Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2025 Apr 14;10(15):14949–14960. doi: 10.1021/acsomega.4c10273

End-Group Modulation in a High Electron Mobility Y-Series Nonfullerene Acceptor Achieved Based on the DFT Method

Zhengli Zhang a,b, Zhao Ding a,b, Xiang Guo a,b, Chen Yang a,b, Yi Wang a,b, Yong Deng a,b, Shaolu Chen a,b, Xuefei Liu c,*, Junli Li a,b,*
PMCID: PMC12019722  PMID: 40290925

Abstract

graphic file with name ao4c10273_0009.jpg

The joining of Y6 has effectively promoted the power conversion efficiency (PCE) of organic solar cells, and the impact of its end-group modification on the PCE is significant. Here, eight different groups are introduced to modify the end-group of Y6, forming eight acceptors named V1, V2, V3, V4, V5, V6, V7, and R. The excited states, light absorption properties, and intermolecular electron transfer are discussed by the density functional theory. The density of state, average local ionization energy, Hirshfeld population, ionization potential, electron affinity, and electron mobility are also calculated. Results show that V7 obtains the largest red-shift in the UV–visible absorption spectra (787.55 nm). V7 and V5 have better electronic coupling while exhibiting the leading electron mobility (0.9577 and 0.4383 cm2 V–1 s–1). Acceptors with rigid skeletons, good planarity, minimal steric hindrance, and locally uniform ALIE distributions have the potential to achieve higher electron mobility. These results indicate that precise end-group engineering can effectively regulate the electron mobility of acceptors, thereby increasing the PCE.

1. Introduction

Organic solar cells (OSCs) have been widely studied due to their advantages such as flexibility, semitransparent, solution processing, and large-area printing, and their power conversion efficiency (PCE) has been continuously improved in recent years.1−4 ITIC5 is one of the earliest high-performance nonfullerene acceptors with a strong absorption in the visible light region. Then, different nonfullerene acceptors based on the ITIC structure appeared one after the other. Y6,6 a new structure, is a prominent nonfullerene acceptor in OSCs with a broad absorption and high charge carrier mobilities. Many high-efficiency nonfullerene acceptors (NFAs) have been derived from the Y-series structure, such as BTP-eC97 and L8-BO.8 The PCE can also be increased via dimer and trimer electron acceptors9,10 or additive engineering.11,12 Y6 and its derivation contribute to very high PCE, and research on the NFA structures of the Y-series remains active until now.13−17 Any fragment of the Y6 could be modified due to its special Y-series structure A-π-D-A’-D-π-A as long as the PCE is promoted.18−23 By these means, the energy levels of NFAs can be greatly influenced by end-group modifications, which can improve alignment with donors and the morphology of the active layer, to enable more effective charge separation and transport.

End-group modified BTP-BO-4FO14 exhibits an upshifted energy level and more sequential crystallinity, reaching a PCE of 18.62% and VOC of 0.993 V. Asymmetric end-group engineering17 can also improve the solubility of nonfullerene acceptors in nonhalogen solvents, resulting in more environmentally friendly and more stable OSCs. Hu et al.24 adjusted the positions of fluorine and chlorine in the end-group to improve the self-assembly properties of the molecules. There is also a study on hybrid end-groups,25 which integrate multiple functional units to balance electronic properties and solubility and enhance PCE. These studies have given the development direction of end-group modification and have improved PCE to some extent. It also provides a research basis and possibility for new end-group modified in Y-series nonfullerene acceptors. However, these are mainly focused on the regulation of energy levels and solubility, and there is still a lack of in-depth research on the impact on electron mobility. Therefore, there is still a need for continued research on end-group modification.

The end-group A of the Y6 is an electron-withdrawing unit that contains highly electronegative cyano- and fluorine groups. Many of its high-efficiency derivatives also retain the cyano-group structure,26 which enhances the internal electron push–pull effect and improves absorption performance. Inspired by the above research, we derived five new structures by adjusting the number and position of the cyano groups in A. The skeletons of these structures tend to exhibit good rigidity and planarity. To obtain a better comparison of results, end-groups with certain spatial structures are also taken into consideration. Thus, three molecules with different spatial structures are proposed. In total, eight acceptors are established in this work, and their structures are shown in Figure 1. The density functional theory (DFT)27 and time-dependent density functional theory (TD-DFT)28 are applied to study the impact of end-group modification on molecular quantum chemical properties, electron mobility, excited states, and other properties of the molecules. The PCEs of the nonfullerene acceptors and the donor PM6 in organic solar cells are also evaluated.29

Figure 1.

Figure 1

Open in a new tab

(a) Model of the Y-series nonfullerene acceptors with an A-π-D-A’-D-π-A structure and the labeling of bond length and dihedral angles. (b) Acceptors’ structure. The A in panel b is replaced by the end-groups in panel d. (c) Correspondence between the eight end-groups (A1–A8) and the eight acceptors (V1–R) formed by their modification. (d) Eight acceptors in this work with the different end-groups of A1–A8.

Specifically, we aim to study the difference in end-group modification at the quantum scale, and the quantum chemical properties are slightly affected.30−32 To get a cheaper calculation, the side chains of these molecules are all made of methane. The acceptor R in this work is the structure of Y6 with an all-methyl side chain. Additionally, we concentrated on new structures modified by end-groups without considering the complexities of molecular structure synthesis.

2. Computation Details

2.1. Basic Computations

All quantum chemical calculations are performed in the software package of Gaussian 16.33 The data postprocessing is in the Multiwfn 3.8,34,35 and the visualizations are based on visual molecular dynamics (VMD),36 and GaussView 6.37 The density of state (DOS) is calculated in GaussSum.38 The structures of the monomers and dimers of the acceptors are optimized at the level of the B3LYP-D3/6-311G(d,p).39−41 It is proven that the functional of B3LYP is suitable for studying the Y-series nonfullene acceptors.42 Thus, the calculations of excited states, absorption spectra, and the preparation data of DOS calculations are performed at the level of the B3LYP/6-311G(d,p). The reorganization energy calculation is completed at the level of M06-2X/def2tzvpp. In the studies of the electron transfer behaviors between donor and acceptor molecules, a monomer unit of the polymer donor PM6 and the acceptor molecules are combined to be dimers. These dimers are optimized at the level of the B3LYP-GD3/6-31G(d,p) due to the entire donor and acceptor system being relatively large; in particular, the basis set is reduced to obtain a converged structure. When calculating charge transfer between donor and acceptor, the B3LYP/6-311G(d,p) level is used. All calculations incorporated the polarizable continuum model (PCM).43−46

2.2. Calculation of Electron Mobility

The fact that π–π stacking is an efficient way of electron transportation is taken into consideration.47,48 In this work, the initial structures of the acceptor dimers are artificially constructed with face-to-face stacking of the monomer structures with a distance of 3.5 Å when calculating the electron mobility. The electron mobility is calculated based on the Einstein–Smoluchowski equation, with the carrier rate constant described using the semiclassical Marcus theory49,50 and electron coupling determined via Koopman’s theorem.

