Defect Engineering in Perovskites for Optoelectronic Devices: Use of Perovskite Polytypes

Metal-halide perovskites have emerged as highly promising materials for next-generation optoelectronic devices including light-emitting diodes (LEDs) and solar cells. However, perovskites inherently suffer from internal defects, which can quench charge carriers through non-radiative recombination, thereby degrading their optoelectronic properties. Moreover, defect migration can lead to issues such as current-voltage hysteresis and luminance overshooting, compromising device efficiency and stability. To overcome these challenges, various defect passivation strategies have been explored, such as the incorporation of organic additives and the application of low-dimensional perovskites.
Here, we introduce a distinct approach involving the 6H polytype of FAPbI₃, which is chemically identical to its cubic counterpart (3C), to enable highly effective defect engineering at the interface with cubic FAPbI₃ while maintaining material homogeneity and crystallinity. The use of hetero-polytypic(3C-6H) perovskite film resulted in a power conversion efficiency (PCE) of 21.92% (certified PCE: 21.44%) for a solar module along with enhanced long-term stability. Furthermore, we highlight the detrimental impact of shallow-level defects, particularly iodide vacancy (VI⁺), which have conventionally been regarded as benign. We believe that our findings pave the way for the employment of perovskite polytypes in practice to achieve high-performing perovskite optoelectronic devices, while also elucidating the necessity of engineering shallow-level defects.

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This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT)(RS-2024-00342991). This research was supported by the Digital Research Innovation Institution Program through the National Research Foundation of Korea(NRF) funded by Ministry of Science and ICT (RS-2023-00283597). This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT)(RS-2024-00437887). This research was supported by the National Research Council of Science & Technology (NST) grant by the Korea government (MSIT)(No. CCL23281-100).