Charge-Transfer Hybridization Simultaneously

6 days ago - High power conversion efficiencies in state-of-the-art nonfullerene organic solar cells (NF OSCs) call for elucidation of the underlying ...
0 downloads 0 Views 1MB Size
Subscriber access provided by University of Rochester | River Campus & Miner Libraries

Energy Conversion and Storage; Plasmonics and Optoelectronics

Local Excitation/Charge Transfer Hybridization Simultaneously Promotes Charge Generation and Reduces Non-Radiative Voltage Loss in Non-Fullerene Organic Solar Cells Guangchao Han, and Yuanping Yi J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.9b00928 • Publication Date (Web): 15 May 2019 Downloaded from http://pubs.acs.org on May 16, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

Guangchao Han,† and Yuanping Yi*,†,‡ †Beijing

National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China ‡University of Chinese Academy Sciences, Beijing 100049, China ABSTRACT: High power conversion efficiencies in state-of-the-art non-fullerene organic solar cells (NF OSCs) call for elucidation of the underlying working mechanisms of both high photocurrent densities and low non-radiative voltage losses under small energy offsets. Here, to address this fundamental issue, we have assessed the nature of interfacial charge-transfer (CT) states in a representative small-molecule NF OSC (DRTB-T:IT-4F) by time-dependent density functional theory calculations. The calculated results point to that the CT states can borrow considerable oscillator strengths from the energyclose local-excitation (LE) states or be fully hybridized with these LE states by molecular aggregation at the donor-acceptor interfaces. The LE/CT hybridization can promote charge generation by direct population of thermalized CT or LE/CT states under illumination. At the same time, the increased oscillator strengths of the lowest CT state will improve the luminescence quantum efficiencies and thus reduce non-radiative voltage losses. Our work suggests that it is crucial to tune the LE/CT hybridization by optimization of the donor and acceptor molecular and interfacial structures for further improving the NF OSC performance.

(TOC)

Organic solar cells (OSCs) have achieved remarkable progress in the last three years, mainly due to the rapid development of non-fullerene (NF) acceptors.1-4 Now the power conversion efficiencies (PCEs) of NF OSCs have reached 16% for single-junction devices,5,6 which outperform the best fullerene-based OSCs (11-12%).7-9 In these NF OSCs, charge generation is very efficient even under small charge-transfer (CT) driving force (ΔECT < 0.1 eV).10-17 We recall that ΔECT = Eg – ECT, and ≈ (ΔEHOMO or ΔELUMO) – ΔEb under the first-order approxation,18 where Eg is the lowest optical gap of either the D or A material, and ECT is the energy of the CT exciton, ΔEHOMO or ΔELUMO is the HOMO or LUMO energy difference between electron donor (D) and electron acceptor (A), ΔEb is the difference of the

binding energies of a local-excitation (LE) exciton and of a CT exciton. Moreover, the non-radiative (NR) voltage loss ΔVnr is quite low due to high electroluminescent external quantum efficiency [EQEEL ~ 10-5-10-4, ΔVnr = (kBT/q) *ln(EQEEL-1)19 ~ 0.2-0.3 V, where kB is the Boltzmann constant, T is the temperature, and q is the elementary charge].10,15,20-22 As a result, high photocurrent and low voltage loss can coexist [ΔVloss = Eg/q – VOC = ΔECT/q + ΔVr + ΔVnr ≤ 0.6 V, where VOC is the open-circuit voltage and ΔVr (≈ 0.3 V) is the radiative voltage loss that is unavoidable for any type of solar cells]. In contrast, for traditional fullerenebased OSCs, charge generation usually becomes inefficient under small ΔECT23-25 and low EQEEL (~ 10-9-10-6) yields large ΔVnr (~ 0.35-0.55 V).26,27 These striking phenomena

ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

thus stimulate us to elucidate the new working mechanisms in the state-of-the-art NF OSCs. It has been well recognized that the CT states at D-A interfaces mediate the processes of exciton dissociation (ED), charge separation (CS), and charge recombination (CR).28,29 Therefore, assessing the nature and energetics of the interfacial CT states is pivotal to understand the fundamental mechanisms of charge generation and recombination as well as voltage loss.30-36 Experimentally, the energy (ECT) and reorganization energy (λ) of the lowest CT state (CT1) can be obtained by fitting the absorption and emission spectra of D-A blends in terms of Marcus37 or Marcus-Levich-Jortner (MLJ)38 theory,24,39-44 and the CT1state lifetime can be determined by ultrafast transient absorption spectroscopy.45-49 It should be noted that when the CT1 state is very close to the LE state, a three-state vibronic model would be imperative.35 Theoretically, firstprinciples calculations, e.g. via (time-dependent) density functional theory [(TD)DFT], can address these issues as well.28,50-53 Moreover, by analyzing the electron-hole density distributions in D-A complexes, charge delocalization and separation can be understood at the molecular level.46,54-57 Most of previous theoretical studied focused on fullerenebased systems (such as pentacene-C60,54,55,58,59 DTDCTBC60,56,60 P3HT-PC61BM,46,57,61-65 and PCPDTBT-PC61BM64,66). Relatively, the high-performance NF systems are rarely calculated, which lags far behind the rapid development of NF acceptors. Generally, high-performance NF OSCs comprise of a wide band gap small-molecule (SM) or polymer donor and a narrow band gap SM acceptor (e.g., ITIC67 and its derivatives68-71) with a small ΔEHOMO (~ 0.2 eV or less) to achieve complementary sunlight absorption and high VOC at the same time. The schematic diagram of frontier molecular orbitals energy levels for such NF OSCs is displayed in Figure 1a. Here, it should be mentioned that the LUMO+1 level of the NF acceptor is usually lying below the donor LUMO level.72 Thus the excitons on donor can be dissociated into high-lying CT states and further separated into free charge carriers through a hot process (see Figure 1b).60,62,73,74 However, owing to the small ΔEHOMO, most of the excitons on acceptor will be dissociated into the CT1 state, which then undergoes a cold CS process,75-77 if geminate CR is suppressed.78-80

Figure 1. Schematic diagrams of energy level alignments of (a) frontier molecular orbitals and of (b) excited states for a high-performance non-fullerene organic solar cell that consists of a wide band gap small-molecule or polymer donor and a narrow band gap SM acceptor with a small ΔEHOMO. The black dashed lines represent the vibrational states of relevant electronic states. D: donor; A: acceptor; S0: ground state; S1D and S1A: the first singlet excited states on D and A; CT: charge-transfer states; CS: charge-separation

