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Investigation of Zinc Cobaltite (ZnCo₂O₄) as a Hole Transport Layer

for Perovskite Solar Cells: Implications for Renewable-Energy

Research and Innovation

Muhammad A. I. Zulkifli

, Zul A. F. M. Napiah

, Muhammad I. Idris

, Abd S. Ja’afar

, Muhammad R.

Kamarudin

, Noorazlan S. Zainudin

, Noorezal A. M. Napiah

, Mohamad A. M. Idin

Fakulti Teknologi dan Kejuruteraan Elektronik dan Computer (FTKEK), University Technical

Malaysia Melaka (UTeM), Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia

Fakulti Kecerdasan Buatan dan Keselamatan Siber (FAIX), University Technical Malaysia Melaka

(UTeM), Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia

Universiti Technology MARA (UiTM), Cawangan Pulau Pinang Kampus Permatang Pauh, 13500

Permatang Pauh, Pulau Pinang, Malaysia

*Corresponding Author

DOI:

https://dx.doi.org/10.47772/IJRISS.2025.910000325

Received: 12 October 2025; Accepted: 18 October 2025; Published: 11 November 2025

ABSTRACT

This study investigates Zinc Cobaltite (ZnCo₂O₄) as a potential hole transport layer (HTL) for perovskite solar

cells (PSCs) to address the long-term performance degradation observed in conventional HTL materials. Owing

to its high stability, wide bandgap, and favorable charge-transport characteristics, ZnCo₂O₄ offers strong

potential for efficient carrier extraction and transport in PSC architectures. The HTL plays a critical role in

selectively extracting and transferring positive charge carriers (holes) to the anode while maintaining overall

device stability. In this work, ZnCo₂O₄-based PSCs were simulated using the GPVDM software, and the Taguchi

optimization method was employed to determine the optimal design parameters for achieving maximum power

conversion efficiency (PCE). The key parameters considered include HTL thickness, operating temperature, and

bandgap energy. Simulation results reveal that a ZnCo₂O₄ thickness of 200 nm yields a PCE of 28.25% using

GPVDM. Through Taguchi optimization, the highest PCE of 32.23% was achieved with an optimized

configuration comprising a 300 nm ZnCo₂O₄ layer, 300 K temperature, 2.0 eV bandgap, and mobility factors of

9.14 × 10⁻⁶ cm² V⁻¹ s⁻¹ for both electrons and holes. These findings demonstrate that ZnCo₂O₄ is a promising

HTL candidate for high-efficiency and thermally stable PSCs. Further experimental validation and interface

engineering could enhance its performance and enable its integration into next-generation perovskite

photovoltaic devices.

Keywords—Zinc Cobaltite, Hole Transport Layer, GPVDM, Taguchi method

INTRODUCTION

In recent decades, the escalating global demand for renewable and clean energy has made solar power a central

pillar of sustainable electricity generation strategies [1]. Among emerging photovoltaic technologies, perovskite

solar cells (PSCs) have attracted substantial interest thanks to their rapidly improving power conversion

efficiencies, solution-processable fabrication, and tunable optoelectronic properties [2], [3]. However, key

challenges include device longevity as well as the cost and durability of interface layers, particularly the hole

transport layer (HTL) [4].

To address these challenges, this study investigates Zinc Cobaltite (ZnCo₂O₄) as a candidate HTL. ZnCo₂O₄

brings advantages such as strong chemical and thermal stability, favorable valence band alignment with

perovskite absorbers, and potentially higher hole-transport capability compared to conventional HTLs like

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PEDOT:PSS and spiro-OMeTAD [5], [6]. Recent experimental work has shown that PSCs employing ZnCo₂O₄

nanoparticle HTLs can outperform PEDOT:PSS-based devices in long-term stability without sacrificing

efficiency [5].

