5 

 This work is licensed under a Creative Commons Attribution 4.0 International License. 

 

  

 

 

A Theoretical Investigation of Charge Transfer Dynamics from Sensitized 

Molecule D35CPDT Dye to 𝑺𝒏𝑶𝟐 and 𝑻𝒊𝑶𝟐 Semiconductor 
 

 

 

 

 

Abstract 

In this research, the dynamics process of charge transfer from the sensitized  D35CPDT 

dye to tin(iv) oxide(𝑆𝑛𝑂2) or titanium dioxide (𝑇𝑖𝑂2 ) semiconductors are carried out by using 
a quantum model for charge transfer. Different chemical solvents Pyridine, 2-Methoxyethanol. 

Ethanol, Acetonitrile, and Methanol have been used with both systems as polar media 

surrounded the systems. The rate for charge transfer from photo-excitation D35CPDTdye and 

injection into the conduction band of 𝑆𝑛𝑂2 or 𝑇𝑖𝑂2 semiconductors vary from a ~10
−26 to 

~10−29 for system and from a  ~10−52 to  ~10−56for the system, depending on the charge 
transfer parameters strength coupling, free energy, potential of donor and acceptor in the 

system. The charge transfer rate in D35CPDT / 𝑆𝑛𝑂2 the system is larger than the rate in 
D35CPDT/ 𝑇𝑖𝑂2 a system depending on transition energy and driving energy. However, the 
charge transfer for both systems to be large is associated with large transition energy, 

decreasing driving energy and potential, and increasing strength coupling with Methanol 

solvent. 

 

Keywords: Charge  transfer dynamics ,  Sensitized D35CPDT Dye  , 𝑆𝑛𝑂2 , 𝑇𝑖𝑂2.   

1. Introduction   
Recently, the energy demand becomes increasingly become one of most problems 

because of the increased requirements in modern life. Photovoltaic and solar cell technology 

is utilized to convert solar energy to electric energy [1]. The dye-sensitized solar cell  DSSC is 

the main promising renewable device because of the low cost and good conversion efficiency 

[2]. The molecules electronics are cooperated with solid materials to be used in various devices 

Ibn Al-Haitham Journal for Pure and Applied Sciences 

http://jih.uobaghdad.edu.iq/index.php/j/index: Journal homepage 

 

Doi:10.30526/35.3.2839 

Article history: Received 3 April 2022, Accepted 17 May 2022, Published in July 2022. 

 

Estabraq Hasan Rasheed 
Department of Physics, College of 

Education for Pure Science \ Ibn Al-Haitham, University 

of Baghdad, Baghdad, Iraq. 

Estabraq.Hasan1204a@ihcoedu.uobaghdad.edu.iq 

 
 

Hadi J. M. Al-Agealy 
Department of Physics, College of 

Education for Pure Science \ Ibn Al-Haitham, 

University of Baghdad, Baghdad, Iraq. 

hadi.j.m@ihcoedu.uobaghdad.edu.iq 

 

 

 

 

 

 

https://creativecommons.org/licenses/by/4.0/
file:///F:/العدد%20الثاني%202022/:%20http:/jih.uobaghdad.edu.iq/index.php/j/index
mailto:Estabraq.Hasan1204a@ihcoedu.uobaghdad.edu.iq
mailto:hadi.j.m@ihcoedu.uobaghdad.edu.iq


IHJPAS. 53 (3)2022 
 

6 

because they are easily fabricated and cheap [3]. Since O’Regan and Gratzel introduced a work 

in1990s,dye-sensitized solar cell DSSCs are attracting more attention to convert light to 

electricity at a low cost [4]. The dye-sensitized had been excitation by light-induced due to 

absorbed light and the electrons will be transferred from the dye to the conduction band of the 

semiconductor[5]. The electron transfer process is an important fundamental reaction in 

different devices and dye-sensitized solar cell devices[6]. It occurs by thermal excitation and 

photo inducement [6]. A basic classical theory for the charge transfer process was introduced 

by Rudolph Marcus to describe the transfer between two states donor and acceptor and was 

awarded Nobel Prize in 1992 [7]. The dye-sensitized had been excited by light-induced due to 

absorbed light, and the electrons will be transferred from the dye to the semiconductor's 

conduction band [5]. The electron transfer process is an important fundamental reaction in 