states; hν1, hν2, and hν3: vertical excitation energies of S1D, S1A, and CT1 (the lowest CT state); k*ED and kED: the rates for exciton dissociation at the D-A interface; k*CS and kCS: the rates for hot CS and cold CS; kr and knr: radiative and nonradiative decay rates of the CT1 state; kCR: the total charge recombination rate. Recently, Hou et al. fabricated NF OSC devices using a wide band gap molecule DRTB-T as donor (Figure S1a)81 and IT-4F (tetra-fluorinated ITIC, Figure S1b) as acceptor,68 and achieved a PCE of 11.24%, among the highest values of all-small-molecule OSCs.82 Same to other high-performance NF OSCs, the DRTB-T:IT-4F based OSCs also have small driving force for hole transfer (Figure S1c). The experimental measured ΔEHOMO between DRTB-T and IT-4F is only ~ 0.15 eV. Considering the Eg of IT-4F (~ 1.52 eV) and VOC (~ 0.92 V), a low ΔVloss of ~ 0.6 V is obtained. If the ΔVr is set to a typical value of 0.3 V, the ΔVnr will be less than 0.3 V due to the presence of ΔECT. Here, taking DRTB-T/IT4F complexes as representative D-A interfaces, we have investigated the nature and energetics of interfacial excited states to elucidate the underlying charge generation mechanisms in high-efficiency NF OSCs by means of highlevel DFT/TDDFT calculations. The D-A interface geometries and molecular aggregation have important impact on the interfacial energetics and electronic processes.28,50-52,54-57,62,83-98 Molecular dynamics simulations have shown that the DRTB-T and IT-4F molecules are inclined to interact with each other by endgroup π-π stacking due to the large steric hindrance of side chains on the central core.90,91,99,100 According to such packing mode, we construct the structures of the (DRTB-T)(IT-4F) complex and the dimers of DRTB-T and IT-4F [2(DRTB-T) and 2(IT-4F)] (see Figure 2 and S2). To reveal the influence of molecular aggregation on charge delocalization and initial CS process, the 2(DRTB-T)-(IT-4F) and (DRTB-T)-2(IT-4F) complexes are constructed by using two donor and one acceptor molecules or one donor and two acceptor molecules. The geometries of all the complexes and dimers are then optimized by DFT at the ωB97XD/6-31G** level. It should be noted that ωB97XD is a range-separated (RS) functional with dispersion correction included, which can reliably describe weak intermolecular interaction.101 Based on the optimized geometries, the excited states are calculated by TDDFT at the ωB97XD/6-31G** level, with the RS parameter (ω) of the functional optimally tuned under the dielectric environment that is considered via the polarizable continuum model (PCM). The dielectric constant εr is set to 4.0, a medium value for organic semiconductors.83 Such tuned RS functionals have been demonstrated to be able to provide reasonable description of the nature and energetics of excited states both in the condensed phase and at the DA interface.56,57,59,83,102-106 All the DFT and TDDFT calculations were carried out by using the Gaussian 16 package.107

ACS Paragon Plus Environment

Page 2 of 9

Page 3 of 9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

Figure 2. DFT-ωB97XD/6-31G** optimized geometries of (a) the DRTB-T and IT-4F molecules, (b) the 2(DRTB-T) and 2(IT4F) dimers, and (c) the (DRTB-T)-(IT-4F), 2(DRTB-T)-(IT-4F), and (DRTB-T)-2(IT-4F) complexes. All alkyl chains are replaced with methyl groups to reduce the computational costs.

The calculated ΔEHOMO between DRTB-T and IT-4F or between 2(DRTB-T) and 2(IT-4F) is 0.24 or 0.22 eV, which is consistent with the small value measured by experiment. The calculated excitation energies of the first singlet excited state (S1) for DRTB-T (2.09 eV) and 2(DRTB-T) (2.07 eV) are very close to the first absorption peak energy measured for the spin-coated DRTB-T film (~ 2.12 eV). And the first absorption peak energy of the IT-4F film (~ 1.73 eV) is between the calculated S1 excitation energies of IT-4F (1.79 eV) and 2(IT-4F) (1.71 eV). This further verifies the computation methods chosen here. The oscillator strengths (f), main electronic transition configurations, and relevant frontier molecular orbitals for S1 are listed in Table S1. The excited states of the three D-A complexes can be classified into LE (local excitation on the D or A region), CT (electron transfer from the D to A region), LE/CT (hybridized), or CS type. The excitation energies are shown in Figure 3. The f and main electronic transition configurations for each excited state along with relevant frontier molecular orbitals can be found in Table S2. To better understand the mechanisms of charge generation, the electron-hole density distributions for these states were also depicted in Figure 4 and S3.108,109

Figure 3. Vertical excitation energies calculated by TDDFT at the PCM-tuned-ωB97XD/6-31G** level for (a) (DRTB-T)-(IT4F), (b) 2(DRTB-T)-(IT-4F) and (c) (DRTB-T)-2(IT-4F). The calculated absorption spectra for single molecules, dimers, and D-A complexes are included inset.

Figure 4. Electron-hole density maps (red: electron; blue: hole) for local-excitation, CT, hybridized (brown), and CS (green) states: (a) (DRTB-T)-(IT-4F), (b) 2(DRTB-T)-(IT-4F), and (c) (DRTB-T)-2(IT-4F). The distance between electron and hole centers for each state is included inset. For (DRTB-T)-(IT-4F), the first LE state (S1A, mainly localized on IT-4F) is at 1.8 eV (f = 2.44), which is only 0.09 eV higher than CT1 (1.71 eV, f = 0.88). This indicates a very small ΔECT for ED, corresponding to a small value of ΔEHOMO. Apart from CT1, the second and third CT states (CT2: 1.96 eV, f =0.02; CT3: 2.04 eV, f = 0.23) are also lying below the second LE state (S1D: 2.05 eV, f = 2.19, mainly localized on DRTB-T), which implies that the DRTB-T excitons can be dissociated into the high-lying CT states. Interestingly, owing to the close energies of S1A and CT1 (S1D and CT3), S1A and S1D have a CT fraction (which leads to a smaller f) while CT1 and CT3 have a LE fraction (which leads to a noticeable f, especially for CT1). Importantly, owing to the incorporation of a degree of LE component, the two CT states can be populated directly by photoexcitation.65,110

Interestingly, molecular aggregation of DRTB-T or IT-4F at the D-A interface can render the formation of fully hybridized LE/CT states: nearly degenerate S1D/CT3 and S1D/CT3’ for 2(DRTB-T)-(IT-4F) and S1A/CT1 and S2A/CT1 for (DRTB-T)-2(IT-4F). As can be seen, the endgroup π-π stacking can decrease the S1 energy to some extent, ~ 0.02 eV for DRTB-T and ~ 0.08 eV for IT-4F. This makes the energy difference between S1D and CT3 (or between S2A and CT1) almost vanished, thus inducing the full hybridization between them. It is worth to note that for the S2A/CT1 hybridized state of (DRTB-T)-2(IT-4F), the electron is distributed over the two IT-4F molecules while the hole over the whole complex. By combining with the CS states in 2(DRTB-T)-(IT-4F) and (DRTB-T)-2(IT-4F), we attempt to unveil the mechanisms of charge generation in the NF OSC devices. From energetics, the DRTB-T excitons can be dissociated into the high-lying CT2 or CT3 states in (DRTB-T)-2(IT-4F) or transferred to the high-lying hybridized S1D/CT3 or S1D/CT3’ states and then to the CT2 state in 2(DRTB-T)-(IT-

ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

4F), which will be further separated into free charge carriers through a fast hot process. By contrast, the IT-4F excitons can be only dissociated into the lowest CT1 state in 2(DRTB-T)-(IT-4F) or transferred to the low-lying hybridized states in (DRTB-T)-2(IT-4F), which will undergo a slow cold CS process before geminate CR. This is consistent with the coexistence of both hot and cold charge separation observed experimentally in the highperformance NF OSCs (as depicted in Figure 1b). In the case of (DRTB-T)-2(IT-4F), there are also two low-hybridization ‘bright’ states on the IT-4F region (S4A: 1.9 eV, f = 0.44; S5A: 1.94 eV, f = 0.6), which can be directly separated by a hot process. Furthermore, the electron in the high-lying CT2 and CT3 states is delocalized, which will facilitate CS. As known, the adiabatic energy of an excited state is equal to the vertical excitation energy minus or the vertical emission energy plus the relaxation energy λ of the excited or the ground state. Considering a medium value of 0.3 eV for λ (generally in the range 0.2-0.4 eV for D-A systems),18,24,39 the adiabic energy of CT1 will be ~ 1.4 eV. According to the Marcus Levich-Jortner (MLJ) formalism,38 the NR decay rate for the CT1 state (knr) is estimated to be ~ 3.5 × 109 s-1 (by using the C=C stretching frequency ωeff = 1500 cm-1 and Huang-Rhys factor Seff = 1 for the effective vibration mode, and the electronic coupling between the CT and ground states V = 200 cm-1). The radiative decay rate (kr) is estimated to be ~ 2.9 × 107 s-1 according to the Einstein coefficient relation (by using the vertical emission energy of ~ 1.1 eV and the calculated transition dipole moment μ = 11.5 D). Thus the total CR rate (kCR) that is mainly determined by knr. To ensure efficient cold CS, the rate of the first CS step (kCS) should be much higher than knr. Since the CS state in (DRTB-T)-2(IT-4F) is lower than that in 2(DRTBT)-(IT-4F) (~ 0.1 eV), the first CS step would be driven by electron transfer rather than hole transfer, with the driving force of ~ -0.1 eV according to the calculations (Figure 3). Under the same values of λ, ωeff, Seff and V as the NR decay, the estimated kCS would be ~ 2.3 × 1011 s-1, which is about two orders of magnitude higher than the kCR. This indicates that the cold CS process in the DRTB-T:IT-4F blends can be efficient compared to geminate CR.78-80 We note that recently CS via thermalized (vibrational) CT1 state has been observed by time-delayed-collectionfield experiments.75,76,111,112 Energetically, the thermalized CT1 state is more favorable to be separated (Figure 5a). Due to the Franck-Condon shift, the thermalized CT1 or LE/CT1 state in the DRTB-T:IT-4F blend can be produced directly by light absorption, rather than by thermal activation. The large f will result in a great number of thermalized CT1 or LE/CT1 states at the D-A interface that can undergo efficient separation. At this stage, we can discuss the crucial role of LE/CT1 hybridization in reducing the NR voltage loss (ΔVnr).20,35,113As pointed out above, ΔVnr = (kBT/q)*ln(EQEEL1), and EQEEL = pe*kr/(knr + pe*kr),114 where pe is the outcoupling efficiency (taking the common value of 0.2 for organic light-emitting diodes). Based on the kr and knr values calculated above, the ΔVnr for the DRTB-T:IT-4F device is estimated to be only ~ 0.16 V at room temperature. As seen in Figure 5b, ΔVnr has strong dependence on ECT and μ. On one hand, as ECT increases, knr will be decreased according to the energy-gap law;115 consequently ΔVnr is reduced

gradually.27,116 On the other hand, the increase of hybridization will enhance μ or f, thus leading to a higher kr and a lower ΔVnr. For comparison between fullerene and NF acceptors, we have also calculated the μ of CT1 for a (DRTBT)-(PC71BM) complex. Because of the large energy difference and negligible hybridization between S1A and CT1 states (Figure S4), the calculated μ is much smaller (~ 0.9 D). Therefore, the LE/CT1 hybridization is critical to achieve a low ΔVnr for NF OSCs with a small ΔECT.

Figure 5. (a) Schematic diagram of charge separation and recombination processes of the CT1 or LE/CT1 state in the DRTB-T:IT-4F blend (1 or 4: vertical absorption or emission; 2 or 3: charge separation via thermalized or relaxed state; 5: nonradiative recombination), (b) Calculated knr, kr, and nonradiative voltage loss (ΔVnr) as a function of the CT1 energy (ECT).

Finally, it is important to note that when the ECT is low (~1.0 eV), the knr will be comparable to the kCS (Figure 5b), which can result in severe recombination and thus inefficient cold CS as well as large ΔVnr. Besides increasing ECT, reducing λ can be another effective strategy to reduce knr, especially in low-Eg and low-ΔECT systems. Once the NR recombination is suppressed, a certain LE/CT hybridization can further promote charge generation and reduce ΔVnr. In summary, we have investigated the nature and energetics of interfacial excited states in model D-A complexes with a wide band gap SM donor of DRTB-T and a narrow band gap SM acceptor of IT-4F by means of TDDFT calculations. The main conclusions we can draw from the calculated results are: (i) The CT states will borrow some oscillator strength from the energy-close LE states. Especially, molecular aggregation at the D-A interface will lead to the formation of fully hybridized LE/CT states. (ii) Energetically, the high-lying CT and hybridized states can be separated into free charge carriers by a hot process, while the separation of CT1 and LE/CT1 states undergoes a cold process. Such cold CS process should be efficient compared to the geminate CR. This is consistent with the experimental observations that hot and cold charge generation can coexist in the state-of-the-art NF OSCs with small ΔEHOMO. (iii) Photoexcitation can directly generate a large number of thermalized CT1 or LE/CT1 states at the D-A interface due to the increased oscillator strength; these thermalized states are energetically favorable to be separated into free charge carriers. (iv) The large oscillator strength for CT1 or LE/CT1 will also be beneficial to improve the luminescence quantum efficiency and thus result in a low non-radiative voltage loss.

ACS Paragon Plus Environment

Page 4 of 9

Page 5 of 9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters These results provide the rationalization of both high charge generation efficiencies and low NR voltage losses in small-ΔECT NF OSCs.35 The optimal trade-off between high photocurrent densities and low voltage losses can be obtained by tuning the LE/CT hybridization at the D-A interface toward high-performance NF OSCs.

Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: xxx. Chemical structures of DRTB-T and IT-4F, side views of optimized geometries of DRTB-T and IT-4F dimers and complexes, detailed excited-state properties for DRTB-T and IT-4F, as well as their dimers and complexes.

*E-mail: [email protected] The authors declare no competing financial interest.

The work is supported by the National Natural Science Foundation of China (Grant No. 91833305, 51773208, 51803216), Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB12020200), and Ministry of Science and Technology of China (Grant No 2017YFA0204502).

(1) J. Hou, O. Inganas, R. H. Friend, F. Gao, Organic solar cells based on non-fullerene acceptors, Nat. Mater. 2018, 17, 119128. (2) Pei Cheng, Gang Li, Xiaowei Zhan, Yang Yang, Nextgeneration organic photovoltaics based on non-fullerene acceptors, Nature Photonics 2018, 12, 131-142. (3) Cenqi Yan, Stephen Barlow, Zhaohui Wang, He Yan, Alex K. Y. Jen, Seth R. Marder, Xiaowei Zhan, Non-fullerene acceptors for organic solar cells, Nature Reviews Materials 2018, 3, 18003. (4) G. Zhang, J. Zhao, P. C. Y. Chow, K. Jiang, J. Zhang, Z. Zhu, J. Zhang, F. Huang, H. Yan, Nonfullerene Acceptor Molecules for Bulk Heterojunction Organic Solar Cells, Chem. Rev. 2018, 118, 3447-3507. (5) Jun Yuan, Yunqiang Zhang, Liuyang Zhou, Guichuan Zhang, Hin-Lap Yip, Tsz-Ki Lau, Xinhui Lu, Can Zhu, Hongjian Peng, Paul A. Johnson, Mario Leclerc, Yong Cao, Jacek Ulanski, Yongfang Li, Yingping Zou, Single-Junction Organic Solar Cell with over 15% Efficiency Using Fused-Ring Acceptor with Electron-Deficient Core, Joule 2019, 3, 1140-1151. (6) Baobing Fan, Difei Zhang, Meijing Li, Wenkai Zhong, Zhaomiyi Zeng, Lei Ying, Fei Huang, Yong Cao, Achieving over 16% efficiency for single-junction organic solar cells, Sci. China Chem. 2019, 62, https://doi.org/10.1007/s11426-11019-1945711425. (7) Jingbo Zhao, Yunke Li, Guofang Yang, Kui Jiang, Haoran Lin, Harald Ade, Wei Ma, He Yan, Efficient Organic Solar Cells Processed from Hydrocarbon Solvents, Nat. Energy 2016, 1, 15027. (8) Dan Deng, Yajie Zhang, Jianqi Zhang, Zaiyu Wang, Lingyun Zhu, Jin Fang, Benzheng Xia, Zhen Wang, Kun Lu, Wei Ma, Zhixiang Wei, Fluorination-Enabled Optimal Morphology