We adopt the General-purpose Photovoltaic Device Model (GPVDM) simulation platform to model cell

architectures incorporating ZnCo₂O₄ as the HTL. GPVDM is an open, freely available (open-source) simulation

tool capable of simulating optoelectronic behavior, including drift-diffusion, trapping, recombination, and

optical propagation—in disordered materials such as perovskites and organic semiconductors [7]. Indeed,

numerous studies have used GPVDM to explore thickness effects, carrier mobility impacts, and device

optimization in perovskite and organic solar cells [8], [9]. Within this framework, we systematically vary HTL

thickness, operating temperature, and bandgap in a design-of-experiments approach to seek optimal power

conversion efficiency (PCE) and durability. Comparative benchmarking against conventional HTLs will then

validate the merits of ZnCo₂O₄ in achieving a balance of cost-effectiveness, stability, and charge-transport

performance.

Device Structure

Nowadays, the third generation of solar cells has been proven to be the future method to generate electricity

using solar power. Due to their high PCE and suitability for scalable procedures, perovskite solar cells, a new

third generation solar cell look to have a very strong possibility of helping to scale up solar energy production.

In no other period in the history of solar cell research has the PCE been increased at such a quick rate as it has

been for perovskite solar cells. Perovskites are considered as ideal photovoltaic materials in solar cells due to

their high absorption in the visible spectrum, long carrier diffusion length, high carrier mobility, low exciton

binding energy, tunable bandgaps by exchanging atomic composition, large area production and low cost owing

to solution process-ability [5].

The effectiveness and lifetime of perovskite solar cells depend on the stability of the HTL. The extraction of

positive charge carriers (holes) from the perovskite layer and their transportation to the anode are accomplished

by the HTL, a crucial part of the device construction. Because it may eventually have an impact on the device's

general effectiveness and performance, the HTL's reliability is crucial.

There are several challenges with HTL in perovskite solar cells, including the possibility of degradation in the

presence of oxygen and moisture. This might lead to a decline in the device's performance over time. Experts

have been examining various materials and manufacturing techniques to improve the stability and lifespan of

HTLs. Because of its advantages, such as high hole mobility, broad band gap, and straightforward solvent

treatment technique, inorganic p-type semiconductor materials have the potential to replace organic hole

transport materials. Table I shows the comparison between ZnCO

with other HTL materials in terms of

stability. The PCE of perovskite solar cells is directly influenced by their stability. Due to its high PCE potential,

perovskite solar cells have attracted interest, but their stability is still a problem that has to be solved for

commercial viability.

Table I Comparison Stability of Various Material as Hole Transport Layer in Perovskite Solar Cell

HTL materials

Stability

Zinc Cobaltite, ZnCO

Exhibits strong hole transport capability, wide optical bandgap, and good

solution processability. ZnCo₂O₄ has been reported as a promising

alternative HTL due to its high stability and applicability in both

photoelectrochemical and photovoltaic systems [5].

Copper Galium Oxide,

CuGaO2

Demonstrates excellent thermal stability and superior resistance to moisture-

induced corrosion, making it a robust inorganic HTL [10].

Copper(I) Iodide, CuI

Possesses higher conductivity than spiro-OMeTAD, enhancing the device’s

fill factor and overall PCE; considered a strong inorganic HTL candidate

[11].

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PEDOT:PSS

Prone to corroding transparent conducting oxides (e.g., FTO), which limits

long-term stability. Its high acidity and large interfacial energy barrier reduce

Voc, Jsc, and overall PCE [5], [12].The photovoltaic performance

including VOC, short circuit current (JSC) and stability are relatively low

because of the huge energy barrier between PEDOT:PSS and the perovskite

layers as well as the high acidity of the PEDOT:PSS solution.[12]

Spiro-OMeTAD

Offers good film-forming properties but exhibits low intrinsic hole mobility

(2 × 10⁻⁴ cm² V⁻¹ s⁻¹), leading to higher resistive losses [12].

Poly[bis(4-phenyl)(2,4,6-

trimethylphenyl)amine], PTAA

Functions effectively only with dopant additives, which can induce

instability under long-term operation [12].

