提升基于钙钛矿的叠层太阳能电池稳定性的策略

近年来,基于有机无机金属卤化物钙钛矿的叠层太阳能电池引起了巨大的研究热潮。但是,不稳定性限制了其商业化。适用于顶部子电池的宽带隙钙钛矿存在相不稳定性,而适用于底部子电池的窄带隙钙钛矿存在空气不稳定性。首先,我们总结了提升基于钙钛矿的叠层太阳能电池稳定性的最新进展。然后,我们系统地分析了导致宽带隙钙钛矿的相不稳定性和窄带隙钙钛矿的空气不稳定性的原因,并为解决这些不稳定性问题总结了合理的策略。我们也简短地总结了中间层带来的不稳定性以及相应的解决措施。最后,我们回顾了钙钛矿材料固有的本征不稳定性和相应的改进方法,这对于将来发展更稳定的叠层太阳能电池中是必要的。我们认为随着对钙钛矿子电池的理解越来越深入,基于钙钛矿的叠层电池特别是钙钛矿/硅叠层电池将会迅速商业化。

Strategies to Improve the Stability of Perovskite-based Tandem Solar Cells

Organic-inorganic metal halide perovskite-based tandem solar cells have attracted significant research attention in recent years. The power conversion efficiency of perovskite-based tandem can efficiently meet the requirements of practical applications; however, their instability limits their commercialization. The most commonly used wide-bandgap perovskites suitable for top sub-cells, which are based on I/Br alloying at X site, often suffer from severe phase segregation. When exposed to light illumination, a smaller bandgap phase appears and acts as a carrier trap, leading to a reduction in the quasi-Fermi level splitting and large V_OC deficit. The narrow-bandgap perovskites suitable for bottom sub-cells, which are based on Sn/Pb alloying at B sites, always face atmospheric instability. When exposed to air, Sn²⁺ is rapidly oxidized to Sn⁴⁺, which can shorten the carrier diffusion length and result in a drop in efficiency. Herein, we summarize the recent advances in perovskite-based tandem solar cells from the viewpoint of stability. We analyzed the stability data of highly efficient perovskite-based tandems reported so far, such as perovskite/silicon, perovskite/perovskite, and perovskite/copper indium gallium selenide (CIGS) tandems. We found that the key to improve the perovskite-based tandems is to improve the stability of the perovskite sub-cells. Then, we systematically analyzed the phase and atmospheric instability of wide- and narrow-bandgap perovskite, respectively, providing some reasonable strategies to tackle the instability. Compositional engineering, crystallinity optimization, and employing other perovskites with wide bandgaps are effective means to avoid phase instability of the I/Br alloying perovskite. Introducing the reducing additives, improving the film morphology, and forming a 2D/3D structure can help in improving the atmospheric stability of Sn-Pb narrow bandgap perovskites. Furthermore, we review the intrinsic instability of perovskite and corresponding improvement methods, which are inevitable in future tandem solar cells. By reducing the methylamine (MA) content in perovskite component and suppressing ion migration, the long-term operational stability is greatly enhanced. Finally, we briefly summarize the instability issues related to the interconnecting layer. In addition to the optimization of perovskite-based tandem devices, encapsulation also plays a crucial role in improving stability against environmental stressors. Studies based on improving the stability of perovskite-based tandems are still in the early stage. However, with a deeper understanding of the stability of perovskite sub-cells and the interconnecting layer, the commercialization of perovskite-based tandems, especially perovskite/silicon tandem devices, is promising to be achieved in the near future.