different devices and dye-sensitized solar cell devices[6]. It occurs by thermal excitation and 

photo inducement [6]. A basic classical theory for the charge transfer process was introduced 

by Rudolph Marcus to describe the transfer between two states, donor and acceptor, and 

awarded Nobel Prize in 1992 [7]. Despite electron transfer theory developments using various 

tools; analytical theory methods, time-resolved, spectroscopy, and computer simulation [8]. In 

recent years, many modifications have been proposed to dye-sensitized solar cell DSSC, 

including the fabrication of indoline organic dyes as sensitizers [9]. The dynamo red dye is a 

sensitized dye known as D35CPDT dye, as shown in figure (1). It has form 3-{6-{4-[bis(2',4'- 

dibutyloxybiphenyl-4-yl)amino-]phenyl}-4,4-dihexyl-cyclopenta-[2,1-b:3,4-b'] dithiophene-

2-yl}-2-cyanoacrylic acid. It is stable, low cost, and high performance to use in DSSCs devices 

[10]. 𝑆𝑛𝑂2 and 𝑇𝑖𝑂2 are used to be an acceptor state in two device systems, its conversion of 

solar energy to electricity and to chemical energy [11]. 𝑆𝑛𝑂2 is one of the n-type used in dye-

sensitized solar cells DSSCs [12]. SnO2 is a wide band gap of about 3.6 eV and has chemical 

and physical steady-state properties at different temperatures [13].  

 
 

 

Figure 1. A-Structure of the D35CPDT dye [10] and B- Energy levels for D35CPDT contact to 𝑆𝑛𝑂2and 𝑇𝑖𝑂2 
[15] 

 



IHJPAS. 53 (3)2022 
 

7 

On the other hand, the 𝑇𝑖𝑂2 is an important n-type semiconductor used in solar cell 

devices. It has a wide energy band gap of about 3.2 eV, is low cost, nontoxic in nature and 

stable [14].The schematic of energy levels for sensitized D35CPDT dye with  𝑆𝑛𝑂2 and 𝑇𝑖𝑂2  

semiconductors is shown in Figure (1) [15].  

In this paper, we utilize the quantum model to investigate charge transfer dynamics 

from Sensitized D35CPDT Dye to the conduction band of 𝑆𝑛𝑂2 or/and 𝑇𝑖𝑂2 Semiconductor. 

 

2. Theory   

The charge transfer rate (Κ𝐶𝑇𝑅) is given by Fermi Golden Rule to transfer charge from 

a donor state to an acceptor state and is given by [16].  

Κ𝐶𝑇𝑅 = ∑
4𝜋2

ℎ
|〈𝐶𝐶𝑇𝑅 〉|

2𝜌𝑑 (𝐸)                                                               (1) 

 

Where ℎ is Planck constant, 〈𝐶𝐶𝑇𝑅 〉 is the charge transfer strength coupling, and 𝜌𝑑 (𝐸)is the 

active density of electrons. The activation density profile is the function of the effective density 

of states 𝐷𝐸𝑆 and effective length 𝑙𝑒𝑙 . It has been determined from the expression [17].  

𝜌𝑑 (𝐸) = 𝐷𝐸𝑆
𝑙𝑒𝑙

 (
6

𝜋
)

1
3⁄
                                                                                 (2) 

The charge transfer rate in Eq.(1) together with Eq.(2) to reduce:  

Κ𝐶𝑇𝑅 = ∑
4𝜋2

ℎ
|〈𝐶𝐶𝑇𝑅 〉|

2𝐷𝐸𝑆
𝑙𝑒𝑙

 (
6

𝜋
)

1
3⁄
 (3) 

The total effective density of states depends on the density of the state〈�̂�𝑗 〉 =
𝑒

−
(Λ+∆𝐹0)2

4Λ𝑘𝐵𝑇

√(4𝜋Λ𝑘𝐵𝑇)
 for the system 

and can be described by [18].  

𝐷𝐸𝑆 = 〈�̂�𝑗 〉𝑑𝐴
−2

3⁄ =
𝑒

−
(Λ+∆𝐹0)2

4Λ𝑘𝐵𝑇

√(4𝜋Λ𝑘𝐵𝑇)
𝑑

𝐴

−2
3⁄                                                          (4) 

Where𝑑𝐴 is the atomic density of a semiconductor.  