Poly(3-hexylthiophene), P3HT

Displays high carrier mobility, a suitable bandgap matching the solar

spectrum, and low cost, though less stable than inorganic alternatives [12]

HTL efficiency

As a hole transport material, each material has very own advantages that only that material has. This efficiency

is based on how much solar energy can be absorbed and how much electricity can be gained from it. There are

so many materials that have been researched so far, and Zinc Cobaltite is the new one on that list. Table II shows

the PCE of various materials that has been used as HTL in PSC from another research since 2019.

Table II Comparison PCE of various material as hole transport layer in perovskite solar cell

Hole Transport Layer

Best PCE (%)

Ref

ZnCO2O4 Nps

11.78

[5]

Nickel Oxide,Nio

15.65

[13]

Spiro-OMeTAD

11.9

[14]

Kesterite Czts Nps

6.0

[15]

Cuox Fs

13.35

[16]

P3HT

16.7

[17]

CuI

7.5

[18]

CuSCN

18.0

[19]

PTAA

18.11

[20]

CuGaO2

16.2

[21]

CuCrO2

20.54

[22]

CuPc

13.65

[23]

MoS2

8.3

[24]

CuAlO2

19.82

[25]

Pedot:Pss Flm

11.8

[26]

METHODOLOGY

This section describes the simulation and optimization procedures used to evaluate ZnCo₂O₄ as a HTL in PSCs.

The methodology consists of two main stages: the device simulation using GPVDM and Taguchi optimization

phase.

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Material Registration and Simulation Setup

Because ZnCo₂O₄ is not included in the default GPVDM material library, the first step involved manually

registering its electrical and optical parameters. These parameters included bandgap energy, electron and hole

mobilities, affinity, and relative permittivity. After successful registration, the software was used to simulate the

PSC device structure incorporating ZnCo₂O₄ as the HTL.

Each simulation was conducted with fixed ETL and absorber materials to ensure valid comparisons across

different HTLs. The PSC structure comprised fluorine-doped tin oxide (FTO) as the anode, titanium dioxide

(TiO₂) as the ETL, cesium lead iodide (CsPbI₃) as the perovskite absorber, ZnCo₂O₄ as the HTL, and gold (Au)

as the cathode, as illustrated in Fig. 2.

Multiple simulations were performed by varying the ZnCo₂O₄ thickness from 50 nm to 500 nm in 25 nm

increments. After each run, the PCE, fill factor (FF), open-circuit voltage (Voc), and short-circuit current density

(Jsc) were extracted. These data were then analyzed to determine the most suitable HTL thickness before

proceeding to parameter optimization.

Taguchi Optimization Phase

To identify the parameters that most significantly influence the PCE, the Taguchi method was implemented

using an L9 (3³) orthogonal array. This approach minimizes the number of simulations while maintaining a

statistically valid evaluation of factor interactions. Three control factors and two noise factors were considered.

The control factors are (1) Thickness of ZnCo₂O₄ HTL (Factor A); (2) Operating temperature (Factor B); and

(3) Bandgap energy of ZnCo₂O₄ (Factor C). The noise factors are (1) Hole mobility; and (2) Electron mobility

Each factor was varied at three levels based on preliminary simulations. The Taguchi L9 array produced nine

unique test conditions, which were simulated in GPVDM under identical illumination and boundary conditions.

For each simulation, PCE, Voc, Jsc, and FF were recorded. The resulting data were analyzed using the signal-

to-noise (S/N) ratio under the “larger-the-better” criterion to identify the factor level combinations that maximize

efficiency. An analysis of variance (ANOVA) was subsequently performed to quantify the contribution of each

factor to the total PCE variance.

A flowchart of the Taguchi phase is shown in Fig. 1, outlining the workflow from factor selection to confirmation

testing.

Fig. 1 Flowchart of the Taguchi optimization phase for ZnCo₂O₄-based perovskite solar cells.

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Device Simulation Using GPVDM

GPVDM is an open-source software platform for modeling the electrical and optical behavior of thin-film and

disordered-semiconductor devices. Unlike equilibrium-based models, GPVDM applies a non-equilibrium

carrier-transport formalism that accurately describes trapped carrier dynamics using the Shockley–Read–Hall

recombination model.

This feature enables reliable simulation of PSCs with complex interfaces and defect states. The software

computes the current–voltage (I–V) response, carrier densities, recombination rates, and electric-field

distributions under steady-state or transient illumination.

