Theoretical design of porphyrin dyes with electron-deficit heterocycles towards near-IR light sensitization in dye-sensitized solar cells

Solar Energy 188 (2019) 742–749

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Theoretical design of porphyrin dyes with electron-deficit heterocycles towards near-IR light sensitization in dye-sensitized solar cells ⁎

T ⁎

Wei Lia, Wenhui Rena, Zhi Chena, Teng-Fei Lub, , Lei Denga, Jianfeng Tanga, Xingming Zhanga, , ⁎ Liang Wanga, , Fu-Quan Baib a

College of Science, Hunan Agricultural University, Changsha 410128, People’s Republic of China International Joint Research Laboratory of Nano-Micro Architecture Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People’s Republic of China

b

A R T I C LE I N FO

A B S T R A C T

Keywords: Dye-sensitized solar cells Absorption spectrum Electronic structure Charge transfer Density functional theory

We develop a series of porphyrin sensitizers with electron-deficit heterocycles based on the well-known YD2-oC8 dye for application in dye-sensitized solar cells with the help of ab initio density functional theory calculations and quantum dynamics simulation based on the tight-binding extended Hückel Hamiltonian at the semiempirical level. The calculation results show that introduction of electron-deficit heterocycles into the porphyrin dyes can remarkably red-shift and broaden the Q band of the absorption spectrum and extend the coverage into nearinfrared region, improving the light-harvesting ability. The key parameters influencing the photocurrent and max ), intramolecular charge transfer, photovoltage performance such as maximum short-circuit photocurrent ( JSC interface electron injection, and the shift of TiO2 conduction band edge (Δ ECB) are superior to YD2-o-C8 dye. Therefore, the designed sensitizers would be promising candidate for utilization in dye-sensitized solar cells.

1. Introduction Dye-sensitized solar cells (DSSCs) have attracted much attentions in the past two decades (Yella et al., 2011; Yuan et al., 2019; Zhang et al., 2009; Luo et al., 2019; Xie et al., 2016; Chen et al., 2019). They are promising alternatives to the conventional Si-based solar cells due to the advantages of low cost and high power conversion efficiency (PCE). The DSSCs device is composed of dye sensitizer, wide band gap semiconductor (i.e., TiO2), redox electrolyte (i.e., I−/I3−), and counter electrode. Dye sensitizer harvests the sunlight and produces the photoexcited electrons which are subsequently transferred to the TiO2 semiconductor, playing important roles in achieving high-performing device. The dye’s performance largely depends on its light-harvesting ability and interface electron transfer (IET) rate which can be separately characterized by the coverage of absorption spectrum with solar spectrum and fundamental details of photo-excited state. Large amounts of dye sensitizers have been synthesized and applied in DSSCs, in particular, the push-pull type metalized porphyrin dyes have attracted significant attentions because of its potential to be utilized as an efficient sensitizer (Keawin et al., 2016; Ding et al., 2017; Lu et al., 2015; Zhang et al., 2014). Porphyrin dyes are subject to benefits of inexpensive metal center, tunable optical properties, and

⁎

photostability (van der Salm et al., 2015). One of the intriguing peculiarities to make porphyrins and their derivatives success is the extremely broad absorption spectrum which covers the visible part and extends into near infrared (NIR) region of solar spectrum. For example, the absorption spectrum of typical porphyrin dyes featuring a strong Soret band (400–500 nm) and a weak Q band (500–700 nm). DSSCs device based on D-π-A style metalized porphyrins dye, such as YD2-oC8, has achieved efficiency over 12% (Yella et al., 2011), which is still far below thermodynamics theoretical limitation. The main problem limits the performance of YD2-o-C8 arises from their poor light-harvesting ability at Q band of absorption spectrum. Fortunately, structural modifications of porphyrin dyes on the same molecular axis by using different functional groups provide flexible way to regulate the optical and electronic properties. Computational investigations can predicate beforehand the target properties, establish the structure-property relationship, and save the experimental expense regarding the development of new dyes (Li et al., 2018a; He et al., 2017; Heng et al., 2019; Chen et al., 2019; Yang et al., 2017). In particular, theoretical investigations of YD2-o-C8 dye have been focused on the replacement of different metal center (Ørnsø et al., 2014), addition of electron donor and acceptor groups (Fu et al., 2018), construction of multiporphyrin (Sánchez-Bojorge et al., 2017), change orientation of adsorption (Zhu

Corresponding authors. E-mail addresses: [email protected] (T.-F. Lu), [email protected] (X. Zhang), [email protected] (L. Wang).

https://doi.org/10.1016/j.solener.2019.06.062 Received 19 April 2019; Received in revised form 5 June 2019; Accepted 25 June 2019 0038-092X/ © 2019 International Solar Energy Society. Published by Elsevier Ltd. All rights reserved.