The charge transfer rate  in Eq.(1) will be set through Eq.( 4) by 

Κ𝐶𝑇𝑅 = ∑
4𝜋2

ℎ
|〈𝐶𝐶𝑇𝑅 〉|

2 𝑒
−

(Λ+∆𝐹0)2

4Λ𝑘𝐵𝑇

√(4𝜋Λ𝑘𝐵𝑇)
𝑑

𝐴

−2
3⁄ 𝑙𝑒𝑙

 (
6

𝜋
)

1
3⁄
                                          (5) 

Introduce the Fermi distribution function f(𝐸) for electrons as a function of the conduction band 

energy EC and electronic energy E in the system and may be written [19]:  

 

f(𝐸) =
1

𝑒

(EC−E)

kBT +1

                                                                                          (6) 

We can insert  Eq.( 6) in Eq.(5) with integration over energy E(0 → EC to obtain:  

Κ𝐶𝑇𝑅 =
4𝜋2

ℎ
|〈𝐶𝐶𝑇𝑅〉|

2 𝑒
−

(Λ+∆𝐹0)2

4Λ𝑘𝐵𝑇

√(4𝜋Λ𝑘𝐵𝑇)
𝑑

𝐴

−2
3⁄ 𝑙𝑒𝑙

 (
6

𝜋
)

1
3⁄

∫
𝑑𝐸

𝑒

(EC−E)

kBT +1

EC

0
                         (7) 

The corresponding driving energy ∆𝐹0 in the charge transfer process are obtained as a function 

of the conduction band energy ECof semiconductor and electrochemical potential ϕ and is 

computed by [20]. 

∆𝐹0 = EC − ϕ                                                                                          (8) 

 Inserting Eq.(8) in Eq.(7) to result: 



IHJPAS. 53 (3)2022 
 

8 

Κ𝐶𝑇𝑅 =
4𝜋2

ℎ
|〈𝐶𝐶𝑇𝑅〉|

2 𝑒
−

(Λ+(EC−ϕ))
2

4Λ𝑘𝐵𝑇

√(4𝜋Λ𝑘𝐵𝑇)
𝑑

𝐴

−2
3⁄ 𝑙𝑒𝑙

 (
6

𝜋
)

1
3⁄

∫
𝑑𝐸

𝑒

(EC−E)

kBT +1

EC

0
                    (9) 

The results solve integral in Eq.(9) reduce to. 

∫
𝑑𝐸

𝑒

(EC−E)

kBT +1

EC

0
= kBT[ln2 − ln (1 + 𝑒

−EC
kBT )]                                            (10) 

The potential energy is obtained by calculating the driving energy and transition energy and is 

given as [21]. 

𝑈(Λ, ϕ) =
((EC−ϕ)+Λ)

2

4Λ
                                                                            (11) 

Therefore, we insert Eq.(10) and Eq.(11)  in Eq.( 9)  to result: 

Κ𝐶𝑇𝑅 =
4𝜋2

ℎ
|〈𝐶𝐶𝑇𝑅〉|

2 𝑒
− 

𝑈(Λ,ϕ)
𝑘𝐵𝑇

√(4𝜋Λ𝑘𝐵𝑇)
𝑑

𝐴

−2
3⁄ 𝑙𝑒𝑙

 (
6

𝜋
)

1
3⁄

kBT[ln2 − ln (1 + 𝑒
−EC
kBT )         (12) 

According to the continuum model of donor - acceptor theory, the transition energy Λ(eV)  can 

be obtained[22]: 

Λ(𝒆𝑽) =
𝑒 2

8𝜋𝜀°
[

1

𝑅
[

1

𝑛2
−

1

𝜖
] −

1

2𝐷
[(

𝑛𝑆
2−𝑛2

𝑛𝑆
2+𝑛2

)( 
1

𝑛2
) −

𝜖𝑆
2−𝜖2

𝜖𝑆
2+𝜖2

1

𝜖2
]]                              (13) 

Where 𝑒 and 𝜀° are charge and  permittivity, 𝑛 and 𝑛𝑆 are  the refractive index of solvent  and 

semiconductor, 𝜖 and 𝜖𝑆 are the dielectric constant of solvent and semiconductor, 𝑹 is the 

radius of dye and D is the distance between the dye and the semiconductor. The radius is given 

as a function of molecular weight 𝑀𝑊 and density 𝜌𝑚due to the spherical approach formula 

[23]. 

