Host-Guest Complexation Strategy for Passivating Pb-Dimer Related Defects in Perovskite Photovoltaics
Although there is extensive attention to the eminent perovskite solar cells, the deep-level defects such as Pb-Pb dimers in the solution-processed polycrystalline perovskites inevitably result in photovoltaic output losses and subsequent degradation. Recently, it is reported that an electron-donating group can passivate Pb dimer defects efficiently. However, the mechanism for the causation of metallic lead (Pb0) from the iodide vacancy (VI) is unclear. Herein, a chain reaction mechanism is proposed for the possible transformation process from VI to Pb0 with the Pb dimer intermediates. In this regard, a host-guest strategy is adopted by using 4-tert-Butyl-1-(ethoxycarbonyl- methoxy) thiacalixarene (tBuTCA) to complex with the cations and out-of-cage (Lead(II) iodide) PbI2. Moreover, a host-guest complexation can be formed due to the Pb2+-π interactions. Continuously, the negative charge compensation for iodine vacancy can hinder the formation of Pb-Pb dimer, thus significantly suppressing non-radiative recombination. Consequently, the resulting solar cells show more than 24% power conversion efficiencies and maintain over 96% of their initial performance without encapsulation for 486 h under an ambient environment. This work highlights the significance of supramolecular engineering in constructing a high-quality perovskite for efficient and stable perovskite solar cells.