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Intramolecular charge transfer (ICT) character is analyzed using the electron density difference maps as visualized by Multiwfn code (Lu and Chen, 2012). In order to describe the dye-TiO2 interaction, we adopted the (TiO2)38 cluster model obtained by cutting from the anatase slab with (1 0 1) exposed surface. The use of (TiO2)38 cluster model in investigations of dye/TiO2 interaction enables the comprise between accuracy and computational cost. It is interesting to note that the same model has been widely employed in previous literatures (Fu et al., 2018; Chitumalla and Jang, 2018), including our previous works (Li et al., 2014a, 2014b, 2015; Lu et al., 2018a, 2018b). The dye/TiO2 combined system used for simulation of IET are based on the stable bidentate binding modes of a carboxylic acid on the anatase (1 0 1) surface, with the dissociated proton to an O atom of the TiO2 surface (Hirva and Haukka, 2010). The dye/(TiO2)38 combined systems are optimized by means of projector-augmented wave (PAW) methods with the generalized gradient approximation (GGA) using the Perdew-BurkeErnzerhof (PBE) exchange-correlation functional, as implemented in VASP code (Kresse and Hafner, 1993). An energy cutoff of 400 eV and Gamma k-point are adopted for the structure optimization. The geometry optimization is stopped until the force on each atom is smaller than 0.01 eV/Å. A vacuum layer of at least 10 Å is added in the x-, y-, and z-directions to ensure there is no interaction between periodic boundary. Simulation of IET process is carried out using the quantum dynamics method based on semiempirical EH Hamiltonian. The EH method has been widely used to calculate the electronic structure of periodic condensed matter systems. It requires small number of transferable parameters and is able to provide reliable description of chemical bonding and energy band of both elemental and bulk materials with relatively small computation expense (Cerdá and Soria, 2000). Previous work showed that the EH method is capable of predication of band gap of TiO2 nanoparticles which agree well with experiment (Rego and Batista, 2003). The EH Hamiltonian is computed in the basis of the atomic orbital (AO). The diagonalization of the EH Hamiltonian gives expansion coefficients which are further used to propagate the timedependent electronic wavefunction. More details regarding the quantum dynamics method used can be found elsewhere (Rego and Batista, 2003; Hoff et al., 2013; Li et al., 2014c, 2014d; Monti et al., 2015; Li et al., 2018b; Torres et al., 2018; Li et al., 2018c; Rego and Bortolini, 2019; Li et al., 2018d; Shahroosvand et al., 2015; Li et al., 2018e).

Fig. 1. Molecular structures of dye 1–6 investigated in this work.

et al., 2018), variation of the position of substitution (β- or meso-pyrrolic positions) (Mapley et al., 2018), etc, generating valuable information for molecular engineering for specific applications. However, the absorption spectrum of YD2-o-C8 and its derivatives still has narrow Q band, which is unfavorable for the harvests of more sunlight. It is therefore essential to develop porphyrin dyes with superior absorption property for further optimization of DSSCs device. In this work, we designed a series of porphyrin dyes 2–6 based on the reference dye (YD2-o-C8, coded as dye 1) by introduction of electron-deficit heterocycles which was demonstrated to significantly alter the electronic and optical properties of dye molecule (Li et al., 2015). The structures of all dyes are shown in Fig. 1. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations are used to determine the geometrical structure, electronic structure, optical absorption, intramolecular charge transfer character, etc. Moreover, quantum dynamics simulation based on tight-binding extended Hückel (EH) Hamiltonian is used to describe the IET of dye-TiO2 combined system. The key parameters influencing the short-circuit photocurrent (Jsc) and open-circuit photovoltage (Voc) are discussed and used to evaluate the performance of different dyes. The simulated results show that introduction of electron-deficit heterocycles into the porphyrin dyes can notably improve the optoelectronic properties, providing valuable strategy for molecular engineering of potential dyes towards high-performing DSSCs devices.

3. Result and discussion 3.1. Isolated dyes Distribution of the frontier molecular orbital (FMO) of dye sensitizer, such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), provides important information on the charge-separation process in DSSCs. Ideally, HOMO and LUMO should localized at different parts of the dye sensitizer, and thus to generate an efficient charge-separation state. We calculated the HOMO and LUMO distributions for all dyes, see Fig. 2. For reference dye 1, HOMO is a π orbital and locates predominately at electron donor and porphyrin, whereas LUMO is a π* orbital and mainly localized on porphyrin, π-bridge, and electron acceptor. Both HOMO and LUMO show sizeable overlap at porphyrin core, providing channel for directional charge transfer from electron donor to electron acceptor. Moreover, electron acceptor has considerable contribution to the LUMO, which is favorable for the electronic coupling between dye excited states and TiO2 conduction band (CB) states, and consequently, the beneficial interface electron transfer. Introduction of heterocycles has minor influence on the distributions of HOMOs which show similar features with dye 1. In contrast, notable difference can be observed for LUMO distributions of designed dyes. We find that introduction of

2. Method All DFT and TD-DFT calculations are performed using Gaussian09 program (Frisch et al., 2016). Geometry optimizations of the isolated dyes are carried out using B3LYP functional with 6-31G(d)/LanL2DZ basis set (Stephens et al., 1994) which has proven to provide reliable description of the ground state structure. TD-DFT calculations for optical properties are performed using the same basis set as geometry optimization, CAM-B3LYP functional is used explicitly since it has demonstrated the accuracy for simulation of absorption spectrum and intramolecular charge transfer state of porphyrin dyes (Fu et al., 2018). The solvent effect of dichloromethane is evaluated by using the polarizable continuum model (PCM) (Cossi and Barone, 2001). 743

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Fig. 2. Distributions of HOMOs and LUMOs for all dyes.