The simulated PSC stack configuration is depicted in Fig. 2, showing the device layers of

FTO/TiO₂/CsPbI₃/ZnCo₂O₄/Au. The input parameters included the material bandgap, electron affinity, relative

permittivity, and carrier mobilities, all of which are essential for accurate performance prediction.

Fig. 2 Simulated PSC device structure using GPVDM (FTO/TiO₂/CsPbI₃/ZnCo₂O₄/Au).

Result and Analysis

In this investigation, the thickness of the Zinc Cobaltite HTL is treated as a key design parameter in determining

the optimum configuration for achieving maximum PCE in the PSC. To systematically evaluate its influence,

multiple ZnCo₂O₄ thicknesses were simulated to identify the level that yields the highest device performance

while maintaining stability and efficient charge extraction. The simulated HTL thicknesses ranged from 50 nm

to 500 nm, with incremental steps of 25 nm (i.e., 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350,

375, 400, 425, 450, 475, and 500 nm). Each configuration was analyzed under identical boundary conditions

using the GPVDM simulation environment to ensure consistent comparison. After completing all simulations,

the output parameters—including current density, open-circuit voltage, fill factor, and PCE—were collected,

tabulated, and analyzed to determine the optimal ZnCo₂O₄ thickness for enhanced photovoltaic performance.

The design architecture and material composition of PSCs play a critical role in determining the optimal HTL

thickness, which directly influences charge extraction efficiency and overall device performance. The HTL

serves as a selective contact that facilitates efficient hole extraction from the perovskite absorber while blocking

electrons, thereby minimizing interfacial recombination losses. An appropriately optimized HTL thickness

ensures a balance between efficient charge transfer and minimal series resistance, leading to higher PCE [27],

[28].

If the HTL is too thin, incomplete perovskite coverage or insufficient hole collection may occur, resulting in

lower photocurrent and increased interfacial recombination [5]. Conversely, an excessively thick HTL can hinder

carrier transport due to higher series resistance and limited conductivity, ultimately degrading fill factor and

efficiency [29]. Previous studies indicate that the optimum HTL thickness for both organic and inorganic systems

typically falls within the range of 50–300 nm, depending on the carrier mobility, energy-level alignment, and

interface quality of the material [28], [29]. Therefore, systematic experimental or simulation-based optimization

is essential to identify the ideal HTL thickness for a specific PSC configuration, accounting for variations in

charge extraction, film conductivity, and contact resistance [30].

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Fig. 3 Variation of PCE over thickness

As illustrated in Fig. 3, the PCE of the PSC exhibits a non-linear dependence on the thickness of the ZnCo₂O₄

HTL. The simulation was conducted while maintaining constant thicknesses for the ETL equal to 200 nm of

TiO₂ and the perovskite absorber layer around 400 nm of CsPbI₃. The HTL thickness was varied from 100 nm

to 500 nm to evaluate its impact on device performance.

According to Fig. 3, the PCE initially increases with HTL thickness due to improved hole extraction and reduced

interfacial recombination. The maximum PCE was achieved at an optimal HTL thickness of approximately 300

nm, beyond which efficiency begins to saturate and eventually decline as the film becomes excessively thick.

When the ZnCo₂O₄ layer exceeded 400 nm, charge transport was impeded due to increased series resistance and

limited carrier mobility, resulting in reduced photocurrent and fill factor. Conversely, a too-thin HTL (< 150 nm)

may lead to incomplete coverage, inefficient hole injection from the perovskite absorber into the HTL, and poor

interfacial charge balance—ultimately diminishing device performance. These findings align with earlier reports

that highlight the crucial role of optimized HTL thickness in achieving balanced charge transport and minimizing

recombination losses in PSCs [5], [8], [28], [29].

Taguchi method result

Following the completion of the thickness optimization study, the Taguchi method was employed as a secondary

optimization approach to identify the key factors that significantly influence the PCE of the PSC. The Taguchi

method is a robust statistical design of experiments (DOE) technique that enables systematic evaluation of

multiple parameters while minimizing the number of simulations or experiments required [8], [31]. In this study,

three control factors were selected: (1) the thickness of the ZnCo₂O₄ HTL, (2) the operating temperature, and (3)

the bandgap energy of ZnCo₂O₄.