The electron mobility of the acceptors is calculated using eq 1:

2.2. 1

where e is the elementary charge, kB is the Boltzmann constant, T is the temperature, and D is the diffusion coefficient, which is determined using eq 2:

2.2. 2

where r represents the centroid distance between the two molecules in the acceptor dimer, which denotes the average distance for charge transfer. k is the electron transfer rate constant, which can be calculated according to eq 3 (the change of Gibbs free energy is ignored):

2.2. 3

where ℏ is the reduced Planck constant and VDA is the electronic coupling constant, which is calculated according to eq 4:

2.2. 4

where ELUMO+1 and ELUMO represent the LUMO + 1 and LUMO energy levels of the acceptor dimer, respectively.

2.2. 5

λ is the reorganization energy of the acceptor, which equals the sum of the internal and external reorganization energies. Since the two acceptor particles involved in electron transport do not carry opposite charges, this calculation of the internal reorganization energy uses the structures of the monomers. Considering that the external reorganization energy depends on solvent effects, the optical dielectric constant of the constructed molecules is difficult to obtain, and the external reorganization energy is relatively small compared to the internal reorganization energy,51,52 the effect of the external reorganization energy is ignored in this work. The internal reorganization energy is determined using eq 5. In eq 5, E0A–, E0A0, E–A0, and E–A– represent the energy difference of the neutral in the anionic structure, the neutral in the neutral structure, the anion in the neutral structure, and the anion in the anionic structure, respectively.

2.3. The Evaluation of the Photovoltaic Parameter

The photovoltaic parameters directly reflect the degree of combination and connection between the donor and acceptor materials. Using PM6 as the donor, the photovoltaic parameter PCE is estimated through the following methods,29 thereby quantitatively describing the photovoltaic performance of these acceptor molecules.

2.3. 6

JSC is the short-circuit current density, FF is the fill factor, and VOC is the open-circuit voltage. They are determined by eqs 7, 8, and 9, respectively. Pin represents the incident light power, which remains constant under identical conditions.

2.3. 7

ELUMOA and EHOMOD represent the LUMO energy level of the acceptor material and the HOMO energy level of the donor material, respectively. Particularly, eq 7 is an empirical estimation of the VOC in fullerene-based OSCs used in this paper. The latest findings on VOC in NFA-based OSCs can be referenced in the research of Zhan’s group.53

2.3. 8

V is the normalized value of VOC, which is denoted as eVOC/(kBT),

2.3. 9

ϕinj is the effectiveness of electron injection, and ηcol is the efficiency of charge collection.

Light harvest efficiency (LHE) can be determined using eq 10, where f is the oscillator strength.

2.3. 10

3. Results and Discussion

3.1. The Optimization of Ground-State Geometries

Figure 1a is the schematic diagram of the A-π-D-A’-D-π-A structure of the Y-series acceptor. θ is the dihedral angle composed of C1, C2, C3, and C4 at the corresponding positions in Figure 1a, which is used to characterize the planarity, a crucial factor for π–π stacking interactions in organic solar cells, of the acceptors.54 The letter d in Figure 1a represents the distance between the two carbon atoms: C3 and C4. Figure 1b shows the acceptor’s structure used in this work, where A represents the end-group of the acceptors. It is replaced by the structures in Figure 1c, thus forming V1, V2, V3, V4, V5, V6, V7, and R.

The data of the specified dihedral angles and C–C bond length of the optimized V1–R acceptors are listed in Table 1, and the structures are collected in Figure S1. It is shown that V5 (1.576°) and V1 (1.465°) have the largest and second-largest dihedral angles, respectively, indicating that these molecules are relatively less planar. This affected the planarity and may decrease their π–π stacking efficiency, negatively impacting their electronic properties. In contrast, the dihedral angles of V6 (0.135°), V3 (0.179°), R (0.203°), and V7 (0.290°) are all below 0.3°, exhibiting the small dihedral angles and the highly planar structures. A better stacking is possible due to the planar structure, which raises the prospect of improved charge mobility. Regarding C–C bond lengths, these molecules display bond lengths ranging from 1.4005 Å (V7) to 1.4086 Å (V1), which are typical for conjugated bonds. V7, with the shortest bond length, indicates the strongest conjugation, potentially resulting in a higher intramolecular charge transfer. Smaller dihedral angles indicate better planar structures, enhance conjugation, and facilitate charge transport. Generally, these molecules have a very rigid and planar structure due to their low dihedral angles and excellent C–C conjugated bonds, making them potentially suitable nonfullerene acceptors for OSCs.

Table 1. Selected C–C Bond length and Dihedral Angles of All Molecules.

acceptors dihedral angle (°) bond length (Å)
V1 1.465 1.4086
V2 0.434 1.4047
V3 0.179 1.4039
V4 0.679 1.4068
V5 1.576 1.4085
V6 0.135 1.4050
V7 0.290 1.4005
R 0.203 1.4048
Open in a new tab

3.2. Frontier Molecular Orbitals

The FMOs include the HOMO and LUMO, and the energy difference between them is the band gap (Eg). Effective exciton separation is a key course of OSCs, and the process will be affected by the FMOs of the donor and acceptor. Moreover, the VOC of the device could be affected by the FMOs.

The HOMO and LUMO energies of V1–R are shown in Figure 2a and Table S1. Their values of Eg indicated by the red squares range from 1.735 to 2.039 eV, and the order from narrowest to widest is V3 < V7 < V6 < V2 < R < V4 < V1 < V5. The energy level of the LUMO ranges from −3.987 to −3.262 eV. The order from lowest to highest is V3 < V7 < V2 < R < V6 < V4 < V1 < V5. V3 has the narrowest band gap and the lowest LUMO, and V5 has the widest Eg and highest LUMO. This may be attributed to the greater number of cyano-groups and fluorine atoms on the consecutive rings in the V3′s terminal part, which possesses strong electron-attracting abilities. These results suggest that V3′s electron excitation is more favorable for undergoing intramolecular electron transfer and it is relatively weak in V5. V3 and V7 will have better light absorption capabilities, and V5, V1, and V4, with their relatively high Eg and LUMO, are likely to be better acceptor candidates for increasing the VOC of OSCs. The total oscillator strength of molecules in the range of 380–1000 nm and their absorption peaks of V1–R are shown in Figure 2b. These data serve as a quantitative result of the total absorption intensity of these molecules in the visible and near-infrared range. It indicates that V1, V2, V3, V6, and V7 all have a higher total oscillator strength than R. This provides some possibility for them to become highly efficient acceptor molecules.

Figure 2.

Figure 2

Open in a new tab

(a) The energy of the FMOs and the Eg of V1–R. (b) The total oscillator strength of molecules in the range of 380–1000 nm and their absorption peaks.

Figure 3 shows the FMOs of the molecules. The electron density in the HOMO is concentrated in the midpart of the molecules, while the LUMO has a greater distribution in the end-groups. This distribution facilitates charge transfer, with V3 standing out the most. V7 has a similar distribution to that of V3, though less pronounced, possibly due to the unfocused cyano-groups in V7 dispersing the push–pull effect of electrons within the molecule. In contrast, the electron density in the LUMO of molecules with spatial structural end-groups (V1, V4, and V5) does not extend fully to the terminal part. This could be caused by their spatial rings lacking atoms or groups with strong electron-attracting abilities.

Figure 3.

Figure 3

Open in a new tab

(a–h) The shape of the FMOs for V1–R, respectively. Isovalue = 0.01.