newly designed dyes. We further quantify the ICT properties using the key parameters such as length of charge transfer (dCT), amount of transfer electrons (qCT), and extent of charge separation (t), as original proposed by Ciofini et al. (2012) and further applied by a number researchers (Li et al., 2018a; He et al., 2017; Lu et al., 2018a; Li et al., 2017; Wu et al., 2016; Yang et al., 2015; Li et al., 2018f; Lu et al., 2017). These parameters are calculated and listed in Table 2. Generally, the dye with longer dCT, stronger qCT, and larger t would have more efficient ICT character. As shown in Table 2, we find that dyes 2–6 exhibit the long dCT (in the range of 2.4–4.2 Å), which is several times larger than the reference dye 1. In addition, dye 1 has a much small qCT among all dyes. The values of t increase following the order: dye 1 < dye 4 < dye 2 < dye 5 < dye 3 < dye 6. We conclude that introduction of electron-deficit heterocycles could lead to a more efficient ICT character. The optical absorption spectra of all dyes are simulated using TDDFT method, as shown in Fig. 5. The calculated excitation energy, oscillator strength, and transition character are reported in Table 1. All dyes show the obvious characteristic absorption bands of porphyrin derivatives, which are intense Soret band and weak Q bands. Obviously, dyes 2–6 show red-shifted and broadened Q band and similar Soret band compared to reference dye 1. The simulated oscillator strengths corresponding to lowest-lying excitation energy are about 1.0793, 1.2279, 1.3582, 1.3332, 1.1696 for dyes 2–6, respectively, exhibiting an increment by a factor of ∼ 3–4 relative to dye 1. In particular, dye 4 has the lowest-lying absorption band at around 1000 nm with its tail extending to ∼ 1400 nm, and shows redshift of ∼ 350 nm compared to dye 1. It is well-known that a broad absorption spectrum covering the whole visible spectra region (400–800 nm) and even expand to the NIR region (∼1000 nm) is necessary to achieve the better photocurrent performance. In this respect, changes in the absorption profile upon introduction of heterocycles into the porphyrin-based dyes are beneficial for harvesting of more low energy photons. The redshift of Q band can be understood from the electronic structure of different dyes. A substantial destabilization of LUMO levels for dyes 2–6 with respect to dye 1 can be observed, see Fig. 3, this is because the introduction of electron-deficit heterocycles causes the more delocalization of LUMO orbital into the electron acceptor through the π-bridge. TD-DFT

heterocycles enables more contribution of electron acceptor to the LUMO orbital and less electron density locates on the porphyrin core, especially in dyes 3 and 6, and this can be rationalized by the strong electron-withdrawing ability of the heterocycles. It is worthy of mention that substantial LUMO electron density reside on electron acceptor moiety is desired for the electronic coupling between dye excited state and TiO2 CB states, accelerating electron injection process. Given the difference in the FMO distributions, we expect the variation of corresponding energy levels. Appropriate energy alignments between dye LUMO and TiO2 CB states are required for an efficient dye. For example, dye HOMO and redox potential of I−/I3− electrolyte in order to guarantee the efficient electron injection and dye regeneration processes. The calculated energy levels for all dyes are shown in Fig. 3. Apparently, all dyes have HOMO levels lower than redox potential of I−/I3− (−4.8 eV) (Zhang et al., 2009) and LUMO levels higher than TiO2 CB (−4.0 eV) (Grätzel, 2001), indicating that all dyes would have the efficient electron injection from dye excited state into TiO2 CB and regeneration of oxidized dye by I−/I3− electrolyte. The HOMO-LUMO energy gaps of designed dyes are smaller than the reference dye 1. Variation of the energy gap in different dyes can be attributed to the destabilization of both HOMO and LUMO energy levels. In particular, dyes 2 and 4 have much smaller energy gap than others which ensures the harvests of more sunlight upon photoexcitation, essential for better photocurrent performance. In order to gain more insights into ICT process, we analyze the electron density difference (Δρ) between first excited state and ground state, as shown in Fig. 4. The blue (purple) region corresponds to decreasing (increasing) electron density. It is clear, from the Δρ plots, that decreasing (increasing) electron density locates mostly at the porphyrin core for the reference dye 1. Dyes 2–6 have more electron density increasing area locates at electron acceptor, forming the efficient chargeseparation state, this is because introduction of heterocycles enhance the electron-accepting ability of the acceptor. With aim of further visualizing the ICT process, two centroids of charges associated with the positive and negative electron density regions are presented in Fig. 4 as well. The relatively small overlaps between the electron density depletion and the increment regions in dyes 2–6 compared to reference dye 1 is observed, indicating the left-to-right ICT process happens in the 744

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Fig. 3. Calculated energy levels and partial density of states (DOS) of corresponding molecular orbitals for all dyes. max clear that dyes 2 ∼ 6 show much larger JSC than the reference dye 1, indicating that the improved absorption in the Q band could outperform the lower absorption in the Soret band. Dyes 2 and 4 exhibit the max largest JSC , 52.02 mA cm−2 and 52.39 mA cm−2, respectively, implying the two dyes should have highest light harvesting ability. The max larger JSC of dyes 2 and 4 relative to other dyes is mainly because of the stronger Q band.

calculations reveal that HOMO and LUMO orbitals are significant involved in the dominated transition of the lowest-lying absorption band (Q band). It is worthy of noticing that although dyes 2–6 exhibit the broadened and stronger Q band, they have a narrower and weaker Soret band. It is unclear whether the weakened absorption in the Soret band could conquer the stronger absorption in the Q band. To give a more quantitative evaluation of the light absorption ability of different dyes, short-circuit photocurrent ( JSC ) can be given as:

JSC = e

∫ LHE (λ)Φing ηreg ηcoll φph.AM1.5G (λ) dλ

3.2. Dye/TiO2 interface Dye/TiO2 interface interaction determines the electronic coupling of the dye’s excited state with TiO2 CB states, and thus the IET process. IET should be fast to avoid the energy loss of photoexcited electron as electron–phonon relaxation pathway. The optimized structures of dye/ (TiO2)38 combined system is shown in Fig. S1. The calculated bond distances between the Ti atom and the O atom of dyes are in the range of 2.000–2.100 Å, which is consistent with previous investigations (Li et al., 2014a, 2014b). The time-dependent state population, shown in Fig. 7, represents the electron injection starting from dye LUMO into TiO2 CB obtained from quantum dynamics simulation based on EH method. Exponential fitting of decay curves gives the characteristic times for electron injection process. It is clear that, for dyes 2–6, the electron injection occurs within ps timescale, suggesting that all dyes have faster IET process. The electron injection in reference dye 1 is an order of magnitude slower than the other dyes. The faster electron injection in dyes 2–6 is because of the favorable orbital distribution and the more efficient ICT benefits the electronic coupling between dye excited state and TiO2 CB,

(1)

where LHE (λ ) is the light harvesting efficiency, it can be further determined by LHE (λ ) = 1 − 10−ε (λ) bc , ε (λ ) is the molar absorption coefficient associated with given wavelength, b is the TiO2 film thickness, and c is the dye concentration. We adopt the experimental values of b and c which are 10 mm and 300 mmol L-1, respectively (Ma et al., 2014). φph . AM1.5G (λ ) is the photon flux under AM 1.5G solar radiation spectrum. Φing to ηreg , ηcoll are the electron injection efficiency, dye regeneration efficiency, and charge collection efficiency, respectively. Under the assumption of the three parameters equal to 1 in calculation, max by we could obtain the maximum short-circuit photocurrent JSC computing the overlap between photon flux and LHE (λ ) . And hence the max JSC is an indication of matching degree between the absorption spectrum and the radiation spectrum of sunlight. The simulated LHE (λ ) and max photon flux curves and calculated JSC of all dyes are presented in Fig. 6 max and Table 2, respectively. The calculated JSC for all dyes increase in the order: dye 1 < dye 6 < dye 5 < dye 3 < dye 2 < dye 4. It is 745

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Fig. 4. Plots of the charge density difference (Δρ) between excited state and ground state, centroids of charges for all dyes. Blue (purple) color denotes decreasing (increasing) of electron density. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

TiO2 surface. Larger ΔECB usually induces impressive Voc performance. It has been demonstrated that the change in TiO2 CB edge (ECB ) arises from the dipole moment of dye molecules. The larger dipole moment of dye molecule perpendicular to TiO2 surface, then higher ECB is expected. The magnitude of ΔECB for different dyes can be determined from the pDOS plots for pristine TiO2 and dye/TiO2 combined system, as shown in Fig. 8. Linear fittings of pDOS curve of TiO2 CB in the lower energy part are performed. The intercept points between the x-axis and the fitted lines are denoted as the ECB . The calculated ΔECB are listed in Table 2. As shown that, Δ ECB decreases following the order of dye 4 (0.68 eV) > dye 2 (0.65 eV) > dye 5 (0.64 eV) > dye 3

thus the fast IET rate. In addition to the photocurrent, photovoltage Voc is another important parameter influencing the DSSCs performance. The Voc can be expressed using the following equation:

Voc =

EF , N E + ΔECB k T n − Eredox = CB + b ln ⎛ c ⎞ − Eredox e q q ⎝ NCB ⎠ ⎜

⎟

(2)

where e, nc, Eredox, and NCB are the elementary charge, the number of injected electrons, the redox potential of the I−/I3− electrolyte, and the density of TiO2 CB states, respectively. Δ ECB is defined as the energy difference of TiO2 CB edge (ΔECB ) before and after dye adsorption onto

Fig. 5. Simulated absorption spectra for all dyes dissolved in dichloromethane solvent at the TD-CAM-B3LYP/6-31G(d) level of theory. 746

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Table 1 Main electronic transition, excitation energy (ΔEcal), wavelength (λcal), oscillator strength (f) for all dyes. Dye

Ex.

Excitation

ΔEcal (eV)

λcal (nm)

f

1

S1 S5 S1 S7 S1 S7 S1 S7 S1 S7 S1 S8

HOMO → LUMO HOMO-1 → LUMO + 1 HOMO → LUMO HOMO-1 → LUMO + 2 HOMO → LUMO HOMO-1 → LUMO + 2 HOMO → LUMO HOMO-1 → LUMO + 2 HOMO → LUMO HOMO-1 → LUMO + 2 HOMO → LUMO HOMO-1 → LUMO + 2

2.0473 3.0997 1.3031 3.0584 1.4261 3.1003 1.3001 3.0920 1.6028 3.0935 1.9428 3.1188

605.60 399.98 951.45 405.39 869.41 399.92 953.64 400.99 773.54 400.79 638.19 397.54

0.3775 2.0031 1.0793 1.7199 1.2279 1.6333 1.3582 1.5160 1.3332 1.4042 1.1696 1.7698

2 3 4 5 6

Fig. 8. Schematic representation of the model used to estimate the shift of TiO2 conduction band edge.

Table 2 Calculated charge transfer parameters, Jsc and ΔEcb of all dye systems. Dye

Ex.

dCT (Å)

qCT (e)

t (Å)

max JSC ( mA cm−2)

ΔEcb (eV)

1 2 3 4 5 6

S1 S1 S1 S1 S1 S1

1.072 2.437 2.776 2.311 2.733 4.270

0.288 0.512 0.544 0.480 0.510 0.568

−3.746 −3.337 −2.992 −3.432 −3.036 −2.598

26.99 52.02 49.57 52.39 44.73 34.02

0.56 0.65 0.63 0.68 0.64 0.55

4 stands out because of its much larger Δ ECB.