Leads to over 11% Efficiency for Inverted Small-Molecule Organic Solar Cells, Nat. Commun. 2016, 7, 13740. (9) Jiahui Wan, Xiaopeng Xu, Guangjun Zhang, Ying Li, Kui Feng, Qiang Peng, Highly Efficient Halogen-Free Solvent Processed Small-molecule Organic Solar Cells Enabled by Material Design and Device Engineering, Energy Environ. Sci. 2017, 10, 1739-1745. (10) Jing Liu, Shangshang Chen, Deping Qian, Bhoj Gautam, Guofang Yang, Jingbo Zhao, Jonas Bergqvist, Fengling Zhang, Wei Ma, Harald Ade, Olle Inganäs, Kenan Gundogdu, Feng Gao, He Yan, Fast charge separation in a non-fullerene organic solar cell with a small driving force, Nat. Energy 2016, 1, 16089. (11) Shangshang Chen, Yuhang Liu, Lin Zhang, Philip C. Y. Chow, Zheng Wang, Guangye Zhang, Wei Ma, He Yan, A WideBandgap Donor Polymer for Highly Efficient Non-fullerene Organic Solar Cells with a Small Voltage Loss, J. Am. Chem. Soc. 2017, 139, 6298-6301. (12) Shangshang Chen, Yuming Wang, Lin Zhang, Jingbo Zhao, Yuzhong Chen, Danlei Zhu, Huatong Yao, Guangye Zhang, Wei Ma, Richard H. Friend, Philip C. Y. Chow, Feng Gao, He Yan, Efficient Nonfullerene Organic Solar Cells with Small Driving Forces for Both Hole and Electron Transfer, Adv. Mater. 2018, 30, 1804215. (13) Pei Cheng, Mingyu Zhang, Tsz-Ki Lau, Yao Wu, Boyu Jia, Jiayu Wang, Cenqi Yan, Meng Qin, Xinhui Lu, Xiaowei Zhan, Realizing Small Energy Loss of 0.55 eV, High Open-Circuit Voltage >1 V and High Efficiency >10% in Fullerene-Free Polymer Solar Cells via Energy Driver, Adv. Mater. 2017, 29, 1605216. (14) Haijun Bin, Liang Gao, Zhi-Guo Zhang, Yankang Yang, Yindong Zhang, Chunfeng Zhang, Shanshan Chen, Lingwei Xue, Changduk Yang, Min Xiao, Yongfang Li, 11.4% Efficiency non-fullerene polymer solar cells with trialkylsilyl substituted 2Dconjugated polymer as donor, Nat. Commun. 2016, 7, 13651. (15) D. Baran, T. Kirchartz, S. Wheeler, S. Dimitrov, M. Abdelsamie, J. Gorman, R. S. Ashraf, S. Holliday, A. Wadsworth, N. Gasparini, P. Kaienburg, H. Yan, A. Amassian, C. J. Brabec, J. R. Durrant, I. McCulloch, Reduced voltage losses yield 10% efficient fullerene free organic solar cells with >1 V open circuit voltages, Energy Environ. Sci. 2016, 9, 3783-3793. (16) Zhong Zheng, Omar M. Awartani, Bhoj Gautam, Delong Liu, Yunpeng Qin, Wanning Li, Alexander Bataller, Kenan Gundogdu, Harald Ade, Jianhui Hou, Efficient Charge Transfer and Fine-Tuned Energy Level Alignment in a THF-Processed Fullerene-Free Organic Solar Cell with 11.3% Efficiency, Adv. Mater. 2017, 29, 1604241. (17) Shuixing Li, Lingling Zhan, Chenkai Sun, Haiming Zhu, Guanqing Zhou, Weitao Yang, Minmin Shi, Chang-Zhi Li, Jianhui Hou, Yongfang Li, Hongzheng Chen, Highly Efficient Fullerene-Free Organic Solar Cells Operate at Near Zero Highest Occupied Molecular Orbital Offsets, J. Am. Chem. Soc. 2019, 141, 3073-3082. (18) Alexander J. Ward, Arvydas Ruseckas, Mohanad Mousa Kareem, Bernd Ebenhoch, Luis A. Serrano, Manal Al-Eid, Brian Fitzpatrick, Vincent M. Rotello, Graeme Cooke, Ifor D. W. Samuel, The Impact of Driving Force on Electron Transfer Rates in Photovoltaic Donor–Acceptor Blends, Adv. Mater. 2015, 27, 2496-2500. (19) Uwe Rau, Reciprocity relation between photovoltaic quantum efficiency and electroluminescent emission of solar cells, Phys. Rev. B 2007, 76, 085303. (20) Deping Qian, Zilong Zheng, Huifeng Yao, Wolfgang Tress, Thomas R. Hopper, Shula Chen, Sunsun Li, Jing Liu, Shangshang Chen, Jiangbin Zhang, Xiao-Ke Liu, Bowei Gao, Liangqi Ouyang, Yingzhi Jin, Galia Pozina, Irina A. Buyanova, Weimin M. Chen, Olle Inganäs, Veaceslav Coropceanu, Jean-Luc Bredas, He Yan, Jianhui Hou, Fengling Zhang, Artem A. Bakulin,

ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Feng Gao, Design rules for minimizing voltage losses in highefficiency organic solar cells, Nat. Mater. 2018, 17, 703-709. (21) Mark E. Ziffer, Sae Byeok Jo, Hongliang Zhong, Long Ye, Hongbin Liu, Francis Lin, Jie Zhang, Xiaosong Li, Harald W. Ade, Alex K. Y. Jen, David S. Ginger, Long-Lived, Non-Geminate, Radiative Recombination of Photogenerated Charges in a Polymer/Small-Molecule Acceptor Photovoltaic Blend, J. Am. Chem. Soc. 2018, 140, 9996-10008. (22) Xi Liu, Xiaoyan Du, Junyi Wang, Chunhui Duan, Xiaofeng Tang, Thomas Heumueller, Guogang Liu, Yan Li, Zhaohui Wang, Jing Wang, Feng Liu, Ning Li, Christoph J. Brabec, Fei Huang, Yong Cao, Efficient Organic Solar Cells with Extremely High Open-Circuit Voltages and Low Voltage Losses by Suppressing Nonradiative Recombination Losses, Adv. Energy Mater. 2018, 8, 1801699. (23) Koen Vandewal, Zaifei Ma, Jonas Bergqvist, Zheng Tang, Ergang Wang, Patrik Henriksson, Kristofer Tvingstedt, Mats R. Andersson, Fengling Zhang, Olle Inganäs, Quantification of Quantum Efficiency and Energy Losses in Low Bandgap Polymer:Fullerene Solar Cells with High Open-Circuit Voltage, Adv. Funct. Mater. 2012, 22, 3480-3490. (24) Eric T. Hoke, Koen Vandewal, Jonathan A. Bartelt, William R. Mateker, Jessica D. Douglas, Rodrigo Noriega, Kenneth R. Graham, Jean M. J. Fréchet, Alberto Salleo, Michael D. McGehee, Recombination in Polymer:Fullerene Solar Cells with Open-Circuit Voltages Approaching and Exceeding 1.0 V, Adv. Energy Mater. 2013, 3, 220-230. (25) Sarah Holliday, Raja Shahid Ashraf, Christian B. Nielsen, Mindaugas Kirkus, Jason A. Röhr, Ching-Hong Tan, Elisa Collado-Fregoso, Astrid-Caroline Knall, James R. Durrant, Jenny Nelson, Iain McCulloch, A Rhodanine Flanked Nonfullerene Acceptor for Solution-Processed Organic Photovoltaics, J. Am. Chem. Soc. 2015, 137, 898-904. (26) Jizhong Yao, Thomas Kirchartz, Michelle S. Vezie, Mark A. Faist, Wei Gong, Zhicai He, Hongbin Wu, Joel Troughton, Trystan Watson, Daniel Bryant, Jenny Nelson, Quantifying Losses in Open-Circuit Voltage in Solution-Processable Solar Cells, Phys. Rev. Applied 2015, 4, 014020. (27) Johannes Benduhn, Kristofer Tvingstedt, Fortunato Piersimoni, Sascha Ullbrich, Yeli Fan, Manuel Tropiano, Kathryn A. McGarry, Olaf Zeika, Moritz K. Riede, Christopher J. Douglas, Stephen Barlow, Seth R. Marder, Dieter Neher, Donato Spoltore, Koen Vandewal, Intrinsic non-radiative voltage losses in fullerenebased organic solar cells, Nat. Mater. 2017, 2, 17053. (28) Jean-Luc Brédas, Joseph E. Norton, Jérôme Cornil, Veaceslav Coropceanu, Molecular Understanding of Organic Solar Cells: The Challenges, Acc. Chem. Res. 2009, 42, 1691-1699. (29) Tracey M. Clarke, James R. Durrant, Charge Photogeneration in Organic Solar Cells, Chem. Rev. 2010, 110, 6736-6767. (30) Dirk Veldman, Stefan C. J. Meskers, RenéA. J. Janssen, The Energy of Charge-Transfer States in Electron Donor–Acceptor Blends: Insight into the Energy Losses in Organic Solar Cells, Adv. Funct. Mater. 2009, 19, 1939-1948. (31) Carsten Deibel, Thomas Strobel, Vladimir Dyakonov, Role of the Charge Transfer State in Organic Donor–Acceptor Solar Cells, Adv. Mater. 2010, 22, 4097-4111. (32) Heinz Bassler, Anna Kohler, "Hot or cold": how do charge transfer states at the donor-acceptor interface of an organic solar cell dissociate?, Phys. Chem. Chem. Phys. 2015, 17, 2845128462. (33) Koen Vandewal, Interfacial Charge Transfer States in Condensed Phase Systems, Annu. Rev. Phys. Chem. 2016, 67, 113133. (34) S. Matthew Menke, Niva A. Ran, Guillermo C. Bazan, Richard H. Friend, Understanding Energy Loss in Organic Solar Cells: Toward a New Efficiency Regime, Joule 2018, 2, 25-35.

Page 6 of 9

(35) Xian-Kai Chen, Veaceslav Coropceanu, Jean-Luc Brédas, Assessing the nature of the charge-transfer electronic states in organic solar cells, Nat. Commun. 2018, 9, 5295. (36) Mohammed Azzouzi, Thomas Kirchartz, Jenny Nelson, Factors Controlling Open-Circuit Voltage Losses in Organic Solar Cells, Trends in Chemistry 2019, 1, 49-62. (37) Rudolph A. Marcus, Electron transfer reactions in chemistry. Theory and experiment, Rev. Mod. Phys. 1993, 65, 599610. (38) Joshua Jortner, Temperature dependent activation energy for electron transfer between biological molecules, J. Chem. Phys. 1976, 64, 4860-4867. (39) Koen Vandewal, Kristofer Tvingstedt, Abay Gadisa, Olle Inganäs, Jean V. Manca, Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells, Phys. Rev. B 2010, 81, 125204. (40) Koen Vandewal, Johannes Benduhn, Karl Sebastian Schellhammer, Tim Vangerven, Janna E. Rückert, Fortunato Piersimoni, Reinhard Scholz, Olaf Zeika, Yeli Fan, Stephen Barlow, Dieter Neher, Seth R. Marder, Jean Manca, Donato Spoltore, Gianaurelio Cuniberti, Frank Ortmann, Absorption Tails of Donor:C60 Blends Provide Insight into Thermally Activated Charge-Transfer Processes and Polaron Relaxation, J. Am. Chem. Soc. 2017, 139, 1699-1704. (41) Zhiqiang Guan, Ho-Wa Li, Yuanhang Cheng, Qingdan Yang, Ming-Fai Lo, Tsz-Wai Ng, Sai-Wing Tsang, Chun-Sing Lee, Charge-Transfer State Energy and Its Relationship with OpenCircuit Voltage in an Organic Photovoltaic Device, J. Phys. Chem. C 2016, 120, 14059-14068. (42) Alyssa N. Brigeman, Michael A. Fusella, Yixin Yan, Geoffrey E. Purdum, Yueh-Lin Loo, Barry P. Rand, Noel C. Giebink, Revealing the Full Charge Transfer State Absorption Spectrum of Organic Solar Cells, Adv. Energy Mater. 2016, 6, 1601001. (43) Mathias List, Tanmoy Sarkar, Pavlo Perkhun, Jörg Ackermann, Chieh Luo, Uli Würfel, Correct determination of charge transfer state energy from luminescence spectra in organic solar cells, Nat. Commun. 2018, 9, 3631. (44) Frank-Julian Kahle, Alexander Rudnick, Heinz Bässler, Anna Köhler, How to interpret absorption and fluorescence spectra of charge transfer states in an organic solar cell, Mater. Horiz. 2018, 5, 837-848. (45) Ian A. Howard, Ralf Mauer, Michael Meister, Frédéric Laquai, Effect of Morphology on Ultrafast Free Carrier Generation in Polythiophene:Fullerene Organic Solar Cells, J. Am. Chem. Soc. 2010, 132, 14866-14876. (46) Artem A. Bakulin, Akshay Rao, Vlad G. Pavelyev, Paul H. M. van Loosdrecht, Maxim S. Pshenichnikov, Dorota Niedzialek, Jérôme Cornil, David Beljonne, Richard H. Friend, The Role of Driving Energy and Delocalized States for Charge Separation in Organic Semiconductors, Science 2012, 335, 13401344. (47) Alex J. Barker, Kai Chen, Justin M. Hodgkiss, Distance Distributions of Photogenerated Charge Pairs in Organic Photovoltaic Cells, J. Am. Chem. Soc. 2014, 136, 12018-12026. (48) Andreas C. Jakowetz, Marcus L. Böhm, Jiangbin Zhang, Aditya Sadhanala, Sven Huettner, Artem A. Bakulin, Akshay Rao, Richard H. Friend, What Controls the Rate of Ultrafast Charge Transfer and Charge Separation Efficiency in Organic Photovoltaic Blends, J. Am. Chem. Soc. 2016, 138, 1167211679. (49) Martina Causa, Jelissa De Jonghe-Risse, Mariateresa Scarongella, Jan C. Brauer, Ester Buchaca-Domingo, Jacques- E. Moser, Natalie Stingelin, Natalie Banerji, The fate of electron–hole pairs in polymer:fullerene blends for organic photovoltaics, Nat. Commun. 2016, 7, 12556.

