materials for advanced photovoltaic devices. The photovoltaic and electronic properties of the derivatives (TTBR and TTB1-TTB6) were determined by employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) analyses using the M06/6-311G(d,p) functional. To enhance the effectiveness of fullerene-free organic photovoltaic cells, modifications were applied to end-capped acceptors by using strong electron-withdrawing moieties. The structural tailoring showed a significant electronic impact for HOMO and LUMO for all chromophores, resulting in decreased band gaps (3.184-2.540 eV). Interestingly, all the designed derivatives exhibited broader absorption spectra in the range of 486.365-605.895 nm in dichloromethane solvent. Among all derivatives, TTB5 was observed to be the promising candidate because of its lowest energy gap (2.54 eV) and binding energy (0.494 eV) values, along with the bathochromic shift (605.895 nm). These chromophores having an A-π-A framework might be considered promising materials for efficient organic cells.

Exploration of the effect of multiple acceptor and π-spacer moieties coupled to indolonaphthyridine core for promising organic photovoltaic properties: a first principles framework

Herein, the indolonaphthyridine-based molecules (INDTD1-INDTD8) with A1-π-A2-π-A1 configuration were designed by the end-capped modification of INDTR reference with various acceptors. The density functional theory (DFT) and time-dependent DFT (TD-DFT) analyses at M06/6-31G(d,p) level were reported in this research to explore their optoelectronic and photovoltaic features. Their geometrical structures were initially optimized at the afore-said level and followed by various calculations such as the frontier molecular orbitals (FMOs), UV-Visible, density of states (DOS), transition density matrix (TDM), binding energy (Eb), open circuit voltage (Voc) and fill factor (FF). Moreover, their global reactivity parameters (GRPs) were depicted by using the HOMO-LUMO band gaps obtained from the FMOs study. The tailored molecules demonstrated lower band gaps (2.183-2.269 eV) than INDTR (2.288 eV). They also showed bathochromic shifts in the visible region in chloroform (735.937-762.318 nm) and gas phase (710.384-729.571 nm) as compared to INDTR (724.710 and 698.498 nm, respectively). Further, intramolecular charge transfer (ICT) was demonstrated via the DOS and TDM graphical maps. Among all the entitled chromophores, INDTD7 showed significantly reduced band gap (2.183 eV), red-shifted absorption value (760.914 nm) in chloroform solvent and minimal Eb value (0.554 eV). The presence of -SO3H groups on the terminal acceptors of INDTD7  may enhance the mobility of charges. The results suggested that the newly designed chromophores can be effective candidates for the future organic solar cell applications. Moreover, this study may encourage the experimentalists to develop photovoltaic materials.

A first principles based prediction of electronic and nonlinear optical properties towards cyclopenta thiophene chromophores with benzothiophene acceptor moieties

In the current work, organic cyclopenta-thiophene (CPT) based derivatives (FICR and FICD1-FICD5) were designed by the modulation of end-capped acceptor group of the reference molecule i.e., FICR, to explore their nonlinear optical (NLO) response. The effect of terminal acceptor and donor groups in the tailored compounds was explored by using DFT based quantum calculations. The UV-Vis analysis, frontier molecular orbitals (FMOs), transition density matrix (TDM), natural bond orbitals (NBOs), density of states (DOS), nonlinear optical (NLO) analyses were performed at M06/6-311G(d,p) functional. The LUMO-HOMO band gaps of FICD1-FICD5 were found to be smaller (1.75-1.92 eV) comparative to FICR (1.98 eV). Moreover, the global reactivity parameters (GRPs) were correlated with the results of other analyses. FICD2 and FICD5 with lowest band gap 1.73 and 1.75 eV showed less hardness (0.86 and 0.87 eV, respectively), high softness (0.58 and 0.57 eV-1), and larger absorption spectrum (815 and 813 nm) in gaseous phase and (889 and 880 nm) in solvent phase among all entitled compounds. All the designed chromophores (FICD1-FICD5) demonstrated a significant NLO response as compared to FICR. Particularly, FICD2 and FICD5 exhibited the highest average linear polarizability (<α>) [2.86 × 10-22 and 2.88 × 10-22 esu], first hyperpolarizability (βtot) (8.43 × 10-27 and 8.35 × 10-27 esu) and second hyperpolarizability (γtot) (13.20 × 10-32 and 13.0 × 10-32 esu) values as compared to the other derivatives. In nutshell, structural modeling of CPT based chromophores with extended acceptors, can be significantly utilized to achieve potential NLO materials.

Influence of benzothiophene acceptor moieties on the non-linear optical properties of pyreno-based chromophores: first-principles DFT framework

Herein, a series of heterocyclic organic compounds (PYFD1-PYFD7) are designed with different acceptor moieties at the terminal position of a reference compound (PYFR) for nonlinear optical (NLO) active materials. The optoelectronic characteristics of the designed chromophores were investigated using density functional theory (DFT) calculations with the M06/6-311G(d,p) functional. Frontier molecular orbital (FMO) analysis revealed a significant decrease in the energy of the band gaps (2.340-2.602 eV) for the derivatives as compared to the PYFR reference compound (3.12 eV). An efficient transfer of charge from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) was seen, which was further corroborated by the density of states (DOS) and transition density matrix (TDM) heat maps. The results of the global reactivity parameters (GRPs) indicated that all derivatives exhibited greater softness (σ = 0.384-0.427 eV) and lower hardness (η = 0.394-1.302 eV) as compared to PYFR, indicating a higher level of polarizability in the derivatives. Moreover, all of the derivatives showed significant findings in terms of nonlinear optical (NLO) results as compared to the reference chromophore. PYFD2 showed the most effective NLO response (α = 1.861 × 10-22 and βtot = 2.376 × 10-28 esu), including a lowered band gap of 2.340 eV, the maximum softness value of 0.4273 eV, and the lowest hardness value of 1.170 eV as compared to other chromophores. The incorporation of different acceptors and thiophene as a π-spacer in this structural alteration significantly contributed to achieving remarkable NLO responses. Therefore, our findings may motivate experimentalists to synthesize these designed NLO active materials for the current advanced technological applications.

