Rational Design of High-Efficiency Organic Dyes in Dye-Sensitized

Subscriber access provided by REGIS UNIV

C: Energy Conversion and Storage; Energy and Charge Transport

Rational Design of High-Efficiency Organic Dyes in Dye-Sensitized Solar Cells by Multiscale Simulations Weiyi Zhang, Panpan Heng, Huishuang Su, Tie-gang Ren, Li Wang, and Jinglai Zhang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b08750 • Publication Date (Web): 17 Oct 2018 Downloaded from http://pubs.acs.org on October 21, 2018

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 41 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

Rational Design of High-Efficiency Organic Dyes in Dye-Sensitized Solar Cells by Multiscale Simulations Weiyi Zhang, Panpan Heng, Huishuang Su, Tiegang Ren*, Li Wang*, Jinglai Zhang* College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475004, P.R. China

Abstract The electrical and optical properties of four T-shaped (D)2-A-π-A organic dyes, 3-(5-(1,4-bis(4-(diphenylamino)phenyl)-6-methyl-6H-indolo[3,2-b]quinoxalin-8-yl)furan -2-yl)-2-cyanoacrylic

acid

(1),

3-(5-(1,4-bis(4-(diphenylamino)phenyl)-6-methyl-6H-indolo[3,2-b]azaquinoxalin-8-yl)fu ran-2-yl)-2-cyanoacrylic

acid

(2),

2-(5-(4,10-bis(4-(diphenylamino)phenyl)-5-methyl-5H-[1,2,5]thiadiazolo[3,4-b]carbazol7-yl)furan-2-yl)-2-cyanoacrylic

acid

(3),

and

3-(5-(4,10-bis(4-(diphenylamino)phenyl)-5-methyl-5H-[1,2,5]oxadiazolo[3,4-b]carbazol7-yl)furan-2-yl)-2-cyanoacrylic acid (4) with triphenylamine as donor, furan as π group, cyanoacrylic acid as acceptor as well as different ancillary acceptors, are theoretical *Corresponding

author 1) Tiegang Ren, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, 475004, China. Tel: +86-371-22196667; Fax: +86-371-22196667. E-mail: [email protected] 2) Li Wang, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, 475004, China. Tel: +86-371-22196667; Fax: +86-371-22196667. E-mail: [email protected] 3) Jinglai Zhang, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, 475004, China. Tel: +86-371-22196667; Fax: +86-371-22196667. E-mail: [email protected] 1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 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

Page 2 of 41

investigated by multiscale simulations. On the basis of the isolated dyes, frontier molecular orbital, the Fӧrster resonance energy transfer, and absorption spectra are studied to explore the effect of different ancillary acceptors. After that, the dye-TiO2 adsorbed system is considered by first-principle. On the basis of the adsorbed system, the accurate values of short-circuit current density, open-circuit voltage, and power conversion efficiency are calculated, which is helpful to distinguish various dyes. It is always a perplexing problem for previous theoretical studies. Additionally, the aggregation effect is also considered to evaluate the performance of dyes. 6-methyl-6H-indolo[3,2-b]azaquinoxaline

and

5-methyl-5H-[1,2,5]oxadiazolo[3,4-b]carbazole are testified to be suitable auxiliary acceptors. As compared with D-π-A dye with the same donor, π group, and acceptor, it testifies that the insertion of ancillary acceptor is important to improve the overall performance.

1. Introduction The requirement of renewable energy resources have resulted in the immense growth and considerable attention for dye-sensitized solar cells (DSSCs) since the breakthrough work in 1991 by O’Regan and Grätzel.1 The low-cost nature of DSSCs affords them lucrative substitute to the conventional silicon-based solar cells. Moreover, their transparent feature inspires us to build the energy-sustainable building for future cities.2 Normally, DSSCs are composed by sensitizers, counter electrodes, redox 2


Page 3 of 41 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


electrolytes, and semiconductor electrodes, in which sensitizer is the critical component.3 Recently, metal-free sensitizers have been the potential alternative for the metal sensitizers due to the facile molecular engineering, high molar extinction coefficient, and low cost. D-π-A (donor-π-acceptor) is the classical architecture for the organic dyes, which is favorable for the intramolecular electron transfer. Later, a series of new type structures, including D-π-D-A type,4 D-A-π-A type,5 and (D)2-π-A type,6 have been designed. However, the largest power conversion efficiency (PCE) of DSSCs is 14.7%,7 which is still less than the thermal-dynamics limitation, ∼33.7%, for single p-n junction solar device.8 Numerous organic dyes have been designed with the centre aim to broad the light harvesting region and enhance the electron injection efficiency. Lots of investigations have testified that a small modification in the dye’s atomic structure would lead to a dramatic difference in performance.9 Theoretical simulations are believed to be a promising alternative to the experimental trial-error investigations since the experimental study is not only time and cost consuming but also non-sensitive to the interfacial properties. However, the accurate prediction of PCE on the basis of the theoretical calculation is still a daunting task. The efficiency of DSSCs would be improved by enlargement of light harvesting region and fast electron injection. The light harvesting ability would be precisely simulated by cautious determination of different functionals and basis sets. However, electron injection is rarely quantitatively determined. Alternatively, some items related with short-circuit current density (JSC) and open-circuit 3