An L9 (3³) orthogonal array was employed to organize the experimental simulations efficiently. This design

allows the investigation of three factors, each at three different levels, across only nine simulation runs instead

of 27 (as required in a full factorial design). Each simulation output was analyzed using the S/N ratio, a key

statistical indicator used to evaluate the robustness of the system. In this context, the “larger-the-better” criterion

was applied to maximize PCE while minimizing variations caused by noise factors [32].

After evaluating the results, the main effects plot and response table were generated to determine which

parameter exerted the greatest influence on device performance. The analysis revealed that bandgap energy and

HTL thickness had the strongest effects on PCE, followed by temperature, consistent with previous research that

employed Taguchi optimization for photovoltaic devices [8], [33]. This approach provided a clear understanding

of parameter interactions, enabling the identification of an optimal ZnCo₂O₄ HTL thickness of 300 nm, a bandgap

of 2.0 eV, and an operating temperature of 300 K for achieving the highest simulated PCE.

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Table III Perovskite solar cell efficiency, PCE result by using Taguchi method.

PCE, %

26.2461

25.1502

20.3966

28.0222

26.7720

25.6031

32.1788

30.8296

29.4924

26.2463

25.1504

20.6049

28.0227

26.7739

25.6036

32.1798

30.8304

29.4932

26.2465

25.1506

20.7637

28.0231

26.7756

25.6040

32.1807

30.8310

29.4939

26.2461

25.1502

20.3966

28.0222

26.7720

25.6031

32.1788

30.8296

29.4924

26.2463

25.1504

20.6049

28.0227

26.7739

25.6036

32.1798

30.8304

29.4932

26.2465

25.1505

20.7637

28.0231

26.7756

25.6039

32.1807

30.8310

29.4939

26.2461

25.1502

20.3966

28.0222

26.7720

25.6031

32.1788

30.8296

29.4924

26.2463

25.1504

20.6049

28.0227

26.7739

25.6036

32.1798

30.8304

29.4932

26.2465

25.1505

20.7637

28.0231

26.7756

25.6038

32.1807

30.8310

29.4939

Table IV Fill factor, FF result by using Taguchi method.

FF, %

71.5

84.1

71.8

71.5

83.7

84.4

68.5

82.7

84.1

71.5

84.1

72.5

71.5

83.7

84.4

68.5

82.7

84.1

71.5

84.1

73.1

71.5

83.7

84.4

68.5

82.7

84.1

71.5

84.1

71.8

71.5

83.7

84.4

68.5

82.7

84.1

71.5

84.1

72.5

71.5

83.7

84.4

68.5

82.7

84.1

71.5

84.1

73.1

71.5

83.7

84.4

68.5

82.7

84.1

71.5

84.1

71.8

71.5

83.7

84.4

68.5

82.7

84.1

71.5

84.1

72.5

71.5

83.7

84.4

68.5

82.7

84.1

71.5

84.1

73.1

71.5

83.7

84.4

68.5

82.7

84.1

Table V Open circuit voltage, Voc result by using Taguchi method.

Voc

1.372753

1.372834

1.3729

1.37275

1.372831

1.372897

1.372747

1.372828

1.372893

1.119604

1.119613

1.11962

1.119604

1.119613

1.11962

1.119604

1.119613

1.11962

1.062949

1.062872

1.062809

1.062949

1.062872

1.062809

1.062949

1.062872

1.062809

1.370915

1.371109

1.371266

1.370915

1.371109

1.371266

1.370915

1.371109

1.371266

1.119132

1.119201

1.119256

1.119132

1.119201

1.119256

1.119132

1.119201

1.119256

1.061612

1.061611

1.06161

1.061611

1.061610

1.061601

1.061611

1.061610

1.061609

1.425072

1.425646

1.426111

1.425072

1.425646

1.426111

1.425072

1.425646

1.426111

1.132573

1.132622

1.132662

1.132572

1.132622

1.132662

1.132572

1.132622

1.132662

1.065460

1.065456

1.065453

1.065460

1.065456

1.065453

1.065460

1.065456

1.065453

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Table VI Current density, Jsc result by using Taguchi method.

