Rev


R. Ndioukane et al., Optical properties. of PZN-PT nanoparticles thin layers for PV applications 

 

OAJ Materials and Devices, Vol 4 (1), 1502 (2019) – DOI: 10.23647/ca.md20191502 

p1 

 

Article type: Conf.-Conference paper (CASAMANSUN) 

 

Optical properties of PZN-PT nanoparticles 

thin layer on ITO glass for photovoltaic 
application 

 

 

R. Ndioukane (1), D. Kobor (1), L. Motte (2), J. Solard (3) 

(1) Laboratoire de Chimie et de Physique des Matériaux, Assane Seck University of 
Ziguinchor, Senegal 
(2) Laboratory for Vascular Translational Science, Paris 13 University, France 
(3) Centrale de proximité en nanotechnologies de Paris Nord, Institut Universitaire de 

Technologie de Villetaneuse, France 
 
Corresponding author: r.ndioukane1532@zig.univ.sn   

RECEIVED: 14 september 2018 / RECEIVED IN FINAL FORM: 12 february 2019  / ACCEPTED: 15 february 2019 

 

Abstract: In this work, undoped and Mn doped Pb(Zn1/3Nb2/3)O3-4.5PbTiO3 nanoparticles were dispersed in 

biopolymer and in mixed biopolymer + pentacene as active layer and deposited by spin coating on ITO glasses. 

Morphological, optical and electrical properties of these layers were investigated. SEM images show the 

superposition of different deposited layers ITO/TiO2/PZN-PT-np-biopolymer on glass substrate with thicknesses of 

1.600 µm, 1.505 µm and 1.765 µm respectively. The absorbance value in UV visible for pentacene layer increases 

from 75 % to 99 % while the transmittance for ITO glasses diminishes from more than 80 % to 2 %. Optical gaps 

of ITO, TiO2, PZN-PT nanoparticles are respectively 3.75 eV, 3.2 eV and 3.15 eV. Pentacene deposition reduced 

the gap to 1.65 eV for undoped sample and 1.60 eV for the doped ones. Intermediate gaps (2.3 eV and 2.6 eV for 

undoped sample and 2.15 eV and 2.7 eV for doped sample) were observed. Photoluminescence performed 

between 450 nm and 750 nm confirms « these intermediate gaps ». 

 Keywords: PEROVSKITE, NANOPARTICLES, THIN FILM, OPTICAL PROPERTIES, BAND GAP 

 

 

 

 

Cite this article: Rémi Ndioukane, Diouma Kobor, 

Laurence Motte and Jeanne Solard, OAJ Materials and 

Devices, Vol 4 (1), 1502 (2019) – DOI: 

10.23647/ca.md20191502 



R. Ndioukane et al., Optical properties. of PZN-PT nanoparticles thin layers for PV applications 

 

OAJ Materials and Devices, Vol 4 (1), 1502 (2019) – DOI: 10.23647/ca.md20191502 

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Introduction 

Among all the solution-processed thin film optoelectronic 
material technologies investigated over the past 2 decades, 
organic–inorganic (or hybrid) methylammonium lead tri-
iodide (MAPbI3) perovskites have emerged as clear front-
runners with proof-of-concept high performance devices 
demonstrated for a broad range of applications [1-8]. The 
MAPbI3-based photovoltaic devices have demonstrated 
constantly increasing power conversion efficiency (PCE), 
which now exceeds 22% [9-10] and is steadily approaching 
that of single-junction monocrystalline Silicon (c-Si) solar 
cells. Although the record for the highest efficiency 
perovskite solar cell was achieved using a mesoporous 
titania (TiO2)-based architecture [10-12] photovoltaic 
devices employing a simple planar architecture are closing 
in with the highest reported efficiency of 20% [6, 13, 14]. 
Despite this breakthrough, hybrid lead-halide perovskites 
are known to degrade due to moisture and heat, upon 
prolonged exposure to light and are prone to ion or halide 
vacancy migration, leading to unstable operation of 
photovoltaic devices. Great efforts have been put forth for 
achieving highly efficient planar solar cells by exploring for 
potential ideal contact layers [15]. In addition, it is now 
realized that the next steps in advancing hybrid perovskite-
based materials toward a viable photovoltaic technology will 
require simultaneously improving both the overall efficiency 
and also intrinsic stability. To overcome such difficulties, we 
oriented our research to inorganic PZN-PT perovskite 
materials with excellent and stable properties compared to 
the organic-perovskite ones. However, despite their 
excellent properties, one of the greatest difficulties to 
integrate widely such materials in electronic devices is to 
achieve them in thin films form because of their incongruent 
melting property. In this paper, undoped and Mn doped PZN-
4.5PT nanoparticles were dispersed in biopolymer and in 
mixed biopolymer + pentacene as active layer and 
deposited by spin coating on ITO glasses. After the 
successful deposition of the thin film, morphological, optical 
and electrical properties were investigated.  