voltage (VOC) are simulated to qualitatively determine the relative performance of different dyes.10,11 The predicted result is far away from the experimental result due to the simple model. It is necessary to quantitatively estimate the JSC and VOC leading to the PCE, which is limited to be reported by Meng and others.12,13 Additionally, the performance of DSSCs is also affected by the aggregation of organic dyes, recombination, quenching, regeneration, and others. Some of them are helpful to refine the overall performance. And they have adverse effect for the PCE. They are even more complicate items to be evaluated accurately for both experimental and theoretical studies. Therefore, it is normally omitted by most of theoretical and experimental studies. Here, we would consider the effect of aggregation qualitatively. It is beneficial to improve the theoretical prediction, although it is a little progress. In this work, not only the PCE is calculated but also the effect of aggregation is considered to estimate the performance of DSSCs based on the organic dyes by multiscale simulations. Three new T-shaped (D)2-A-π-A organic dyes are developed on the basis of reported dye, QX23 (1),14 with the variation of different auxiliary acceptors (See Scheme 1). Triphenylamine is an electron rich moiety, which is favorable for electron donation. Moreover, both the nonplanar shape of triphenylamine and T-shaped architecture of organic dyes are favorable for retarding aggregation. Therefore, only the auxiliary acceptor is varied. It is expected that the slight modification would result in the great enhancement of PCE. More importantly, the quantitative calculation is looking forward to improving the precision of theoretical estimation. In the future, the 4


Page 4 of 41

Page 5 of 41 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


development of organic dyes would follow the steps of theoretical design, screen, and experimental synthesis, which is greatly related with the precision of theoretical prediction. The successful configuration of effective dyes is an insurance to build high efficiency DSSCs. 2. Computational details The ground-state geometries of all the isolated dyes in gas phase were optimized by Becke's three-parameter nonlocal-exchange functional with the nonlocal correlation of Lee-Yang-Parr method (B3LYP)15,16 with the 6-31G(d,p) basis set.17 The frequency calculations were performed at the same level to confirm the stationary nature of optimized geometries at energy minimum with none imaginary frequency. Based on the ground-state geometry of 1, absorption spectra were simulated by a series of time-dependent density functional theory (TD-DFT) including B3LYP, CAM-B3LYP,18 LC-BLYP,19,20 M06-2X,21 and PBE0,22 with polarized continuum model (PCM)23,24 in dichloromethane (DCM) (See Figure S1). The absorption wavelength of 1 simulated by PBE0 method presents the best performance with respect to the experimental data.14 Therefore, the absorption spectra of other dyes were simulated by the same method. All the aforementioned calculations were performed by the Gaussian 09 program.25 The structure of dye adsorbed on the TiO2 anatase (101) surface was simulated by the plane-wave code VASP (Vienna ab initio simulation package)26-28 with the generalized gradient approximation (GGA) as well as Perdew-Burke-Ernzerhof (PBE) exchange-correlation

function

supplemented

with

5


Grimme’s

D2

dispersion


correction.29,30 The energy cutoff was set to be 400 eV and the optimization would stop when the force on each atom was smaller than 0.1 eV Å-1. To get better insight into the interfacial properties of the dye-TiO2 system, the 4 × 8 × 6 supercell has been constructed corresponding to a vacuum buffer space of 21, 31 and 46 Ǻ in x-, y- and z-direction. Furthermore, the densities of states (DOS) and projected density of states (PDOS) were calculated at the same level. For the dimeric dyes adsorbed on the TiO2 surface, the molecular dynamics simulations were carried out for 10 ps with an integration time step of 1 fs at T = 298 K in the constant volume constant internal energy (NVE ensemble), which is completed by the DFTB+ 1.3 package.31 The SK-parameters of mio-1-132-34 for C, N, O, H, and S and tiorg-0-135 for Ti were employed. 3. Results and discussion 3.1 Frontier molecular orbital (FMO) energy levels After the sensitizer harvests light, the excited electron is injected into the conduction band (CB) of the metal oxide semiconductor (normally TiO2). Therefore, the lowest unoccupied molecular orbital (LUMO) should be higher in energy than the CB edge of the TiO2.36 The oxidized dye gets electrons to be regenerated by accepting an electron from the electrolyte (normally iodine/triiodide redox shuttle). Then, the highest occupied molecular orbital (HOMO) should be lower in energy than the iodine/triiodide redox potential.37 The corresponding HOMO and LUMO energy levels are plotted in Figure 1 along with the corresponding energy levels of TiO2 and iodine/triiodide. The investigated 6


Page 6 of 41

Page 7 of 41 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


four dyes are eligible for above basic requirements to form DSSCs. The difference among them is not large enough to differentiate them. Moreover, the energy levels would be varied when the dyes are adsorbed on the TiO2 surface. Therefore, it is not suitable to compare device performance by FMO energy levels of isolated dyes. 3.2 Absorption spectrum The light harvesting ability is one of the most important roles played by dyes including the absorption region and intensity. The strongest absorption wavelength for 1 is 444 nm, which is consistent with the experimental result of 438 nm. The maximum absorption wavelength (λmax) would reach 612-642 nm (See Figure 2). Moreover, the λmax of designed dyes are all red-shifted as compared with 1 indicating that the more light would be harvested. According to the following equation:38 J SC  e  LHE ( )injregcollph.AM1.5G ( )

(1)

the larger light harvesting efficiency (LHE) indicates the larger JSC. If the electron injection efficiency (Фinj), the dye regeneration efficiency (ηreg), and collection efficiency (ηcoll) are regarded as 1, the JSC is only determined by LHE. The LHE is related with molar absorption coefficient and dye concentration via the relationship of

LHE = 1 - 10 - ε ( λ ) Γ

(2).39 The ε(λ) is the molar absorption coefficient at certain

wavelength and Γ is the surface loading of sensitizers (mol cm-2) that is assigned as experimental value of 130 nmol cm-2. The LHE curves and their corresponding maximum JSC are shown in Figure 3. The simulated maximum JSC are 21.19, 27.63, 26.01, and 30.04 mA cm−2 for 1-4, respectively. Three designed dyes, 2, 3, and 4, have the better 7



Page 8 of 41

photocurrent performance than 1, which is consistent with their red-shifted absorption spectrum.