Designed complexes combining brazilein and brazilin with betanidin for dye-sensitized solar cell application: DFT and TD-DFT study

Dye-sensitized solar cells (DSSCs) are promising third-generation photovoltaic cell technology owing to their easy fabrication, flexibility and better performance under diffuse light conditions. Natural pigment sensitizers are abundantly available and environmentally friendliness. However, narrow absorption spectra of natural pigments result in low efficiencies of the DSSCs. Therefore, combining two or more pigments with complementary absorption spectra is considered an appropriate method to broaden the absorption band and boost efficiency. This study reports three complex molecules: brazilin-betanidin-oxane (Braz-Bd-oxane), brazilin-betanidin-ether (Braz-Bd-ether) and brazilein-betanidin-ether (Braze-Bd-ether), obtained from the etherification and bi-etherification reactions of brazilin dye and brazilein dye with betanidin dye. The equilibrium geometrical structure properties, frontier molecular orbital, electrostatic surface potential, reorganization energy, chemical reactivities, and non-linear optical properties of the studied dyes were investigated using density functional theory (DFT)/B3LYP methods, with 6-31+G(d,p) basis sets and LANL2DZ for light atom and heavy atoms respectively. The optical-electronic properties were calculated using TD-DFT/B3LYP/6-31+G(d,p) for isolated dye and TD-DFT/CAM-B3LYP/6-31G(d,p)/LANL2DZ for dyes@(TiO2)9H4. The results reveal that spectra for Braz-Bd-oxane and Braze-Bd-ether complexes red-shifted compared to the individually selected dyes. The simulated absorption spectra of the adsorbed dyes on (TiO2)9H4 are red-shifted compared to the free dye. Moreover, Braz-Bd-oxane and Braz-Bd-ether exhibit better charge transfer and photovoltaic properties than the selected natural dyes forming these complexes. Based on the dyes' optoelectronic properties and photovoltaic properties, the designed molecules Braz-Bd-oxane and Braze-Bd-ether are considered better candidates to be used as photosensitizers in dye solar cells.

Heterocyclic Donor Moiety Effect on Optical Nonlinearity Behavior of Chrysene-Based Chromophores with Push-Pull Configuration via the Quantum Chemical Approach

Organic-based nonlinear optical (NLO) materials may be used in many optical-electronic systems and other next-generation defense technologies. With the importance of NLO materials, a series of push-pull architecture (D-π-A) derivatives (DTMD2-DTMD6) were devised from DTMR1 through structural alteration of different efficient donor heterocyclic groups. Density functional theory-based computations were executed at the MPW1PW91/6-31G(d,p) level to explore the NLO behavior of the derivatives. To investigate the optoelectronic behavior of the said compounds, various analyses like the frontier molecular orbital (FMO), global reactivity parameters, density of state (DOS), absorption spectra (UV-vis), natural bond orbital, and transition density matrix (TDM) were performed. The derivatives have a smaller band gap (2.156-1.492 eV) and a larger bathochromic shift (λmax = 692.838-969.605 nm) as compared to the reference chromophore (ΔE = 2.306 eV and λmax = 677.949 nm). FMO analysis revealed substantial charge conduction out of the donor toward the acceptor via a spacer that was also shown by TDM and DOS analyses. All derivatives showed promising NLO results, with the maximum amplitude of linear polarizability ⟨α⟩ and first (βtotal) and second (γtotal) hyperpolarizabilities over their reference chromophore. DTMD2 contained the highest βtotal (7.220 × 10-27 esu) and γtotal (1.720 × 10-31 esu) values corresponding with the reduced band gap (1.492 eV), representing potential futures for a large NLO amplitude. This structural modification through the use of various donors has played a significant part in achieving promising NLO behavior in the modified compounds.

An efficient end-capped engineering of pyrrole-based acceptor molecules for high-performance organic solar cells

CONTEXT

Various innovative molecules have been designed and explored for use in organic photovoltaics. In this study, we devised novel molecules (KZ1-KZ7) specifically for organic solar cells (OSCs). The newly formulated acceptor compounds possess a lower bandgap (Eg = 1.85-2.02), along with bathochromic shift (λmax = 713-788 nm) compared to the reference (Eg = 2.04 eV and λmax = 774 nm). Moreover, the FMO results identified the distinct charge transfer from HOMO to LUMO, which was strongly corroborated by the TDM maps. Similarly, the new designed molecules show less excitation energy (Ex = 1.31-1.54(gas)) than reference (Ex = 1.72). Likewise, all designed molecules (KZ1-KZ7) have demonstrated an analogous open circuit voltage (Voc) with the donor polymer PTB7-Th. All seven designed molecules (KZ1-KZ7) exhibited more fill factor ranging from 97.08 to 97.29 than reference 95.25 and PCE of between 8 and 20% at short circuit current densities of 9, 12, and 15 mA cm-2. Overall, the findings support that designed molecules can be potential molecules for future practical applications.

METHODS

Geometric calculations were conducted with Gaussian 09W software, and the findings were visualized using Gauss View software. DFT and TD-DFT were employed to evaluate various parameters for R and designed molecules (KZ1-KZ7). Firstly, four functionals including B3LYP, CAM-B3LYP, MPW1PW91, and ωB97XD with 6-31G(d,p) DFT level were applied to R to decide the best level for results. After appropriate analysis, the MPW1PW91/6-31G(d,p) was selected for further examination by comparing the experimental and DFT-based absorption graphs of R. External and internal reorganization energy are the two main factors contributing to reorganization energy. External energy refers to changes in external environment, while internal energy deals with information related to internal geometrical symmetry or the internal environment. The effect of outside factors or external reorganizational energy is omitted because it creates too little change.

Comparative Study of the Optical and Electronic Properties of Y6 Derivatives: A Theoretical Study

A series of Y-series nonfullerene acceptors (Y-NFAs) including symmetric acceptors (Y6 and TTY6) as well as asymmetric acceptors (KY6, TY6, and KTY6) have been constructed, and the electronic structure, electronic properties, and excited-state properties have been comparatively studied. The optoelectronic properties, interfacial charge-transfer (CT) mechanism, and interfacial CT rate for the solar cells composed of PM6 as the donor and Y6 derivatives as the acceptors are investigated further. We show that asymmetric Y6 derivatives have high molecular planarity, strong and wide absorption spectra, and large intramolecular charge transfer (ICT). For the solar cells, the complexes of Y6 derivatives show increased open-circuit voltage, larger fill factor, and smaller energy loss compared to Y6. In addition, the complexes of Y6 derivatives have more charge-transfer states than Y6 in the low-energy region, such that there are multiple ways for CT generations, such as hot excitation, intermolecular electric field (IEF), and direct excitation. The detailed CT mechanism as well as interfacial CT rate depends on the type of complexes, and all Y6 derivatives have a similar magnitude of charge-transfer rate to the one of Y6. This work not only reveals the differences in performance between symmetric and asymmetric NFA but also reveals that proper terminal tuning is an effective way to improve photovoltaic properties.

