2021 Adv. Funct. Mater., How does HAc assist tin-based perovskite solar cells to achieve stable and high efficiency?
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The excellent optoelectronic properties make organic-inorganic halide perovskite materials attract great attention in the photovoltaic field. However, perovskite materials contain heavy metal lead, which is harmful to the environment and human body, hindering their commercialization. Tin is the most promising alternative to lead-based perovskites because it has a more ideal optical band gap, the same outer electronic structure and similar ionic radius as lead. Besides, it can form the same type of three-dimensional perovskite structure.
The current research on tin-based perovskite solar cells also faces many challenges. Compared with lead-based perovskites, the crystallization process of tin-based perovskite films is more difficult to control, the film morphology is worse, and disordered grains are easily formed, resulting in many three-dimensional defects. These defects easily lead to the erosion of oxygen and moisture, which greatly reduces the performance and stability of the device. In addition, the tin-based perovskite material itself is also easily oxidized and generates Sn vacancies, resulting in severe non-radiative recombination loss and voltage loss. The current research rarely takes into account the above two problems at the same time, and most of them only consider how to inhibit Sn2+ oxidation or regulate crystallization unilaterally.
Advanced Functional Materials (IF 18.808) in December 2021 published a study on acetic acid to tune crystallization kinetics and suppress Sn2+ oxidation in tin-based perovskite solar cells. In this study, the research team used acetic acid (HAc) to reduce the supersaturated concentration of the precursor solution, forming pre-nucleated clusters to effectively tune the crystallization kinetics. The hydrogen ions and acetate ions contained in HAc can effectively inhibit the oxidation of Sn2+, and the hydrogen bond between HAc and iodide ions (I-) greatly reduced the loss of I- and ensured the stoichiometric ratio of I-/Sn2+.
The current density-voltage (J−V) measurement was performed by Enlitech’s Solar Simulator, and the external quantum efficiency (EQE) detection was also performed by Enlitech’s QE-R Quantum Efficiency Measurement System. In addition to the EQE (External Quantum Efficiency) spectrum analysis of solar cells, the Quantum Efficiency Measurement System of Enlitech also provides Jsc (short-circuit current density) comparison for the short-circuit current of solar cells under the solar simulator to prove the authenticity of the experiment. The solar simulator and KA-6000 software of Enlitech also provide monitoring of the short-circuit current over time to prove the stability of the solar cell!
The research results found that the corresponding perovskite film ratio was close to the theoretical value, effectively reducing the defect density and maintaining a perfect lattice. HAc-assisted tin-based perovskite solar cells achieved a power conversion efficiency (PCE) of 12.26% with an open-circuit voltage as high as 0.75 V. In addition, the unencapsulated device maintained nearly 90% of the initial PCE even after 3000 hours of storage in nitrogen. This lays the foundation for the preparation of high-quality tin-based perovskite films.
Under standard AM 1.5 G illumination, J-V curves of devices with 5 mol% and 15 mol% HAc.
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Keyword: Tin-based perovskite solar cells, HAc, Modulation of Crystallization Kinetics, Inhibition of Sn2+ Oxidation, solar simulator, quantum efficiency, sun simulator
Article link: https://doi.org/10.1002/adfm.202109631