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Recently, a research team led by Tianqing Wen and Shengzhong Liu from Shaanxi Normal University published a breakthrough study in the renowned journal Angew. The study primarily focuses on inorganic halide perovskite solar cells, discovering the similar formation energies of iodine interstitials (Ii) and iodine vacancies (VI). These defects induce charge recombination, which in turn affects the performance and stability of the solar cells. To address this issue, the research team successfully applied diaminopyridine (2,6-DAPy) passivator and achieved effective passivation, thus greatly improving the performance of the solar cells. The power conversion efficiency increased from 19.6% to 21.8% using this technique.
Solar cells are one of the most promising renewable energy sources nowadays. With the growing global energy demand and worsening environmental issues, it is imperative to develop efficient, stable and eco-friendly solar cell technologies. Inorganic halide perovskite solar cells have attracted extensive research interests owing to their excellent photovoltaic properties and simple fabrication techniques. However, the stability issue of such cells during operation has been the major obstacle hindering their commercialization. In particular, the halide-related surface defects in halide perovskite solar cells are the primary cause of performance and stability degradation.
In recent years, many researchers have been devoted to finding solutions to this problem. However, despite some progress made, eliminating these defects, especially iodine interstitials (Ii) and iodine vacancies (VI), remains a huge challenge. These defects induce charge recombination, thus reducing the performance and stability of the solar cells. To address this issue, it is necessary to gain an in-depth understanding of the formation mechanisms and properties of these defects, and develop effective approaches to eliminate or mitigate them.
A research team led by Tianqing Wen and Shengzhong Liu from Shaanxi Normal University conducted an in-depth study of this problem. They first performed calculations using density functional theory, determining the similar formation energies of iodine interstitials (Ii) and iodine vacancies (VI). The study found that these defects can easily form during the fabrication of inorganic halide perovskite solar cells and may severely affect the performance.
To solve this problem, the research team chose 2,6-diaminopyridine (2,6-DAPy) as the passivator. This passivator can eliminate Ii and dissociative I2, and passivate abundant VI through the synergetic effects of halogen-Npyridine and coordination bonds. With this approach, the research team successfully eliminated these defects and greatly improved the performance of the solar cells. Experimental results showed that the power conversion efficiency increased from 19.6% to 21.8% using this technique, setting the record for this type of solar cell. Additionally, the study also found that (2,6-DAPy) treated CsPbI3-xBrx films demonstrated better environmental stability.
- Precisely weighed CsI and HPbI3 raw materials were used to prepare 0.6 M CsPbI3 precursor solution, and the preparation process was conducted under nitrogen protection. The solution was spin-coated on TiO2 substrates at 4000 rpm for 40 s, then annealed at 210°C for 5 min to form CsPbI3 perovskite films.
- Raman spectroscopy with 785 nm laser was utilized to test the CsPbI3 film samples, detecting the Raman peak positions to determine whether the 210 cm-1 peak of iodine interstitials existed on the film surface. Meanwhile, thermal desorption spectrometry was used to detect iodine-related species released from the films under high temperature.
- 0.75 mg/mL (2,6-DAPy) solution was prepared and spin-coated onto CsPbI3 films at 5000 rpm for 30 s. After drying, the film samples were re-tested using the same parameters to observe the disappearance of iodine interstitial peaks.
- CsPbI3 films were thermally evaporated onto TiO2 electrodes, followed by spin-coating Spiro-OMeTAD to form a triple-layer structure. The transient PL decay curves of glass/CsPbI3/Spiro stacks with and without (2,6-DAPy) treatment were measured to calculate the change in carrier lifetimes.
- Complete solar cells were fabricated with (2,6-DAPy) introduced as the passivation layer, and the J-V curves were tested to determine the increases in open-circuit voltage, short-circuit current density, fill factor and power conversion efficiency.
- Reference cells and (2,6-DAPy) treated cells were placed in a nitrogen glove box (humidity <20%) for accelerated light soaking aging tests under 100 mW/cm2 illumination intensity, and cell parameters were continuously monitored to compare stability differences.
- Enlitech SS-F5-3A solar simulator and SRC-2020 Si reference cell were used in the experiments.
This study by Tianqing Wen and Shengzhong Liu’s research team paves a new way for the development of inorganic halide perovskite solar cells. Through effective passivation technology, the team not only resolved the surface defects issue, but also greatly enhanced the performance and stability of the solar cells. This implies these solar cells may find extensive commercial applications in the future, providing more efficient and stable green energy to people. Moreover, this study offers valuable experience and data for other researchers, laying an important theoretical foundation for further research and development.
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