Exploration of linear and third-order nonlinear optical properties for donor-π-linker-acceptor chromophores derived from ATT-2 based non-fullerene molecule

In the current study, seven non-fullerene compounds abbreviated as ATTD2-ATTD8 were designed through structural tailoring and their nonlinear optical (NLO) properties were reported. The objective of this study was to explore the potential for newly configured D-π-A type non-fullerene-based compounds. Quantum chemical methods were adopted and revealed the molecules as highly efficient materials with favorable NLO characteristics for use in optoelectronic devices. The M06 functional along with the 6-311G(d,p) basis set in chloroform solvent were utilized for the natural bonding orbital (NBO) analysis, absorption spectra and computational assessments of frontier molecular orbitals (FMOs), global reactivity descriptors (GRPs), transition density matrix (TDM) and nonlinear optical properties (NLO) for ATTR1 and ATTD2-ATTD8. The HOMO-LUMO energy gap was significantly reduced in all the designed moieties compared to the reference compound in the following decreasing order: ATTR1 > ATTD8 > ATTD4 > ATTD5 > ATTD2 > ATTD7 > ATTD6 > ATTD3. All of the designed molecules (ATTD2-ATTD8) showed good NLO response. Global reactivity parameters were found to be closely associated with the band gap between the HOMO and LUMO orbitals, and the compound with the smallest energy gap, ATTD3, exhibited a lower hardness value of 1.754 eV and higher softness value of 0.570 eV with outstanding NLO response. For the reference compound and ATTD2-ATTD8 derivatives, attributes like dipole moment (μtot), average polarizability 〈α〉, first hyperpolarizability (βtot), and second hyperpolarizability γtot were calculated. Out of all the derivatives, ATTD3 revealed the highest amplitude with a βtot of 8.23 × 10-27 esu, which was consistent with the reduced band gap (1.754 eV) and suggested it was the best possibility for NLO materials in the future.

Designing of banana shaped chromophores via molecular engineering of terminal groups to probe photovoltaic behavior of organic solar cell materials

To meet the rising requirement of photovoltaic compounds for modernized hi-tech purpose, we designed six new molecules (DTPD1-DTPD6) from banana shaped small fullerene free chromophore (DTPR) by structural tailoring at terminal acceptors. Frontier molecular orbitals (FMOs), density of states (DOS), open circuit voltage (Voc), transition density matrix (TDM) analysis, optical properties, reorganization energy value of hole and electron were determined utilizing density function theory (DFT) and time-dependent density function theory (TD-DFT) approaches, to analyze photovoltaic properties of said compounds. Band gap contraction (∆E = 2.717-2.167 eV) accompanied by larger bathochromic shift (λmax = 585.490-709.693 nm) was observed in derivatives contrary to DTPR. The FMOs, DOS and TDMs investigations explored that central acceptor moiety played significant role for charge transformation. The minimum binding energy values for DTPD1-DTPD6 demonstrated the higher exciton dissociation rate with greater charge transferal rate than DTPR, which was further endorsed by TDM and DOS analyses. A comparable Voc (1.49-2.535 V) with respect to the HOMOPBDBT-LUMOacceptor for entitled compounds was investigated. In a nutshell, all the tailored chromophores can be considered as highly efficient compounds for promising OSCs with a good Voc response.

Influence of azacycle donor moieties on the photovoltaic properties of benzo[c][1,2,5]thiadiazole based organic systems: a DFT study

Fullerene free organic chromophores are widely utilized to improve the efficacy of photovoltaic materials. Herein, we designed D-π-A-π-D form chromophores (TAZD1-TAZD5) via end-capped redistribution of donor moieties by keeping the same π-bridge and central acceptor unit for organic solar cells (OSCs). To analyze the photovoltaic characteristics of these derivatives, DFT estimations were accomplished at B3LYP/6-311 G (d,p) functional. Different investigations like frontier molecular orbital (FMO), absorption spectra (UV-Vis), density of states (DOS), binding energy (Eb), open circuit voltage (Voc), and transition density matrix (TDMs) were performed to examine the optical, photophysical and electronic characteristics of afore-mentioned chromophores. A suitable band gap (∆E = 2.723-2.659 eV) with larger bathochromic shift (λmax = 554.218-543.261 nm in acetonitrile) was seen in TAZD1-TAZD5. An effective charge transference from donor to acceptor via spacer was observed by FMO analysis which further supported by DOS and TDM. Further, lower binding energy values also supported the higher exciton dissociation and greater CT in TAZD1-TAZD5. Among all the designed chromophores, TAZD5 exhibited the narrowest Egap (2.659 eV) and maximum red-shifted absorption in solvent as well as gas phase i.e. 554.218 nm and 533.219 nm, respectively which perhaps as a result of the phenothiazine-based donor group (MPT). In a nutshell, all the tailored chromophores can be considered as efficient compounds for promising OSCs with a good Voc response, interestingly, TAZD5 is found to be excellent chromophores as compared to all these designed compounds.

Conformer Ring Flip Enhances Mechanochromic Performance of ansa-Donor-Acceptor-Donor Mechanochromic Torsional Springs

Mechanochromophores based on conformational changes of donor-acceptor-donor (DAD) springs allow sensing of forces acting on polymer chains by monotonic changes of absorbance or photoluminescence (PL) wavelength. Here, we identify a series of thiophene (D)-flanked quinoxalines (A) as molecular torsional springs for force sensing in bulk polymers at room temperature. The mode of DAD linkage to the polymer matrix and linker rigidity are key parameters that influence the efficacy of force transduction to the DAD spring and thus mechanochromic response, as probed by in situ PL spectroscopy of bulk films during stress-strain experiments. The largest shift of the PL maximum, and thus the highest sensitivity, is obtained from an ansa-DAD spring exhibiting bridged D units and a stiff A linker. Using detailed spectroscopy and density functional theory calculations, we reveal conformer redistribution in the form of a thiophene ring flip as the major part of the overall mechanochromic response. At forces as low as 27 pN at early stages of deformation, the ring flip precedes mechanically induced planarization of the ansa-DAD spring, the latter process producing a PL shift of 21 nm nN^-1. Within the stress-strain diagram, the thiophene ring flip and DAD planarization are thus two separated processes that also cause irreversible and reversible mechanochromic responses, respectively, upon sample failure. As the thiophene ring flip requires much smaller forces than planarization of the DAD spring, such micromechanical motion gives access to sensing of tiny forces and expands both sensitivity and the force range of conformational mechanochromophores.