𝑅( 𝐴𝑜 ) = (
3

4𝜋
)

1

3(
𝑀𝑊

𝑁𝐴𝜌𝑚
)

1

3                                                                              (14)     

Where 𝑁𝐴 is Avogadro number. 

 

3. Results  

To study the charge transfer dynamics from  D35CPDT sensitized dye to conduction 

band 𝑆𝑛𝑂2 or 𝑇𝑖𝑂2 In a semiconductor, we can calculate the rate of the charge transfer process 

in this system. It can enable us to know the electronic properties. The charge transfer rate at 

interfaces is calculated depending on the transition energy, driving force, potential at the 

interface, and strong coupling of charge transfer in the system. Transition energy was 

calculated depending on the donor-acceptor system with polarity media of solvents. The 

physical properties of solvents and 𝑆𝑛𝑂2 and 𝑇𝑖𝑂2 semiconductors are shown in Tables (1) 

and (2), respectively. 

 

Table 1. Physical properties of solvents [24]. 

 

 

 

Solvents Density 

g/cm3 

Boiling 

point(C°) 

Melting 

point(C°) 

Viscosity 

 ( cp) 

Dielectric 

constant (Ɛ) 

Refractive 

index (n) 

Pyridine 0.978 115.4 −41.6 0.88 12.3 1.510 

2-Methoxyethanol 0.965 124 -85 1.7 16.90 1.402 

Ethanol 0.78945 78.37 -114.1 1.08 24.5 1.3614 

Acetonitrile 0.786 82 -45 0.38 37.5 1.3441 

Methanol 0.792 64.7 -97.6 0.54 32.7 1.3284 



IHJPAS. 53 (3)2022 
 

9 

 

 

 

Table 2. Physical properties of 𝑆𝑛𝑂2 and 𝑇𝑖𝑂2  semiconductors . 

 

Firstly, we must calculate the radius 𝑅 of D35CPDT dye and the distance (𝐷) between 

D35CPDT dye and  𝑆𝑛𝑂2 and 𝑇𝑖𝑂2. Depending on the approach of the spherical formula, the 

radii of the D35CPDT molecule, 𝑆𝑛𝑂2 and 𝑇𝑖𝑂2 are estimated using Eq.(14), from which we 

may calculate the association transition energy, driving energy coefficient, the potential at the 

interface and charge transfer rate of the charge transfer process in both systems.The radii are 

calculated using the expression in Eq.(14) with inserting the value of molecular weight  MW 

= 1125.58 g/mol [28], 150.71g/ mol [25] and79.866 g/ mol [27] for D35CPDT molecule, 𝑆𝑛𝑂2 

and 𝑇𝑖𝑂2 and taking the density ρ_m=1.154  g/cm
3 [28], 6.95 g/cm3 [25] and 4.23 g/cm3 [27] 

for D35CPDT dye, 𝑆𝑛𝑂2 and 𝑇𝑖𝑂2. Results are  found to be 7.28404 Å, 2.0487Å and 1.9563 

Å  for D35CPDT, 𝑆𝑛𝑂2 and𝑇𝑖𝑂2, respectively. The calculation of the transition energy was 

carried out using Eq.(13) for D35CPDT / 𝑆𝑛𝑂2 and D35CPDT / 𝑇𝑖𝑂2 by taking the dielectric 

constant and refractive index for solvents in the table (1) and the dielectric constant with the 

refractive index for 𝑆𝑛𝑂2and 𝑇𝑖𝑂2 in Table(2), and distance is taken  D=9.33274Å between 

D35CPDT dye to 𝑆𝑛𝑂2 and  D=9.24034Å  from D35CPDT dye to 𝑇𝑖𝑂2. 𝑅esults are listed in 

Table (3). 

 
Table 3.  Results of transition  energy for D35CPDT / 𝑆𝑛𝑂2  and D35CPDT / 𝑇𝑖𝑂2. 