3.3. Density of States

The evaluation of the DOS diagrams can effectively assist in understanding the distribution of HOMO and LUMO. The DOS diagrams are shown in Figure 4, and the quantitative contributions of each part of the molecules to the electron density of the HOMO and LUMO are listed in Table 2. Each part of the molecules in Table 2 is shown in Figure S2, and parts D and A refer to the donor part (electron-deficient groups) and the acceptor part (electron-rich groups) in the molecule, respectively. Part D has more contribution to HOMO, while part A has a greater contribution to LUMO, which is often expected, forming an effective electron separation. These results confirm that the primary contribution to the HOMO comes from the core part of the molecules. For the LUMO, even the acceptor with the smallest terminal part contribution, V5, shows that the terminal part’s contribution is greater than that of the core. Specifically, the contributions from part A to LUMO and D to HOMO are 96.682 and 71.387%, respectively, realizing the most effective electron separation. These findings suggest that charge transfer of the V1–V7 occurs efficiently from the core to the acceptor groups.

Figure 4.

Figure 4

Open in a new tab

(a–h) The DOS diagrams of V1–R, respectively.

Table 2. Contribution of Each Part of the Molecules to the Electron Density of the HOMO and LUMO.

molecules contribution of D to HOMO contribution of A to HOMO contribution of B to HOMO contribution of D to LUMO contribution of A to LUMO contribution of B to LUMO
V1 73.072% 25.810% 1.119% 40.031% 43.343% 16.626%
V2 71.812% 26.723% 1.465% 38.375% 45.047% 16.578%
V3 71.387% 27.091% 1.522% 2.053% 96.682% 1.265%
V4 72.568% 26.158% 1.275% 39.565% 43.592% 16.812%
V5 72.933% 25.946% 1.121% 40.043% 43.298% 16.659%
V6 69.657% 29.093% 1.249% 36.967% 45.999% 17.034%
V7 69.133% 29.059% 1.809% 35.814% 47.423% 16.763%
R 72.153% 26.362% 1.486% 39.79% 43.149% 17.061%
Open in a new tab

As shown in Table 2, after the molecule is matched with different end-groups, the contribution value of part D with the same structure in all molecules to their HOMO changes and the contribution value of part A to the LUMO are also different and shows a greater difference. From the perspective of molecular structure, the end-groups of V1, V4, V5, and V6 do not contain strongly electronegative groups or atoms. Except for molecule V6, the end-groups of these molecules all have a certain spatial structure, and the contribution of their part A to LUMO is around 43%. On the contrary, V2, V3, and V7 containing cyano-groups and fluorine groups in the terminal structure all exceed 45%, indicating the electron push–pull effect inside is more obvious. Among them, the contribution of part A in V3 to LUMO is very high, reaching 96.682%, followed by V7, reaching 47.423%. This may be because the cyano-group arrangement position in the terminal part of V3 is concentrated and a stronger negative center is formed. These results indicate that a higher electron-withdrawing ability of part A of the acceptors contributes to improved electron distribution.

3.4. Average Local Ionization Energy and Hirshfeld Population

The average local ionization energy (ALIE)55 represents the average energy required to remove an electron from a specific region within a molecule and can characterize charge transfer behavior and transport properties to some extent. Figure 5 presents the ALIE visual maps for eight end-groups, where the color gradient transitions from blue to white and then to red, indicating increasing energy levels, with the deepest blue corresponding to 0.25 au (6.80 eV) and the deepest red to 0.48 au (12.96 eV). Within panels a–h, metallic luster-coated light blue spheres denote the points of local minimum ALIE. It can be observed in panels a, d, and e of Figure 5 that the spatially structured end-groups A1, A4, and A5 all exhibit areas with deeper blue tones located at the spatial ring structures at their ends. This indicates that the spatial ring structures have a weaker hold on electrons, which may localize more easily within the group but not necessarily delocalize between molecules. The most profound blue in A4 suggests that the sulfur atom at this position has the weakest electron constraint, resulting in the most pronounced characteristic of internal localization behavior of nearby electrons. In contrast, the rigid planar end-groups (including panels b, c, f, g, and h in Figure 5) A2, A3, A6, A7, and A8 possess a lower spatial hindrance and a relatively uniform distribution of ALIE positions. This allows them to benefit from electronic structural boosts at the acceptor molecular level rather than the end-group level, facilitating potential intermolecular delocalization of electrons under face-on molecular stacking modes. The specific ALIE values for these end-groups are listed in Table S2. The order of the ALIE values from the minimum to maximum is as follows: A7 < A6 < A5 < A1 < A8 < A3 < A2 < A4. This ranking also can be used as a measure of how easily the electron distribution can be localized on these end-groups.

Figure 5.

Figure 5

Open in a new tab

(a–h) The average local ionization energy of the end-groups A1–R, respectively.

The result of Hirshfeld population56 is qualitatively consistent with the electronegativity rule and insensitive to the quality of wave function. The Hirshfeld population across atoms is shown in Figure S6. It is a color gradient scheme with quantitative charge values labeled (blue indicates positive charges, and red indicates negative charges). It reveals that negative charges are located on the nitrogen atoms of the cyano-groups, the oxygen atoms of the carbonyl groups, the sulfur atoms of the thiocarbonyl groups, and near fluorine atoms. Atoms within the rings exhibit similar Hirshfeld charge values. The calculated end-group dipole moments and molecular dipole moments are listed in Table S4. According to the table, the end-group dipole moments rank from smallest to largest as follows: A7 < A8 < A4 < A2 < A3 < A5 < A1 < A6. For molecular dipole moments, the order is V4 < V2 < R < V3 < V5 < V1 < V6 < V7. The distribution of Hirshfeld charges can influence the molecular dipole moment, which in turn can alter intermolecular interactions and thereby affect electron mobility. Notably, while end-group A7 has the smallest group dipole moment, the V7 molecule, which features A7 as an end-group, exhibits the largest molecular dipole moment. This promotes the formation of charge transfer pathways between molecules. From the Hirshfeld population, the area with a higher negative charge of A7 is around the edge of it, showing the most uniform distribution and rich π electron cloud density. This distribution does not interfere with the charge transfer path between molecules, which helps to maintain good molecular stacking and charge transport. In general, a larger molecular dipole moment, more uniform end-group Hirshfeld population and ALIE, and smaller end-group steric hindrance can promote effective π–π stacking, making it difficult for electrons to localize in certain areas within the molecule but instead providing better conditions for their delocalization between molecules.

3.5. Ionization Potential and Electron Affinity

The ionization potential (IP) and electron affinity (EA) are fundamental electronic characteristics that describe the intrinsic capability of a molecule to lose or acquire an electron, respectively. Such properties play a critical role in determining the electronic behavior of materials and can indirectly impact the electron mobility within organic solar cells. Based on the following eqs 11 and 12, the IP and EA values of these acceptors V1 to R are calculated, and the resultant values are summarized in Table S5.

