Interfacial Optimization Enhances Performance of Perovskite Solar Cells

Background Introduction

In recent years, perovskite solar cells (PSCs) have emerged as one of the most promising candidates for third-generation photovoltaic technology due to their high power conversion efficiency (PCE) and relatively low manufacturing costs. However, despite significant progress in laboratory conditions, the commercial application of PSCs still faces many challenges. Particularly prominent are issues related to interfacial recombination and device stability. These problems mainly stem from the sensitivity of perovskite materials to moisture, oxygen, heat, and ultraviolet light, as well as poor contact between the electron transport layer (ETL) and the perovskite absorber layer.

To address these issues, researchers have proposed optimizing the contact between the ETL and the perovskite layer through interfacial engineering to reduce interfacial recombination losses and improve charge transport efficiency. Against this backdrop, Muhammad Anwar Jan et al. conducted a study to explore the application effects of a novel interfacial layer—piperazine dihydriodide (PZDI)—in PSCs based on hematite (α-Fe₂O₃) ETLs. This research not only focuses on the performance enhancement brought by PZDI but also explores its potential in long-term stability.

Source of the Paper

This paper was co-authored by Muhammad Anwar Jan, Hafiz Muhammad Noman, Akbar Ali Qureshi, and Fuchun Yang, who are affiliated with the Key Laboratory of High Efficiency and Clean Mechanical Manufacture of the Ministry of Education at Shandong University, the National Demonstration Center for Experimental Mechanical Engineering Education at Shandong University, and the Department of Mechanical Engineering at Bahauddin Zakariya University in Pakistan. The paper was submitted on October 31, 2024, accepted on December 31 of the same year, and ultimately published in the journal Optical and Quantum Electronics (DOI: 10.1007/s11082-024-08033-8).

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Research Content and Process

a) Research Process

This study mainly includes the following steps:

1. Material Preparation

The research team used a series of chemical reagents and precursor solutions to prepare the core components of PSCs. For example, the hematite ETL was prepared by dissolving iron(III) nitrate nonahydrate (Fe(NO₃)₃·9H₂O) in ethanol; the PZDI interfacial layer was prepared by dissolving PZDI in chlorobenzene and stirring overnight. Additionally, the perovskite precursor solution was made by mixing formamidinium iodide (FAI), methylammonium bromide (MABr), lead(II) iodide (PbI₂), and lead(II) bromide (PbBr₂) to form a triple-cation perovskite film.

2. Device Fabrication

The study adopted a standard N-I-P structure to fabricate PSCs. The specific steps are as follows: - Substrate Cleaning: ITO glass substrates were sequentially cleaned with deionized water, acetone, and isopropanol. - ETL Deposition: The hematite precursor solution was spin-coated onto the ITO substrate and annealed in air at 300°C for 1 hour. - Interfacial Layer Deposition: The PZDI solution was spin-coated onto the hematite layer and annealed at 100°C for 10 minutes. - Perovskite Layer Deposition: The perovskite precursor solution was spin-coated onto the interfacial layer using an anti-solvent method and annealed at 120°C for 10 minutes to promote crystallization. - Hole Transport Layer (HTL) Deposition: Spiro-OMeTAD solution was spin-coated onto the perovskite layer and left to oxidize in a dry environment for 12 hours. - Metal Electrode Evaporation: Silver (Ag) was deposited as the top electrode via thermal evaporation.

3. Characterization and Testing

To comprehensively evaluate device performance, the research team employed various characterization methods: - X-ray Diffraction (XRD): Analyzed the crystal structure of hematite and perovskite films. - Scanning Electron Microscopy (SEM): Observed the surface morphology and cross-sectional structure of the films. - Photoluminescence (PL) and Time-Resolved Photoluminescence (TRPL): Studied charge transport mechanisms and recombination dynamics. - Electrochemical Impedance Spectroscopy (EIS): Measured the recombination resistance of the devices. - Current-Voltage (J-V) Curves: Evaluated the photovoltaic performance of the devices. - External Quantum Efficiency (EQE): Analyzed the photocurrent generation capability.

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b) Main Results

1. Structural and Optical Properties

XRD analysis showed that the addition of the PZDI interfacial layer did not significantly alter the crystal structures of hematite and perovskite but effectively reduced surface defect density. Transmission spectra indicated that the introduction of PZDI had little impact on overall transparency, with only a slight decrease in transmittance in the visible light range. SEM images further confirmed that the PZDI-modified films had smoother and more uniform surfaces, which helped reduce interface roughness and defects.

2. Photovoltaic Performance

• PCE Improvement: The unmodified reference device had a PCE of only 13.0%, while the target device with the PZDI interfacial layer showed a significant increase in PCE to 17.5%. This improvement was mainly attributed to higher short-circuit current density (Jsc = 21.29 mA/cm²), open-circuit voltage (Voc = 1.13 V), and fill factor (FF = 72.91%).
• Enhanced Stability: After 500 hours of testing under ambient conditions, the target device retained 91.8% of its initial efficiency, while the reference device retained only 82.9%. This indicates that the PZDI interfacial layer can effectively suppress moisture ingress and interfacial recombination.

3. Charge Transport and Recombination Dynamics

PL and TRPL analyses showed that the PZDI interfacial layer significantly reduced radiative recombination intensity while shortening the fast decay time constant (τ₁ = 4.82 ns), indicating higher charge extraction efficiency. Additionally, EIS results showed that PZDI-modified devices had higher recombination resistance, further verifying its advantages in reducing interfacial recombination.

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c) Conclusions and Significance

This study demonstrates that the PZDI interfacial layer plays a key role in optimizing the contact between the hematite ETL and the perovskite absorber layer. It not only improves the PCE and stability of the devices but also enhances reproducibility and the potential for scalable production. These findings are of great significance for advancing the commercialization process of PSCs.

From a scientific perspective, this research reveals the central role of interfacial engineering in improving the performance of perovskite solar cells. From an application standpoint, PZDI, as a simple and effective interfacial material, is expected to play an important role in future high-performance, long-lasting, and scalable PSC technologies.

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d) Research Highlights

1. Innovative Interfacial Material: PZDI was applied for the first time between the hematite ETL and the perovskite layer, achieving significant performance improvements.
2. Comprehensive Performance Optimization: PZDI not only increased PCE but also enhanced the stability and reproducibility of the devices.
3. Systematic Characterization: Combined with various advanced characterization techniques, the mechanism of PZDI was comprehensively analyzed.

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e) Other Valuable Information

The research team emphasized that future work should further explore other types of interfacial materials and their application potential in different ETL systems. Additionally, they suggested combining theoretical simulations with experimental studies to gain deeper insights into the impact mechanisms of interfacial layers on charge transport and recombination dynamics.