The

6-methyl-6H-indolo[3,2-b]quinoxaline

group

combined

with

triphenylamine as donor and cyanoacrylic acid as acceptor is not suitable to enlarge the absorption region. Besides the wide absorption range, the high efficiency sensitizer should have the fast energy transfer between donor and acceptor. According to the kF 

and R0 6 

1

0

(

R0 6 ) (3) | rA  rD |6

9000  ln(10) 2QD J ( ) (4), the Fӧrster resonance energy transfer (FRET)40,41 128π 5 n 4 N A

are mainly determined by the following three items (See Table 1): (1) the distance between donor and acceptor (r); (2) the spectrum overlap between the donor emission and acceptor absorption (J(λ)); and (3) the orientation of the transition dipole moment of the donor and acceptor (к2). The donor (triphenylamine) is defined in the Scheme 1 by blue circle. As compared with 1, 4 has the faster FRET due to the smaller r, the larger к2 and J(λ). Similarly, 3 has the comparable к2 and J(λ) along with the smaller r leading to the similar FRET to 1. Although 2 has the largest к2, its FRET would not be much larger because of the smaller J(λ) and the largest r. In general, 4 has the faster FRET than 1, while 2 and 3 have the comparable FRET with 1. 3.3 Dye-TiO2 adsorbed system When the TiO2 is firstly employed as semiconductor, the PCE of DSSCs is greatly improved. Therefore, the interfacial properties between dye and TiO2 would greatly affect the overall performance. The optimized adsorbed structures for four dyes on TiO2 8


Page 9 of 41 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


(101) surface calculated by the first principle are plotted in Figure S2 along with the Ti-O distance. Note that only the bidentate bridging adsorption model is considered. The Ti-O distance is in a range of 1.87-2.03 Ǻ indicating the strong adsorption, which is favorable for the electron injection from dye into the TiO2. DOS and PDOS for the pure and adsorbed dyes are shown in Figure 4 along with those of TiO2 surface. After adsorption, both the LUMO of dye and the CB of dye-adsorbed TiO2 surface shift toward the higher energy. Note that the Fermi energy level is fixed on the same value in the adsorbed and isolated systems. And the energy difference between the LUMO of dye and CB of TiO2 is enlarged, which is beneficial for the electron injection. The energy difference between the LUMO of dye and CB of TiO2 of 3 is the largest indicating the largest injecting driving force (ΔGinj), while the ΔGinj of 2 is the smallest (See Table 2). However, the difference among various dyes is too small to distinguish them. The similar conclusion is suitable for the electron injection time (τinj)42-44 and energy gap. In general, the qualitative comparison could not clearly differentiate them for not only the isolated dyes but also the dye-TiO2 systems. It is necessary to calculate the JSC, VOC, and PCE to compare the device performance. 3.4 JSC, VOC, and PCE The PCE of DSSC is defied as follow: PCE 

J SCVOC FF Pin

(5)

in which fill factor (FF) is regarded as constant, and Pin is incident light power that is 9



Page 10 of 41

considered to be the same for all dyes.45 The PCE is mainly determined by JSC and VOC. The JSC is deduced according to eq. (1). The Фinj and ηcoll are defined by the following relationship:

inj  1/ (1 

 inj )  relax

(6)

 trans )  rec

(7)

coll  1/ (1 

where τinj is the electron injection lifetime from dye to the TiO2 substrate, τrelax is the relaxation lifetime for excited state of dye in solution, τtrans is the electron transport time from the CB of TiO2 toward the electrode, and τrec is the electron-hole recombination time. The τrelax and τtrans are assumed to be 10 ps and 2 ps according to the experimental measurements.46 The τinj and τrec are equal to k-1inj and k-1rec, which would be calculated by Marcus theory.47 The kinj/rec is defined as follows:

kinj/rec

 (G 0   ) 2 exp(  r ) exp( ) A 4 kBT h kBT

(8)

in which A is constant, β is the attenuation factor, r is the electron-transfer distance, ΔG0 is the driving force for the reaction, and λ is the reorganization energy. The transfer distance of the injection process rinj is between the cyanoacrylic acid anchoring group and the TiO2 surface, while for the recombination process, electrons transfer back from the CB of TiO2 to the HOMO orbital of the dye. The transfer distance rrec is defined by the distance between the donor moiety (the central nitrogen atom) of the dye to the TiO2 interface. The λ is another important factor to determine the final kinj/rec. The definition of 10


Page 11 of 41 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


λ refers to refs. 48-51. The smaller λ would result in the larger kinj/rec because they are the inverse proportion. Aforementioned data related with JSC are listed in Table 3. The λ of 2 is equal to that of 1, which is also the smallest in four dyes indicating the better charge and hole equilibrium. The λ of other two dyes are slightly larger than that of 1 and 2. It is interesting that if only one item is considered, the difference among them is very slight that is even in the acceptable computational error. Therefore, it is difficult to get the relative sequence for their performance on the basis of some isolated factors. When all of them in eq. (8) are employed, the kinj is in a range of 3.2 × 1012-5.0 × 1013 s-1. The largest deviation would reach about one order of magnitude. The quantitative result is more necessary and reliable to determine their performance although the computational cost is expensive and time consuming. Finally, the JSC of 4 is still the largest with the value of 29.89 mA cm−2, which is similar with that calculated in section 3.2. The VOC is the other critical factor to determine the final PCE, which is the difference between the Fermi level of the semiconductor under illumination and the redox potential of the mediator. Whereas, the measured VOC rarely reaches half of the maximum theoretical attainable values. The main reason for the drop in VOC comes from the charge recombination in the TiO2 film that determines the final Fermi level position.52 However, VOC has attracted even less attention in previous literature.53,54 Or it is simply equal to the energy difference between the LUMO of dye and the CB of TiO2. In this work, the VOC is calculated by the following relationship:55