First theoretical framework for highly efficient photovoltaic parameters by structural modification with benzothiophene-incorporated acceptors in dithiophene based chromophores

Now a days, researchers are constantly doing efforts to upgrade the performance of solar based devices with the aim of increasing the role of photovoltaic materials in modern hi-tech optoelectronic applications. Realizing the recent energy conditions across the globe, research is diverted from fullerene to non-fullerene electron acceptor moieties in this era, considering their remarkable contribution in organic solar cells (OSCs). Therefore, we designed seven novel non-fullerene fused ring electron acceptor chromophores (MD2-MD8) from DOC2C6-2F by structural tailoring with different acceptors at end-capped units. DFT study was performed at B3LYP functional to discover the opto-electronic characteristics of the newly tailored chromophores. Various analysis such as frontier molecular orbitals (FMOs), transition density matrix (TDM), density of states (DOS), binding energy (Eb), reorganization energy, open circuit voltage (Voc) was carried out to comprehend the photovoltaic response of MD2-MD8. Decrease in band gaps (1.940-1.571 eV) with wider absorption spectrum (725.690-939.844 nm in chloroform) along with greater charge transfer rate from HOMO towards LUMO were examined in derivatives as compared to MR1 (Egap = 1.976 eV, λmax = 738.221 nm) except MD7. Further, in all derivatives, smaller values of Eb (0.252-0.279 eV) were examined than that of reference (0.296 eV). These lower binding energy values of MD2-MD8 indicated the higher rate of excitation dissociation with lager charger transfer rate than MR1, which further supported by DOS and TDM analyses. Additionally, least reorganization energy in the aforesaid compounds for hole with electron was also inspected. Moreover, Voc a good photovoltaic response was noted for all studied compounds which indicated that these compounds are suitable to synthesize OSCs in future.

Exploration of the interesting photovoltaic behavior of the fused benzothiophene dioxide moiety as a core donor with modification in acceptors for high-efficacy organic solar cells

Non-fullerene-based chromophores with end-capped acceptor modification used in organic solar cells (OSCs) have proven to offer improved performance. Therefore, eight unique benzothiophene-based molecules (D2-D9) were designed by the end-capped acceptor manipulation of a reference molecule (R1). Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations at the B3LYP level were performed to investigate various parameters such as the optical properties, frontier molecular orbitals (FMOs), transition density matrix (TDM), binding energy, density of states (DOS), open-circuit voltage (V oc), and reorganization energies of electrons (λ e) and holes (λ h), to better understand the optoelectronic properties of the newly designed compounds. All the derivatives had broader absorption spectra of 737.562-700.555 nm with a reduced energy gap of 2.132-1.851 eV compared to those of the reference (719.082 nm), except for D8 and D9. A comparable value of V oc and lower reorganization energies were found in the derivatives compared to those of R1. Within the studied compounds, D3 was predicted to be a good optoelectronic material for environmentally friendly organic solar cells (EFOSCs) because of its superior optoelectronic capabilities, low-energy band gap (1.851 eV), highest λ max values of 794.516 and 744.784 nm in chloroform and the gas phase, respectively, and lowest transition energy (1.561 eV) than those of the reference and the other derivatives. Subsequently, end-capped acceptor modification was proven to be an effective method to achieve desired optoelectronic characteristics.

Evaluating the impact of Hartree-Fock exact exchange on the performance of global hybrid functionals for the vertical excited-state energies of fused-ring electron acceptors using TD-DFT

The acceptor-donor-acceptor structured fused-ring electron acceptors (FREAs) have piqued interest for organic solar cells. We herein employ time-dependent density functional theory to evaluate the effect of Hartree-Fock exact exchange (HFX) on the performance of 16 global hybrid functionals for computing the maximum absorption wavelengths (λ_ver-theo) and the vertical excitation energies (E_ver-theo) of 34 molecules. We customize the HFX ratio in the functionals used to perform an in-depth analysis of its impact on the E_ver-theo values. The computed λ_ver-theo values strictly follow an inverse proportionality to the HFX percentage. The performance of the methods with the same ratio of HFX is almost identical, such as B3LYP, B3PW91, and mPW3PBE containing 20% HFX. The performance enhances with a relatively higher HFX ratio of 21% in X3LYP, B971, B972, and 22% in B98 giving smaller deviations. APF and APFD containing 23% HFX provide the smallest deviations for all compounds, with a mean signed error limited to 0.02 eV and a mean absolute error (MAE) of 0.06 eV. The performance drops using M06 and M05 with comparatively higher HFX ratios providing MAE values of 0.07 eV and 0.1 eV, respectively. M06-2X with 54% HFX provides the largest MAE value of 0.35 eV. The lowest obtained MAE is 0.06 eV at 23 to 25% HFX in most of the functionals considered in this study, suggesting that these are the optimal values for the prediction of excitation energies of FREAs. It has also been found that global hybrids seem to be more efficient for larger-sized molecules with a smaller bandgap.

Influence of End-Capped Modifications in the Nonlinear Optical Amplitude of Nonfullerene-Based Chromophores with a D-π-A Architecture: A DFT/TDDFT Study

Nonlinear optical (NLO) materials have several uses in many fields such as solid physics, biology, medicine, nuclear physics, and material research. Therefore, a series of nonfullerene-based derivatives (CC10D1-CC10D8) with a D-π-A configuration was planned for the NLO investigation using CC10R as the reference molecule with structural alternations at acceptor moieties. Natural bonding orbital (NBO), UV-vis spectra, frontier molecular orbitals (FMOs), global reactivity parameters (GRPs), transition density matrix (TDM), and density of states (DOS) were analyzed using the M06/6-311G(d,p) functional in chloroform solvent to understand the NLO responses of CC10R and CC10D1-CC10D8. The highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) band gaps of CC10D1-CC10D6 were illustrated to be lower than that of CC10R, with the larger bathochromic shift (726.408-782.674 nm) resulting in a significant NLO response. Along with the band gap, the FMO method also identified an efficient interfacial charge transfer from D to A moieties via a π-bridge, which was further supported by the DOS and TDM map. Moreover, NBO calculations demonstrated that extended hyperconjugation and strong internal molecular interactions were important in their stabilization. The dipole moment (μ), linear polarizability ⟨α⟩, hyperpolarizability (β_total), and second-order hyperpolarizability (γ_total.) were studied for CC10R and CC10D1-CC10D8. Among all of the derivatives, CC10D2 was proven to be the most appropriate candidate because of its suitable NLO behavior such as being well-supported by a reduced band gap (2.093 eV) and having a suitable maximum absorption wavelength (782.674 nm). Therefore, CC10D2 was reported to have a greater value of first hyperpolarizability (208 659.330 a.u.) compared with other derivatives and CC10R. For the second hyperpolarizability, a greater value was obtained for CC10R (5.855 × 10⁷ a.u.), and its derivatives showed results comparable to that of the parent chromophore for γ_total. This theoretical framework reveals that structural customization with different acceptor units plays a significant role in obtaining attractive NLO materials for optoelectronic applications.