3.5. 11
3.5. 12

In eqs 11 and 12, E+A+, E0A0, and E–A– represent the energy difference of the cations in cationic structures, the anion in the neutral structure, and the anion in the anionic structure, respectively. From the data listed in Table S5, the IP values range from 5.956 eV for V5 to 6.225 eV for V7, with a difference of 0.269 eV. The values are ranked in ascending order as follows: V5 < V1 < V4 < V6 < R < V2 < V3 < V7. For EA, the range is from 3.256 eV for V1 to 3.759 eV for V7, with a difference of 0.503 eV, and they are ordered as V1 < V5 < V4 < R < V6 < V2 < V3 < V7. Overall, molecules with spatially structured end-groups exhibit lower IP and EA values (V1, V4, and V5). This suggests that these molecules have a weaker hold on electrons and can easily accept electrons. Molecules with lower IP values, such as V1, V4, and V5, may contribute to a higher ratio of hole to electron mobility (μh/μe) in blend films due to their facilitation of hole transport. Conversely, molecules with higher EA values, such as V7 and V3, favor electron migration, potentially leading to higher electron mobility and thus a greater μe/μh ratio. Molecules with moderate IP and EA values, such as V2 and R, tend to achieve balanced transport performance. Specifically, the differences in IP between these molecules are relatively small, but lower IP and higher EA are all beneficial for electron transport.

3.6. Absorption Properties

Excitons are generated after the donor–acceptor blend film in the active layer absorbs photons. Excitons diffuse to the donor–acceptor interface and separate under the energy difference of the donor and acceptor, creating a free carrier that may be gathered and employed in solar cells. Therefore, the absorption of light by the donor and acceptor is significant. Based on the optimized ground-state geometry in Section 3.1, the first 50 excited states of V1–R are calculated by TD-DFT to explore their absorption properties further. The excited state with the maximum oscillator strength is focused on, as it provides the absorption peak (λmax values). The UV–visible spectra of all molecules in the solvent xylene are obtained and are plotted in Figure 6. To show more details of the absorption spectrum, the spectra of V1–V4 and V5–R are plotted separately in panels a and b. Details of the excited states are given in Table S1.

Figure 6.

Figure 6

Open in a new tab

(a) UV–visible absorption spectra in the xylene including acceptors V1, V2, V3, and V4. (b) UV–visible absorption spectra in the xylene including acceptors V5, V6, V7, and R.

As can be seen, the spectrum of V7 with the concentrated cyano-group in the end-groups achieved the max redshift, and its absorption peak is 787.55 nm. It is 57.55 nm larger than that of R (730 nm). The absorption peak closest to the blue light region is for V1. The order of absorption peaks of all molecules from low to high is V1 < V5 < V4 < R < V2 < V3 < V6 < V7. From a structural point of view, the three molecules with the smallest absorption peaks, V1, V5, and V4, are all end-groups with a spatial structure, and their ends do not contain strongly electronegative groups or atoms. Moreover, the details in Table S1 show that the absorption peak of V5 (with the six-ring in the end group) is red-shifted compared to V1 (with the five-ring in the end group), and the absorption peak of V4 (with the five-ring containing sulfur atoms) is red-shifted compared to V5. This shows that it is easier for the six-ring than the five-ring in the end-group to absorb longer wavelength waves, and sulfur atoms also contribute to the red shift of the absorption peak. In addition, V3 and V7 are the opposite. Their ends contain cyano-groups and fluorine groups, and the flatness of their end-groups tends to be high. They all have good long-wavelength light absorption capabilities. V6 also has better light absorption, probably due to the anthracene on its ends. Adding aromatic polycyclic structures to the end-groups can effectively enhance the absorption of red shift. The structural differences of these end-groups are also the fundamental reason for the differences in their ALIE and electronegativities, as shown in Section 3.4. These indicate that the absorption peak can be controlled through end-groups with their different electronegativities and structural features.

3.7. Molecular Electrostatic Potential

The study of the molecular electrostatic potential (MESP) could help investigate the charge transfer and its reactivity of specific compounds. MESP topology investigations can provide strong predictions on the intermolecular interaction behavior of molecular systems.57,58 Areas with low and high electrostatic potentials can be distinguished with color coding. The MESP maps of the eight molecules are shown in Figure 7 using a color scale where red and blue represent the minimum and maximum potentials (−7e – 2 and 7e – 2, respectively), and green indicates neutral charge sites. As depicted in Figure 7, overall, the positive centers of all molecules are similarly positioned, primarily located in the central core. The negative centers are concentrated near the cyano-groups, carbonyl groups, and sulfur atoms. Among the molecules, V3 has the strongest and most concentrated negative center. These electron-deficient areas are more vulnerable to attack by electrophiles. In contrast, the negative charge center of V4 is relatively dispersed. This difference is due to the proximity of the two cyano-groups in V3′s acceptor part, enhancing the electron-withdrawing ability of the end-group, while in V4, the electron-withdrawing groups are more dispersed. The green areas in V2, V3, and R are relatively uniform, which indicates that they have more distinct positive and negative centers. Therefore, it is easier to connect with other molecules through weak interactions at the central core and end-groups of these molecules.

Figure 7.

Figure 7

Open in a new tab

MESP maps of all molecules (a–h) correspond to V1–R, respectively. Isovalue (MO = 0.01, density = 0.001). The red refers to the negative charge center, and the blue refers to the positive charge center.

3.8. Electron Mobility

Electron mobility is an important tool to evaluate the efficiency of a photovoltaic cell. It is one of the key parameters for characterizing the transport properties of acceptors. The electron mobility was calculated using eqs 1 to 5, and the values are presented in Table 3. The electron mobility values range from 0.0028 to 0.9577 cm2 V–1 s–1, indicating that all studied molecules are effective electron transport materials. The order of electron mobility is V4 < V3 < V1 < V2 < R < V6 < V5 < V7. V7 and V5 dimers have electronic couplings of 0.0580 and 0.0491 eV, respectively. They are larger than V3 (0.057 eV) and V4 (0.0037 eV). Figure S3 illustrates the optimized stacking morphology of all dimers, showing that their stacking involves some lateral movement and rotation due to intermolecular interactions. This variation in stacking contributes to differences in the electronic coupling. Figures S4 and S5 show the HOMO and LUMO of all dimers in two different views. The results indicate that electron transfer between dimers mainly occurs between LUMOs, with backbone overlaps mostly happening between the adjacent end-groups.

Table 3. Values of the Reorganization Energy λ (the Energy of the Molecule as Its Structure Changes from Neutral to Anion), the Electronic Coupling VDA, the Centroid Distance of the Dimer r, the Charge Transfer Rate Constant k, the Charge Diffusion Coefficient D, and the Electron Mobility μ.

molecule λ (eV) VDA (eV) r (Å) k (S–1) D (S–1 Å2) μ (cm2 V–1 S–1)
V1 0.2078 0.0180 4.257 1.59 × 1012 1.44 × 10–3 0.0558
V2 0.1786 0.0264 3.559 4.94 × 1012 3.13 × 10–3 0.1208
V3 0.1828 0.0057 3.625 2.21 × 1011 1.46 × 10–4 0.0056
V4 0.1990 0.0037 4.411 7.48 × 1010 7.28 × 10–5 0.0028
V5 0.2074 0.0491 4.357 1.20 × 1013 1.13 × 10–2 0.4383
V6 0.1599 0.0328 3.668 9.62 × 1012 6.47 × 10–3 0.2499
V7 0.1342 0.0580 3.433 4.21 × 1013 2.48 × 10–2 0.9577
R 0.2054 0.0350 3.571 6.23 × 1012 3.97 × 10–3 0.1534
Open in a new tab