3.3. Conclusion In summary, we have designed a series of Zn-porphyrin derivative dyes by introduction of electron-deficit heterocycles based on the YD2o-C8 dye. The important properties relevant to the photocurrent and photovoltage performance of dye sensitizer, including light-harvesting ability, intramolecular charge transfer, interface electron transfer, and the shift of TiO2 CB edge, are analyzed in detail. The calculation results show that all the designed dyes exhibit smaller HOMO-LUMO energy gap relative to the reference dye 1, leading to red-shifted and broadened absorption band which extends into NIR region. The decreased HOMO-LUMO gap in dyes 2–6 can be attributed to the significant delocalization of LUMO orbitals into electron acceptor moiety. Such favorable FMO distribution has two major outcomes. First, the intramolecular charge transfer efficiency is enhanced due to the longer charge transfer distance, larger amount of transferred electron, and better charge separation since HOMO and LUMO have less overlap on the π-spacer. Second, the electron transfer across the dye/TiO2 interface is accelerated since more contribution of electron acceptor moiety to the LUMO orbitals causes downshift of LUMO levels which match in energy with the lower manifold of electronic states in the TiO2 CB and favor the electronic coupling between dye excited state and TiO2 CB states. We also find that introduction of electron-deficit heterocycles has non-negligible influences on the shift of TiO2 CB edge. The results demonstrated that all designed dyes would be promising to challenge max the performance of reference dye 1 since they perform well on JSC , ICT parameters, electron injection, and shift of TiO2 CB edge. The simulations performed in this work is expected to pave the way for design Znporphyrin based sensitizers for high-performing DSSCs device.

Fig. 6. The calculated LHE curves for all dyes.

Acknowledgement W.L. acknowledges startup funding from Hunan Agricultural University (grant Nos. 540499818006 and 18QN02). L.W. acknowledge support of the National Science Foundation of China, grant 11802092. F.Q.B. acknowledges the Opening Foundation of State Key Laboratory of Chemo/Biosensing and Chemometrics of Hunan University and the Young Scholar Training Program of Jilin University, the support by the department of education, Jilin province, grant No. JJKH20180558KJ.

Fig. 7. The time-dependent survival probability curves for electron injection starting from the initial state for all dyes.

Appendix A. Supplementary material (0.63 eV) > dye 1 (0.56 eV) > dye 6 (0.55 eV). Apparently, most of the designed dyes would have better Voc performance than the reference dye 1. Dye 6 has the comparable Voc with respect to dye 1. Dye

Supplementary data to this article can be found online at https:// doi.org/10.1016/j.solener.2019.06.062. 747