11



VOC 

ECBM  Eredox  CB kBT n  ln( c ) q q N CB

Page 12 of 41

(9)

in which ECBM is conduction band maximum of TiO2, ΔCB is the shift of ECBM when the dyes are adsorbed on TiO2, nc is the number of injected electrons in TiO2 due to dye adsorption, and NCB is the accessible density of conduction band states in the semiconductor. The temperature of 300 K and typical NCB density of 7 × 1020 cm−3 are adopted according to the experiment.12,56 The standard iodide/triiodide redox potential, -5.04 eV, is regarded as the reduction-oxidation potential of electrolyte (Eredox).12 The ECBM is calculated on the basis of dye-TiO2 system involving the energy shift due to the dye adsorption. Both the dye loading density and the thick of semiconductor are got from the literature.14 The corresponding values are tabulated in Table 4. If only one determining factor is considered, the differences among various dyes are too small to differentiate them. However, the difference is enlarged when they are combined. Different from the JSC, the VOC(s) for 2-4 are all smaller than that of 1. Combined JSC and VOC, the PCE is calculated according to the eq. (5), in which FF and Pin are regarded as the same for all studied dyes. Although the VOC of 2, 3, and 4 are smaller than that of 1, their PCE(s) are still higher than that of 1 because of the larger JSC. Both the calculated JSC and VOC of 1 are higher than the corresponding experimental values, which would be induced by the dye loading density, charge transfer process, and others. However, it is better than only the qualitative judgment on the basis of only one or two isolated items. 3.5 D-π-A dye 12


Page 13 of 41 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


Another dye, 5, with D-π-A configuration is designed by taking triphenylamine as donor, furan as π group, and cyanoacrylic acid as acceptor to uncover the effect of auxiliary acceptor group. The ΔGinj of 5 is much larger than that of aforementioned four dyes indicating the best injecting ability (See Table 2). Moreover, the λ of 5 is comparable with that of 3 and 4 leading to the acceptable electron-hole equilibrium. The nc of 5 is the second largest, which is only smaller than that of 3. However, 5 has the smallest JSC (See Table 3) and VOC resulting in the smallest PCE (See Table 4), which is even smaller than 1. Therefore, it is necessary to get the accurate values of JSC and VOC with factors as much as possible. The JSC of 5 has significant variation when the precise Фinj and ηcoll are considered. The insertion of ancillary acceptor would greatly improve the light harvesting and electron transfer capabilities of the dye. 3.6 Effect of aggregation The pure organic sensitizers would like forming the π-π stacking on the semiconductor surface resulting in the fast fluorescence decay from the excited state to the ground state, which is called the “dark” current of DSSCs. To reduce the negative effect is also an available pathway to enhance the overall performance. However, the influence of aggregation is rarely included when a new sensitizer is designed. The optimized dimer-TiO2 adsorbed systems are presented in Figure 5. As shown in Table 5, both the injection time and ΔGinj have no obvious variation. The strong intermolecular interaction leads to lateral charge transfer and intermolecular excited state quenching, which is adverse to the process of electron injection into the CB of TiO2. Then, the electronic coupling between stacking monomers is studied by the direct method, which is 13



Page 14 of 41

defined via the relationship:57,58 0, site1 0 0, site 2 0, site1 0, site 2 V12  LUMO / HOMO F LUMO / HOMO  LUMO / HOMO hcore LUMO / HOMO 



0, site 2 0, site1 0, site 2 0 0  LUMO / HOMO  LUMO / HOMOLUMO / HOMOl l

0, site1 0 LUMO / HOMO l

l ( occ )



(10)

0, site1 where V12 is the charge transfer integral for the electron/hole and LUMO and / HOMO 0, site 2 LUMO / HOMO represent the LUMOs/HOMOs of two adjacent molecules 1 and 2 when no

intermolecular interaction is presented. F0 is the Fock operator and its density matrix is constructed from orbitals of two adjacent molecules.59 On the basis of the optimized dimer-TiO2 adsorbed system, the electronic coupling of 1 is the smaller than that of other three dyes. While other three dyes have the comparable electronic couplings. In the static state, two dyes are almost perpendicular to the TiO2 surface, which deviates from the true situation. Dynamic simulations have been performed for dimer-TiO2 adsorbed system for 10 ps. Three snapshots at 0, 5, and 10 ps are shown in Figure 6. It is clear that two dyes tilt towards the TiO2 surface in the simulations. The electronic couplings are calculated with an interval of one ps. Then, the average electronic couplings are listed in Table S1. The electronic coupling of 2 and 4 are comparable, which are smaller than that of 1. 3 has the largest electronic coupling in both the static state and the average dynamic state. It is necessary to consider the dye aggregation on the TiO2 surface by dynamic model. In general, 4 has the largest PCE and smaller aggregation negative effect leading the best performance. 2 is the second best one, which is still better than that of 1. Although 3 has the larger PCE than 1, the electronic coupling of the former is also larger than that of

