Numerical Simulation and Performance Optimization of Perovskite Solar Cells: A Study Based on Cs₂TiBr₆ Material

Academic Background

In recent years, perovskite solar cells (Perovskite Solar Cells, PSCs) have garnered significant attention due to their excellent optoelectronic properties. These materials possess advantages such as appropriate bandgap, high carrier mobility, significant diffusion length, and excellent light absorption coefficient, which have rapidly established them in the photovoltaic field. However, traditional lead-based perovskite materials suffer from issues like toxicity, insufficient stability, and short lifespan, limiting their large-scale application. To address these problems, researchers have begun exploring non-toxic and stable alternative materials. Among them, cesium titanium bromide (Cs₂TiBr₆), as a single-halide perovskite material, has become a research hotspot due to its low toxicity and high stability.

Cs₂TiBr₆ is an environmentally friendly material that does not contain lead and has a direct bandgap of approximately 1.8 eV, making it suitable for the development of highly efficient solar cells. Additionally, this material exhibits high thermal and chemical stability, laying a foundation for its commercial application. Although some experimental and simulation studies have explored the performance of Cs₂TiBr₆-based PSCs, how to further enhance their efficiency and resolve interface recombination issues still requires in-depth study. Therefore, this research aims to optimize the design of Cs₂TiBr₆-based PSCs by introducing interfacial defect layers (Interfacial Defect Layers, IDL) and systematically analyze the key factors contributing to performance enhancement.

Research Source

This paper was co-authored by Jaspinder Kaur, Ajay Kumar Sharma, Rikmantra Basu, and Harjeevan Singh, who are respectively from the National Institute of Technology Delhi (NIT Delhi) and Chandigarh University in Mohali, Punjab. The study was submitted on May 28, 2024, accepted on December 29 of the same year, and published in the journal Optical and Quantum Electronics in 2025. The paper’s title is “Numerical Simulation and Performance Optimization of Non-Toxic Cs₂TiBr₆ Single-Halide Perovskite Solar Cell by Introducing Interfacial Defect Layers.”

Research Details

a) Research Process

This study utilized SCAPS-1D software to numerically simulate the FTO/SnO₂/Cs₂TiBr₆/MoOₓ/Au structure of PSCs. The entire research was divided into the following steps:

1. Structural Design and Parameter Settings
   The study initially designed a planar heterojunction PSC structure, including transparent conductive oxide (FTO), electron transport layer (SnO₂), light-absorbing layer (Cs₂TiBr₆), hole transport layer (MoOₓ), and metal back contact (Au). To reduce interface recombination, two interfacial defect layers (IDL1 and IDL2) were introduced. All material input parameters were based on existing literature data, such as bandgap, dielectric constant, and carrier concentration.

2. Key Parameter Optimization

   • Absorber Layer Thickness Optimization: By varying the thickness of the Cs₂TiBr₆ layer (from 0.1 to 3.0 µm), the study examined its impact on short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE). Results indicated that the optimal thickness was 800 nm.
   • Doping Concentration Optimization: The study investigated the effect of doping concentration (from 10¹⁶ to 10²⁰ cm⁻³) in the Cs₂TiBr₆ layer on device performance, ultimately determining the optimal doping concentration to be 10¹⁸ cm⁻³.
   • Defect Density Optimization: By adjusting the defect density (from 10¹³ to 10¹⁹ cm⁻³) in the Cs₂TiBr₆ layer, the study analyzed its impact on recombination rate and efficiency, finding the optimal defect density to be 10¹⁴ cm⁻³.

3. Role of Interfacial Defect Layers
   The study analyzed the impact of defect density in IDL1 and IDL2 on device performance. Results showed that when defect density was below 10¹⁵ cm⁻³, interface recombination was significantly reduced, thereby improving efficiency.

4. Temperature Impact Analysis
   By simulating device performance under different operating temperatures (300 to 420 K), the study found the optimal operating temperature to be 300 K.

5. Comparative Analysis
   Finally, the optimized structure was compared with previously reported experimental and simulated results to verify the superiority of the new design.

b) Main Results

1. Impact of Absorber Layer Thickness
   When the thickness of the Cs₂TiBr₆ layer increased from 0.1 to 3.0 µm, Jsc and PCE peaked at a thickness of 0.8 µm, then rapidly declined. This was because, in thicker absorber layers, defect density and series resistance increased, leading to a higher recombination rate. The optimal thickness was ultimately determined to be 800 nm.

2. Impact of Doping Concentration
   An increase in doping concentration significantly reduced Jsc because high doping led to increased recombination of photogenerated carriers. However, an appropriate doping concentration (10¹⁸ cm⁻³) could enhance Voc and FF, thus optimizing overall efficiency.

3. Impact of Defect Density
   An increase in defect density led to a significant rise in recombination rate, thereby reducing efficiency. The study found that when defect density was below 10¹⁵ cm⁻³, device performance was optimal.

4. Role of Interfacial Defect Layers
   After introducing IDL, interface recombination was significantly reduced, thereby enhancing carrier lifetime and efficiency. The optimal defect density for IDL was 10¹⁴ cm⁻³.

5. Impact of Temperature
   An increase in temperature led to a decrease in carrier mobility and an increase in recombination rate, thereby reducing efficiency. The optimal operating temperature was 300 K.

6. Results of Comparative Analysis
   The optimized structure achieved a PCE of 20.11%, significantly higher than previously reported results (2%-6%). This was mainly attributed to the introduction of IDL and optimization of key parameters.

c) Conclusions and Significance

Through the introduction of interfacial defect layers and optimization of key parameters, this study successfully designed an efficient Cs₂TiBr₆-based PSC. The results showed that the optimal absorber layer thickness was 800 nm, the optimal doping concentration was 10¹⁸ cm⁻³, and the optimal defect density was 10¹⁴ cm⁻³. The optimized structure achieved a PCE of 20.11%, far surpassing previous experimental and simulated results. This achievement not only provides theoretical guidance for designing non-toxic and stable perovskite solar cells but also lays the groundwork for their commercial application.

d) Highlights of the Study

1. Innovative Methodology: For the first time, IDL was introduced to reduce interface recombination, significantly enhancing device efficiency.
2. Systematic Optimization: A comprehensive analysis of the impact of absorber layer thickness, doping concentration, and defect density on performance provided a reference for future research.
3. Breakthrough in Efficiency: Achieved a PCE of 20.11%, far exceeding previously reported results.

e) Other Valuable Information

The study also explored the impact of different hole transport materials (such as MoOₓ, Spiro-OMeTAD, etc.) on device performance, finding that MoOₓ performed best due to its high stability, low cost, and excellent energy level matching characteristics.

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Value and Significance of the Study

This study not only theoretically advances the development of non-toxic perovskite solar cells but also provides important guidance for their experimental fabrication and commercial application. By optimizing key parameters and introducing IDL, the study demonstrates how to achieve highly efficient energy conversion while maintaining environmental friendliness. This achievement is of great significance to the progress of renewable energy technology and also opens new directions for future research on perovskite materials.