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References

Li, W., Rego, L.G.C., Bai, F.-Q., Kong, C.-P., Zhang, H.-X., 2014d. Theoretical investigation of the adsorption, IR, and electron injection of hydroxamate anchor at the TiO2 anatase (1 0 1) surface. RSC Adv. 4, 19690–19693. https://doi.org/10.1039/ C4RA01116C. Li, W., Bai, F.-Q., Chen, J., Wang, J., Zhang, H.-X., 2015. Planar amine-based dye features the rigidified O-bridged dithiophene π-spacer: a potential high-efficiency sensitizer for dye-sensitized solar cells application. J. Power Sources. 275, 207–216. https:// doi.org/10.1016/j.jpowsour.2014.11.013. Li, W., Zhou, L., Prezhdo, O.V., Akimov, A.V., 2018c. Spin-orbit interactions greatly accelerate nonradiative dynamics in lead halide perovskites. ACS Energy Lett. 2159–2166. https://doi.org/10.1021/acsenergylett.8b01226. Li, W., Long, R., Hou, Z., Tang, J., Prezhdo, O.V., 2018e. Influence of encapsulated water on luminescence energy, line width, and lifetime of carbon nanotubes: time domain ab initio analysis. J. Phys. Chem. Lett. 4006–4013. https://doi.org/10.1021/acs. jpclett.8b02049. Li, W., Tang, J., Casanova, D., Prezhdo, O.V., 2018d. Time-domain ab initio analysis rationalizes the unusual temperature dependence of charge carrier relaxation in lead halide perovskite. ACS Energy Lett. 3, 2713–2720. https://doi.org/10.1021/ acsenergylett.8b01608. Li, P., Wang, Z., Song, C., Zhang, H., 2017. Rigid fused π-spacer in D-π-A type molecule for dye-sensitized solar cell: a computational investigation. J. Mater. Chem. C. https://doi.org/10.1039/C7TC03112B. Li, W., Lu, T.-F., Ren, W., Deng, L., Zhang, X., Wang, L., Tang, J., Kuznetsov, A.E., 2018f. Influence of exciton-delocalizing ligands on the structural, electronic, and spectral features of the Cd33S33 quantum dot: insights from computational studies. J. Mater. Chem. C. https://doi.org/10.1039/C8TC03342K. Li, W., Sun, Y.-Y., Li, L., Zhou, Z., Tang, J., Prezhdo, O.V., 2018b. Control of charge recombination in perovskites by oxidation state of halide vacancy. J. Am. Chem. Soc. 140, 15753–15763. https://doi.org/10.1021/jacs.8b08448. Lu, T., Chen, F., 2012. Multiwfn: a multifunctional wavefunction analyzer. J. Comput. Chem. 33, 580–592. https://doi.org/10.1002/jcc.22885. Lu, T.-F., Li, W., Bai, F.-Q., Jia, R., Chen, J., Zhang, H.-X., 2017. Anionic ancillary ligands in cyclometalated Ru (II) complex sensitizers improve photovoltaic efficiency of dyesensitized solar cells: insights from theoretical investigations. J. Mater. Chem. A. 5, 15567–15577. https://doi.org/10.1039/C7TA03360E. Lu, T.-F., Li, W., Chen, J., Tang, J., Bai, F.-Q., Zhang, H.-X., 2018b. Promising pyridinium ylide based anchors towards high-efficiency dyes for dye-sensitized solar cells applications: insights from theoretical investigations. Electrochimica Acta 283, 1798–1805. https://doi.org/10.1016/j.electacta.2018.07.108. Lu, T.-F., Li, W., Zhang, H.-X., 2018a. Rational design of metal-free organic D-π-A dyes in dye-sensitized solar cells: Insight from density functional theory (DFT) and timedependent DFT (TD-DFT) investigations. Org. Electron. 59, 131–139. https://doi.org/ 10.1016/j.orgel.2018.05.005. Lu, X., Shao, Y., Wei, S., Zhao, Z., Li, K., Guo, C., Wang, W., Zhang, M., Guo, W., 2015. Effect of the functionalized π-bridge on porphyrin sensitizers for dye-sensitized solar cells: an in-depth analysis of electronic structure, spectrum, excitation, and intramolecular electron transfer. J. Mater. Chem. C. 3, 10129–10139. https://doi.org/ 10.1039/C5TC02286J. Luo, J., Wan, Z., Han, F., Malik, H.A., Zhao, B., Xia, J., Jia, C., Wang, R., 2019. Origin of increased efficiency and decreased hysteresis of perovskite solar cells by using 4-tertbutyl pyridine as interfacial modifier for TiO2. J. Power Sources 415, 197–206. https://doi.org/10.1016/j.jpowsour.2019.01.064. Ma, W., Jiao, Y., Meng, S., 2014. Predicting energy conversion efficiency of dye solar cells from first principles. J. Phys. Chem. C. 118, 16447–16457. https://doi.org/10.1021/ jp410982e. Mapley, J.I., Wagner, P., Officer, D.L., Gordon, K.C., 2018. Computational and spectroscopic analysis of β-Indandione modified zinc porphyrins. J. Phys. Chem. A. 122, 4448–4456. https://doi.org/10.1021/acs.jpca.8b02746. Monti, A., Negre, C.F.A., Batista, V.S., Rego, L.G.C., de Groot, H.J.M., Buda, F., 2015. Crucial role of nuclear dynamics for electron injection in a dye-semiconductor complex. J. Phys. Chem. Lett. 6, 2393–2398. https://doi.org/10.1021/acs.jpclett. 5b00876. Ørnsø, K.B., Pedersen, C.S., Garcia-Lastra, J.M., Thygesen, K.S., 2014. Optimizing porphyrins for dye sensitized solar cells using large-scale ab initio calculations. Phys. Chem. Chem. Phys. 16, 16246–16254. https://doi.org/10.1039/C4CP01289E. Rego, L.G.C., Batista, V.S., 2003. Quantum dynamics simulations of interfacial electron transfer in sensitized TiO2 semiconductors. J. Am. Chem. Soc. 125, 7989–7997. https://doi.org/10.1021/ja0346330. Rego, L.G.C., Bortolini, G., 2019. Modulating the photoisomerization mechanism of semiconductor-bound azobenzene functionalized compounds. J. Phys. Chem. C. https://doi.org/10.1021/acs.jpcc.8b11057. Sánchez-Bojorge, N.A., Flores-Armendáriz, S., Fuentes-Montero, M.E., Ramos-Sánchez, V.H., Zaragoza-Galán, G., Rodríguez-Valdez, L.M., 2017. Theoretical and experimental analysis of porphyrin derivatives with suitable anchoring groups for DSSC applications. J. Porphyr. Phthalocyan. 21, 88–102. https://doi.org/10.1142/ S1088424617500109. Shahroosvand, H., Zakavi, S., Sousaraei, A., Eskandari, M., 2015. Saddle-shaped porphyrins for dye-sensitized solar cells: new insight into the relationship between nonplanarity and photovoltaic properties. Phys. Chem. Chem. Phys. 17, 6347–6358. https://doi.org/10.1039/C4CP04722B. Stephens, P.J., Devlin, F.J., Chabalowski, C.F., Frisch, M.J., 1994. Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields. J. Phys. Chem. 98, 11623–11627. https://doi.org/10.1021/j100096a001. Torres, A., Prado, L.R., Bortolini, G., Rego, L.G.C., 2018. Charge transfer driven structural relaxation in a push-pull azobenzene dye-semiconductor complex. J. Phys. Chem. Lett. 9, 5926–5933. https://doi.org/10.1021/acs.jpclett.8b02490.

