CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 52, 2016 

A publication of 

 

The Italian Association 
of Chemical Engineering 
Online at www.aidic.it/cet 

Guest Editors: Petar Sabev Varbanov, Peng-Yen Liew, Jun-Yow Yong, Jiří Jaromír Klemeš, Hon Loong Lam 
Copyright © 2016, AIDIC Servizi S.r.l., 

ISBN 978-88-95608-42-6; ISSN 2283-9216 
 

Glass Texturing Affects Optical Properties of  

Perovskite Solar Cells: Comparison Study 

between Mesoscopic and Planar Structure  

Dong In Kima, Sang-Hun Namb, Ki-Hwan Hwanga,b, Yong-Min Leea,  

Jin-Hyo Booa,b* 

aDepartment of Chemistry, Sungkyunkwan University, Suwon 440-746, Korea 
b Institute of Basic Science, Sungkyunkwan University, Suwon 440-746, Korea 

jhboo@skku.edu 

Glass texturing is an effective method for changing the surface morphology to improve light trapping. In this 

paper, the technique is applied to hybrid inorganic-organic solar cells (perovskite solar cell) to enhance light 

trapping and current density. We optimized wet chemical etched fluorine doped tin oxide (FTO) coated glass 

substrates using a simple treatment then compared the mesoscopic and planar structures. Thus, we present 

the implication study of the wet etching process with a random pattern surface that enables punch light 

scattering and ideally balanced the optical and electrical properties of the perovskite solar cell. As a result, we 

achieved short-circuit current density for 26.5 mA/cm2 and PCE for 15.2 %. 

1. Introduction 

Clean and renewable sources need to be developed to meet the increasing energy demand. Renewable 

energy technology is important because of insufficient fossil fuels and pollution. Especially, it is highly 

anticipated that the solar cell industry will become an alternative green energy source. Though the silicon solar 

cell is commercially available worldwide, it has a number of limitations including cost effectiveness. The next 

generation solar cell, the perovskite solar cell, is intended to overcome the economic and technical limitations 

of silicon solar cells. Perovskite materials are well recognized as a very attractive photovoltaic material 

because of several attractive properties. The rapid evolution of Methyl ammonium lead halide perovskite solar 

cells, specifically due to their higher power conversion efficiency, raises new potentials for practical 

applications (Kazim et al., 2014). Perovskite materials were first used as dyes instead of N-719 in liquid dye 

sensitized solar cells in 2009 (Kojima et al., 2009). The perovskite solar cells brought about technological 

innovation when the first solid-state mesoscopic heterojunction perovskite solar cell was introduced in 2012 

(Kim et al., 2012). The power conversion efficiency of mesoscopic heterojunction and planar heterojunction 

perovskite solar cells has exceeded 18%, while the most recent, verified perovskite solar cell efficiency is as 

high as 20.1 % (Nie et al., 2015). However, several problems related to mesoscopic heterojunction devices 

such as the high processing temperature above 400 °C for the n-type layer as well as the existence of a 

mesoporous structure in TiO2 coated substrates can lead to pore-filling problems, which may not only 

decrease the performance, but also lower the stability and cause I-V curve hysteresis (Lee et al., 2012). In 

order to overcome the foregoing discussions, researchers have attempted to find a solution to these issues. 

The first reports on planar structure discussed the evaporation of the perovskite material, achieving a uniform 

perovskite film with more than 15 % efficiency (Liu et al., 2013). Moreover, a vapor-assisted solution process 

was demonstrated as an efficient deposition technique for the planar structure, achieving 12.1 % efficiency 

(Chen et al., 2014). 

The loss of light in solar cells is a matter of concern in the scientific research community. In the past decade, 

there have been a number of suggestions for the use of light scattering through external and internal 

reflections to increase effective absorption in solar cells. In particular, it was suggested that light trapping 

                                

 
 

 

 
   

                                                  
DOI: 10.3303/CET1652062 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Please cite this article as: Kim D. I., Nam S.-H., Hwang K.-H., Lee Y.-M., Boo J.-H., 2016, Glass texturing affects optical properties of 
perovskite solar cells: comparison study between mesoscopic and planar structure, Chemical Engineering Transactions, 52, 367-372  
DOI:10.3303/CET1652062   