14


Page 15 of 41 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 latter resulting in the larger “dark” current. It is difficult to judge their overall performance in device. For the safe reason, 6-methyl-6H-indolo[3,2-b]azaquinoxaline and 5-methyl-5H-[1,2,5]oxadiazolo[3,4-b]carbazole are to be suitable ancillary acceptors with triphenylamine as donor and furan as π group. 4. Conclusion On the basis of new efficient T-shaped (D)2-A-π-A organic dye 1, other three dyes (2, 3, and 4) are theoretically designed by employment of different ancillary acceptors. The performance of dyes was compared by multiscale simulations. When only isolated dye is considered, 2 and 3 have the comparable FRET with 1. 4 has the faster FRET suggesting the faster intramolecular transfer. If Фinj and ηcoll are regarded as 1, 4 has the largest maximum JSC. Besides the isolated dye, the dye-TiO2 adsorbed system is considered. After adsorption, the energy difference between LUMO of dye and CB of TiO2 surface is further enlarged to promote the electron injection. However, it is still difficult to distinguish them due to the close various items. When all possible factors are included, the JSC of three new designed dyes are larger than that of 1. In contrast, their VOC(s) are lower than that of 1. Finally, the overall PCE(s) of 2, 3, and 4 are still higher than that of 1. Although the PCE of 3 is larger than that of 1, aggregation effect of 3 is also larger to induce the great inverse effect. In contrast, the aggregation effect of 2 and 4 are

smaller

than

that

of

1.

6-methyl-6H-indolo[3,2-b]azaquinoxaline

and

5-methyl-5H-[1,2,5]oxadiazolo[3,4-b]carbazole would be more suitable auxiliary acceptors along with triphenylamine as donor and furan as π group along with 15



Page 16 of 41

cyanoacrylic acid as acceptor group leading to the better performance. Supporting Information Simulated absorption spectrum of 1 with the experimental value, adsorption configurations for dye-TiO2 complexes of 1, 2, 3, and 4, and electronic coupling between stacking dimer. Acknowledgements We thank the National Supercomputing Center in Shenzhen (Shenzhen Cloud Computing Center) for providing computational resources and software. This work was supported by the National Natural Science Foundation of China (21476061, 21503069, 21676071),

Program

for

He’nan

Innovative

Research

Team

in

University

(15IRTSTHN005). References (1) O’Regan, B.; Grätzel, M. A Low-cost, High-Efficiency Solar Cell based on Dye-Sensitized Colloidal TiO2 Films. Nature 1991, 353, 737-740. (2) Ye, M.; Wen, X.; Wang, M.; Iocozzia, J.; Zhang, N.; Lin, C.; Lin, Z. Recent Advances in Dye-Sensitized Solar Cells: From Photoanodes, Sensitizers and Electrolytes to Counter Electrodes. Mater. Today 2015, 18, 155-162. (3) Qian, X.; Shao, L.; Li, H.; Yan, R.; Wang, X.; Hou, L. Indolo[3,2-b]carbazole-based Multi-Donorepeacceptor Type Organic Dyes for Highly Efficient Dye-Sensitized Solar Cells. J. Power Sources 2016, 319, 39-47. (4) Zhang, X.; Gou, F.; Zhao, D.; Shi, J.; Gao, H.; Zhu, Z.; Jing, H. π-Spacer effect in Dithiafulvenyl-π-Phenothiazine Dyes for Dye-Sensitized Solar Cells. J. Power Sources 2016, 324, 484-491.

16


Page 17 of 41 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


(5) Song, X.; Zhang, W.; Li, X.; Jiang, H.; Shen, C.; Zhu, W.-H. Influence of Ethynyl Position on Benzothiadiazole based D-A-π-A Dye-Sensitized Solar Cells: Spectral Response and Photovoltage Performance. J. Mater. Chem. C 2016, 4, 9203-9211. (6) Ooyama, Y.; Kanda, M.; EnoKi, T.; Adachi, Y.; Ohshita, J. Synthesis, Optical and Electrochemical Properties, and Photovoltaic Performance of a Panchromatic and Near-Infrared (D)2-π-A Type BODIPY Dye with Pyridyl Group or Cyanoacrylic Acid. RSC Adv. 2017, 7, 13072-13081. (7) Kakiage, K.; Aoyama, Y.; Yano, T.; Oya, K.; Fujisawa, J.; Hanaya, M. Highly-Efficient Dye-Sensitized Solar Cells with Collaborative Sensitization by Silyl-Anchor and Carboxy-Anchor Dyes. Chem. Commun. 2015, 51, 15894-15897. (8) Shockley, W.; Queisser, H. J. Detailed Balance Limit of Efficiency of p-n Junction Solar Cells. J. Appl. Phys. 1961, 32, 510-519. (9) Haid, S.; Marszalek, M.; Mishra, A.; Wielopolski, M.; Teuscher, J.; Moser, J.-E.; Humphry-Baker, R.; Zakeeruddin, S. M.; Grätzel, M.; Bäuerle, P. Signifcant Improvement of Dye-Sensitized Solar Cell Performance by Small Structural Modifcation in π-Conjugated Donor-Acceptor Dyes. Adv. Funct. Mater. 2012, 22, 1291-1302. (10) Galappaththi, K.; Ekanayake, P.; Petra, M. I. A Rational Design of High Efficient and Low-Cost Dye Sensitizer with Exceptional Absorptions: Computational Study of Cyanidin based Organic Sensitizer. Sol. Energy 2018, 161, 83-89. (11) Zhang, J.; Kan, Y.-H.; Li, H.-B.; Geng, Y.; Wu, Y.; Su, Z.-M. How to Design Proper π-Spacer Order of the D-π-A Dyes for DSSCs? A Density Functional Response. Dyes Pigments 2012, 95, 313-321. (12) Ma, W.; Jiao, Y.; Meng, S. Predicting Energy Conversion Efficiency of Dye Solar