Molecular Modeling of Pentacyclic Aromatic Bislactam-Based Small Donor Molecules by Altering Auxiliary End-Capped Acceptors to Elevate the Photovoltaic Attributes of Organic Solar Cells

Small-molecule (SM)-based organic solar cells (OSCs) have dominated the photovoltaic industry on account of their efficient optical and electronic properties. This quantum mechanical study addresses a DFT study of pentacyclic aromatic bislactam (PCL)-based small molecules for extremely proficient OSCs. Five novel small molecules (PCLM1-PCLM5) retaining the A-π-A-π-D-π-A-π-A arrangement were fabricated from the reference PCLR. At the MPW1PW91/6-31G** level of theory, detailed profiling of these novel molecules was performed by accurately following DFT, along with the time-dependent density functional theory (TD-DFT) hypothetical simulations to analyze the UV-visible absorption (λ_max), light-harvesting efficiency (LHE), dipole moment (μ), fill factor (FF), open-circuit voltage (V _OC), power conversion efficiency (PCE), frontier molecular orbitals (FMOs), binding energy (E _b), density of states (DOS), electrostatic potential (ESP), and transition density matrix (TDM) plots. Alteration of peripheral acceptors in all of the molecular structures drastically modified their charge-transfer properties, such as a strong light-harvesting capability in the range of 0.9993-0.9998, reduced exciton E _b (from 0.34 to 0.39 eV), a reduced bandgap (E _g) in the range of 1.66-1.99 eV, an elevated λ_max (775-959 nm) along with a higher μ in the solvent phase (1.934-7.865 D) when studied in comparison with PCLR, possessing an LHE of 0.9986, an E _b of 0.40, an E _g 2.27 eV, λ_max at 662 nm, and a μ of 0.628 D. The FMO analysis revealed the uniform dispersal of charge density entirely along the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals in newly constructed moieties. Electron as well as hole mobility rates, V _OC, FF, and PCE of all novel molecules (PCLM1-PCLM5) were higher as compared with those of PCLR, ultimately making them exceptional candidates for solar devices. Focusing on the outcomes, terminal acceptor modification was found to be a suitable method for the development of highly tuned OSCs in the future.

Exploration of the Intriguing Photovoltaic Behavior for Fused Indacenodithiophene-Based A-D-A Conjugated Systems: A DFT Model Study

Many researchers are engaged nowadays in developing efficient photovoltaic materials to accomplish the demand of modern technology. Nonfullerene small molecular acceptors (NF-SMAs) show potential photovoltaic performance, accelerating the development of organic solar cells (OSCs). Herein, the first theoretical designing of a series of indacenodithiophene-based (IDIC1-IDIC6) acceptor chromophores was done by structural tailoring with various well-known acceptors from the recently synthesized IDICR molecule. For the selection of the best level of density functional theory (DFT), various functionals such as B3LYP, M06-2X, CAM-B3LYP, and ωB97XD with the 6-311G(d,p) basis set were used for the UV-visible analysis of IDICR. Consequently, UV-visible results revealed that an interesting agreement was found between experimental and DFT-based values at the B3LYP level. Therefore, quantum chemical investigations were executed at the B3LYP/6-311G(d,p) level to evaluate the photovoltaic and optoelectronic properties. Structural tailoring with various acceptors resulted in a narrowing of the energy gap (2.245-2.070 eV) with broader absorption spectra (750.919-660.544 nm). An effective transfer of charge toward lowest unoccupied molecular orbitals (LUMOs) from highest occupied molecular orbitals (HOMOs) was studied, which played a crucial role in conducting materials. Further, open circuit voltage (V _oc) analysis was performed with respect to HOMO _PBDB-T -LUMO_ACCEPTOR, and all of the derivatives exhibited a comparable value of voltage with that of the parent chromophore. Lower reorganization energies in titled chromophores for holes and electrons were examined, which indicated the higher rate of mobility of charges. Interestingly, all of the designed chromophores exhibited a preferable optoelectronic response compared to the reference molecule. Therefore, this computed framework demonstrates that conceptualized chromophores are preferable and might be used to build high-performance organic solar cells in the future.

Rational Design and Characterization of Symmetry-Breaking Organic Semiconductors in Polymer Solar Cells: A Theory Insight of the Asymmetric Advantage

Asymmetric molecule strategy is considered an effective method to achieve high power conversion efficiency (PCE) of polymer solar cells (PSCs). In this paper, nine oligomers are designed by combining three new electron-deficient units (unitA)-n1, n2, and n3-and three electron-donating units (unitD)-D, E, and F-with their π-conjugation area extended. The relationships between symmetric/asymmetric molecule structure and the performance of the oligomers are investigated using the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. The results indicate that asymmetry molecule PEn2 has the minimum dihedral angle in the angle between two planes of unitD and unitA among all the molecules, which exhibited the advantages of asymmetric structures in molecular stacking. The relationship of the values of ionization potentials (IP) and electron affinities (EA) along with the unitD/unitA π-extend are revealed. The calculated reorganization energy results also demonstrate that the asymmetric molecules PDn2 and PEn2 could better charge the extraction of the PSCs than other molecules for their lower reorganization energy of 0.180 eV and 0.181 eV, respectively.