367



would have important benefits for solar cells and that high efficiency can be maintained without a mesoporous 

layer. Light scattering is an essential approach in thin film perovskite solar cells used to reduce optical losses 

in the absorber layer. The approach involves the scattering of light at rough interfaces, introduced into the 

solar cell by means of substrates treated with random-pattern surface substrates (Zeman et al., 2006). The 

multi junction approach is widely used in these solar cells (Yang et al., 1997). TCO substrates with different 

surface textures have recently been developed and tested in solar cells, such as optimized wet-etched 

(Sittinger et al., 2006), or surface plasma-treated (Dominé et al., 2008), zinc-oxide, double-textured tin-oxide 

(Kambe et al., 2008), and a combination of etched glass with zinc-oxide (Hongsingthong et al., 2010). Even 

though the potential of high performance TCOs has already been investigated oxide (Krč et al., 2010), a 

physical explanation of why these textures result in high scattering properties is still missing. In this study, the 

key challenge for the fabrication of substrates with a random pattern is the optimal compromise between 

electrical, optical, light-trapping and light-scattering properties using elementary methods. In the ideal case, 

the scattered light is confined within the multi-layered thin films of the solar cell and is almost completely 

absorbed after multiple passes through the absorption layer. The overall thickness of the solar cells while 

minimizing, light trapping is very important in order to enhance the optical property. The reflection at the 

air/glass interface decreases and the refractive index increases in accordance with the amount of light 

reflected through the mesoporous layer or the number of counter electrodes at the glass/interior interface of 

the solar cell. Glass texturing was applied to the perovskite solar cell. Surface texturing was successfully used 

to enhance the light absorption. By comparing the external quantum efficiency of two types of solar cells on 

texturing glass substrates, it was found that a texture that exhibits random patterns and roughness also 

exhibits good light scattering in the solar cells. The current density and cell efficiency were affected because of 

light trapping by the glass texturing in the perovskite solar cells. The enhancement of light harvesting by the 

light scattering and the light trapping effects in the visible region was confirmed. 

2. Experimental 

2.1 Glass texturing 
In this study, a FTO coated glass substrate with a size of 20 × 20 mm2 was used. The glass substrate was 

etched using HF solution of 14 M concentration. We prepared texture-glasses and non-texture for cover glass.  

2.2 Fabrication of perovskite solar cells 

The FTO electrodes were fabricated by etching the FTO coated glass with a mixture of zinc metal powder and 

2 M hydrochloric acid solution. The substrate was rinsed with water and then cleaned in an ultrasonic bath 

with acetone and, deionized water each for 10 min and then washed with ethanol and dried with N2 gas. The 

etched FTO electrodes were rinsed with water. These electrodes were cleaned in an ultrasonic bath 

containing acetone and distilled water for 10 min, respectively, and then treated with oxygen plasma cleaner 

for 5 min. To make a TiOx compact layer, the FTO electrode was coated with 0.15 M titanium diisopropoxide 

bis(acetylacetonate) in 1-butanol solution via the spin-coating method by heating on a hot-plate at 155 °C for 

10 min. A mesoporous TiO2 layer was coated on the prepared TiOx compact layer by the spin-coating method 

using TiO2 paste (18NR-T), and then annealed at 500 °C for 60 min in a box furnace. The perovskite layers 

were fabricated by two-step processes. First, the mesoporous TiO2 photoanode layers were coated using PbI2 

solution by spin-coating, and drying at 120 °C. Then, perovskite layers were deposited by spin-coating (10 

mg/mL) using a CH3NH3I solution on the PbI2 coated layers, which dried at 135 °C. The hole-transporting 

materials (HTM) solution was prepared by dissolving spiro-MeOTAD (72.3 mg), 4-tert-bytylpyridine(28.8 μL) 

and a Li-TSFI stock solution(17.5 μL) in 1 mL chlorobenzene loaded on the perovskite layer, which was 

coated by the spin-coating method. Finally, Au electrode was deposited on the top of the HTM over layer by 

the thermal evaporation system. 

2.3 Characterizations 
The simulated solar light was achieved using a xenon lamp and an AM 1.5 filter. The J-V curves were 

obtained by measuring the photocurrent using a source meter. External quantum efficiency (EQE) was 

measured using an EQE system (PV measurement Inc.) under DC mode, where a 75 W xenon lamp was 

used a light source for generating a monochromatic beam. Transmittance and diffusion transmittance spectra 

were recorded using a Spectral Response Measurement System in the 300 ~ 1,100 nm wavelength range and 

Haze was calculated both the transmittance and diffusion transmittance by using the following equation. 