17



Page 18 of 41

Cells from First Principles. J. Phys. Chem. C 2014, 118, 16447-16457. (13) Feng, J.; Jiao, Y.; Ma, W.; Nazeeruddin, M. K.; Grätzel, M.; Meng, S. First Principles Design of Dye Molecules with Ullazine Donor for Dye Sensitized Solar Cells J. Phys. Chem. C 2013, 117, 3772-3778. (14) Qian, X.; Lan, X.; Yan, R.; He, Y.; Huang, J.; Hou, L. T-Shaped (D)2-A-π-A Type Sensitizers

Incorporating

Indoloquinoxaline

and

Triphenylamine

for

Organic

Dye-Sensitized Solar Cells. Electrochim. Acta 2017, 232, 377-386. (15) Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648-5652. (16) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785-789. (17) Gill, P. M. W.; Johnson, B. G.; Pople, J. A.; Frisch, M. J. The Performance of the Becke-Lee-Yang-Parr (B-LYP) Density Functional Theory with Various Basis Sets. Chem. Phys. Lett. 1992, 197, 499-505. (18) Yanai, T.; Tew, D. P.; Handy, N. C. A New Hybrid Exchange-Correlation Functional Using the Coulomb-Attenuating Method (CAM-B3LYP). Chem. Phys. Lett. 2004, 393, 51-57. (19) Iikura, H.; Tsuneda, T.; Yanai, T.; Hirao, K. A Long-Range Correction Scheme for Generalized-Gradient-Approximation Exchange Functionals. J. Chem. Phys. 2001, 115, 3540-3544. (20)

Tawada,

Y.;

Tsuneda,

T.;

Yanagisawa,

S.

A

Long-Range-Corrected

Time-Dependent Density Functional Theory. J. Chem. Phys. 2004, 120, 8425-8433.

18


Page 19 of 41 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


(21) Zhao, Y.; Truhlar, D. G. The M06 Suite of Density Functionals for Main Group Thermochemistry, Thermochemical Kinetics, Noncovalent Interactions, Excited States, and Transition Elements: Two New Functionals and Systematic Testing of Four M06-Class Functionals and 12 other Functionals. Theor. Chem. Acc. 2008, 120, 215-241. (22) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865-3868. (23) Cossi, M.; Barone, V.; Mennucci, B.; Tomasi, J. Ab Initio Study of Ionic Solutions by a Polarizable Continuum Dielectric Model. Chem. Phys. Lett., 1998, 286, 253-260. (24) Cancès, E.; Mennucci, B.; Tomasi, J. A New Integral Equation Formalism for the Polarizable Continuum Model: Theoretical Background and Applications to Isotropic and Anisotropic Dielectrics. J. Chem. Phys., 1997, 107, 3032-3041. (25) 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.; et al. Gaussian 09, revision A.02; Gaussian, Inc.: Wallingford, CT, 2010. (26) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54, 11169-11186. (27) Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comp. Mater. Sci. 1996, 6, 15-50. (28) Kresse, G.; Hafner, J. Ab Initio Molecular Dynamics for Liquid Metals. Phys. Rev. B 1993, 47, 558-561. (29) Elmér, R.; Berg, M.; Carlén, L.; Jakobsson, B.; Norén, B.; Oskarsson, A.; Ericsson, G.; Julien, J.; Thorsteinsen, T. F.; Guttormsen, M.; et al. K+ Emission in Symmetric

19



Page 20 of 41

Heavy Ion Reactions at Subthreshold Energies. Phys. Rev. Lett., 1996, 77, 4884-4886. (30) Bučko, T.; Hafner, J.; Lebègue, S.; Ángyán, J. G. Improved Description of the Structure of Molecular and Layered Crystals: Ab Initio DFT Calculations with van der Waals Corrections. J. Phys. Chem. A 2010, 114, 11814-11824. (31) Aradi, B.; Hourahine, B.; Frauenheim, T. DFTB+, a Sparse Matrix-Based Implementation of the DFTB Method. J. Phys. Chem. A 2007, 111, 5678-5684. (32) Elstner, M.; Porezag, D.; Jungnickel, G.; Elsner, J.; Haugk, M.; Frauenheim, T.; Suhai, S.; Seifert, G. Self-Consistent-Charge Density-Functional Tight-Binding Method for Simulations of Complex Materials Properties. Phys. Rev. B 1998, 58, 7260-7268. (33) Niehaus, T. A.; Elstner, M.; Frauenheim, T.; Suhai, S. Application of an Approximate Density-Functional Method to Sulfur Containing Compounds. J. Mol. Struct. (Theochem) 2001, 541, 185-194. (34) Gaus, M.; Cui, Q.; Elstner, M. DFTB3: Extension of the Self-Consistent-Charge Density-Functional Tight-Binding Method (SCC-DFTB). J. Chem. Theory Comput. 2011, 7, 931-948. (35) Dolgonos, G.; Aradi, B.; Moreira, N. H.; Frauenheim, T. An Improved Self-Consistent-Charge

Density-Functional

Tight-Binding

(SCC-DFTB)

Set

of

Parameters for Simulation of Bulk and Molecular Systems Involving Titanium. J. Chem. Theory Comput. 2010, 6, 266-278. (36) Yan, R.; Qian, X.; Jiang, Y.; He, Y.; Hang, Y.; Hou, L. Ethynylene-Linked Planar Rigid Organic Dyes Based on Indeno[1,2-b]indole for Efficient Dye-Sensitized Solar Cells. Dyes Pigments 2017, 141, 93-102. (37) Maragani, R.; Misra, R.; Roy, M. S.; Singh, M. K.; Sharma, G. D. (D-π-A)2-π-D-A

20


Page 21 of 41 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


Type Ferrocenyl Bisthiazole Linked Triphenylamine Based Molecular Systems for DSSC: Synthesis, Experimental and Theoretical Performance Studies. Phys. Chem. Chem. Phys. 2017, 19, 8925-8933. (38) Lu, T.-F.; Li, W.; Bai, F.-Q.; Jia, R.; Chen, J.; Zhang, H.-X. Anionic Ancillary Ligands in Cyclometalated Ru(II) Complex Sensitizers Improve Photovoltaic Efficiency of Dye-Sensitized Solar Cells: Insights from Theoretical Investigations. J. Mater. Chem. A 2017, 5, 15567-15577. (39) Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humphry-Baker, R.; Müller, E.; Liska, P.; Vlachopoulos,

N.;

Grätzel,

M.