ACS Paragon Plus Environment

Page 7 of 9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters (50) Frederic Castet, Gabriele D'Avino, Luca Muccioli, Jerome Cornil, David Beljonne, Charge separation energetics at organic heterojunctions: on the role of structural and electrostatic disorder, Phys. Chem. Chem. Phys. 2014, 16, 20279-20290. (51) Sheridan Few, Jarvist M. Frost, Jenny Nelson, Models of charge pair generation in organic solar cells, Phys. Chem. Chem. Phys. 2015, 17, 2311-2325. (52) Guangchao Han, Yuanping Yi, Zhigang Shuai, From Molecular Packing Structures to Electronic Processes: Theoretical Simulations for Organic Solar Cells, Adv. Energy Mater. 2018, 8, 1702743. (53) Kenley M. Pelzer, Seth B. Darling, Charge generation in organic photovoltaics: a review of theory and computation, Mol. Syst. Des. Eng. 2016, 1, 10-24. (54) Bing Yang, Yuanping Yi, Cai-Rong Zhang, Saadullah G. Aziz, Veaceslav Coropceanu, Jean-Luc Brédas, Impact of Electron Delocalization on the Nature of the Charge-Transfer States in Model Pentacene/C60 Interfaces: A Density Functional Theory Study, J. Phys. Chem. C 2014, 118, 27648-27656. (55) Zilong Zheng, Naga Rajesh Tummala, Yao-Tsung Fu, Veaceslav Coropceanu, Jean-Luc Brédas, Charge-Transfer States in Organic Solar Cells: Understanding the Impact of Polarization, Delocalization, and Disorder, ACS Appl. Mater. Interfaces 2017, 9, 18095-18102. (56) Xingxing Shen, Guangchao Han, Yuanping Yi, The nature of excited states in dipolar donor/fullerene complexes for organic solar cells: evolution with the donor stack size, Phys. Chem. Chem. Phys. 2016, 18, 15955-15963. (57) Daniele Fazzi, Mario Barbatti, Walter Thiel, Hot and Cold Charge-Transfer Mechanisms in Organic Photovoltaics: Insights into the Excited States of Donor/Acceptor Interfaces, J. Phys. Chem. Lett. 2017, 8, 4727-4734. (58) Cai-Rong Zhang, John S. Sears, Bing Yang, Saadullah G. Aziz, Veaceslav Coropceanu, Jean-Luc Brédas, Theoretical Study of the Local and Charge-Transfer Excitations in Model Complexes of Pentacene-C60 Using Tuned Range-Separated Hybrid Functionals, J. Chem. Theory Comput. 2014, 10, 2379-2388. (59) Zilong Zheng, Jean-Luc Brédas, Veaceslav Coropceanu, Description of the Charge Transfer States at the Pentacene/C60 Interface: Combining Range-Separated Hybrid Functionals with the Polarizable Continuum Model, J. Phys. Chem. Lett. 2016, 7, 2616-2621. (60) Xingxing Shen, Guangchao Han, Di Fan, Yujun Xie, Yuanping Yi, Hot Charge-Transfer States Determine Exciton Dissociation in the DTDCTB/C60 Complex for Organic Solar Cells: A Theoretical Insight, J. Phys. Chem. C 2015, 119, 11320-11326. (61) David P. McMahon, David L. Cheung, Alessandro Troisi, Why Holes and Electrons Separate So Well in Polymer/Fullerene Photovoltaic Cells, J. Phys. Chem. Lett. 2011, 2, 2737-2741. (62) Hiroyuki Tamura, Irene Burghardt, Ultrafast Charge Separation in Organic Photovoltaics Enhanced by Charge Delocalization and Vibronically Hot Exciton Dissociation, J. Am. Chem. Soc. 2013, 135, 16364-16367. (63) Gabriele D’Avino, Sébastien Mothy, Luca Muccioli, Claudio Zannoni, Linjun Wang, Jérôme Cornil, David Beljonne, Frédéric Castet, Energetics of Electron–Hole Separation at P3HT/PCBM Heterojunctions, J. Phys. Chem. C 2013, 117, 1298112990. (64) Dorota Niedzialek, Ivan Duchemin, Thiago Branquinho de Queiroz, Silvio Osella, Akshay Rao, Richard Friend, Xavier Blase, Stephan Kümmel, David Beljonne, First Principles Calculations of Charge Transfer Excitations in Polymer–Fullerene Complexes: Influence of Excess Energy, Adv. Funct. Mater. 2015, 25, 1972-1984. (65) Gabriele D’Avino, Luca Muccioli, Yoann Olivier, David Beljonne, Charge Separation and Recombination at