 

Properties SnO2 [25] TiO2 [26-27] 

Molecular weight (g/mol) 150.71 79.866 

Dielectric Constant 2.19 55 

Mass Density (g/cm3) 6.95 4.23 

Density of state  Ns /cm
3) 3.5× 1019 1.163× 1025 

Refractive index 1.45 2.609 

Lattice constant(Å) a = b = 4.731 A˚ and c = 

3.189A˚ 

a = 4.5936 ,c =2.9587 

Radius(Å) 2.0487 1.9563 

Conduction band energy(eV) 3.2 𝑒𝑉 4.05 

Electron concentration (1/cm3 ) 5×1020cm-3 2×1020cm-3 

Electron affinity (eV) 4.5 eV 4.2 

Solvents Chemicals 

Formula 

Dielectric 

constant  Ɛ ) 

Refractive 

index (n) 

Orientation energy for 

D35CPDT/ 𝑆𝑛𝑂2  D35CPDT/
 𝑇𝑖𝑂2 

Pyridine C5H5N 12.3 1.510 0.35762 0.27036 

2-Methoxyethanol C3H8O2 16.90 1.402 0.43648 0.33614 

Ethanol C2H6O 24.5 1.3614 0.47924 0.37318 



IHJPAS. 53 (3)2022 
 

10 

 

We can also calculate the driving energy for the charge transfer process using Eq.(8) 

as a function of the conduction band of  Ecb = 3.2 eV for 𝑆𝑛𝑂2 , Ecb = 4.05 eV for 𝑇𝑖𝑂2, and 

the electrochemical potential energy of D35PCDT are taken in the range  ϕ=3.1 eV to 2.5 eV; 

results are listed in Table (4). 

 

Table 4. Results of driving energy as a function of conduction Ecb =3.2 eV for𝑆𝑛𝑂2andEcb =4.05 eV for 𝑇𝑖𝑂2 
with electrochemical potential ϕ (𝑒𝑉) of dye. 

 

Here, we can use values of the transition energy in the table (3) and the driving energy in the 

table (4) to calculate the potential energy using Eq.(11). Results are listed in the table (5) for 

D35CPDT / 𝑆𝑛𝑂2 the system with the driving energy ∆𝐹
0(𝑒𝑉) = 0.6 eV and D35CPDT / 

𝑇𝑖𝑂2 system with the driving energy∆𝐹
0(𝑒𝑉) = 1.25 𝑒𝑉, respectively  . 

Table 5. Data of potential energy 𝑈(Λ, ϕ)for D35CPDT/ 𝑆𝑛𝑂2 and  D35CPDT/ 𝑇𝑖𝑂2System.  

Solvent type 

 

potential barrier 𝑼(𝚲, 𝛟) (eV) 

D35CPDT/ 𝑺𝒏𝑶𝟐 D35CPDT/ 𝑻𝒊𝑶𝟐 

𝚲(𝐞𝐕) ∆𝐹0 = 0.6 𝑒𝑉.6eV 𝚲(𝐞𝐕) ∆𝐹0 = 1.25 𝑒𝑉 

Pyridine 0.35762 0.6411 0.27036 2.1374 

2-Methoxyethanol 0.43648 0.6153 0.33614 1.8711 

Ethanol 0.47924 0.6076 0.37318 1.7650 

Acetonitrile 0.50434 0.6045 0.39569 1.7111 

Methanol 0.51046 0.6039 0.40022 1.7011 

 
 

To understand the charge transfer properties, it has been pointed to calculate the charge 

transfer rate (Κ𝐶𝑇𝑅) associated with the transition energy Λ(eV)of D35CPDT/ 𝑆𝑛𝑂2 and 

D35CPDT/ 𝑇𝑖𝑂2. We calculate the charge transfer rate using Eq.(12) associated to the 

transition energy in table (3) for D35CPDT/ 𝑆𝑛𝑂2 using the driving energy ∆𝐹
0=0.6 eV and  

D35CPDT/ 𝑇𝑖𝑂2 using the driving energy ∆𝐹
0=1.25eV and take the strong coupling  

|〈𝐶𝐶𝑇𝑅〉|
2 = 1.25 × 10−1,. 2.25× 10−2, 3.25× 10−3, 4.25× 10−4 and 5.25× 10−5(eV/

 state)2  and  take the atomic density 𝑑𝐴=6.95 ( 1)/cm3  [29]  for 𝑆𝑛𝑂2  and 𝑑𝐴=4.23 ( 1)/cm3   

for 𝑇𝑖𝑂2 [27-28] with the effective length   𝑙𝑒𝑙 = 3 × 10
−10m   [29]. Results are shown in 

Tables (6) and (7)forD35CPDT/ 𝑆𝑛𝑂2 and D35CPDT/ 𝑇𝑖𝑂2, respectively. 

 

Acetonitrile C₂H₃N 37.5 1.3441 0.50434 0.39569 

Methanol CH4O 32.7 1.3284 0.51046 0.40022 

Electrochemical  potential 𝛟 (𝒆𝑽) The driving energy∆𝑭𝟎(𝒆𝑽) 

D35CPDT/ 𝑆𝑛𝑂2  D35CPDT/ 𝑇𝑖𝑂2 

3.1 0.1 0.95 

3.0 0.2 1.05 

2.9 0.3 1.15 

2.8 0.4 1.25 

2.7 0.5 1.35 

2.6 0.6 1.45 

2.5 0.7 1.55 



IHJPAS. 53 (3)2022 
 

11 

Table 6. Results of electrons transfer rate for D35CPDT/ 𝑆𝑛𝑂2at ∆𝐹
0 = 0.6𝑒𝑉. 

Solvent 𝚲(𝐞𝐕)  
The charge transfer rate  Κ𝐶𝑇𝑅  𝟏/ 𝐒𝐞𝐜 

|〈𝐶𝐶𝑇𝑅 〉|
2(𝐞𝐕/ 𝐬𝐭𝐚𝐭𝐞)𝟐 

1.25×
𝟏𝟎−𝟏 

2.25×
𝟏𝟎−𝟐 

3.25×
𝟏𝟎−𝟑 

4.25×
𝟏𝟎−𝟒 

5.25×
𝟏𝟎−𝟓 

Pyridine 0.35762 1.1877E-

26 

2.1378E-

27 

3.0880E-

28 

4.0381E-

29 

4.9883E-30 

2-

Methoxyethanol 

0.43648 3.0119E-

26 

5.4214E-

27 

7.8310E-

28 

1.0240E-

28 

1.2650E-29 

Ethanol 0.47924 3.9123E-

26 

7.0422E-

27 

1.0172E-

27 

1.3302E-

28 

1.6432E-29 

Acetonitrile 0.50434 4.3124E-

26 

7.7623E-

27 

1.1212E-

27 

1.4662E-

28 

1.8112E-29 

Methanol 0.51046 4.3922E-

26 

7.9060E-

27 

1.1420E-

27 

1.4934E-

28 

1.8447E-29 

1.1877E-26  to 1.8447E-29 

Table 7. Results of electrons transfer rate for D35CPDT/ 𝑇𝑖𝑂2at ∆𝐹
0 = 1.25𝑒𝑉. 

Solvent 𝚲(𝐞𝐕)  
The charge transfer rate  Κ𝐶𝑇𝑅  𝟏/ 𝐒𝐞𝐜 

|〈𝐶𝐶𝑇𝑅 〉|
2(𝐞𝐕/ 𝐬𝐭𝐚𝐭𝐞)𝟐 

1.25×
𝟏𝟎−𝟏 

2.25×
𝟏𝟎−𝟐 

3.25×
𝟏𝟎−𝟑 

4.25×
𝟏𝟎−𝟒 

5.25×
𝟏𝟎−𝟓 

Pyridine 0.27036 1.2631E-

52 

2.2735E-

53 

3.2840E-

54 

4.2945E-

55 

5.3049E-56 

2-

Methoxyethanol 

0.33614 4.7813E-

48 

8.6064E-

49 

1.2431E-

49 

1.6256E-

50 

2.0081E-51 

Ethanol 0.37318 3.1614E-

46 

5.6904E-

47 

8.2195E-

48 

1.0749E-

48 

1.3278E-49 

Acetonitrile 0.39569 2.6545E-

45 

4.7782E-

46 

6.9018E-

47 

9.0255E-

48 

1.1149E-48 

Methanol 0.40022 3.9436E-

45 

7.0984E-

46 

1.0253E-

46 

1.3408E-

47 

1.6563E-48 

 

 

 
4. Discussion  

The transition energy in Table (3)  for both systems have been calculated in room 

temperature. It increases upon decreasing the refractive index and increases the dielectric 

constant (Ɛ) of solvents. Also, the transition energy increases with the decrease of the 

refractive index and dielectric constant of the semiconductor which is shown in Table (3). 

Table (3) shows the transition energy increasing with 𝑆𝑛𝑂2 which has low dielectric constant 

2.19 and a low refractive index 1.45 compared with 𝑇𝑖𝑂2 has a large dielectric constant 55 

and large refractive index 2.609. 

 

According the results in Table (2), we can find the transition energy for both 

D35CPDT/ 𝑆𝑛𝑂2 and  D35CPDT/ 𝑇𝑖𝑂2 systems has large values with Methanol solvent but 

the D35CPDT/ 𝑇𝑖𝑂2 system has smaller transition energy than D35CPDT/ 𝑆𝑛𝑂2 that has large  

transition energy. Table (3) shows the transition energy for D35CPDT / 𝑆𝑛𝑂2 system is larger 

than the transition energy for  D35CPDT / 𝑇𝑖𝑂2 by 0.1 eV with the same solvent; this is  

because of the effect of dielectric and refrective index of semiconductor. However, the 

transition energy can be noted to be large; it has about 0.40022eV for D35CPDT /𝑇𝑖𝑂2 and 



IHJPAS. 53 (3)2022 
 

12 

0.51046eV for D35CPDT / 𝑆𝑛𝑂2 with Methanol  and about 0.39569 eV for D35CPDT / 𝑇𝑖𝑂2 

and 0.50434 eV for D35CPDT / 𝑆𝑛𝑂2 Acetonitrile  solvents comparing to the low transition 

energy around 0.27036 eV for D35CPDT / 𝑇𝑖𝑂2and 0.35762 eV for D35CPDT / 𝑆𝑛𝑂2 with 

the Pyridine solvent.Table (6) shows the charge transfer rate in range 1.6692E-47 to 4.3922E-

26 with the strength |〈𝐶𝐶𝑇𝑅 〉|
2 = 1.25 × 10−1(eV/ state)2 associated with the transition 

energy in the range 0.35762 -0.51046eV for D35CPDT /SnO2system. Table (7) shows the 

charge transfer rate in the range 1.2631E-52 to 3.9436E-45with strength |〈𝐶𝐶𝑇𝑅 〉|
2 = 1.25 ×

10−1(eV/ state)2 associated with the transition energy in the range 0.27036-0.40022 eV for 

D35CPDT /𝑇𝑖𝑂2system. A large charge transition rate of the D35CPDT/ 𝑆𝑛𝑂2 system is 

achieved 4.3922E-26 with the transition energy 0.51046 eV and the Methanol solvent. On the 

other hand, it can be seen that the charge  transfer for D35CPDT/ 𝑇𝑖𝑂2 is to be large 3.9436E-

45 associated with the transition energy 0.40022eV and the Methanol solvent. It is influenced 

by the transition energy and increased with the increased transition energy and polarity media 

with the increased dielectric constant. It decreases the refractive index in both systems. The 

results of the charge transfer rate found that the charge transfer process depends on the driving 

force. Hence, in both systems, there are the same values of electrochemical potential ϕ (.1-

2.5eV)  which are taken with different conduction band energy. Table (4) indicates that the 

driving energy is a function of the electrochemical potential of D5CPDT dye. The driving 

energy increases with decreases in the electrochemical potential and vice versa in both 

systems. However, the driving energy is large for  D35CPDT / 𝑇𝑖𝑂2 in scale (0.95 to 1.55eV) 

compared to D35CPDT / 𝑆𝑛𝑂2 in scale (0.1 to 0.7 eV).Further, it is supported by Table 

(4)which indicates its conduction band energy effect. From Table (4), we can see different 

driving energy values in the inset of Tables (6) and (7). The driving energy is ∆𝐹0 ≈

0.6 eVfor D35CPDT / 𝑆𝑛𝑂2compared to ∆𝐹
0 = 1.25 eV for D35CPDT / 𝑇𝑖𝑂2. Table (6) 

show the charge transfer rate in the range from 1.1877E-26  to 1.8447E-29 for D35CPDT / 𝑆𝑛𝑂2while 

the charge transfer rate in the table (7) for D35CPDT / 𝑇𝑖𝑂2 in the range from 1.2631E-52to3.9436E-

.That means the charge transfer rate for D35CPDT / 𝑆𝑛𝑂2 is larger than the charge transfer 

rate for D35CPDT / 𝑇𝑖𝑂2 .The charge transfer rate was substantially less from 1.1877E-26 at 

strength coupling 1.25× 10−1(eV/ state)2 and reach 4.9883E-30 at coupling 1.25×

10−5(eV/ state)2 in the case of D35CPDT / 𝑆𝑛𝑂2at  ∆𝐹
0 = 0.6 eV with Pyridine solvents. 