V7 exhibits the best electron transfer due to its lower value of reorganization energy λ compared to that of the others and its relatively flat structure, attributed to its excellent FMO charge integral. This is likely because V7 dimers achieve more flexibility and stronger π–π stacking of backbones. Molecules with spatially structured end-groups (V1, V4, and V5) exhibit relatively large reorganization energies. For V4, the notably lower ALIE near the sulfur atom at the end-group may lead to a pronounced electron push–pull effect within the end-group. This makes electrons more prone to localize within the end-group rather than delocalize between molecules, which could be the reason for its significantly reduced electronic coupling, resulting in the lowest mobility of V4. Conversely, V5 benefits from a lower IP and an appropriate ALIE distribution, leading to enhanced electronic coupling and improved electron transport capability. The strong electron-withdrawing characteristics of the end-group in V3 result in excellent HOMO–LUMO separation but also cause uneven charge distribution, affecting the FMOs and drastically reducing electronic coupling, thereby leading to a smaller mobility. On the other hand, V6 shares minimal steric hindrance, similar molecular planarity, and uniformity in ALIE distribution with V7, along with a high EA. These features contribute to favorable electronic coupling, granting V6 the third-highest electron mobility. Molecules V1, V2, and R possess moderate reorganization energies, electronic couplings, and intermolecular distances, placing their electron mobilities at intermediate levels. In summary, acceptors with rigid skeletons, good planarity, minimal steric hindrance, low IP, high EA, and locally uniform ALIE distributions have the potential to achieve higher electron mobility.

3.9. Electron Transfer at PM6-Acceptor Interface

The PCE of OSCs is significantly influenced by the degree of exciton separation and electron transfer at the donor–acceptor interface in the active layer. Figure 8 shows the transition density matrix (TDM) maps for the excited state with the strongest oscillator strength during excitation. The TDM maps use a color intensity scale from deep blue (0.00) to red (0.70) to represent electronic transition density. The number 1 in panels a–h in Figure 8 refers to the donor PM6, while 2 in panels a–h represent the acceptors V1–R, respectively. High-intensity colors (green, yellow, and red) in the upper left (1, 2) and lower right (2, 1) indicate strong interactions between PM6 and acceptors, which are crucial for effective charge transfer. The lower left (1, 1) and the upper right (2, 2) represent the internal excitation of the donors and the acceptors, respectively.

Figure 8.

Figure 8

Open in a new tab

Transition density matrix (TDM) map of all donor–acceptor compounds (1 in panels a–h refers to the donor PM6, and 2 in panels a–h refers to the acceptors V1–R that are designed in this work, respectively).

As can be seen from the color of the upper left grid (1, 2) in Figure 8, PM6-V4 and PM6-R are both very dark blue followed by PM6-V2, PM6-V5, and PM6-V6 are that lighter blue, PM6-V3 and PM6-V7 are green, and the closest to red is PM6-V1. This also represents the order of measurement of the intensity of electron transfer between PM6 and various acceptors. Table 4 provides a quantitative overview of the electronic transfer between donor–acceptor composite structures. It shows that, except for PM6-V3, the strongest oscillator strength for excitation occurs in the second excited state. The intermolecular electron transfer ratios, ranked from highest to lowest, are as follows: PM6-V1 > PM6-V3 > PM6-V7 > PM6-V5 > PM6-V2 > PM6-V6 > PM6-R > PM6-V4. Interactions between PM6 and acceptors V1, V3, and V7 show moderate transition densities, suggesting reasonable compatibility and potential charge transfer efficiency. The excitation oscillator strengths of these designed molecules, when combined with PM6, are generally weaker compared to those of the individual acceptor molecules. Moreover, significant differences are observed between the composite structures. This disparity may arise from the complex stacking interactions at the donor–acceptor interface in the dimers.

Table 4. Relevant Parameters at the Absorption Peaks of the Donor–Acceptor compounds.

donor–acceptor compounds excited state λm(nm) f transfer ratio
PM6-V1 2 732.36 0.7372 50.60%
PM6-V2 2 767.00 1.4847 27.40%
PM6-V3 7 759.65 0.9386 39.90%
PM6-V4 2 738.29 1.8303 <5%
PM6-V5 2 728.32 1.5574 27.60%
PM6-V6 2 770.52 1.5866 25.50%
PM6-V7 2 812.68 1.0252 36.60%
PM6-R 2 757.66 1.9253 <5%
Open in a new tab

It can also be seen from the color in the upper right corner of Figure 8 that in addition to the strong interaction between the donor and the acceptor in the dimers, there are also varying degrees of excitation within the acceptor. Among them, PM6-V2 and PM6-V5 are the strongest. More molecule fragments are divided into dimers, as shown in Figure S7, to further study the complex electron transfer process and the differences in electron transfer among several acceptors. The transfer matrix heat map is plotted in Figure S8. It can be seen from the figure that V4 and R, which have the weakest intermolecular electron transfer, have undergone strong intramolecular electron transfer inside the receptor (the color of the box (4, 4) has reached deep red). The transfer heat map reveals that electron transfer primarily occurs through the core part of the acceptor molecules, eventually moving to the end-groups. Figure S8d shows substantial charge density in both the core and end-groups of the V4 acceptor, likely due to the molecule’s weak oscillator strength and relatively low electron mobility. Figure S9 indicates the electron transfer and oscillator strength between the first 20 excited states of the donor and acceptor dimers.

To optimize device performance, it is crucial to not only have well-performing individual molecules but also ensure appropriate matching with the donor material. Addressing weak intermolecular interactions and achieving optimal donor–acceptor stacking and morphology are key strategies for enhancing the device efficiency.

4. Conclusions

In this work, the impact of the end-group modulation on Y-series nonfullerene acceptors in OSCs is investigated through the DFT and TD-DFT methods. The photovoltaic parameters of their composite systems with donor PM6 are also evaluated. The flatness of monomers and tighter acceptor dimer stacking (V7) can obtain better electron coupling and thus more possibilities for improving the electron mobility. Molecules with concentrated positive and negative charge centers exhibit a strong push–pull effect of electrons within the molecule, which can cause the molecule to obtain more red-shifted absorption peaks. V1, V4, and V5 with spatially structured end-groups can effectively complement the light absorption in the area of the shorter wavelengths. It suggests that careful modification of end-groups might improve electron mobility and light absorption and hence the overall PCE of OSCs.

Acknowledgments

The work was supported by the National Natural Science Foundation of China (NSFC grant no. 62065003) and Functional Materials and Devices Technology Innovation Team of Guizhou Province University, Qian Jiaoji ([2023]058).

Data Availability Statement

The data (the structures of the acceptors and the acceptor dimers) that support the findings of this study are available from https://github.com/ZhengliZhang/OSCs/tree/Structure_V1-R

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.4c10273.