Exploration of promising optical and electronic properties of (non-polymer) small donor molecules for organic solar cells

Non-fullerene based organic compounds are considered promising materials for the fabrication of modern photovoltaic materials. Non-fullerene-based organic solar cells comprise of good photochemical and thermal stability along with longer device lifetimes as compared to fullerene-based compounds. Five new non-fullerene donor molecules were designed keeping in view the excellent donor properties of 3-bis(4-(2-ethylhexyl)-thiophen-2-yl)-5,7-bis(2ethylhexyl) benzo[1,2-:4,5-c']-dithiophene-4,8-dione thiophene-alkoxy benzene-thiophene indenedione (BDD-IN) by end-capped modifications. Photovoltaic and electronic characteristics of studied molecules were determined by employing density functional theory (DFT) and time dependent density functional theory (TD-DFT). Subsequently, obtained results were compared with the reference molecule BDD-IN. The designed molecules presented lower energy difference (ΔΕ) in the range of 2.17-2.39 eV in comparison to BDD-IN (= 2.72 eV). Moreover, insight from the frontier molecular orbital (FMO) analysis disclosed that central acceptors are responsible for the charge transformation. The designed molecules were found with higher λmax values and lower transition energies than BDD-IN molecule due to stronger end-capped acceptors. Open circuit voltage (Voc) was observed in the higher range (1.54-1.78 V) in accordance with HOMOdonor-LUMOPC61BM by designed compounds when compared with BDD-IN (1.28 V). Similarly, lower reorganization energy values were exhibited by the designed compounds in the range of λe(0.00285-0.00370 Eh) and λh(0.00847-0.00802 Eh) than BDD-IN [λe(0.00700 Eh) and λh(0.00889 Eh)]. These measurements show that the designed compounds are promising candidates for incorporation into solar cell devices, which would benefit from better hole and electron mobility.

Tuning the optoelectronic properties of ZOPTAN core-based derivatives by varying acceptors to increase efficiency of organic solar cell

In this theoretical study, quantum chemical analysis of five novel non-fullerene donor molecules designed from recently reported highly efficient (11.5%) donor molecule P2TBR, containing non-fused ring central thiophene-benzene-thiophene core, 2-D benzodithiophene donors, and end capped 3-methylrhodanine acceptors, has been performed to evaluate the photovoltaic parameters and their application in organic solar cells. These donor molecules consist of centrally introduced acrylonitrile acceptors in between thiophene-benzene-thiophene core of P2TBR, namely M1. Compounds M2-M5 were designed from M1 containing ZOPTAN core, through peripheral acceptor group modification by 2-methylenemalononitrile (M2), methyl 2-cyanoacrylate (M3), 2-(5,6-difluoro-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (M4), and 2-(3-methyl-5-methylene-4-oxothiazolidin-2-ylidene) malononitrile (M5). DFT and TD-DFT simulations of all molecules including reference were carried out using MPW1PW91 functional in conjunction with 6-31G (d, p) basis set. Optoelectronic properties, exciton dynamics, electron density distribution pattern, and charge mobility were further analyzed by absorption spectra, TDM plots, frontier molecular orbitals (FMO) analysis, and calculation of reorganization energies, respectively. Results reveal that central addition and end capped modification of acceptors in designed molecules proved to be effective strategy to finely tune the electronic and optical characteristics. Amongst all designed molecules, M4 exhibited improved opto-electronic parameters such as highest maximum absorption (695 nm) in chloroform, least band gap (2.24 eV), lowest values of λ_h (0.0034 eV), and λ_e (0.0054 eV) and lowermost binding energy (0.46 eV), because of mutual effect of extended pi-conjugation and significant electron pulling nature of terminal acceptors. Moreover, higher dipole moment, lower values of hole reorganization energy, and improved V_oc of designed molecules than reference (R) make them efficient donors to enhance PCE of photovoltaic materials.

Exploration of efficient electron acceptors for organic solar cells: rational design of indacenodithiophene based non-fullerene compounds

The global need for renewable sources of energy has compelled researchers to explore new sources and improve the efficiency of the existing technologies. Solar energy is considered to be one of the best options to resolve climate and energy crises because of its long-term stability and pollution free energy production. Herein, we have synthesized a small acceptor compound (TPDR) and have utilized for rational designing of non-fullerene chromophores (TPD1-TPD6) using end-capped manipulation in A2-A1-D-A1-A2 configuration. The quantum chemical study (DFT/TD-DFT) was used to characterize the effect of end group redistribution through frontier molecular orbital (FMO), optical absorption, reorganization energy, open circuit voltage (Voc), photovoltaic properties and intermolecular charge transfer for the designed compounds. FMO data exhibited that TPD5 had the least ΔE (1.71 eV) with highest maximum absorption (λmax) among all compounds due to the four cyano groups as the end-capped acceptor moieties. The reorganization energies of TPD1-TPD6 hinted at credible electron transportation due to the lower values of λe than λh. Furthermore, open circuit voltage (Voc) values showed similar amplitude for all compounds including parent chromophore, except TPD4 and TPD5 compounds. These designed compounds with unique end group acceptors have the potential to be used as novel fabrication materials for energy devices.

Efficient tuning of zinc phthalocyanine-based dyes for dye-sensitized solar cells: a detailed DFT study

The growing energy demand speed up the designing of competent photovoltaic materials. Herein, five zinc phthalocyanine-based donor materials T1–T5 are designed by substituting various groups (isopropoxy, cyano, fluoro, methoxycarbonyl, and dicyanomethyl) around zinc phthalocyanine. B3LYP/6-31G (d,p) level density functional theory (DFT) was used to investigate the optoelectronic properties of five zinc phthalocyanine-based dyes T1–T5 for dye-sensitized solar cells. The designed molecule T1 shows maximum absorption wavelength (λ_max) in the absorption spectrum at 708.89 and 751.88 nm both in gaseous state and in THF (tetrahydrofuran) solvent. The E_g value of T1 (1.86 eV) is less than reference R, indicating a greater charge transfer rate for T1 among the molecules. The values of open-circuit voltages achieved with acceptor polymer PC₇₁BM are higher than R except for T1 and are 0.69 V, 1.95 V, 1.20 V, 1.44 V, and 1.84 V for T1, T2, T3, T4, and T5, respectively. The lower the reorganization energy, the higher the charge transfer for T1 due to its lower hole mobility (0.06297 eV) than R. Thus, the designed T1–T5 molecules are expected to exhibit superior performance in dye-sensitized solar cells.

We used a quantum chemical approach to investigate the optoelectronic properties of dyes T1–T5 for dye-sensitized solar cells using DFT and TD-DFT computation. The newly designed molecules exhibited outstanding photovoltaic and optoelectronic properties.