Cerdá, J., Soria, F., 2000. Accurate and transferable extended Hückel-type tight-binding parameters. Phys. Rev. B. 61, 7965–7971. https://doi.org/10.1103/PhysRevB.61. 7965. Chen, Y.-Z., Wu, R.-J., Lin, L.-Y., Chang, W.-C., 2019. Novel synthesis of popcorn-like TiO2 light scatterers using a facile solution method for efficient dye-sensitized solar cells. J. Power Sources 413, 384–390. https://doi.org/10.1016/j.jpowsour.2018.12. 065. Chen, C.-J., Zhang, J., Fu, Z.-H., Zhu, H.-C., Li, H., Zhu, X.-F., 2019. Theoretical insights on the comparison of champion dyes SM315 and C275 used for DSSCs reaching over 12% efficiency and the further optimization of C275. Spectrochim. Acta A. Mol. Biomol. Spectrosc. 117217. https://doi.org/10.1016/j.saa.2019.117217. Chitumalla, R.K., Jang, J., 2018. Density functional theory study on ruthenium dyes and dye@TiO2 assemblies for dye sensitized solar cell applications. Sol. Energy. 159, 283–290. https://doi.org/10.1016/j.solener.2017.10.058. Ciofini, I., Le Bahers, T., Adamo, C., Odobel, F., Jacquemin, D., 2012. Through-space charge transfer in rod-like molecules: lessons from theory. J. Phys. Chem. C. 116, 11946–11955. https://doi.org/10.1021/jp3030667. Cossi, M., Barone, V., 2001. Time-dependent density functional theory for molecules in liquid solutions. J. Chem. Phys. 115, 4708. https://doi.org/10.1063/1.1394921. Ding, W.-L., Cui, Y.-M., Yang, L.-N., Li, Q.-S., Li, Z.-S., 2017. Rational design of nearinfrared Zn-porphyrin dye utilized in co-sensitized solar cell toward high efficiency. Dyes Pigm. 136, 450–457. https://doi.org/10.1016/j.dyepig.2016.09.002. Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Scalmani, G., Barone, V., Mennucci, B., Petersson, G.A., Nakatsuji, H., Caricato, M., Li, X., Hratchian, H.P., Izmaylov, A.F., Bloino, J., Zheng, G. Sonnenberg, J.L., Hada, M., Ehara, M., Toyota, K., Fukuda, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y., Kitao, O., Nakai, H., Vreven, T., Montgomery Jr. J.A., Peralta, J.E., Ogliaro, F., Bearpark, M., Heyd, J.J., Brothers, E., Kudin, K.N., Staroverov, V.N., Kobayashi, R., Normand, J., Raghavachari, K., Rendell, A., Burant, J.C., Iyengar, S.S., Tomasi, J., Cossi, M., Rega, N., Millam, J.M., Klene, M., Knox, J.E., Cross, J.B., Bakken, V., Adamo, C., Jaramillo, J., Gomperts, R., Stratmann, R.E., Yazyev, O., Austin, A.J., Cammi, R., Pomelli, C., Ochterski, J.W., Martin, R.L., Morokuma, K., Zakrzewski, V. G., Voth, G.A., Salvador, P., Dannenberg, J.J., Dapprich, S., Daniels, A.D., Farkas, Foresman, J.B., Ortiz, J.V., Cioslowski, J., Fox, D.J., 2016. Gaussian, Inc., Wallingford CT, Gaussian09 Revision E.01. Fu, Y., Lu, T., Xu, Y., Li, M., Wei, Z., Liu, H., Lu, W., 2018. Theoretical screening and design of SM315-based porphyrin dyes for highly efficient dye-sensitized solar cells with near-IR light harvesting. Dyes Pigm. 155, 292–299. https://doi.org/10.1016/j. dyepig.2018.03.045. Grätzel, M., 2001. Photoelectrochemical cells. Nature 414, 338–344. https://doi.org/10. 1038/35104607. He, L.-J., Wei, W., Chen, J., Jia, R., Wang, J., Zhang, H.-X., 2017. The effect of D–[D e –π–A] n (n = 1, 2, 3) type dyes on the overall performance of DSSCs: a theoretical investigation. J. Mater. Chem. C. 5, 7510–7520. https://doi.org/10.1039/ C7TC02499A. Heng, P., Xu, J., Mao, L., Wang, L., Wu, W., Zhang, J., 2019. Rational design of D-π-A organic dyes to prevent “trade off” effect in dye-sensitized solar cells. Spectrochim. Acta A. Mol. Biomol. Spectrosc. 221, 117167. https://doi.org/10.1016/j.saa.2019. 117167. Hirva, P., Haukka, M., 2010. Effect of different anchoring groups on the adsorption of photoactive compounds on the anatase (101) surface. Langmuir 26, 17075–17081. https://doi.org/10.1021/la102468s. Hoff, D.A., Rego, L.G.C., 2013. Chapter 4. Modelling electron quantum dynamics in large molecular systems. In: Springborg, M., Joswig, J.-O. (Eds.), Chem. Model. Royal Society of Chemistry, Cambridge, pp. 102–126. https://doi.org/10.1039/ 9781849737241-00102. accessed August 1, 2016. Keawin, T., Tarsang, R., Sirithip, K., Prachumrak, N., Sudyoadsuk, T., Namuangruk, S., Roncali, J., Kungwan, N., Promarak, V., Jungsuttiwong, S., 2016. Anchoring numberperformance relationship of zinc-porphyrin sensitizers for dye-sensitized solar cells: a combined experimental and theoretical study. Dyes Pigm. https://doi.org/10.1016/j. dyepig.2016.09.035. Kresse, G., Hafner, J., 1993. Ab initio molecular dynamics for liquid metals. Phys. Rev. B. 47, 558–561. https://doi.org/10.1103/PhysRevB.47.558. Li, M., Kou, L., Diao, L., Zhang, Q., Li, Z., Wu, Q., Lu, W., Pan, D., Wei, Z., 2015. Theoretical study of WS-9-based organic sensitizers for unusual Vis/NIR absorption and highly efficient dye-sensitized solar cells. J. Phys. Chem. C. 119, 9782–9790. https://doi.org/10.1021/acs.jpcc.5b03667. Li, W., Rego, L.G.C., Bai, F.-Q., Wang, J., Jia, R., Xie, L.-M., Zhang, H.-X., 2014c. What makes hydroxamate a promising anchoring group in dye-sensitized solar cells? Insights from theoretical investigation. J. Phys. Chem. Lett. 5, 3992–3999. https:// doi.org/10.1021/jz501973d. Li, P., Song, C., Wang, Z., Li, J., Zhang, H., 2018a. Molecular design towards suppressing electron recombination and enhancing the light-absorbing ability of dyes for use in sensitized solar cells: a theoretical investigation. New J. Chem. 42, 12891–12899. https://doi.org/10.1039/C8NJ02188K. Li, W., Wang, J., Chen, J., Bai, F.-Q., Zhang, H.-X., 2014a. Theoretical investigation and design of high-efficiency dithiafulvenyl-based sensitizers for dye-sensitized solar cells: the impacts of elongating π-spacers and rigidifying dithiophene. Phys. Chem. Chem. Phys. 16, 9458. https://doi.org/10.1039/c4cp00968a. Li, W., Wang, J., Chen, J., Bai, F.-Q., Zhang, H.-X., 2014b. Theoretical investigation of triphenylamine-based sensitizers with different π-spacers for DSSC. Spectrochim. Acta. A. Mol. Biomol. Spectrosc. 118, 1144–1151. https://doi.org/10.1016/j.saa. 2013.09.080.

748

Solar Energy 188 (2019) 742–749

W. Li, et al.

Yella, A., Lee, H.-W., Tsao, H.N., Yi, C., Chandiran, A.K., Nazeeruddin, M.K., Diau, E.W.G., Yeh, C.-Y., Zakeeruddin, S.M., Gratzel, M., 2011. Porphyrin-sensitized solar cells with cobalt (II/III)-based redox electrolyte exceed 12 percent efficiency. Science 334, 629–634. https://doi.org/10.1126/science.1209688. Yuan, H., Zhao, Y., Wang, Y., Duan, J., He, B., Tang, Q., 2019. Sonochemistry-assisted black/red phosphorus hybrid quantum dots for dye-sensitized solar cells. J. Power Sources 410–411, 53–58. https://doi.org/10.1016/j.jpowsour.2018.11.011. Zhang, G., Bai, Y., Li, R., Shi, D., Wenger, S., Zakeeruddin, S.M., Grätzel, M., Wang, P., 2009. Employ a bisthienothiophene linker to construct an organic chromophore for efficient and stable dye-sensitized solar cells. Energy Env. Sci. 2, 92–95. https://doi. org/10.1039/B817990E. Zhang, J., Zhang, J.-Z., Li, H.-B., Wu, Y., Geng, Y., Su, Z.-M., 2014. Rational modifications on champion porphyrin dye SM315 using different electron-withdrawing moieties toward high performance dye-sensitized solar cells. Phys. Chem. Chem. Phys. 16, 24994–25003. https://doi.org/10.1039/C4CP03355H. Zhu, H.-C., Zhang, J., Wang, Y.-L., 2018. Adsorption orientation effects of porphyrin dyes on the performance of DSSC: comparison of benzoic acid and tropolone anchoring groups binding onto the TiO2 anatase (101) surface. Appl. Surf. Sci. 433, 1137–1147. https://doi.org/10.1016/j.apsusc.2017.10.087.

van der Salm, H., Lind, S.J., Griffith, M.J., Wagner, P., Wallace, G.G., Officer, D.L., Gordon, K.C., 2015. Probing donor-acceptor interactions in meso-substituted Zn(II) porphyrins using resonance Raman spectroscopy and computational chemistry. J. Phys. Chem. C. 119, 22379–22391. https://doi.org/10.1021/acs.jpcc.5b07129. Wu, H., Zhang, T., Wu, C., Guan, W., Yan, L., Su, Z., 2016. A theoretical design and investigation on Zn-porphyrin-polyoxometalate hybrids with different π-linkers for searching high performance sensitizers of p-type dye-sensitized solar cells. Dyes Pigm. 130, 168–175. https://doi.org/10.1016/j.dyepig.2016.03.025. Xie, M., Bai, F.-Q., Zhang, H.-X., Zheng, Y.-Q., 2016. The influence of an inner electric field on the performance of three types of Zn-porphyrin sensitizers in dye sensitized solar cells: a theoretical study. J. Mater. Chem. C. 4, 10130–10145. https://doi.org/ 10.1039/C6TC02457B. Yang, L.-N., Chen, S.-L., Li, Z.-S., 2015. How does the silicon element perform in JD-dyes: a theoretical investigation. J. Mater. Chem. A. 3, 8308–8315. https://doi.org/10. 1039/C5TA00812C. Yang, P., Shen, W., Li, M., He, R., 2017. Exploring the effect of vibronic contributions on light harvesting efficiency of NKX-2587 derivatives through vibrationally resolved electronic spectra. Spectrochim. Acta A. Mol. Biomol. Spectrosc. 171, 406–414. https://doi.org/10.1016/j.saa.2016.08.019.

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