Conversion

of

Light

to

Electricity

by

cis-XzBis(2,2’-bipyridyl-4,4’-dicarboxylate)ruthenium(11) Charge-Transfer Sensitizers (X = C1-, Br-, I-, CN-, and SCN-) on Nanocrystalline TiO2 Electrodes. J. Am. Chem. Soc. 1993, 115, 6382-6390. (40) Pastore, M.; Angelis, F. D. First-Principles Computational Modeling of Fluorescence Resonance Energy Transfer in Co-Sensitized Dye Solar Cells. J. Phys. Chem. Lett. 2012, 3, 2146-2153. (41) Gopi, A.; Lingamoorthy, S.; Soman, S.; Yoosaf, K.; Haridas, R.; Das, S. Modulating FRET in Organic-Inorganic Nanohybrids for Light Harvesting Applications. J. Phys. Chem. C 2016, 120, 26569-26578. (42) Persson, P.; Lundqvist, M. J.; Ernstorfer, R.; Goddard III, W. A.; Willing, F. Quantum Chemical Calculations of the Influence of Anchor-Cum-Spacer Groups on Femtosecond Electron Transfer Times in Dye-Sensitized Semiconductor Nanocrystals. J. Chem. Theory Comput. 2006, 2, 441-451. (43) Labat, F.; Ciofini, I.; Hratchian, H. P.; Frisch, M.; Raghavachari, K.; Adamo, C.

21



First Principles Modeling of Eosin-Loaded ZnO Films: A Step toward the Understanding of Dye-Sensitized Solar Cell Performances. J. Am. Chem. Soc. 2009, 131, 14290-14298. (44) Labat, F.; Le Bahers, T.; Ciofini, I.; Adamo, C. First-Principles Modeling of Dye-Sensitized Solar Cells: Challenges and Perspectives. Accounts Chem. Res. 2012, 45, 1268-1277. (45) Pastore, M.; De Angelis, F. Intermolecular Interactions in Dye-Sensitized Solar Cells: A Computational Modeling Perspective. J. Phys. Chem. Lett. 2013, 4, 956-974. (46) Cherepy, N. J.; Smestad, G. P.; Grätzel, M.; Zhang, J. Z. Ultrafast Electron Injection: Implications for a Photoelectrochemical Cell Utilizing an Anthocyanin Dye-Sensitized TiO2 Nanocrystalline Electrode. J. Phys. Chem. B 1997, 101, 9342-9351. (47) Meade, T. J.; Gray, H. B.; Winkler, J. R. Driving-Force Effects on the Rate of Long-Range Electron Transfer in Ruthenium-Modified Cytochrome c. J. Am. Chem. Soc. 1989, 111, 4353-4356. (48) Datta, A.; Mohakud, S.; Pati, S. K. Electron and Hole Mobilities in Polymorphs of Benzene and Naphthalene: Role of Intermolecular Interactions. J. Chem. Phys. 2007, 126, 144710-144717. (49) Datta, A.; Mohakud, S.; Pati, S. K. Comparing the Electron and Hole Mobilities in the α and β Phases of Perylene: Role of π-Stacking. J. Mater. Chem. 2007, 17, 1933-1938. (50) Mohan, V.; Datta, A. Structures and Electronic Properties of Si-Substituted Benzenes and Their Transition-Metal Complexes. J. Phys. Chem. Lett. 2010, 1, 136-140. (51) Mohakud, S.; Pati, S. K. Large Carrier Mobilities in Octathio[8]circulene Crystals: A Theoretical Study. J. Mater. Chem. 2009, 19, 4356-4361.

22


Page 22 of 41

Page 23 of 41 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


(52) Amit Kumar, S.; Urbani, M.; Medel, M.; Ince, M.; González-Rodríguez, D.; Chandiran, A. K.; Bhaskarwar, A. N.; Torres, T.; Nazeeruddin, Md. K.; Grätzel, M. Adapting Ruthenium Sensitizers to Cobalt Electrolyte Systems. J. Phys. Chem. Lett. 2014, 5, 501-505. (53) Lu, T.-F.; Li, W.; Bai, F.-Q.; Jia, R.; Chen, J.; Zhang, H.-X. Anionic Ancillary Ligands in Cyclometalated Ru(II) Complex Sensitizers Improve Photovoltaic Efficiency of Dye-Sensitized Solar Cells: Insights from Theoretical Investigations. J. Mater. Chem. A 2017, 5, 15567-15577. (54) Lu, T.-F.; Li, W.; Zhang, H.-X. Rational Design of Metal-Free Organic D-π-A Dyes in Dye-Sensitized Solar Cells: Insight from Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) Investigations. Org. Electron. 2018, 59, 131-139. (55) Marinado, T.; Nonomura, K.; Nissfolk, J.; Karlsson, M. K.; Hagberg, D. P.; Sun, L.; Mori, S.; Hagfeldt, A. How the Nature of Triphenylamine-Polyene Dyes in Dye-Sensitized Solar Cells Affects the Open-Circuit Voltage and Electron Lifetimes. Langmuir 2010, 26, 2592-2598. (56) Marinado, T.; Hagberg, D. P.; Hedlund, M.; Edvinsson, T.; Johansson, E. M. J.; Boschloo, G.; Rensmo, H.; Brinck, T.; Sun, L.; Hagfeldt, A. Rhodanine Dyes for Dye-Sensitized Solar Cells : Spectroscopy, Energy Levels and Photovoltaic Performance. Phys. Chem. Chem. Phys. 2009, 11, 133-141. (57) Yang, X.; Li, Q.; Shuai, Z. Theoretical Modelling of Carrier Transports in Molecular Semiconductors: Molecular Design of Triphenylamine Dimer Systems. Nanotechnology 2007, 18, 424029. (58) Yin, S.; Yi, Y.; Li, Q.; Yu, G.; Liu, Y.; Shuai, Z. Balanced Carrier Transports of

