Cost-Effective Tin Chloride Boosts Efficiency of Perovskite Solar Cells

Abstract
The prominent chemical bath deposition (CBD) method leverages tin dioxide (SnO2) as an electron transport layer (ETL) in perovskite solar cells (PSCs), achieving exceptional efficiency. The deposition of SnO2, however, can lead to the formation of oxygen vacancies and surface defects, which subsequently contribute to performance challenges such as hysteresis and instability under light-soaking conditions. To alleviate these issues, it is crucial to address heterointerface defects and ensure the uniform coverage of SnO2 on fluorine-doped tin oxide substrates. Herein, the efficacy of tin(IV) chloride (SnCl4) post-treatment in enhancing the properties of the SnO2-ETL and the performances of PSCs are presented. The treatment with SnCl4 not only removes undesired agglomerated SnO2 nanoparticles from the surface of CBD SnO2 but also improves its crystallinity through a recrystallization process. This leads to an optimized interface between the SnO2-ETL and perovskite, effectively minimizing defects while promoting efficient electron transport. The resultant PSCs demonstrate improved performance, achieving an efficiency of 25.56% (certified with 24.92%), while retaining 95.84% of the initial PCE under ambient storage conditions. Additionally, PSCs treated with SnCl4 endure prolonged light-soaking tests, particularly when subjected to quasi-steady-state-IV measurements. This highlights the potential of SnCl4 treatment as a promising strategy for advancing PSC technology.

The commercialization of perovskite solar cells (PSCs) is anticipated to accelerate through the use of inexpensive tin (IV) chloride (SnCl4).

A research team jointly led by Professor Dong Suk Kim from the Graduate School of Carbon Neutrality at UNIST and Dr. Yimhyun Jo from the Korea Institute of Energy Research (KIER) has significantly enhanced the stability of PSCs. By applying IV chloride to a layer of tin oxide, the team has improved the stability of these solar cells.

To achieve high efficiency in PSCs, it is crucial to manage surface defects in the electron transport layer (ETL)—a thin film that facilitates the efficient extraction and transport of electrons. Such defects greatly influence both the stability and efficiency of PSCs.

Figure 1. Schematic illustration of the SnCl4 treatment process applied to the SnO2 ETL prepared via the CBD method.

The research team dissolved IV SnCl4 in water and applied it to the oxide layer. This process has resulted in the complete oxidation of the upper layer of tin oxide and facilitated recrystallization, leading to enhanced electron mobility.

Figure 2. (Top) Storage stability of the PSCs tested in ambient condition (25 °C, 25% RH), (Center) Thermal stability of the PSCs subjected to thermal stress at 65 °C (25% RH). QSS J–V curves of the (Bottom) control- and d) target-PSCs.

Chemical bath deposition (CBD) is a widely used approach that leverages tin dioxide (SnO2) as the electron transport layer (ETL) in PSCs, achieving exceptional efficiency. However, the deposition of SnO2 can lead to the formation of surface defects, which are inevitable due to the incomplete oxidation of tin. Addressing these defects post-film formation is vital for achieving both high efficiency and long-term stability.

For the successful commercialization of PSCs, it is essential to pass various certification tests. The research team demonstrated the effectiveness of their approach by enhancing the electron transport layer (ETL) and showcasing long-term resistance to heat and ultraviolet exposure.

Professor Kim stated, “Through this study, we succeeded in suppressing the aggregation of tin oxides and improving their crystallinity,” adding, “This technology will play a pivotal role in enhancing the stability of solar cells.”

Researchers Ji Won Song and Dr. Yun Seop Shin noted, “We expect to positively impact the energy industry by simultaneously achieving high efficiency, durability, and low cost with affordable IV SnCl4.”

The findings of this research have been published online in Advanced Energy Materials on July 3, 2024.

Journal Reference
Ji Won Song, Yun Seop Shin, Minjin Kim, et al., “Post-Treated Polycrystalline SnO2 in Perovskite Solar Cells for High Efficiency and Quasi-Steady-State-IV Stability,” Adv. Energy Mater., (2024).