Also, we note, that the charge transfer rate is large from4.3922E-26 at coupling 1.25×

10−1(eV/ state)2to reach 1.8447E-29 at coupling 1.25× 10−5(eV/ state)2for D35CPDT 

/ 𝑆𝑛𝑂2 with Methanol solvents. However, the charge transfer rate has become minimum at 

coupling 11.25× 10−5(eV/ state)2 with Pyridine solvents at  ∆𝐹0 = 1.25eV  and to reach to 

5.3049E-56 . On the other hand ,charge transfer rate reach to maximum  1.6563E-48 at 

strength coupling 1.25× 10−5(eV/ state)2for D35CPDT / 𝑇𝑖𝑂2 with Methanol solvent. The 

other parameter that is affected and limits the charge transfer process is potential energy. The 

other parameter that is affected and limits the charge transfer process is the potential energy. 

It further influences on charge transfer rate. Furthermore, we find the results in Table (5) that 

the potential energy of charge transfer is increased with decreased transition energy. Potential 

energy reaches to maximum 2.1374eV and 0.6411 eV for D35CPDT / 𝑇𝑖𝑂2 and D35CPDT 

/ 𝑆𝑛𝑂2 with Pyridine  solvents while reaching to minimum 1.7011eV and 0.6039 eV for 

D35CPDT / 𝑇𝑖𝑂2 and D35CPDT / 𝑆𝑛𝑂2 with Methanol solvents, respectively. The greater 

transfer rate increases for both systems with the coupling 1.25× 10−1(eV/ state)2and 



IHJPAS. 53 (3)2022 
 

13 

decreases in the charge transfer rate with decreasing of the coupling. It reaches the minimum 

with the strength coupling 5.25 × 10−5(eV/ state)2 and reduces to decrease the charge 

transfer process. The charge transfer rate becomes low with the Pyridine solvent in both 

systems. It has in range1.1877 × 10−26-4.9883 × 10−30 for D35CPDT/ 𝑆𝑛𝑂2and reaches 

1.2631 × 10−52 - 5.3049E × 10−56 for D35CPDT / 𝑇𝑖𝑂2.The D35CPDT / 𝑆𝑛𝑂2 and 

D35CPDT / 𝑇𝑖𝑂2   systems with Methanol have a charge transfer rate large in range 4.3922 ×

10−26-1.8447 × 10−29 for D35CPDT / 𝑆𝑛𝑂2and reaches 3.9436 × 10
−45 - . 6563 × 10−48 

for D35CPDT / 𝑇𝑖𝑂2.Table (5) shows the potential in both systems increasing with the 

decrease of the transition energy and the charge transfer rate will be increasing tremendously 

with the decrease of the potential energy. The results in Table (6) indicate that D35CPDT 

contact to 𝑆𝑛𝑂2 with Methanol solvents at driving energy  0.6eV giving us a large rate 

compared to the results in a table (7) or D35CPDT contact to 𝑇𝑖𝑂2 with Methanol solvent and 

the D35CPDT / 𝑆𝑛𝑂2 is a good system and can be used in electronic devices. 

 

5. Conclusion 

 

In conclusion, the influence of transition energy in both systems can show the charge 

transfer rate, the rate increases with the transition energy increase. In contrast, the driving 

energy in both systems increases with the decreased electrochemical potential and substantially 

reduces the charge transfer rate. It can be concluded that the charge transfer for both systems 

increases with decreases in the potential, and the rate is large for D35CPDT / 𝑆𝑛𝑂2  compared 

to  D35CPDT / 𝑇𝑖𝑂2. A large charge transfer rate is observed from a charge donating 

D35CPDT dye  attached to the 𝑆𝑛𝑂2 surface compared to the small rate of charge transfer from  

D35CPDT dye  attached to the 𝑇𝑖𝑂2 surface with the same solvents. The results of the charge 

transfer rate allow for further systematic analysis of the influence of transfer parameters on the 

flow of electronic transfer from donor to an acceptor in the device's system and to know the 

influences on the efficiency of devices 

 

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