Theoretical design of D-π-A system new dyes candidate for DSSC application

Currently, dye-sensitized solar cells (DSSCs) are one of the energy technologies that has piqued the interest of researchers, due to their distinct characteristics such as excellent air stability, ease of synthesis and photovoltaic properties interesting. This work aims to study the optoelectronic properties and photovoltaic of six organic dyes based on phenothiazine (PTZ). The effects of bridging core modifications of recently synthesized PSB-4(R) molecule on structural, photovoltaic, electronic, and optical properties of D1-D6 are studied. Using the method Density Functional Theory (DFT) level of the B3LYP (Becke three-parameter Lee-Yang-Parr) exchange correlation functional with 6-31G (d, p) and time-dependent DFT (TD-DFT). According to the obtained results, optoelectronic properties and photovoltaic of the dyes, we can suggest that these designed molecules are better sensitizers as a candidate for the production of dye solar cells (DSSCs). This theoretical study paves the way for chemists to synthesize more efficient sensitizers for applications in dye solar cells.

Evaluating the nature of the vertical excited states of fused-ring electron acceptors using TD-DFT and density-based charge transfer

Acceptor-donor-acceptor structured fused-ring electron acceptors (FREAs) are the most efficient electron acceptors used in organic solar cells. We use density functional theory (DFT), its time-dependent version (TD-DFT), and an intra-molecular charge transfer index to evaluate the nature of the excited states of FREAs. Typically, several efficient electronic transitions contribute to the absorption spectra of FREAs. An investigation of every efficient electronic transition of each FREA is performed based on the electronic density variation in the donor and acceptor moieties of the molecules upon absorbing solar photons. Not all these transitions are equivalent for light-to-electricity conversion. The first transition contributes the most to the absorption spectra. This transition is intense and extremely efficient for light-to-electricity conversion, giving a higher value of intra-molecular charge transfer. For certain effective transitions of FREAs, the phenyl rings in the donor unit behave as the electron-donating units, such as IDT-NTI-2EH, BTCN-M, and MeIC. The foremost finding of the present research work is that the furthermost strong electronic transitions are not essentially the most effective ones for the conversion of sunlight into electricity.

Narrow-energy gap conjugated polymers based on benzobisthiadiazole and thiadiazoloquinoxaline: DFT and TDDFT study

Herein, the HOMO-LUMO energy gaps (Eg) and UV spectra of benzo[1,2-c:4,5-c']bis([1,2,5]thiadiazole (BBT) and [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ)-based donor-acceptor-donor type-conjugated polymers were computed by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) at B3LYP/6-31G(d,p) level. The donor groups consist of thiophene (TH), 3,4-ethylenedioxythiophene (EDOT), and 3,4-propylene dioxythiophene (ProDOT) units and the bisthiadiazole and thiadiazoloquinoxaline were chosen as electron acceptor groups. To examine the effects of the alkyl side chain on the molecular structure and Eg of the polymer, methyl groups were added at the 3,4-, 2,3-, and 3,3-positions of TH, EDOT, and ProDOT donor groups, respectively. Our calculated HOMO-LUMO energy gaps are in the range of 0.05 to 1.37 eV. The calculation results show that the energy gaps are in line with the available experimental values. The novel BBT and TQ derivatives with improved optical and electronic properties may find use in electronic applications. Graphical abstract.

In Silico Modeling of New "Y-Series"-Based Near-Infrared Sensitive Non-Fullerene Acceptors for Efficient Organic Solar Cells

This work was inspired by a previous report [Janjua, M. R. S. A. Inorg. Chem. 2012, 51, 11306-11314] in which the optoelectronic properties were improved with an acceptor bearing heteroaromatic rings. Herein, we have designed four novel Y-series non-fullerene acceptors (NFAs) by end-capped acceptor modifications of a recently synthesized 15% efficient Y21 molecule for better optoelectronic properties and their potential use in solar cell applications. Density functional theory (DFT) along with time-dependent density functional theory (TDDFT) at the B3LYP/6-31G(d,p) level of theory is used to calculate the band gap, exciton binding energy along with transition density matrix (TDM) analysis, reorganizational energy of electrons and holes, and absorption maxima and open-circuit voltage of investigated molecules. In addition, the PM6:YA1 complex is also studied to understand the charge shifting from the donor polymer PM6 to the NFA blend. Results of all parameters suggest that the DA'D electron-deficient core and effective end-capped acceptors in YA1-YA4 molecules form a perfect combination for effective tuning of optoelectronic properties by lowering frontier molecular orbital (FMO) energy levels, reorganization energy, and binding energy and increasing the absorption maximum and open-circuit voltage values in selected molecules (YA1-YA4). The combination of extended conjugation and excellent electron-withdrawing capability of the end-capped acceptor moiety in YA1 makes YA1 an excellent organic solar cell (OSC) candidate owing to promising photovoltaic properties including the lowest energy gap (1.924 eV), smallest electron mobility (λe = 0.0073 eV) and hole mobility (λh = 0.0083 eV), highest λmax values (783.36 nm (in gas) and 715.20 nm (in chloroform) with lowest transition energy values (E x) of 1.58 and 1.73 eV, respectively), and fine open-circuit voltage (V oc = 1.17 V) with respect to HOMOPM6-LUMOacceptor. Moreover, selected molecules are observed to have better photovoltaic properties than Y21, thus paving the way for experimentalists to look for future developments of Y-series-based highly efficient solar cells.

Designing of near-infrared sensitive asymmetric small molecular donors for high-efficiency organic solar cells

Herein, we have designed four small molecular donors (SMDs) with Donor–Acceptor–Acceptor (D–Á–A) backbone having different acceptor units for highly efficient organic solar cells (OSCs). The specific molecular modeling has been made by replacing the additional acceptor unit (A) of recently synthesized TPA-DAA-MDN molecule (R) by employing different highly efficient acceptor units in order to improve the photovoltaic performances of the molecules. A theoretical approach (DFT and TD-DFT) has been applied to investigate the photophysical, opto-electronic and photovoltaic parameters of the designed molecules (DAA1–DAA4) and compared with the reference molecule (R). The red-shifting absorption of SMDs is the most important factor for highly efficient OSCs. Our all formulated molecules showed a red shifted absorption spectrum and also exhibit near IR sensitivity. Acceptor unit modification of R molecule causes reduction in HOMO-LUMO energy gap; therefore, all designed molecules offer better opto-electronic properties as compared to R molecule. A variety of certain critical factors essential for efficient SMDs like frontier molecular orbitals (FMOs), absorption maxima, dipole moment, exciton binding energy along with transition density matrix, excitation energy, open circuit voltages and charge mobilities of (DAA1–DAA4) and R have also been investigated. Generally, low values of reorganizational energy (hole and electron) offer high charge mobility and our all designed molecules are enriched in this aspect. High open circuit voltage values, low excitation energies, large dipole moment values indicate that our designed SMDs are suitable candidates for high-efficiency OSCs. Furthermore, conceptualized molecules are superior and thus are suggested to experimentalist for out-looking future progresses of highly efficient OSCs devices.

Designing Star-Shaped Subphthalocyanine-Based Acceptor Materials with Promising Photovoltaic Parameters for Non-fullerene Solar Cells

Star-shaped three-dimensional (3D) twisted configured acceptors are a type of nonfullerene acceptors (NFAs) which are getting considerable attention of chemists and physicists on account of their promising photovoltaic properties and manifestly promoted the rapid progress of organic solar cells (OSCs). This report describes the peripheral substitution of the recently reported highly efficient 3D star-shaped acceptor compound, STIC, containing a 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) end-capped group and a subphthalocyanine (SubPc) core unit. The 3D star-shaped SubPc-based NFA compound STIC is peripherally substituted with well-known end-capped groups, and six new molecules (S1-S6) are quantum chemically designed and explored using density functional theory (DFT) and time-dependent DFT (TDDFT). Density of states (DOS) analysis, frontier molecular orbital (FMO) analysis, reorganization energies of electrons and holes, open-circuit voltage, transition density matrix (TDM) surface, photophysical characteristics, and charge-transfer analysis of selected molecules (S1-S6) are evaluated with the synthesized reference STIC. The designed molecules are found in the ambience of 2.52-2.27 eV with a reduction in energy gap of up to 0.19 eV compared to R values. The designed molecules S3-S6 showed a red shift in the absorption spectrum in the visible region and broader shift in the range of 605.21-669.38 nm (gas) and 624.34-698.77 (chloroform) than the R phase values of 596.73 nm (gas) and 616.92 nm (chloroform). The open-circuit voltages are found with the values larger than R values in S3-S6 (1.71-1.90 V) and comparable to R in the S1 and S2 molecules. Among all investigated molecules, S5 due to the combination of extended conjugation and electron-withdrawing capability of end-capped acceptor moiety A5 is proven as the best candidate owing to promising photovoltaic properties including the lowest band gap (2.27 eV), smallest λe = 0.00232 eV and λh = 0.00483 eV, highest λmax values of 669.38 nm (in gas) and 698.77 nm (in chloroform), and highest V oc = 1.90 V with respect to HOMOPTB7-Th-LUMOacceptor. Our results suggest that the selected molecules are fine acceptor materials and can be used as electron and/or hole transport materials with excellent photovoltaic properties for OSCs.

Polymerization-induced photothermy: A non-donor-acceptor approach to highly effective near-infrared photothermal conversion nanoparticles

Photothermal conversion nanoagents based on conjugated polymers (CPs) are attracting increasing attention for in vivo disease theranostics and high-performing ones are in urgent pursuit. Herein, we report a new and non-donor-acceptor approach to photothermal conversion CPs that combine several merits including low bandgaps, strong near-infrared absorption, low intersystem crossing rate and non-emissive nature. Three CPs based on 6,7; 6',7'-fused isoindigos (nIIDs), i.e., P2IIDV, P3IIDV and P4IIDV that have optical bandgaps of 1.30, 1.22 and 1.17 eV, respectively, are synthesized. The nanoparticles (NPs) of the CPs in water are prepared via nanocoprecipitation, which are non-fluorescent due to the rapid intramolecular twisting in the CP backbone within NPs, enabling most of the excitation energy flow to generate heat. The photothermal conversion efficiencies of the NPs as measured under irradiation at 808, 880 and 980 nm are 62.4%, 40.5% and 15.8% for P2IIDV, 65.1%, 41.0% and 38.9% for P3IIDV and 71.5%, 48.9% and 41.7% for P4IIDV, which are significantly higher than indocyanine green and many popularly reported photothermal conversion materials. In vivo studies using xenograft 4T1 tumor-bearing mouse model demonstrate that the P4IIDV NPs can serve as a rather effective photothermal conversion nanoagent for enhanced photoacoustic imaging and photothermal therapy of tumors.

Designing indenothiophene-based acceptor materials with efficient photovoltaic parameters for fullerene-free organic solar cells

Non-fullerene small molecular acceptors (NFSMAs) exhibit promising photovoltaic performance which promoted the rapid progress of organic solar cells (OSCs). In this study, an attempt is done to explore indenothiophene-based high-performance small molecular electron acceptors for organic solar cells. We have designed five acceptor molecules (M1-M5) with strong donor moiety indenothiophene linked to five different end-capped group acceptor moieties: diflouro-2-methylene-3-oxo-2,3-dihydroindene-1-ylidene)malononitrile (A1), 1-(dicyanomethylene)-2-methylene-3-oxo-2,3-dihydro-1H-indene-5,6-dicarbonitrile (A2), methyl-6-cyano-3-(dicyanomethylene)-2-methylene-1-oxo-2,3-dihydro-1H-indene-5-carboylate (A3), 2-(6-cyano-5-fluoro-2-methylene-3-oxo-2,3 dihydro-1H-indene-1-ylidene)malononitrile (A4), and (Z)-methyl 3-(benzo [c][1,2,5]thiadiazol-4-yl)-2-cyanoacrylate (A5) respectively. The structure-property relationship was studied and effects of structural modification on the optoelectronic properties of these acceptors (M1-M5) were determined systematically by comparing it with reference molecule R, which is recently reported as excellent non-fullerene-based small acceptor molecule. Among all designed molecules, M5 is proven as a suitable candidate for organic solar cell applications due to better photovoltaic properties including narrow HOMO-LUMO energy gap (2.11 eV), smallest electron mobility (λ_e = 0.0038 eV), highest λ_max values (702.82 nm in gas) and (663.09 nm in chloroform solvent) and highest open-circuit voltage (V_oc = 1.49 V) with respect to HOMO_PTB7-Th-LUMO_acceptor. Our results indicate that introducing more end-capped electron-accepting units is a simple and effective alternative strategy for the design of promising NFSMAs. This theoretical framework also proves that the conceptualized NFSMAs are superior and thus are recommended for the future construction of high-performance organic solar cell devices. Graphical abstract.