Experimental procedure 

The quality of the layers depends strongly on the state of 

the materials surfaces and their interfaces, whether organic-

organic or metal-polymer. Thus a chemical treatment of the 

ITO substrate surface is necessary to eliminate the 

contaminating elements. For this, we combined the 

ultrasonic method with piranha to clean substrates. The 
piranha solution is composed of H2SO4 96 % (30 ml) and 

H2O2 (10 ml). After cleaning, the different layers, namely 

titanium oxide (TiO2), undoped and Mn doped PZN-4.5PT 

nanoparticles dispersed in a biopolymer and pentacene were 

successively deposited by spin coating. In this study we 

used a natural biopolymer containing polysaccharides with 

short side chains. This polymer can take several 

conformations that allow it to adapt or intercalate depending 

on the environment. 

Colloidal suspension of TiO2 

The titanium oxide used in this study is a finished product 

marketed by Sigma-Aldrich (CAS number 13463-67-7). The 

suspension is obtained by grounding TiO2 powder in a mortar 

and adding a few drops of acetic acid giving a white paste. The 

as prepared paste is deposited on ITO glass substrate at room 

temperature using a spin coater Midas 1200D at 3500 rpm 

with an initial acceleration of 5 seconds and an operating time 

of 2 min. 

PZN-PT nanoparticles thin film 

fabrication 

Undoped and Mn doped PZN-4.5PT single crystals synthesized 

by the flux method [16] were grounded in a mortar to obtain a 

very fine powder (TEM characterizations revealed nanoparticles 

of the nanometer order and studies (not shown here) have 

confirmed that the population of spherical particles having a 

diameter of 30 nm was more representative). The grounded 

powder was dispersed in biopolymer solution. To obtain a 

homogeneous film, spin coating process was carried out at 

room temperature at 3500 rpm with an initial acceleration of 5 

seconds and an operating time of 10 min. The biopolymer is 

used to disperse undoped and Mn doped PZN-4.5PT perovskite 

nanoparticles but also as a hole-injecting layer through the 

organic layer/ITO interface. Secondly it serves buffer layer to 

prevent diffusion of oxygen and indium to active layer, these 

impurities can act as exciton recombination centers or 

photogenerated traps carriers. 

Results and discussion 

SEM images 

Surface morphology was observed by using an electron beam 

lithography system Pioneer Raith model in C(PN)2 (Paris 13 

University). Observation of film surfaces in a scanning electron 

microscope makes it possible to verify the homogeneity of 

films, grains shapes and aggregates as well as the qualitative 

analysis of layers. 

SEM images of samples composed of ITO/TiO2/PZN-PT-np-

biopolymer films (DKRN-ITO2), ITO/TiO2/PZN-PT+1%Mn-np-

biopolymer (DKRN-ITO4), ITO/TiO2/PZN-PT-np-

biopolymer/pentacene (DKRN-ITO7), ITO/TiO2/PZN-

PT+1%Mn-np-biopolymer/pentacene (DKRN-ITO8) deposited 

at room temperature on glass substrates are shown 

respectively in figure 1. DKRN-ITO2 and DKRN-ITO4 (Fig. 1a 

and 1b) shows a homogeneous, sparse and porous surface, 

showing white gray coloured non-regular agglomerated grains 

with an average size of 30 nm. DKRN-ITO7 and DKRN-ITO8 

samples (Fig. 1c and 1d), developed in the same conditions 

with the only difference of adding a pentacene layer, have 

uniform, compact and homogeneous slightly black surfaces. 

This suggests that pentacene leads to a coalescence of the 

grains by diffusion through the pores. The morphology of the 
surface is initially related to the energy of the particles. 

Indeed, when the particle on the substrate acquires a great 

energy, it will have a large surface diffusion length. Then, this 

allows it to reach the sites energetically favorable and thus to 



R. Ndioukane et al., Optical properties. of PZN-PT nanoparticles thin layers for PV applications 

 

OAJ Materials and Devices, Vol 4 (1), 1502 (2019) – DOI: 10.23647/ca.md20191502 

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complete the possible gaps, reducing the irregularities of the 

surface. In the other case, the particles deposited on the 

substrate in contact with the air having lost a large part of 

the energy, their diffusion length will be very short. 