Polymer–Fullerene Heterojunctions: Delocalization and Hybridization Effects, J. Phys. Chem. Lett. 2016, 7, 536-540. (66) Can Leng, Haimei Qin, Yubing Si, Yi Zhao, Theoretical Prediction of the Rate Constants for Exciton Dissociation and Charge Recombination to a Triplet State in PCPDTBT with Different Fullerene Derivatives, J. Phys. Chem. C 2014, 118, 1843-1855. (67) Yuze Lin, Jiayu Wang, Zhi-Guo Zhang, Huitao Bai, Yongfang Li, Daoben Zhu, Xiaowei Zhan, An Electron Acceptor Challenging Fullerenes for Efficient Polymer Solar Cells, Adv. Mater. 2015, 27, 1170-1174. (68) Wenchao Zhao, Sunsun Li, Huifeng Yao, Shaoqing Zhang, Yun Zhang, Bei Yang, Jianhui Hou, Molecular Optimization Enables over 13% Efficiency in Organic Solar Cells, J. Am. Chem. Soc. 2017, 139, 7148-7151. (69) H. Zhang, H. Yao, J. Hou, J. Zhu, J. Zhang, W. Li, R. Yu, B. Gao, S. Zhang, J. Hou, Over 14% Efficiency in Organic Solar Cells Enabled by Chlorinated Nonfullerene Small-Molecule Acceptors, Adv. Mater. 2018, 30, 1800613. (70) Yuze Lin, Fuwen Zhao, Qiao He, Lijun Huo, Yang Wu, Timothy C. Parker, Wei Ma, Yanming Sun, Chunru Wang, Daoben Zhu, Alan J. Heeger, Seth R. Marder, Xiaowei Zhan, HighPerformance Electron Acceptor with Thienyl Side Chains for Organic Photovoltaics, J. Am. Chem. Soc. 2016, 138, 4955-4961. (71) Shuixing Dai, Fuwen Zhao, Qianqian Zhang, Tsz-Ki Lau, Tengfei Li, Kuan Liu, Qidan Ling, Chunru Wang, Xinhui Lu, Wei You, Xiaowei Zhan, Fused Nonacyclic Electron Acceptors for Efficient Polymer Solar Cells, J. Am. Chem. Soc. 2017, 139, 13361343. (72) Alina Kuzmich, Daniele Padula, Haibo Ma, Alessandro Troisi, Trends in the electronic and geometric structure of nonfullerene based acceptors for organic solar cells, Energy Environ. Sci. 2017, 10, 395-401. (73) Askat E. Jailaubekov, Adam P. Willard, John R. Tritsch, Wai-Lun Chan, Na Sai, Raluca Gearba, Loren G. Kaake, Kenrick J. Williams, Kevin Leung, Peter J. Rossky, X. Y. Zhu, Hot chargetransfer excitons set the time limit for charge separation at donor/acceptor interfaces in organic photovoltaics, Nat. Mater. 2013, 12, 66-73. (74) Andrey Yu Sosorev, Dmitry Yu Godovsky, Dmitry Yu Paraschuk, Hot kinetic model as a guide to improve organic photovoltaic materials, Phys. Chem. Chem. Phys. 2018, 20, 36583671. (75) Koen Vandewal, Steve Albrecht, Eric T. Hoke, Kenneth R. Graham, Johannes Widmer, Jessica D. Douglas, Marcel Schubert, William R. Mateker, Jason T. Bloking, George F. Burkhard, Alan Sellinger, Jean M. J. Fréchet, Aram Amassian, Moritz K. Riede, Michael D. McGehee, Dieter Neher, Alberto Salleo, Efficient charge generation by relaxed charge-transfer states at organic interfaces, Nat. Mater. 2014, 13, 63-68. (76) Steve Albrecht, Koen Vandewal, John R. Tumbleston, Florian S. U. Fischer, Jessica D. Douglas, Jean M. J. Fréchet, Sabine Ludwigs, Harald Ade, Alberto Salleo, Dieter Neher, On the Efficiency of Charge Transfer State Splitting in Polymer:Fullerene Solar Cells, Adv. Mater. 2014, 26, 2533-2539. (77) Stavros Athanasopoulos, Steffen Tscheuschner, Heinz Bässler, Anna Köhler, Efficient Charge Separation of Cold ChargeTransfer States in Organic Solar Cells Through Incoherent Hopping, J. Phys. Chem. Lett. 2017, 2093-2098. (78) S. Matthew Menke, Alexandre Cheminal, Patrick Conaghan, Niva A. Ran, Neil C. Greehnam, Guillermo C. Bazan, Thuc-Quyen Nguyen, Akshay Rao, Richard H. Friend, Order enables efficient electron-hole separation at an organic heterojunction with a small energy loss, Nat. Commun. 2018, 9, 277. (79) D. Baran, N. Gasparini, A. Wadsworth, C. H. Tan, N. Wehbe, X. Song, Z. Hamid, W. Zhang, M. Neophytou, T. Kirchartz, C. J. Brabec, J. R. Durrant, I. McCulloch, Robust nonfullerene solar

ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

cells approaching unity external quantum efficiency enabled by suppression of geminate recombination, Nat. Commun. 2018, 9, 2059. (80) Yun Liu, Lijian Zuo, Xueliang Shi, Alex K. Y. Jen, David S. Ginger, Unexpectedly Slow Yet Efficient Picosecond to Nanosecond Photoinduced Hole-Transfer Occurs in a Polymer/Nonfullerene Acceptor Organic Photovoltaic Blend, ACS Energy Letters 2018, 3, 2396-2403. (81) Liyan Yang, Shaoqing Zhang, Chang He, Jianqi Zhang, Huifeng Yao, Yang Yang, Yun Zhang, Wenchao Zhao, Jianhui Hou, New Wide Band Gap Donor for Efficient Fullerene-Free AllSmall-Molecule Organic Solar Cells, J. Am. Chem. Soc. 2017, 139, 1958-1966. (82) Liyan Yang, Shaoqing Zhang, Chang He, Jianqi Zhang, Yang Yang, Jie Zhu, Yong Cui, Wenchao Zhao, Hao Zhang, Yun Zhang, Zhixiang Wei, Jianhui Hou, Modulating Molecular Orientation Enables Efficient Nonfullerene Small-Molecule Organic Solar Cells, Chem. Mater. 2018, 30, 2129-2134. (83) Xian-Kai Chen, Mahesh Kumar Ravva, Hong Li, Sean M. Ryno, Jean-Luc Brédas, Effect of Molecular Packing and Charge Delocalization on the Nonradiative Recombination of Charge-Transfer States in Organic Solar Cells, Adv. Energy Mater. 2016, 6, 1601325. (84) David Beljonne, Jérôme Cornil, Luca Muccioli, Claudio Zannoni, Jean-Luc Brédas, Frédéric Castet, Electronic Processes at Organic−Organic Interfaces: Insight from Modeling and Implications for Opto-electronic Devices, Chem. Mater. 2011, 23, 591-609. (85) Julien Idé, Raphaël Méreau, Laurent Ducasse, Frédéric Castet, Harald Bock, Yoann Olivier, Jérôme Cornil, David Beljonne, Gabriele D’Avino, Otello Maria Roscioni, Luca Muccioli, Claudio Zannoni, Charge Dissociation at Interfaces between Discotic Liquid Crystals: The Surprising Role of Column Mismatch, J. Am. Chem. Soc. 2014, 136, 2911-2920. (86) Hantang Zhang, Lang Jiang, Yonggang Zhen, Jing Zhang, Guangchao Han, Xiaotao Zhang, Xiaolong Fu, Yuanping Yi, Wei Xu, Huanli Dong, Wei Chen, Wenping Hu, Daoben Zhu, Organic Cocrystal Photovoltaic Behavior: A Model System to Study Charge Recombination of C60 and C70 at the Molecular Level, Adv. Electron. Mater. 2016, 2, 1500423. (87) Yuanping Yi, Veaceslav Coropceanu, Jean-Luc Bré das, Exciton-Dissociation and Charge-Recombination Processes in Pentacene/C60 Solar Cells: Theoretical Insight into the Impact of Interface Geometry, J. Am. Chem. Soc. 2009, 131, 15777-15783. (88) Guangchao Han, Xingxing Shen, Yuanping Yi, Deposition Growth and Morphologies of C60 on DTDCTB Surfaces: An Atomistic Insight into the Integrated Impact of Surface Stability, Landscape, and Molecular Orientation, Adv. Mater. Interfaces 2015, 2, 1500329. (89) Guangchao Han, Yuan Guo, Ruihong Duan, Xingxing Shen, Yuanping Yi, Importance of side-chain anchoring atoms on electron donor/fullerene interfaces for high-performance organic solar cells, J. Mater. Chem. A 2017, 5, 9316-9321. (90) Guangchao Han, Yuan Guo, Xiaoyi Ma, Yuanping Yi, Atomistic Insight Into Donor/Acceptor Interfaces in HighEfficiency Nonfullerene Organic Solar Cells, Sol. RRL 2018, 2, 1800190. (91) Guangchao Han, Yuanping Yi, Rationalizing SmallMolecule Donor Design toward High-Performance Organic Solar Cells: Perspective from Molecular Architectures, Adv. Theory Simul. 2018, 1, 1800091. (92) Zhen Wang, Guangchao Han, Lingyun Zhu, Yuan Guo, Yuanping Yi, Zhigang Shuai, Zhixiang Wei, Suppressing charge recombination in small-molecule ternary organic solar cells by modulating donor–acceptor interfacial arrangements, Phys. Chem. Chem. Phys. 2018, 20, 24570-24576.