  • Additional figures and tables as mentioned in the text, including structural optimization diagrams of acceptor monomers and dimers, frontier molecular orbital diagrams of acceptor dimers, Hirshfeld population of end-groups, fragment segmentation diagrams, the TDM heat map of donor–acceptor fragment, the first 20 excited-state electron transfers and oscillator strengths of donor–acceptor dimers, DOS diagrams of acceptors and typical interface materials PDIN, the data tables of quantum chemistry calculations of acceptors, ALIE data tables of end-groups and acceptors, dipole moment data tables of end-groups, and IP and EA data tables of acceptors, and additional description and analysis of the results (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao4c10273_si_001.pdf (2.4MB, pdf)

References

  1. Yu H.; Wang J.; Zhou Q.; Qin J.; Wang Y.; Lu X.; Cheng P. Semi-transparent organic photovoltaics. Chem. Soc. Rev. 2023, 52 (13), 4132–4148. 10.1039/D3CS00233K. [DOI] [PubMed] [Google Scholar]
  2. Li Y.; Wang J.; Yan C.; Zhang S.; Cui N.; Liu Y.; Li G.; Cheng P. Optical and electrical losses in semitransparent organic photovoltaics. Joule 2024, 8 (2), 527–541. 10.1016/j.joule.2023.12.011. [DOI] [Google Scholar]
  3. Yan X.; Wang J.; He W.; Dela Peña T. A.; Zhu C.; Yu H.; Hu Y.; Yan C.; Ren S.; Chen X.; Wang Z.; Wu J.; Li M.; Xia J.; Meng L.; Lu S.; Zhao D.; Artemyev M.; Li Y.; Cheng P. Semitransparent organic photovoltaics enabled by transparent p-type inorganic semiconductor and near-infrared acceptor. J. Energy Chem. 2024, 96, 351–358. 10.1016/j.jechem.2024.05.008. [DOI] [Google Scholar]
  4. Wu J.; Gao M.; Chai Y.; Liu P.; Zhang B.; Liu J.; Ye L. Towards a bright future: The versatile applications of organic solar cells. Materials Reports: Energy 2021, 1 (4), 100062 10.1016/j.matre.2021.100062. [DOI] [Google Scholar]
  5. Lin Y.; Wang J.; Zhang Z. G.; Bai H.; Li Y.; Zhu D.; Zhan X. An electron acceptor challenging fullerenes for efficient polymer solar cells. Adv. Mater. 2015, 27 (7), 1170–1174. 10.1002/adma.201404317. [DOI] [PubMed] [Google Scholar]
  6. Yuan J.; Zhang Y.; Zhou L.; Zhang G.; Yip H.-L.; Lau T.-K.; Lu X.; Zhu C.; Peng H.; Johnson P. A.; et al. Single-Junction Organic Solar Cell with over 15% Efficiency Using Fused-Ring Acceptor with Electron-Deficient Core. Joule 2019, 3 (4), 1140–1151. 10.1016/j.joule.2019.01.004. [DOI] [Google Scholar]
  7. Cui Y.; Yao H.; Zhang J.; Xian K.; Zhang T.; Hong L.; Wang Y.; Xu Y.; Ma K.; An C.; He C.; Wei Z.; Gao F.; Hou J.; et al. Single-Junction Organic Photovoltaic Cells with Approaching 18% Efficiency. Adv. Mater. 2020, 32 (19), 1908205. 10.1002/adma.201908205. [DOI] [PubMed] [Google Scholar]
  8. Li C.; Zhou J.; Song J.; Xu J.; Zhang H.; Zhang X.; Guo J.; Zhu L.; Wei D.; Han G.; et al. Non-fullerene acceptors with branched side chains and improved molecular packing to exceed 18% efficiency in organic solar cells. Nat. Energy 2021, 6 (6), 605–613. 10.1038/s41560-021-00820-x. [DOI] [Google Scholar]
  9. Li Y.; Ge Z.; Mei L.; Ma H.; Chen Y.; Wang X.; Yu J.; Lu G.; Yang R.; Chen X.; Yin S.; Sun Y.; et al. Isomeric Dimer Acceptors for Stable Organic Solar Cells with over 19% Efficiency. Angew. Chem., Int. Ed. 2024, 63 (50), e202411044 10.1002/anie.202411044. [DOI] [PubMed] [Google Scholar]
  10. Zhou W.; Liu J.; Xie J.; You S.; Deng J.; Yu F.; Jeong S. Y.; Woo H. Y.; Wu F.; Chen L. Non-Fused Star-Shape Giant Trimer Electron Acceptors for Organic Solar Cells with Efficiency over 19%. Angew. Chem., Int. Ed. 2025, 10.1002/anie.202415141. [DOI] [PubMed] [Google Scholar]
  11. Han C.; Cheng B.; Guo Q.; Fu Z.; Qiao J.; Cheng S.; Huo Y.; Xia X.; Wang H.; Fu Y.; et al. A Halogen-free and Universally Volatile Solid Additive Enables Binary Organic Solar Cells to Exceed 19% Efficiency. Adv. Funct. Mater. 2025, 10.1002/adfm.202416381. [DOI] [Google Scholar]
  12. Mei L.; Xia X.; Sun R.; Pan Y.; Min J.; Lu X.; Jen A. K.; Chen X. Molecular-Level Insight into Impact of Additives on Film Formation and Molecular Packing in Y6-based Organic Solar Cells. Small 2024, 20 (10), 2305977. 10.1002/smll.202305977. [DOI] [PubMed] [Google Scholar]
  13. Zhang C.; Zheng R.; Huang H.; Ran G.; Liu W.; Chen Q.; Wu B.; Wang H.; Luo Z.; Zhang W.; Ma W.; Bo Z.; Yang C.; et al. High-Performance Ternary Organic Solar Cells with Enhanced Luminescence Efficiency and Miscibility Enabled by Two Compatible Acceptors. Adv. Energy Mater. 2024, 14 (12), 2303756. 10.1002/aenm.202303756. [DOI] [Google Scholar]
  14. Wu W.; Zou B.; Ma R.; Yao J.; Li C.; Luo Z.; Xie B.; Qammar M.; Dela Peña T. A.; Li M.; Wu J.; Yang C.; Fan Q.; Ma W.; Li G.; Yan H.; et al. A Difluoro-Methoxylated Ending-Group Asymmetric Small Molecule Acceptor Lead Efficient Binary Organic Photovoltaic Blend. Small 2024, 20 (37), 2402793. 10.1002/smll.202402793. [DOI] [PubMed] [Google Scholar]
  15. Wu H.; Lu H.; Li Y.; Zhou X.; Zhou G.; Pan H.; Wu H.; Feng X.; Liu F.; Vandewal K.; Tress W.; Ma Z.; Bo Z.; Tang Z.; et al. Decreasing exciton dissociation rates for reduced voltage losses in organic solar cells. Nat. Commun. 2024, 15 (1), 2693. 10.1038/s41467-024-46797-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Lin C.; Peng R.; Song W.; Chen Z.; Feng T.; Sun D.; Bai Y.; Ge Z. Multi-component Copolymerized Donors enable Frozen Nano-morphology and Superior Ductility for Efficient Binary Organic Solar Cells. Angew. Chem., Int. Ed. 2024, 63 (31), e202407040 10.1002/anie.202407040. [DOI] [PubMed] [Google Scholar]