Reflectance and absorption were measured using a UV-3600 spectrophotometer.  

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Figure 1: (a) Total transmittance and Diffusion transmittance. (b) Spectral haze value (texture glass and bare 

glass) 

3. Results and discussion  

3.1 Transmittance and diffusion transmittance spectra 
The effect of glass texturing on light scattering and trapping properties was observed by the naked eye. 

Texturable films change their clear transparent appearance to a milky form after a short dip in diluted HF acid. 

If the glass is textured, the process has a big impact on the optical properties, reducing the transmittance 

properties, solar cell’s performance will deteriorate. Therefore we measured the transmittance to confirm 

Figure 1, shows the specular transmittance and diffusion transmittance spectra of the textured glass films. The 

glass surface changed to a milky form after the etching process. When both films were highly transparent, the 

average specular transmittance curves in the entire wavelength range was above 80 %. We confirmed that 

transmittance was not affected by the etching process. The diffuse transmittance of the different surfaces is 

presented in (Figure 1(a)). Both the textured and non-textured films exhibited an almost diffusion 

transmittance over a broad range of whole wavelength. The diffuse transmittance curve for both film exhibited 

an exponential rapid decay. The glass textured substrate had the highest total diffuse transmittance in the 

entire wavelength range. One can observe that the diffusion transmittance of the glass textured surface 

correlates with the optical behaviour. We observed haze phenomenon by the naked eye on the glass surface 

with wet etching and the average specular transmittance curves were maintained while the diffuse 

transmittance rose gradually, which shows the increasing roughness of the substrate. Especially, the intensity 

of the diffuse transmittance curve increased at 370 nm. The haze value (Total diffuse transmittance / Total 

transmittance) was calculated. The haze value provided an index for the characteristics of light scattering and 

trapping effects in the textured film. In the overall visible light wavelength range, the value of the haze was 

above 10. The haze level at the wavelength of 400 nm increased by about 50 % even after the etching 

process. In order to further study light scattering and trapping in the texture-etched glass, the haze in the 

layers was determined (Figure 1(b)). shows the haze values and analysis of the diffusion transmittance 

showed a continuous shift in the crater opening angle. The origin of the optical effects produced by the wet 

etching process can be understood from the random order morphologies of the etched glass surface. 

Transparency ≥ 80 % over the entire visible region is a good optical property in solar cells. We also expect 

that the light scattering and trapping properties can be controlled by varying the etchant, etchant concentration 

and etching time. 

3.2 Reflectance spectra 
Figure 2, shows the results of reflectance measurements on the textured and non-textured glass (Figure 2(a)), 

curves are shown for the front side of the glass (when the light enter the glass, light scattering occurs at the 

air/glass interface). The other curves are for the back side of the glass (when the light enter the glass, part of 

the light is reflected back by the mesoporous layer or the back contact and then, part of the reflected light can 

be reflected once again at the FTO/glass interface). The results of the bare glass provide a good indication of 

the effectiveness of glass texturing in glass substrates with random order patterns, which will further change 

the overall reflection property. The reflectance of the solar cell with glass texturing is significantly reduced in 

the visible range at the front side of the glass when compared with the bare cell. This reduction is attributed to 

an increased light scattering property at the front side of the glass. The random pattern on the glass surface 

leads to light scattering and the perovskite layer absorbs more light. The sample with textured surfaces has  

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Figure 2: Reflectance of the etched glass surfaces. (a) Front side of glass (Air/glass). (b) Back side of glass 

(glass/FTO) 

relatively enhanced reflection ability due to light trapping at the inner solar cell. A more direct illustration of the 

light trapping effect is observed in the visible region for the reflectance curves in (Figure 2(b)). Little difference 

is observed in the reflectivity of the back side of the glass substrate after treatment. The reflectance value 

increased as more light was trapped at the inner solar cell. Especially, the intensity of the reflectance curves 

also increased at 370 nm, these results were affected by diffusion transmittance. A major advantage of glass 

texturing is that it leading to reduced optical losses. 

3.3 Absorbance spectra 
To examine the light scattering and trapping effects of the random pattern, glass substrates were prepared 

using two types of substrates. The amount of absorbed light was significantly enhanced after wet etching. The 

spectra in (Figure 3(a)) quantifies the similar, uniformly reflectivity value of as little as 1 ~ 3 % in the high 

absorption at visible region of glass texturing samples. This resulted in a nearly complete suppression of 

surface reflectivity in the entire high optical absorption region of the perovskite layer, with an enhancement of 

light scattering and trapping in the inner solar cell. These results can be partly explained by the optical images 

and haze data see Figure 1, with the assumption that higher diffusion transmittance results in better light 

scattering. Absorbance curves maintain as similar as from 300 nm to 550 nm and then rapidly decay. 

Absorbance value was increased at visible region. We can know that absorbance region was wider than 

before. The utilization of the light was increased due to of the foregoing effect. In particular, it increased 

significantly the optical properties, the result is good influence on characteristics of current density. These 

effects exert a positive influence on optical property of solar cell. Thus, in other to allow a good incoupling of 

incident light as well as light scattering and trapping in perovskite solar cells. 

3.4 Cell property 
The EQE was measured to demonstrate both the scattering effect at the air/glass interface and light trapping 

at the glass surface/inner solar cell. EQE is drastically increased in the wavelength range between 400 nm 

and 800 nm when compared with the reference cell. This upswing is attributed to increased absorbance at the 

 

 

Figure 3: (a) Absorbance (b) EQE (including mesoscopic and planar structure) 

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Figure 4: J-V curves of Perovskite solar cells 

perovskite layer. Due to the scattering effect for the perovskite solar cells on the textured glass substrate, 

interferences in the reflectance are apparent at the front side. These interferences induce light scattering at 

the front side, at the structure of the textured glass/FTO/solar cell. As shown in (Figure 3(b)), when comparing 

the EQE curves measured in substrate configuration, a strongly increased EQE is apparent in the visible 

region. Quantum efficiency above 80 % at wavelengths of 400 ~ 600 nm was obtained when glass texturing 

was applied to the perovskite solar cell. The EQE of the perovskite solar cell after glass texturing was higher 

than without glass texturing.  

The solar cell characteristics with respect to the mesoporous layer and etching process for the cells fabricated 

using these specimens are shown in Figure 4. Unfortunately the cell performance deteriorates drastically in 

the planar structured cell without a mesoporous layer and non-glass texturing process. Jsc contributes 

significantly to the overall cell performance in textured glass substrates. In this case, the cell current density 

reached 26.5 mA/cm2 due to an improved QE in the visible wavelength ranges. The gain in efficiency is 

considerable because of the superior electrical properties of the glass textured samples, leading to a high 

optical property. Finally, 11.7 % ~ 15.2 % efficiency was achieved with the textured glass substrates. All these 

results demonstrate the effectiveness of optical confinement at the inner solar cells using textured surfaces 

with a certain haze ratio, which results in higher absorption of the incident light. Furthermore, notable 

differences can be found among the textured surface with respect to the Voc. Texturing samples with higher 

roughness show lower Voc.  

Table 1: J-V curves of Perovskite solar cells 

 Jsc (mA/cm2) Voc (V) FF (%) PCE (%) 

Non-texture planar 17.7 0.93 63.1 10.5 

Texture planar 20.4 0.90 63.6 11.7 

Non-texture mesoscopic 21.3 0.93 63.7 12.6 

Texture mesoscopic 26.5 0.92 62.4 15.2 

4. Conclusions 

We optimized the effect of glass texturing on mesoscopic and planar structures as well as the light scattering 

and trapping ability of perovskite solar cells. The random pattern of the glass affects light trapping by the 

perovskite solar cell as determined by the absorption and EQE. The scattering and light trapping effects were 

enhanced for the Perovskite solar across all ranges because of the increased optical property. As a result, the 

photovoltaic property of the perovskite solar cell using textured glass improved the photocurrent density by up 

to 24.4 % and the conversion efficiency was 21.1 %. 

Acknowledgements 

This work was supported by the Human Resources Development program(No. 20144030200580) of the Korea 

Institute of Energy Technology Evaluation and Planning(KETEP) grant funded by the Korea government 

Ministry of Trade, Industry and Energy 

This work was supported by Mid-career Researcher Program (2015R1A2A2A01007150) through NRF grant 

funded by the MEST. 

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