Page 8 of 9

(93) Fiona C. Jamieson, Ester Buchaca Domingo, Thomas McCarthy-Ward, Martin Heeney, Natalie Stingelin, James R. Durrant, Fullerene crystallisation as a key driver of charge separation in polymer/fullerene bulk heterojunction solar cells, Chem. Sci. 2012, 3, 485-492. (94) Barry P. Rand, David Cheyns, Karolien Vasseur, Noel C. Giebink, Sébastien Mothy, Yuanping Yi, Veaceslav Coropceanu, David Beljonne, Jérôme Cornil, Jean-Luc Brédas, Jan Genoe, The Impact of Molecular Orientation on the Photovoltaic Properties of a Phthalocyanine/Fullerene Heterojunction, Adv. Funct. Mater. 2012, 22, 2987-2995. (95) Kenneth R. Graham, Clement Cabanetos, Justin P. Jahnke, Matthew N. Idso, Abdulrahman El Labban, Guy O. Ngongang Ndjawa, Thomas Heumueller, Koen Vandewal, Alberto Salleo, Bradley F. Chmelka, Aram Amassian, Pierre M. Beaujuge, Michael D. McGehee, Importance of the Donor:Fullerene Intermolecular Arrangement for High-Efficiency Organic Photovoltaics, J. Am. Chem. Soc. 2014, 136, 9608-9618. (96) John R. Tumbleston, Brian A. Collins, Liqiang Yang, Andrew C. Stuart, Eliot Gann, Wei Ma, Wei You, Harald Ade, The Influence of Molecular Orientation on Organic Bulk Heterojunction Solar Cells, Nat. Photon. 2014, 8, 385-391. (97) Zhi Guo, Doyun Lee, Richard D. Schaller, Xiaobing Zuo, Byeongdu Lee, TengFei Luo, Haifeng Gao, Libai Huang, Relationship between Interchain Interaction, Exciton Delocalization, and Charge Separation in Low-Bandgap Copolymer Blends, J. Am. Chem. Soc. 2014, 136, 10024-10032. (98) Simon Gélinas, Akshay Rao, Abhishek Kumar, Samuel L. Smith, Alex W. Chin, Jenny Clark, Tom S. van der Poll, Guillermo C. Bazan, Richard H. Friend, Ultrafast Long-Range Charge Separation in Organic Semiconductor Photovoltaic Diodes, Science 2014, 343, 512-516. (99) Guangchao Han, Yuan Guo, Xiaoxian Song, Yue Wang, Yuanping Yi, Terminal π -π stacking determines three-dimensional molecular packing and isotropic charge transport in an A-π -A electron acceptor for non-fullerene organic solar cells, J. Mater. Chem. C 2017, 5, 4852-4857. (100) Guangchao Han, Yuan Guo, Lu Ning, Yuanping Yi, Improving the Electron Mobility of ITIC by End-Group Modulation: The Role of Fluorination and π -Extension, Sol. RRL 2019, 3, 1800251. (101) Jeng-Da Chai, Martin Head-Gordon, Long-range corrected hybrid density functionals with damped atom–atom dispersion corrections, Physical Chemistry Chemical Physics 2008, 10, 6615-6620. (102) Huifeng Yao, Yu Chen, Yunpeng Qin, Runnan Yu, Yong Cui, Bei Yang, Sunsun Li, Kai Zhang, Jianhui Hou, Design and Synthesis of a Low Bandgap Small Molecule Acceptor for Efficient Polymer Solar Cells, Adv. Mater. 2016, 28, 8283-8287. (103) Zilong Zheng, David A. Egger, Jean-Luc Brédas, Leeor Kronik, Veaceslav Coropceanu, Effect of Solid-State Polarization on Charge-Transfer Excitations and Transport Levels at Organic Interfaces from a Screened Range-Separated Hybrid Functional, J. Phys. Chem. Lett. 2017, 8, 3277-3283. (104) Stephan Kümmel, Charge-Transfer Excitations: A Challenge for Time-Dependent Density Functional Theory That Has Been Met, Adv. Energy Mater. 2017, 7, 1700440. (105) Leeor Kronik, Stephan Kümmel, Dielectric Screening Meets Optimally Tuned Density Functionals, Adv. Mater. 2018, 30, 1706560. (106) Arun K. Manna, Sivan Refaely-Abramson, Anthony M. Reilly, Alexandre Tkatchenko, Jeffrey B. Neaton, Leeor Kronik, Quantitative Prediction of Optical Absorption in Molecular Solids from an Optimally Tuned Screened Range-Separated Hybrid Functional, J. Chem. Theor. Comput. 2018, 14, 2919-2929. (107) M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,

ACS Paragon Plus Environment

Page 9 of 9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, Williams, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J. Heyd, E. N. Brothers, K. N. Kudin, V. N. Staroverov, T. A. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. P. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B. Foresman, D. J. Fox: Gaussian 16 Rev. A.03. Wallingford, CT, 2016. (108) Tian Lu, Feiwu Chen, Multiwfn: A multifunctional wavefunction analyzer, J. Comput. Chem. 2012, 33, 580-592. (109) William Humphrey, Andrew Dalke, Klaus Schulten, VMD: Visual molecular dynamics, J. Molec. Graphics 1996, 14, 33-38. (110)Martin Rosenberg, Christian Dahlstrand, Kristine Kilså, Henrik Ottosson, Excited State Aromaticity and Antiaromaticity: Opportunities for Photophysical and Photochemical Rationalizations, Chemical Reviews 2014, 114, 5379-5425. (111) Andreas Zusan, Koen Vandewal, Benedikt Allendorf, Nis Hauke Hansen, Jens Pflaum, Alberto Salleo, Vladimir Dyakonov, Carsten Deibel, The Crucial Influence of Fullerene

Phases on Photogeneration in Organic Bulk Heterojunction Solar Cells, Adv. Energy Mater. 2014, 4, 1400922. (112) Jona Kurpiers, Thomas Ferron, Steffen Roland, Marius Jakoby, Tobias Thiede, Frank Jaiser, Steve Albrecht, Silvia Janietz, Brian A. Collins, Ian A. Howard, Dieter Neher, Probing the pathways of free charge generation in organic bulk heterojunction solar cells, Nat. Commun. 2018, 9, 2038. (113) Flurin Eisner, Mohammed Azzouzi, Zhuping Fei, Xueyan Hou, Thomas D. Anthopoulos, Terence John Stephen Dennis, Martin J. Heeney, Jenny Nelson, Hybridization of Local Exciton and Charge-Transfer States Reduces Non-Radiative Voltage Losses in Organic Solar Cells, J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.1029b01465. (114) Beatrix Blank, Thomas Kirchartz, Stephan Lany, Uwe Rau, Selection Metric for Photovoltaic Materials Screening Based on Detailed-Balance Analysis, Phys. Rev. Applied 2017, 8, 024032. (115) Robert Englman, Joshua Jortner, The energy gap law for radiationless transitions in large molecules, Mol. Phys. 1970, 18, 145-164. (116) Elisa Collado-Fregoso, Silvina N. Pugliese, Mariusz Wojcik, Johannes Benduhn, Eyal Bar-Or, Lorena Perdigón Toro, Ulrich Hörmann, Donato Spoltore, Koen Vandewal, Justin M. Hodgkiss, Dieter Neher, Energy-Gap Law for Photocurrent Generation in Fullerene-Based Organic Solar Cells: The Case of Low-Donor-Content Blends, J. Am. Chem. Soc. 2019, 141, 23292341.

ACS Paragon Plus Environment