Therefore, the morphology of the surface will reflect a part 

of the morphology of the substrate but with greater 

irregularities due to the shading effect, and secondly the 

nature of the deposited material [17]. 

Observation in scanning electron microscope in transverse 

mode, allowed us to see the disposition of the various 

deposited layers but also to determine their thickness. For 

example, in figure 2a showing the SEM image in transverse 

mode of the DKRN-ITO2 sample composed of the ITO / TiO2 

/ np-PZN-4.5PT-biopolymer layers, we obtained thicknesses 

of 1.600 μm, 1.505 μm and 1.765 μm respectively for ITO, 

TiO2 and np-PZN-PT-biopolymer. This allowed us to confirm 

the value of the thickness of the ITO given by the supplier 

(1.600 μm). 

 

Figure 1: SEM Images of thin film (a) DKRN-

ITO2, (b) DKRN-ITO4, (c) DKRN-ITO7 and (d) 

DKRN-ITO8 

 

Figure 2: SEM Images in transversal mode (a) 

DKRN-ITO2, (b) DKRN-ITO4, (c) DKRN-ITO7 and 

(d) DKRN-ITO8 

 

Table 1: Thickness values of different layers 

Thicknesse (µm) ITO TiO2 Biopolymer Pentacene 

DKRN-ITO2 1,600 1,505 1,765 - 

DKRN-ITO4 1,600 2,401 1,667 - 

DKRN-ITO7 1,600 1,709 1,680 1,431 

DKRN-ITO8 1,600 1,691 1,582 1,322 

Optical properties 

Optical properties of thin films were investigated using an UV-

Visible spectrophotometer with an integrating sphere model 

LAMBDA 950S in IM2NP (Marseille). Measurements are made 

with a pitch of 5 on a wavelength spectrum ranging from 250 

and 1500 nm. 

Transmittance and absorption 

Typical transmission spectra obtained for the different 

deposited layers at room temperature are shown in figure 3a. 

For the ITO reference sample composed of ITO layer only, 

there is a strong transmission of more than 80 % throughout 

the visible band. This confirms the transmission value given by 

the supplier. This transmission decreases with the deposition 

respectively of TiO2/np-PZN-4.5PT-biopolymere, TiO2/np-PZN-

4.5PT+1%Mn-biopolymer, TiO2/np-PZN-4.5PT-

biopolymere/pentacene and TiO2/np-PZN-4.5PT+1 %Mn-

biopolymer/pentacene. 

For the different deposits, the general patterns of the spectra 

are similar. Two transmission domains can be distinguished 

according to the wavelength: 

- A domain (λ < 800 nm) characterized by high absorption and 

low transmission of the different layers, which corresponds to 

the absorption of the layer in question. 

- A relatively high transmission domain for λ range of 800 - 

1500 nm, it increases sharply and tends to values between 30 

and 56 % for the DKRN-ITO2 sample, 26 and 47 % for the 

DKRN-ITO4 sample, 25 and 45 % for the DKRN-ITO7 sample, 

45 and 70 % for the DKRN-ITO8 sample. Authors in the 

literature, such as D. Kobor [18] report transmission values of 

25 and 45 % for wavelengths between 600 and 900 nm of 

PZN-4.5PT single crystals. This confirms the values obtained in 

this study, although we can also consider the influence of the 

organic layers of biopolymer and pentacene which tend to 

attenuate this transparency. In figure 3b, it can be seen that 

the addition of the pentacene layer greatly increases the 

absorption throughout the visible spectrum. It is deduced that 



R. Ndioukane et al., Optical properties. of PZN-PT nanoparticles thin layers for PV applications 

 

OAJ Materials and Devices, Vol 4 (1), 1502 (2019) – DOI: 10.23647/ca.md20191502 

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pentacene increases the absorption band in the visible (~ 90 

%). Indeed, pentacene is a semiconductor that absorbs well 

in the visible and authors like A. Skaiky [19] have shown it. 

This is a good thing for photovoltaic applications. On the 

other hand, the biopolymer seems to have less influence on 

the absorption compared to pentacene. 

 

Figure 3: (a) transmittance and (b) absorbance 

according to the UV-Visible-NIR wavelength for 

different samples 

Determination of band gap 

To calculate the optical gap Eg, we used Tauc relation [20]. 

( )                                        (1)
n

g
h A h E                    

Where A is a constant, hν is photon energy, Eg is the allowed 

energy gap, n = ½ for allowed direct transition, α is the 

absorption coefficient and n = 2 for allowed indirect 

transition. 

Thus, from the value of the absorption coefficient and by 

plotting the curve of (αhν)² as a function of the photons 

energy, we have determined the optical gap Eg: it suffices to 

draw the slope in the region of absorption as shown in figure 

4 and the intersection of this line with the abscissa axis (for 

αhν = 0) gives directly Eg. The values found are shown in 

table 2. 

For the ITO reference sample, the value of the gap found 

(3.75 eV) is in perfect correlation with that found by G. 

Fatma-Zohra [21] (3.80 eV). For the DKRN-ITO2 and DKRN-

ITO4 samples, the gap remains high with values of 3.20 eV 

and 3.15 eV that can respectively correspond to the TiO2 gap 

that is 3.02 eV according to Schon [22] and PZN-PT gap equal 

to 3.04 eV according to He Chong-Jun [23]. Pentacene 

deposition reduced the gap to 1.65 eV for the DKRN-ITO7 

sample and 1.60 eV for DKRN-ITO8. We also note the presence 

of intermediate gaps (2.30 eV and 2.60 eV for DKRN-ITO7 and 

2.15 eV and 2.70 eV for DKRN-ITO8). These intermediate gaps 

could be due to the heterogeneity of the layers (presence of 

TiO2, nanoparticles of PZN-4.5PT undoped or doped Mn, 

biopolymer, pentacene). These values could correspond 

respectively to the gap of the pentacene layer (1.65 and 1.60 

eV), the combination of the biopolymer with pentacene (2.30 

and 2.15 eV) and TiO2 (2.60 and 2.70 eV). It appears from the 

results that pentacene tends to influence even the gap of the 

inner layers (TiO2, nanoparticles and biopolymer) whose 

absorption is considerably reduced. The results are in perfect 

correlation with the curves of figure 3. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4: Tauc plot curves of (x) ITO, ( ) DKRN-

ITO2, ( ) DKRN-ITO4, ( ) DKRN-ITO7 and ( ) 

DKRN-ITO8 

 

 

 

 



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Table 2: Gap values of different samples 

Samples Eg1 (eV) Eg2 (eV) Eg3 (eV) 

ITO 3,75 - - 

DKRN-ITO2 3,20 - - 

DKRN-ITO4 3,15 - - 

DKRN-ITO7 1,65 2,30 2,60 

DKRN-ITO8 1,60 2,15 2,70 

Photoluminescence 

To confirm the effect of pentacene on the reduction of the 

optical gap, we investigate photoluminescence on samples 

DKRN-ITO7 and DKRN-ITO8. Figure 5 shows the 

photoluminescence (PL) spectra obtained. We observe a first 

emission peak at 2.3 eV and a second peak at 2.5 eV for 

DKRN-ITO7 while for DKRN-ITO8 we have a peak at 2.2 eV 

and another at 2.6 eV. This confirms the values of the 

intermediate gaps found by the Tauc method. 

Photoluminescence was performed between 450 nm and 

750 nm. This does not allow observing the peak of 1.6 eV 

revealed by the method of Tauc. Indeed, this peak would 

probably appear in the infrared. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 5: Photoluminescence of (a) DKRN-ITO7 and (b) 

DKRN-ITO8 

Conclusion 

PZN-4.5PT nanoparticles thin layers were successfully 

prepared using a biopolymer. SEM images revealed the 

superposition of different deposited layers. It shows uniform, 

compact and homogeneous surface with deposition of 

pentaconene layer. Optical characterization by transmittance 

and absorbance measurements allowed us to observe the 

influence of the layers on absorption and optical gap. It also 

made it possible to follow the evolution of the gap according to 

the nature of the deposited layer. Pentacene has been very 

successful in improving photovoltaic properties. 

 

Acknowledgements:  

This work is supported by Agence Universitaire de la Francophonie 

(AUF). 

 

Complementary informations on authors: 

Rémi Ndioukane: r.ndioukane1532@zig.univ.sn, Research Gate (Rémi Ndioukane), LinkedIn (REMI NDIOUKANE) 

Diouma Kobor: dkobor@univ-zig.sn, Research Gate (Diouma Kobor) 

Laurence Motte: lmotte2009@hotmail.fr, Research Gate (L. Motte) 

Jeanne Solard: jeanne.solard@iutv.univ-paris13.fr, Research Gate (Jeanne Solard) 

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