Jsc

-26.707

-26.709

-26.721

-28.553

-28.580

-28.549

-32.922

-32.883

-32.886

-26.707

-26.709

-26.721

-28.553

-28.580

-28.549

-32.921

-32.883

-32.886

-26.707

-26.709

-26.721

-28.553

-28.580

-28.549

-32.921

-32.883

-32.886

-26.707

-26.709

-26.721

-28.553

-28.580

-28.549

-32.921

-32.883

-32.886

-26.707

-26.709

-26.721

-28.553

-28.580

-28.549

-32.921

-32.883

-32.886

-26.707

-26.709

-26.721

-28.553

-28.580

-28.549

-32.921

-32.883

-32.886

-26.707

-26.709

-26.721

-28.553

-28.580

-28.549

-32.921

-32.883

-32.886

-26.707

-26.709

-26.721

-28.553

-28.580

-28.549

-32.921

-32.883

-32.886

-26.707

-26.709

-26.721

-28.553

-28.580

-28.549

-32.921

-32.883

-32.886

Based on the analysis of Tables III to VI, which summarize the simulation results obtained using the Taguchi

method, a clear variation in the PCE values can be observed across different parameter combinations. These

results indicate that all investigated factors—the ZnCo₂O₄ HTL thickness, operating temperature, and bandgap

energy—exert measurable influences on the PCE, even if their individual effects vary in magnitude. The

observed pattern reveals that among these parameters, the HTL thickness has the most significant impact on

device performance, confirming its critical role in determining efficient charge extraction, carrier mobility, and

recombination suppression within the PSC structure.

This finding is consistent with previous optimization studies, which reported that fine-tuning the HTL thickness

substantially affects the balance between series resistance and charge transport, thereby influencing both the fill

factor and overall efficiency of the device [29], [32]. While temperature and bandgap energy also contribute to

PCE variation, their effects are secondary compared to the dominant influence of the HTL thickness, as

confirmed by the main effects plot and S/N ratio analysis derived from the Taguchi design [31].

Fig. 3 Factor effects plot of the S/N ratio for the “larger-the-better” criterion in Taguchi optimization, illustrating

the influence of control factors on the PCE of the perovskite solar cell. The S/N ratio increases markedly with

ZnCo₂O₄ HTL thickness up to 300 nm, followed by a gradual decline at higher values, indicating the existence

of an optimal HTL thickness.

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As shown in Fig. 3, the S/N ratio for the “larger-the-better” criterion demonstrates a strong correlation between

the ZnCo₂O₄ HTL thickness and the PCE of the device. The ratio rises sharply from 100 nm to 300 nm, indicating

significant improvements in charge extraction and reduced interfacial recombination at this range. Beyond 300

nm, a decline in S/N ratio is observed, suggesting that excessively thick HTLs introduce additional series

resistance and impede hole transport, thereby reducing device efficiency. The maximum S/N ratio (~30 dB)

recorded at 300 nm corresponds to the optimal thickness, at which the perovskite device achieves a stable and

balanced carrier transport pathway. This trend aligns with previous studies reporting similar optimization

behavior for inorganic HTLs, where moderate film thicknesses ensure complete coverage, adequate

conductivity, and minimized recombination losses [5], [29], [32].

Table VII Result of ANOVA for PCE.

PCE

Factor

Thickness (nm)

Temperature (K)

Bandgap (Eg)

Degrees of Freedom

Sum of Squares

Mean Square

Factor Effect, %

The results of the ANOVA presented in Table VII indicate that the thickness of the ZnCo₂O₄ HTL exerts the

most dominant influence on the PCE of the PSC. The factor contributes approximately 70 % of the total variance

in PCE, followed by temperature (22 %) and bandgap energy (4 %). This outcome confirms that HTL thickness

plays a pivotal role in determining charge-transport balance and minimizing recombination losses within the

PSC structure. A variation in the HTL thickness directly alters the charge extraction pathway and the series

resistance, leading to significant efficiency changes.