  17. Gopikrishna P.; Choi H.; Kim D. H.; Lee D.; Hwang J. H.; Jin S.; Lee E.; Cho S.; Kim B. Halogenated 9H-Indeno[1,2-b]Pyrazine-2,3-Dicarbonitrile End-groups Based Asymmetric Non-Fullerene Acceptors for Green Solvent-Processable, Additive-Free, and Stable Organic Solar Cells. Small 2024, 20 (33), 2401080. 10.1002/smll.202401080. [DOI] [PubMed] [Google Scholar]
  18. Lu B.; Xia J.; Quan H.; Huang Y.; Zhang Z.; Zhan X. End-group Engineering for Constructing A-D-A Fused-Ring Photosensitizers with Balanced Phototheranostics Performance. Small 2024, 20 (14), 2307664. 10.1002/smll.202307664. [DOI] [PubMed] [Google Scholar]
  19. Lu B.; Quan H.; Zhang Z.; Li T.; Wang J.; Ding Y.; Wang Y.; Zhan X.; Yao Y. End-group Nonplanarization Enhances Phototherapy Efficacy of A–D–A Fused-Ring Photosensitizer for Tumor Phototherapy. Nano Lett. 2023, 23 (7), 2831–2838. 10.1021/acs.nanolett.3c00119. [DOI] [PubMed] [Google Scholar]
  20. Zhang K.; Jiang Z.; Qiao J.; Lu P.; Qin C.; Yin H.; Du X.; Qin W.; Hao X. Dredging photocarrier trapping pathways via “charge bridge” driven exciton–phonon decoupling enables efficient and photothermal stable quaternary organic solar cells. Energy Environ. Sci. 2023, 16 (8), 3350–3362. 10.1039/D3EE01270K. [DOI] [Google Scholar]
  21. Chen L.; Zhao C.; Yu H.; Sergeev A.; Zhu L.; Ding K.; Fu Y.; Ng H. M.; Kwok C. H.; Zou X.; Yi J.; Lu X.; Wong K. S.; Ade H.; Zhang G.; Yan H.; et al. Tailoring Cyano Substitutions on Quinoxaline-based Small-Molecule Acceptors Enabling Enhanced Molecular Packing for High-Performance Organic Solar Cells. Adv. Energy Mater. 2024, 14 (30), 2400285. 10.1002/aenm.202400285. [DOI] [Google Scholar]
  22. Zhang Y.; Ji Y.; Zhang Y.; Zhang W.; Bai H.; Du M.; Wu H.; Guo Q.; Zhou E. Recent Progress of Y6-Derived Asymmetric Fused Ring Electron Acceptors. Adv. Funct. Mater. 2022, 32 (35), 2205115. 10.1002/adfm.202205115. [DOI] [Google Scholar]
  23. Xu R.; Jiang Y.; Liu F.; Ran G.; Liu K.; Zhang W.; Zhu X. High Open-Circuit Voltage Organic Solar Cells with 19.2% Efficiency Enabled by Synergistic Side-Chain Engineering. Adv. Mater. 2024, 36 (26), 2312101. 10.1002/adma.202312101. [DOI] [PubMed] [Google Scholar]
  24. Yu H.; Wang Y.; Zou X.; Han H.; Kim H. K.; Yao Z.; Wang Z.; Li Y.; Ng H. M.; Zhou W.; Zhang J.; Chen S.; Lu X.; Wong K. S.; Zhu Z.; Yan H.; Hu H.; et al. Effects of Halogenation of Small-Molecule and Polymeric Acceptors for Efficient Organic Solar Cells. Adv. Funct. Mater. 2023, 33 (22), 2300712. 10.1002/adfm.202300712. [DOI] [Google Scholar]
  25. Gao Y.; Chen Q.; Wang L.; Huang H.; Zhang A.; Li C.; Xu X.; Bo Z. End-group modification of non-fullerene acceptors enables efficient organic solar cells. J. Mater. Chem. C 2022, 10 (28), 10389–10395. 10.1039/D2TC01344D. [DOI] [Google Scholar]
  26. Liu H.; Dai T.; Zhou J.; Wang H.; Guo Q.; Guo Q.; Zhou E. The development of A-DA’D-A type nonfullerene acceptors containing non-halogenated end-groups. Nano Res. 2023, 16 (12), 12949–12961. 10.1007/s12274-023-5693-z. [DOI] [Google Scholar]
  27. Kohn W.; Sham L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, 140 (4A), A1133–A1138. 10.1103/PhysRev.140.A1133. [DOI] [Google Scholar]
  28. Trani F.; Scalmani G.; Zheng G.; Carnimeo I.; Frisch M. J.; Barone V. Time-Dependent Density Functional Tight Binding: New Formulation and Benchmark of Excited States. J. Chem. Theory Comput. 2011, 7 (10), 3304–3313. 10.1021/ct200461y. [DOI] [PubMed] [Google Scholar]
  29. Kosyachenko L. A.; Grushko E. V. Open-circuit voltage, fill factor, and efficiency of a CdS/CdTe solar cell. Semiconductors 2010, 44 (10), 1375–1382. 10.1134/S1063782610100234. [DOI] [Google Scholar]
  30. Akram S. J.; Iqbal J.; Ans M.; El-Badry Y. A.; Mehmood R. F.; Khera R. A. Designing of the indacenodithiophene core-based small molecules for optoelectronic applications: A DFT approach. Sol. Energy 2022, 237, 108–121. 10.1016/j.solener.2022.03.072. [DOI] [Google Scholar]
  31. Zhang G.; Chen X. K.; Xiao J.; Chow P. C. Y.; Ren M.; Kupgan G.; Jiao X.; Chan C. C. S.; Du X.; Xia R.; Chen Z.; Yuan J.; Zhang Y.; Zhang S.; Liu Y.; Zou Y.; Yan H.; Wong K. S.; Coropceanu V.; Li N.; Brabec C. J.; Bredas J. L.; Yip H. L.; Cao Y.; et al. Delocalization of exciton and electron wavefunction in non-fullerene acceptor molecules enables efficient organic solar cells. Nat. Commun. 2020, 11 (1), 3943. 10.1038/s41467-020-17867-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Chebil S.; chemek M.; Mestiri T.; Alimi K. Theoretical enhancement of the electronic and optical properties of a new D-π-A-π-D synthesized donor molecule for a new generation of fullerene-based bulk heterojunction (BHJ) for new organic solar cells devices. J. Mol. Graphics Modell. 2022, 115, 108226 10.1016/j.jmgm.2022.108226. [DOI] [PubMed] [Google Scholar]
  33. Frisch M. J.; Trucks G. W.; Schlegel H. B.; Scuseria G. E.; Robb M. A.; Cheeseman J. R.; Scalmani G.; Barone V.; Petersson G. A.; Nakatsuji H.,. et al. Gaussian 16 Rev. C.01; Gaussian Inc.: Wallingford, CT, 2016. [Google Scholar]
  34. Lu T.; Chen F. Multiwfn: a multifunctional wavefunction analyzer. J. Comput. Chem. 2012, 33 (5), 580–592. 10.1002/jcc.22885. [DOI] [PubMed] [Google Scholar]
  35. Lu T. A comprehensive electron wavefunction analysis toolbox for chemists. Multiwfn. J. Chem. Phys. 2024, 10.1063/5.0216272. [DOI] [PubMed] [Google Scholar]
  36. Humphrey W.; Dalke A.; Schulten K. VMD: Visual molecular dynamics. J. Mol. Graphics 1996, 14 (1), 33–38. 10.1016/0263-7855(96)00018-5. [DOI] [PubMed] [Google Scholar]
  37. Roy Dennington T. A. K.; Millam John M.. GaussView Version 6.1; Semichem Inc.: Shawnee Mission, KS, 2016. [Google Scholar]