23



Electrons and Holes in Silole-Based Compoundss-A Theoretical Study. J. Phys. Chem. A 2006, 110, 7138-7143. (59) Nan, G.; Wang, L.; Yang, X.; Shuai, Z.; Zhao, Y. Charge Transfer Rates in Organic Semiconductors beyond First-Order Perturbation: From Weak to Strong Coupling Regimes. J. Chem. Phys. 2009, 130, 024704.

24


Page 24 of 41

Page 25 of 41 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


Scheme 1 The sketch map structures of all dyes.

25



Figure 1 Energy diagram of HOMO and LUMO for 1, 2, 3, and 4 calculated at the PBE0/6-31G(d,p) level of theory along with the corresponding energy levels of TiO2, and electrolyte.

26


Page 26 of 41

Page 27 of 41 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


Figure 2 The UV/Vis absorption spectra of 1, 2, 3, and 4 calculated in dichloromethane solvent at the PBE0/6-31G(d,p) level of theory.

27



Figure 3 Simulated maximum JSC (in mA cm-2) and light-harvesting efficiency LHE(λ) of all dyes. The gray line is the Air Mass 1.5 Global (AM 1.5G) solar spectrum.

28


Page 28 of 41

Page 29 of 41 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


29



Figure 4 Calculated total density of states (DOS) and projected density of states (PDOS) for clean TiO2 surface and interfaces of TiO2 adsorbed with 1 (a), 2 (b), 3 (c), and 4 (d).

30


Page 30 of 41

Page 31 of 41 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


31



Figure 5 The graph is the adsorption configurations for dye-TiO2 complexes of Dimer-1, Dimer-2, Dimner-3, and Dimer-4, respectively.

32


Page 32 of 41

Page 33 of 41 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


33



Figure 6 Evolutions of the total electronic energy as a function of the simulation time. 34


Page 34 of 41

Page 35 of 41 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


35



Page 36 of 41

Table 1 Calculated FRET parameters for 1, 2, 3, and 4. Dye

r (Ǻ)

K2

J(λ) (M-1 cm-1 nm4)

1

7.192

0.367

4.249 × 1014

2

7.227

0.733

3.858 × 1014

3

6.747

0.343

4.761 × 1014

4

6.803

0.701

4.315 × 1014

36


Page 37 of 41 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


Table 2 The calculated H-L energy gaps (Eg) on TiO2 surface, driving force for electron injection (ΔGinj) and electron injection time (τinj) for all the dyes. Dye

Eg (eV)

ΔGinj (eV)

τinj (fs)

1

0.76

1.02

1.49

2

0.50

0.82

1.59

3

0.78

1.05

1.23

4

0.72

0.99

1.32

5

1.18

1.34

1.83

37


The Journal of Physical Chemistry 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

Page 38 of 41

Table 3 Estimated electrochemical parameters for all the dyes. ΔG* inj Dye

ΔG* rec

λ (eV) (eV)

(eV)

rinj (Ǻ)

rrec (Ǻ)

kinj (s-1)

krec (s-1)

Фinj

ηcoll

JSC (mA cm-2)

1

0.55

0.101

0.299

2.50

9.99

3.2 × 1012

3.8 × 107

0.970

1.000

20.55

2

0.55

0.033

0.343

2.30

9.97

5.0 × 1013

6.8 × 106

0.998

1.000

27.58

3

0.62

0.075

0.319

2.51

8.45

8.3 × 1012

3.4 × 107

0.988

1.000

25.69

4

0.63

0.052

0.325

2.49

8.35

2.0 × 1013

2.8 × 107

0.995

1.000

29.89

5

0.61

0.219

0.242

2.51

11.98

3.2 × 1010

1.1 × 108

0.244

1.000

5.02

G *  (G 0   ) 2 / 4

38


Page 39 of 41 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


Table 4 Estimations of nc, VOC, and PCE for all dyes and corresponding experiment electrochemical parameters for 1.14 dye

nc (cm-3)

ECBM

VOC (mV)

PCE (%)

VOC (exp; mV)

JSC (exp; mA cm-2)

PCE (exp; %)

1

4.7×1019

-3.19

1781

24.62

817

12.9

7.09

2

4.8×1019

-3.23

1743

32.34

3

5.3×1019

-3.20

1772

30.63

4

5.2×1019

-3.23

1742

35.03

5

5.2×1019

-3.45

1525

5.16

39



Page 40 of 41

Table 5 The calculated H-L energy gaps (Eg) on TiO2 surface, driving force for electron injection (ΔGinj) and electron injection time (τinj) for the dimers. Dye

Eg (eV)

ΔGinj (eV)

τinj (fs)

1-dimer

0.59

0.87

1.49

2-dimer

0.37

0.68

1.30

3-dimer

0.62

0.93

1.27

4-dimer

0.54

0.86

1.39

40


Page 41 of 41 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


TOC Graphic

41


Rational Design of High-Efficiency Organic Dyes in Dye-Sensitized

Recommend Documents