Table VIII Best setting selection for respective parameter.

Control factor parameter

Thickness (nm)

Temperature (K)

Bandgap (Eg)

Best level

Best value

300

2.0

The best parameter settings obtained through the Taguchi optimization are summarized in Table VIII. The

optimal configuration corresponds to a ZnCo₂O₄ thickness of 300 nm (Level 3), ambient temperature of 300 K

(Level 1), and bandgap of 2.0 eV (Level 2). These levels were selected based on the highest mean signal-to-

noise ratios, confirming that this combination yields a robust and stable operating condition for the PSC under

study.

Table IX Result after the confirmation experiment.

Experiment

PCE,%

FF, %

Voc

Jsc

32.2307

68.7

1.425845

-32.887

32.2314

68.7

1.426271

-32.886

32.232

68.7

1.426615

-32.886

32.2307

68.7

1.425845

-32.887

32.2314

68.7

1.426271

-32.886

32.232

68.7

1.426615

-32.886

INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN SOCIAL SCIENCE (IJRISS)

ISSN No. 2454-6186 | DOI: 10.47772/IJRISS | Volume IX Issue X October 2025

Page 3986

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32.2307

68.7

1.425845

-32.887

32.2314

68.7

1.426271

-32.886

32.232

68.7

1.426615

-32.886

A confirmation experiment was subsequently conducted using the optimized parameter set, and the results are

shown in Table IX. The observed PCE values ranged narrowly between 32.230 % and 32.232 %, indicating

strong reproducibility and model reliability. The corresponding fill factor (FF) remained stable at approximately

68.7 %, while the open-circuit voltage (Voc) and short-circuit current density (Jsc) values were consistent at

around 1.426 V and −32.89 mA/cm², respectively. The highest simulated efficiency of 32.232 % was obtained

at Level 9, validating the accuracy of the Taguchi-based optimization.

The high consistency of results across all nine trials confirms that the selected control parameters yield an

optimized and stable PSC configuration. This aligns with recent studies demonstrating that fine-tuning inorganic

HTL parameters—particularly ZnCo₂O₄ thickness and bandgap—can markedly improve PCE and thermal

stability compared with organic HTLs such as PEDOT:PSS or spiro-OMeTAD [5], [29], [32], [33]. Furthermore,

incorporating noise factors (hole and electron mobilities at Level 3, 9.14 × 10⁻⁶ cm² V⁻¹ s⁻¹) enhances the

robustness of the model by accounting for potential material variability.

In summary, the Taguchi-based ANOVA and confirmation analysis conclusively establish that the ZnCo₂O₄

HTL thickness (300 nm), ambient temperature (300 K), and bandgap (2.0 eV) represent the optimal conditions

for achieving maximum PCE (~32.23 %) in the simulated perovskite solar cell.

CONCLUSION

This study successfully demonstrated that ZnCo₂O₄ is a highly promising HTL material for PSCs, offering

superior stability, durability, and PCE compared with conventional organic HTLs. Using GPVDM simulation

and Taguchi statistical optimization, the device achieved an optimal PCE of 32.23% at a ZnCo₂O₄ thickness of

300 nm, temperature of 300 K, and bandgap of 2.0 eV. The ANOVA and S/N ratio analyses confirmed that HTL

thickness exerts the strongest influence on PCE, followed by temperature and bandgap energy. These results

validate ZnCo₂O₄ as a robust and efficient HTL capable of enhancing carrier extraction and minimizing

recombination losses.

ACKNOWLEDGMENT

The authors would like to express their thanks to the Fakulti Teknologi dan Kejuruteraan Elektronik dan

Komputer (FTKEK) at the Universiti Teknikal Malaysia Melaka (UTeM) for their assistance in acquiring the

essential information and resources for the successful completion of the research. The authors would also like to

extend their gratitude to their collaborators at Universiti Teknologi MARA (UiTM) for the assistance and

scientific support they provided.

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