  38. O’boyle N. M.; Tenderholt A. L.; Langner K. M. Cclib: a library for package-independent computational chemistry algorithms. J. Comput. Chem. 2008, 29 (5), 839–845. 10.1002/jcc.20823. [DOI] [PubMed] [Google Scholar]
  39. Raghavachari K. Perspective on ″Density functional thermochemistry. III. The role of exact exchange″. Theor. Chem. Acc. 2000, 103 (3–4), 361–363. 10.1007/s002149900065. [DOI] [Google Scholar]
  40. Antony J.; Grimme S. Density functional theory including dispersion corrections for intermolecular interactions in a large benchmark set of biologically relevant molecules. Phys. Chem. Chem. Phys. 2006, 8 (45), 5287–5293. 10.1039/b612585a. [DOI] [PubMed] [Google Scholar]
  41. Francl M. M.; Pietro W. J.; Hehre W. J.; Binkley J. S.; Gordon M. S.; DeFrees D. J.; Pople J. A. Self-consistent molecular orbital methods. XXIII. A polarization-type basis set for second-row elements. J. Chem. Phys. 1982, 77 (7), 3654–3665. 10.1063/1.444267. [DOI] [Google Scholar]
  42. Saeed M. U.; Iqbal J.; Mehmood R. F.; Akram S. J.; El-Badry Y. A.; Noor S.; Khera R. A. End-capped modification of Y-Shaped dithienothiophen[3,2-b]-pyrrolobenzothiadiazole (TPBT) based non-fullerene acceptors for high performance organic solar cells by using DFT approach. Surf. Interfaces 2022, 30, 101875 10.1016/j.surfin.2022.101875. [DOI] [Google Scholar]
  43. Miertuš S.; Scrocco E.; Tomasi J. Electrostatic interaction of a solute with a continuum. A direct utilizaion of AB initio molecular potentials for the prevision of solvent effects. Chem. Phys. 1981, 55 (1), 117–129. 10.1016/0301-0104(81)85090-2. [DOI] [Google Scholar]
  44. Miertus̃ S.; Tomasi J. Approximate evaluations of the electrostatic free energy and internal energy changes in solution processes. Chem. Phys. 1982, 65 (2), 239–245. 10.1016/0301-0104(82)85072-6. [DOI] [Google Scholar]
  45. Improta R.; Barone V.; Scalmani G.; Frisch M. J. A state-specific polarizable continuum model time dependent density functional theory method for excited state calculations in solution. J. Chem. Phys. 2006, 125 (5), 054103 10.1063/1.2222364. [DOI] [PubMed] [Google Scholar]
  46. York D. M.; Karplus M. A Smooth Solvation Potential Based on the Conductor-Like Screening Model. J. Phys. Chem. A 1999, 103 (50), 11060–11079. 10.1021/jp992097l. [DOI] [Google Scholar]
  47. Song X.; Gasparini N.; Ye L.; Yao H.; Hou J.; Ade H.; Baran D. Controlling Blend Morphology for Ultrahigh Current Density in Nonfullerene Acceptor-Based Organic Solar Cells. ACS Energy Lett. 2018, 3 (3), 669–676. 10.1021/acsenergylett.7b01266. [DOI] [Google Scholar]
  48. Coropceanu V.; Cornil J.; da Silva Filho D. A.; Olivier Y.; Silbey R.; Brédas J.-L. Charge Transport in Organic Semiconductors. Chem. Rev. 2007, 107 (4), 926–952. 10.1021/cr050140x. [DOI] [PubMed] [Google Scholar]
  49. Marcus R. A.; Sutin N. Electron transfers in chemistry and biology. Biochimica et Biophysica Acta (BBA) - Reviews on Bioenergetics 1985, 811 (3), 265–322. 10.1016/0304-4173(85)90014-X. [DOI] [Google Scholar]
  50. Marcus R. A. Electron Transfer Reactions in Chemistry: Theory and Experiment (Nobel Lecture). Angew. Chem., Int. Ed. 1993, 32 (8), 1111–1121. 10.1002/anie.199311113. [DOI] [Google Scholar]
  51. Zubair I.; Khera R. A.; Naveed A.; Shehzad R. A.; Iqbal J. Designing the optoelectronic properties of BODIPY and their photovoltaic applications for high performance of organic solar cells by using computational approach. Mater. Sci. Semicond. Process. 2022, 148, 106812 10.1016/j.mssp.2022.106812. [DOI] [Google Scholar]
  52. Naveed A.; Khera R. A.; Azeem U.; Zubair I.; Farhat A.; Ayub A. R.; Iqbal J. Tuning the optoelectronic properties of benzodithiophene based donor materials and their photovoltaic applications. Mater. Sci. Semicond. Process. 2022, 137, 106150 10.1016/j.mssp.2021.106150. [DOI] [Google Scholar]
  53. Wang J.; Xie Y.; Chen K.; Wu H.; Hodgkiss J. M.; Zhan X. Physical insights into non-fullerene organic photovoltaics. Nat. Rev. Phys. 2024, 6 (6), 365–381. 10.1038/s42254-024-00719-y. [DOI] [Google Scholar]
  54. Akram S. J.; Iqbal J.; Mehmood R. F.; Iqbal S.; El-Badry Y. A.; Khan M. I.; Ans M.; Khera R. A. Impact of side-chain engineering on the A-π-D-π-A type SM-BF1 donor molecule for bulk heterojunction and their photovoltaic performance: A DFT approach. Sol. Energy 2022, 240, 38–56. 10.1016/j.solener.2022.05.013. [DOI] [Google Scholar]
  55. Politzer P.; Murray J. S.; Bulat F. A. Average local ionization energy: a review. J. Mol. Model. 2010, 16 (11), 1731–1742. 10.1007/s00894-010-0709-5. [DOI] [PubMed] [Google Scholar]
  56. Hirshfeld F. L. Bonded-atom fragments for describing molecular charge densities. Theor. Chim. Acta 1977, 44, 129–138. 10.1007/BF00549096. [DOI] [Google Scholar]
  57. Suresh C. H.; Remya G. S.; Anjalikrishna P. K. Molecular electrostatic potential analysis: A powerful tool to interpret and predict chemical reactivity. WIREs Comput. Mol. Sci. 2022, 12 (5), e1601 10.1002/wcms.1601. [DOI] [Google Scholar]
  58. Riaz S.; Hussain R.; Adnan M.; Khan M. U.; Muhammad S.; Yaqoob J.; Alvi M. U.; Khalid M.; Irshad Z.; Ayub K. Ab Initio Study of Two-Dimensional Cross-Shaped Non-Fullerene Acceptors for Efficient Organic Solar Cells. ACS Omega 2022, 7 (12), 10638–10648. 10.1021/acsomega.2c00285. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao4c10273_si_001.pdf (2.4MB, pdf)

Data Availability Statement

The data (the structures of the acceptors and the acceptor dimers) that support the findings of this study are available from https://github.com/ZhengliZhang/OSCs/tree/Structure_V1-R

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES